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Printed Wiring Board
Pollution Prevention and Control Technology:
Analysis of Updated Survey Results
6 EPA
This document was produced under grant #X 823856
from EPA's Design for the Environment Branch,
Economics, Exposure, and Technology Division, Office
of Pollution Prevention and Toxics. Funding was
provided through EPA's Environmental Technology
Initiative Program.
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ACKNOWLEDGEMENTS
This document was prepared by CAI Resources, Inc., Oakton, VA, for the Microelectronics and Computer
Technology Corporation as part of the collaborative Design for the Environment (DfE) Printed Wiring
Board (PWB) Project. This document is an update to the 1995 report, Printed Wiring Board Pollution
Prevention and Control: Analysis of Survey Results (EPA 744-R-95-006), also produced as part of the
DfE PWB Project. The Project Officer for this grant was Kathy Hart of EPA's DfE Program, in the Office of
Pollution Prevention and Toxics. This report would not have been possible without the assistance of the
industry members and technology vendors who supplied the data and information analyzed in this report.
DfE PWB Project Core Group members provided valuable guidance and feedback during the preparation
of this report. Core Group members include: Kathy Hart, EPA (Core Group Co-Chair); Christopher
Rhodes (Core Group Co-Chair) and Holly Evans, Institute for Interconnecting and Packaging Electronic
Circuits (IPC); Dipti Singh, U.S. EPA (Technical Workgroup Co-Chair); Gary Roper, Substrate
Technologies Inc. (Technical Workgroup Co-Chair); Michael Kerr, Circuit Center, Inc., (Communication
Workgroup Co-Chair); John Lott, DuPont Electronics; John Sharp, Teradyne, Inc.; Lori Kincaid, Jack
Geibig and Mary Swanson, University of Tennessee Center for Clean Products and Clean Technologies;
Greg Pitts, Microelectronics and Computer Technology Corporation; and Ted Smith, Silicon Valley Toxics
Coalition. We also thank the other industry representatives and interested parties who reviewed and
provided suggestions for this report.
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Table of Contents
1.0 PROJECT SUMMARY 1
1.1 Description of Project 1
1.2 Purpose of the Survey 1
1.3 Survey Procedures 1
1.4 Overview of Results 2
2.0 LAWS AND REGULATIONS AFFECTING POLLUTION
PREVENTION AND RECYCLING FOR PWB MANUFACTURERS 15
2.1 Introduction 15
2.2 Federal Laws and Regulations Affecting Pollution Prevention and
Recycling 15
2.3 State Pollution Prevention Laws 21
2.4 Local Pollution Prevention Requirements 21
3.0 PREVAILING AND ALTERNATIVE PRINTED WIRING BOARD
PRODUCTION METHODS AND MATERIALS 24
3.1 Overview of PWB Manufacturing Processes 24
3.2 Rigid Multilayer PWB Manufacturing 25
3.3 Waste Generation and Pollution Prevention Methods 58
4.0 WASTEWATER GENERATION AND FUNDAMENTAL WASTE
REDUCTION PRACTICES 65
4.1 General 65
4.2 Wastewater Survey Data 65
4.3 Good Operating Practices 67
4.4 Drag-out Reduction and Recovery Methods 70
4.5 Rinse Water Use Reduction 76
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5.0 PROCESS SOLUTION MAINTENANCE AND CHEMICAL
RECOVERY TECHNOLOGIES 82
5.1 Introduction 82
5.2 Solution Maintenance 83
5.3 Chemical Recovery Technologies 97
5.4 Off-Site Recycling 109
6.0 END-OF-PIPE TREATMENT 114
6.1 General 114
6.2 Wastewater Characterization 114
6.3 Types of Processes/Systems Employed 115
6.4 End-of-Pipe Treatment Capital Costs 117
6.5 End-of-Pipe Treatment Operation Costs 118
6.6 Sludge Generation and Disposal 119
REFERENCES 120
APPENDIX A-SURVEY DATA 123
in
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List of Exhibits
Exhibit 1-1 Distribution of Annual Sales 3
Exhibit 1-2 Mean and Median Sales 3
Exhibit 1-3 Mean and Median Facility Size 4
Exhibit 1-4 Mean and Median Production 4
Exhibit 1-5 Number of Employees 5
Exhibit 1-6 Employees Per S100K of Sales 5
Exhibit 1-7 Distribution by Technology Level 5
Exhibit 1-8 Distribution of Product Type 6
Exhibit 1-9 Through-Hole Metallization Methods 6
Exhibit 1-10 Outer-Layer Etch Resists in Production 7
Exhibit 1-11 Outer-Layer Etch Resists in Production (Aggregate) 8
Exhibit 1-12 Etchants Used 8
Exhibit 1-13 Water Usage 9
Exhibit 1-14 Production-Based Water Usage 10
Exhibit 1-15 Recycle, Recovery, and Bath Maintenance Technologies Used 11
Exhibit 1-16 Environmental and Occupational Health Challenges 13
Exhibit 1-17 Information Needs 14
Exhibit 1-18 Sources of Technical Information Used 14
Exhibit 2-1 Summary of Federal Legislation Affecting Pollution Prevention and
Recycling 15
Exhibit 2-2 Definitions of Terms Related to Waste Management/Recycling 17
Exhibit 2-3 Federal Regulatory Determinations 17
Exhibit 2-4 Pretreatment Standards for the Electroplating Category (40 CFR 413) 20
Exhibit 2-5 Pretreatment Standards for the Metal Finishing Category (40 CFR 433) 21
Exhibit 2-6 State Pollution Prevention Programs 23
Exhibit 3-1 Typical Process Flow for Rigid Board PWB Manufacture 25
Exhibit 3-2 Process Flow to Design and Produce Film with Data 26
Exhibit 3-3 Inner Layer Image Transfer 28
Exhibit 3-4 Common Primary Etchants Used in PWB Manufacturing 30
Exhibit 3-5 Etchant Use 32
Exhibit 3-6 Typical Oxide Line 32
Exhibit 3-7 Process Flow for a Buried Via Processing 34
Exhibit 3-8 Blind Via Process Using Sequential Lamination 35
Exhibit 3-9 Blind Via Process Using Controlled Depth Drilling 35
Exhibit 3-10 Drill Holes Process Step 37
Exhibit 3-11 Clean Holes Process Step 39
Exhibit 3-12 Distribution of Desmear Methods 40
Exhibit 3-13 Permanganate Desmear Process 41
Exhibit 3-14 Desmear/Etchback Methods 42
Exhibit 3-15 Make Holes Conductive 43
Exhibit 3-16 Comparison of Primary Alternatives for Making Holes Conductive 44
Exhibit 3-17 Typical Electroless Copper Plating Line 45
Exhibit 3-18 Outer Layer Image Transfer 50
Exhibit 3-19 Typical Pattern Plate, Etch-Resist, Photoresist Strip Process Line 51
Exhibit 3-20 Outer Layer Etch Resist 53
Exhibit 3-21 Percentage of Total Production with Various Types of Etchant Resistance 53
Exhibit 3-22 Surface Finish Processes 55
Exhibit 3-23 Selected Waste Volume Estimates from PWB Processes 59
Exhibit 3-24 Potential Substitute Processes for Common Multilayer PWB
Manufacturing Processes 59
Exhibit 3-25 Potential Bath Maintenance and Recovery Options Applicable to Common
PWB Processes 61
Exhibit 4-1 Water Use and Wastewater Discharge Data 66
Exhibit 4-2 Good Operating Practices Used 68
Exhibit 4-3 Drag-Out Reduction and Recovery Methods Data — Survey Results 72
Exhibit 4-4 Summary of Micro-Etch Results 73
IV
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Exhibit 4-5 Summary of Electroless Copper Results 73
Exhibit 4-6 Drag-Out Tank Recovery Rates for a Range of Common Conditions 75
Exhibit 4-7 Rinse Water Use Reduction Methods Data 74
Exhibit 5-1 Recovery, Recycle, and Bath Maintenance Technologies Used 83
Exhibit 5-2 Basic Bath Maintenance for Common Plating Solutions 85
Exhibit 5-3 Amount of Copper Wasted for Various Streams as a Percent of Total
Discharge 86
Exhibit 5-4 Ammoniacal Etchant Regeneration System 87
Exhibit 5-5 Continuous Flow Microetchant Reuse System 91
Exhibit 5-6 Porous Pot Technology Data (1995 Survey) 92
Exhibit 5-7 Porous Pot Technology Data (1997 Survey) 93
Exhibit 5-8 Acid Sorption Operating Cycle 96
Exhibit 5-9 Acid Sorption Flow Diagram 96
Exhibit 5-10 Ion Exchange Recovery-Metal Scavenging Configuration 99
Exhibit 5-11 Ion Exchange Recovery-Metal Recovery/Deionized Water Cycle 100
Exhibit 5-12 Central Copper Recovery System Utilizing Ion Exchange and
Electrowinning 101
Exhibit 5-13 Ion Exchange Technology Data (1995 Survey) 102
Exhibit 5-14 Ion Exchange Technology Data (1997 Survey) 103
Exhibit 5-15 Electrowinning Technology Applied to a Drag-Out Tank 105
Exhibit 5-16 Electrowinning Technology Data (1995 Survey 107
Exhibit 5-17 Electrowinning Technology Data (1997 Survey) 108
Exhibit 5-18 Off-Site Recycling of Spent Process Fluids 112
Exhibit 5-19 Off-Site Recycling/Disposal of Wastewater Treatment Sludge 113
Exhibit 6-1 Discharge Limitations and Compliance Difficulties 116
Exhibit 6-2 Wastewater Treatment Equipment Data 117
Exhibit 6-3 Wastewater Treatment Operating Costs 119
Exhibit 6-4 Waste Treatment System Operational Costs as a Percentage of Annual
Sales 120
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1.0 Project Summary
1.1 Description of Project
This report presents results of a pollution prevention (P2) and control survey for printed wiring board (PWB)
manufacturers and related information from literature and other sources. The survey was conducted by CAI
Resources, Inc., with assistance from the Institute for Interconnecting and Packaging Electronic Circuits (IPC). The
survey results were analyzed and this report was prepared by CAI Resources, Inc., under a subcontract to
Microelectronics and Computer Technology Corporation (MCC). The Design for the Environment (DIE) Printed
Wiring Board Project partners provided significant input to the final report. The work was funded by grant #X
823856 under EPA's Environmental Technology Initiative Program. This report is a follow up to a previous report
that analyzed results of an earlier survey (ref. 1).
The DIE PWB Project is a voluntary cooperative partnership with EPA, industry, and other interested parties that
promotes implementation of environmentally beneficial and economically feasible alternatives by PWB
manufacturers. The ultimate goal of this project is to help the PWB industry increase efficiency and reduce waste
generation by giving individual PWB manufacturers the information they need to make informed decisions that fit
their particular needs. The initial focus of the project was to evaluate processes or technologies for "making holes
conductive" (MHC), the process of depositing a conductive surface in drilled through-holes prior to electroplating. In
support of these efforts, the DfE project conducted a Cleaner Technologies Substitutes Assessment (CTSA) of
several alternative MHC processes and tests were conducted to evaluate the performance of alternative processes (ref.
2). The draft MHC CTSA was published in August 1997. The DfE PWB Project is now conducting a similar
analysis of alternative surface finishes for PWB manufacturing.
1.2 Purpose of the Survey
The pollution prevention and control survey was performed to gather and organize information about the current state
of environmental technology and practices for this industry segment. The focus of the survey was on determining
the types of technologies and alternative processes used, the extent of their use, key factors with regard to
implementation, including costs, and their success and failure rate. Pollution prevention and control technologies
covered by the survey include substitute raw materials and manufacturing processes, reuse and recycle technologies,
procedural changes, and innovative treatment/disposal methods that reduce chemical use or water use and/or prevent
the production of hazardous waste material and its release to the air, water, or land.
The survey results are useful to all those associated with the PWB manufacturing industry. PWB manufacturers can
use the results of the survey to compare their own manufacturing operations to those of the survey respondents.
Using the survey results, manufacturers can evaluate how their operations compare in terms of chemical and other
raw material usage rates, water use, waste generation, technology level used, and other key factors. The results also
show which treatment, recovery, and bath maintenance technologies have been most successful, trends in chemical
substitution, the identification of regulated pollutants, sludge generation rates, off-site waste recovery and disposal
options, and many other pertinent topics. In addition to the manufacturing segment, the results will also be useful
to companies that service the PWB industry, including engineering firms, chemical suppliers, manufacturers/vendors
of pollution prevention and control equipment, and off-site recycling and disposal sites.
1.3 Survey Procedures
The survey of PWB manufacturing facilities was accomplished using a mailed questionnaire. To ensure that the
survey adequately addressed the key production processes and pollution prevention methods, a draft form was prepared
and reviewed by various industry participants, EPA, and other interested parties. The questionnaire was then tested
by surveying a selected group of PWB facilities. Based on these responses, the survey form was revised. The final
survey form was then distributed by IPC during 1995 to all IPC PWB manufacturing facility members
(approximately 400).1 There were 40 responses to the survey. A preliminary report was prepared to distribute the
results of the survey (ref. 1). During 1997, a revised survey process was implemented in order to increase the
response rate by PWB shops. The scope of the survey was reduced in order to shorten the amount of time necessary
to complete the form. The second survey was distributed to 250 members of the California Circuit Association. An
1 The methodology employed during the PWB survey project and the format of the questionnaire employed were based on the experiences of
a similar project conducted for the electroplating industry by the National Center for Manufacturing Sciences (NCMS) and the National
Association of Metal Finishers during 1993 and 1994 (see reference 4). Permission to use the survey format and information gathering
techniques of that study were given by the NCMS Project Steering Group.
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additional 45 responses were received from the second survey. Therefore, a total of 85 different facilities responded to
the survey.
Overall, there were few noticeable differences between the responses from the two surveys. One notable exception
was a decrease in the use of the electroless copper method of making holes conductive. These results are discussed in
Section 1.4.3. Raw data from the two surveys are presented in Appendix A.
The survey covered eight major areas:
• Facility and Point of Contact Identification. In order to maintain confidentiality, this portion of the
survey form was kept separate from other portions of the form. Used only in the event that clarification to
responses was needed, a procedure was employed that prevented anyone from connecting responses to their
originator.
• Facility Characterization. Requested data concerning facility size, product type, base materials used,
process capabilities, and technology level.
• Wastewater Discharges. Requested data concerning the type of discharge (i.e., direct, indirect, zero), flow
rates, discharge limitations, compliance problems, and costs for water and sewer use.
• Process Data. Requested data concerning various elements of the manufacturing process, including etch
resist, inner- and outer-layer etching, through-hole metallization, oxide, etchback/desmear, solder mask, and
chemical usage.
• Recovery, Recycle, or Bath Maintenance Technology. Requested data concerning pollution
prevention technologies, including costs, savings, labor needs, maintenance requirements, residuals generation,
and other important information.
• Pollution Prevention Methods. Requested data concerning pollution prevention (P2) methods used by
the facilities for improving operating procedures, reducing water use, preventing the loss of chemicals, and
making other improvements.
• End-of-Pipe Treatment. Requested data concerning the type of treatment processes used, capital and
operating costs, sludge generation, and compliance problems.
• Identification of Problems and Needs. Requested data concerning environmental and occupational
health challenges, technology needs, and information needs.
1.4 Overview of Results
A total of 85 survey responses were received. Based on dollar sales, the 85 responses represent approximately 36%
of the total U.S. PWB production (ref. 4). The following are some important findings from the survey.
1.4.1 Facility Characterization
Facility characterization data were collected as part of the survey to enable comparisons among the participants and as
a way to relate the respondents as a group to the overall PWB industry population. Among the data collected are the
facility size, production numbers, product mix, and the number of employees.
Comparison of Facility Sizes. Several measures of facility size were employed to help characterize the
respondents and compare them to the overall PWB industry sector, including: annual sales in dollars, square footage
of manufacturing facility, number of employees, and PWB production rate measured in square footage. The
following is a summary of key information.
• Based on an IPC Technology Marketing Research Council survey conducted in 1994, facilities under $5 million
represented 77% of all facilities and facilities over $50 million were only 2.1% of the total. The mix of
respondents from the current Industry survey was substantially different than these industry figures. Among
current survey respondents, 25.6% are small shops, while 14.1% are facilities with more than $50 million in
sales. Any conclusions drawn from the current study should consider that the respondents may be more
representative of larger facilities than the industry average.
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The mean sales reported among respondents is $20,958,000 and the median amount is $12,000,000.
The physical size of the survey respondent's manufacturing facilities ranges from 4,000 sq. feet to 600,000 sq.
feet. The mean size is 61,262 sq. feet and the median size is 31,800 sq. feet.
Square footage of PWB production ranged from 1,100 square feet to 5,000,000 square feet. These values include
single- and double-sided boards as well as multilayer PWBs. The mean and median values are 728,085 square
feet and 273,000 square feet respectively.
Exhibit 1-1. Distribution of Annual Sales
30!
o 20-
15-
/
Under $5-$10 $10- $20- Over
$5 Million $20 $50 $50
Million Million Million Million
Annual Sales
Exhibit 1-2. Mean and Median Sales
25,000,000 -,
20,000,000
15,000,000
10,000,000
5,000,000
median
• Of the facilities responding to the survey, the number of employees ranges from 4 to 1,200. Themeanis 191
employees and the median is 123 employees.
• For the respondents, a mean of 10.9 employees and a median of 10.6 employees are needed for each $100,000 of
annual sales.
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Exhibit 1-3. Mean and Median Facility Size of Survey Respondents
70,000 -,
"o
rt
o
1>
1
r5T 90 000
10 000
0-
median
Exhibit 1-4. Mean and Median Production
800,000
700,000
^ 600,000
OJ
^ 500,000
| 400,000
01
•g 300,000
ra 200,000
100,000
0
median
1.4.2 General Process Information
The survey collected data for numerous process related topics. Some of the general process characterization data are
presented in this section.
• PWB substrate can be rigid, flexible or a combination of the two. Rigid boards are the most common and are
made exclusively by 88.5% of the survey respondents. Flexible circuits are made by 18.4% of the facilities and
11.5% make a combination of rigid/flexible (regi-flex) circuits.
• Another method of classification of PWB manufacturers is by the number of layers they are able to produce.
Higher layer counts require more sophisticated equipment and processes. Double-sided boards are the most
commonly produced boards among survey respondents (87.3% of respondents). Of the facilities that produce
multilayers, 4-6 layer boards are the most common type (80.5% of respondents). Only 12.6% of the facilities
produce multilayers with more than 20 layers.
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Exhibit 1-5. Number of Employees
200
180
160
1 140
>i
•5, I20
£ 100
60
40
20
0
median
Exhibit 1-6. Employees Per $100K of Sales
10.9 -,
10 85
10.8
10 75 -
10.7
10 65
10.6
10 55
10 5
10 45
10.4
/'"
/
/'"
median
Exhibit 1-7. Distribution by Technology Level
f
•1 70
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dn OU
w
^
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n i r\
0 -
O
-, O
'
Number of Layers
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Exhibit 1-8. Distribution of Product Type
90 -i
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CO
$ 50
o 40
On
g 20 "
0 -
/
^o
o
_- o
I
Number of Layers
1.4.3 Production Methods and Materials
Certain manufacturing methods and materials used in PWB production are of particular concern with respect to waste
generation or pollution prevention and are highlighted in this section. A detailed description of all applicable
processes is presented in Section 3.
Making Holes Conductive. This process step has received much attention due to the chemicals used, the
wastes generated and employee exposure concerns. Making holes Conductive (MHC) was the focus of the first
Design for the Environment CTSA project (ref. 2). The draft MHC CTSA was published in August, 1997. Due to
the emphasis placed on this process during the DfE project, both surveys (see description of survey process in
Section 1.3) requested detailed information about making holes conductive from the PWB shops. Overall, there were
few noticeable differences between the responses from the two surveys which were conducted approximately two
years apart. However, with respect to making holes conductive, there appears to be some differences. Therefore, the
data presented in Exhibit 1-9 show the individual survey results as well as the overall results.
During the making holes conductive step, a thin seed layer of conductive material (copper, carbon, nickel, palladium
or other conductive material) is deposited to facilitate subsequent copper electroplating. Prior to the 1990's, few
choices for making holes conductive existed other than electroless copper, which remains the predominate process.
Due to the health risks and increasing regulation of formaldehyde, the waste treatment complications presented by
EDTA or other complexing agents, and the complex pre-treatment line associated with electroless copper, interest in
alternatives to electroless copper has been high. Considerable research has resulted in an array of substitute
processes. Among the alternatives are palladium-based, carbon-based, graphite-based and electroless nickel processes.
Each of these processes address some or all of the problems identified with electroless copper.
Exhibit 1-9. Through-Hole Metallization Methods
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Although electroless copper remains the predominant method of making holes conductive, its use appears to have
declined. Twenty percent fewer facilities from the 1997 survey employ electroless copper than did in the 1995
survey (electroless copper is used by 70% of the 1997 respondents, down from 86% in the 1995 survey). The
carbon-based alternative, although not used by any respondents from the 1995 survey, is used by 11.4% of the
respondents from 1997 survey. Use of graphite-based systems rose to 9% in 1997 from 2.7% in 1995. The use of
palladium-based alternatives declined from 14% of the 1995 respondents to 6.8% in 1997. Electroless nickel use
remained nearly unchanged at approximately 2%.
Design for the Environment (DfE) Printed Wiring Board Project participants are encouraged by this increase in the
use of alternative MHC technologies, especially because it occurred while awareness of the alternatives was being
increased by the MHC project. Additional increases in alternative MHC technology use can now be expected because
the CTSA results were presented in seven seminars around the United States in 1997, and because the final MHC
CTSA will be published in summer 1998.
Etch Resists. Etch resists are needed on any PWB manufactured using the subtractive process. The etch resist
protects the underlying copper circuitry from being etched away. Dry film, screened ink, or a plated metal can act as
a resist. Many facilities employ more than one etch resist.
Tin-lead has been losing ground to other resists for the last several years due to health and environmental concerns
and the readily available substitute of tin-only plating (Exhibit 1-10). Tin-lead was still in use by 52% of survey
respondents.
In the case of solder mask over bare copper (SMOBC) panels, tin plating easily replaces tin-lead since the etch resist
is stripped after etching. Tin is used as an etch resist by 49% of the survey respondents.
Among other etch resists, dry film is used by 41% of the respondents and nickel-gold is used by 43%.
Exhibit 1-10. Outer-Layer Etch Resists in Production
60!
•I 50-1
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Exhibit 1-11. Outer Layer Etch Resists in Production (Aggregate)
IN
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Solder Mask. Most PWBs, including nearly all high-technology circuits, require solder mask. The survey results
show a very substantial use of liquid photoimageable masks (LPI). Seventy-six percent of respondents apply LPI to
at least a portion of their product. Thermal masks are used by 74% of the respondents. Forty percent use dry film
masks on at least some of their product. A significant percentage of respondents indicated that they use all three
common mask types (26%).
1.4.4 Wastewater Generation and Discharge
The survey collected information about wastewater generation rates, discharge types, discharge limits, compliance
difficulties, wastewater treatment methods, and other related information. Some key findings include:
• The survey data show that the majority of the respondents are indirect dischargers.2 This is especially true for
the small to mid-sized PWB manufacturing facilities. Seventy-seven percent of all respondents indicated that
they are indirect dischargers, whereas 94% of the facilities with a production rate below 300,000 board ft2 are
indirect dischargers. None of the survey respondents indicated they are zero discharge shops.
• Average daily wastewater flow rates range from 5,200 gpd to 400,000 gpd.
Exhibit 1-13. Water Usage
70000
60000
50000
40000
.2 30000
13
o
20000
10000
median
For the purpose of this survey, the discharge type refers to the destination of wastewater discharges regulated by categorical effluent
standards. The three possible selections in the survey questionnaire were direct discharge (i.e., to surface water such as a river or stream),
indirect discharge (to a publicly owned treatment works or POTW), or zero discharge (no process wastewater discharge).
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Exhibit 1-14. Production-Based Water Usage
40 n
35
30
25
15
10
5
0
All Shops
20 Largest Shops
• Not suprisingly, the data indicate that overall water usage was related to the product mix of the shop,
particularly the layer-count mix. Therefore, an adjusted, production-based flow rate was calculated. Comparing
the adjusted production-based flow rates, the range of water use among respondents is extremely wide; 8% of
respondents reported water usage of over 50 gallons/layer-ft2, whereas 51% reported water use of less than 10
gal/lay er-ft2.
• A very sharp distinction can be drawn between the mean water use of larger and smaller shops. The largest 20
facilities in terms of production had mean production-based water usage rates less than one-third that of all
respondents. Since facilities that did not have formal data were encouraged to estimate their water usage, it is
possible that some of the very high usage rates among the smaller shops are a result of poor estimates of either
the production rate or water usage. Following this line of reasoning, it is also possible that the rates shown in
Exhibit 1-14 for the largest 20 facilities are a more accurate estimate of true water usage by this industry sector.
• There is a relationship between the adjusted production-based flow rates and the cost of water and sewer use. For
facilities that have very high combined water and sewer costs, the adjusted production-based flow rates are very
low. Variation of water and sewer use costs among survey respondents is likely due in part to geographical
location, with higher costs in coastal and arid regions.
• Low water use rates are achieved by PWB facilities through the implementation of simple water conservation
techniques and/or by using technologies such as ion exchange that recycle water.
• The data indicate that the use of water conservation methods does not always result in low water use. The four
facilities with the highest production-based flow rates do not use ion exchange recycling, but they all indicated
that they employ counterflow rinsing, plus some other methods of water conservation. In such cases, it is
possible that water is simply being wasted by having unnecessarily high flow rates in the rinse tanks (e.g.,
flowing water during periods of non-production).
• The data indicate that the majority of respondents (63%) must meet discharge limitations that are more stringent
than the Federal standards.
• Very few respondents reported any wastewater compliance difficulties. Of the respondents that reported
difficulties, 11% reported difficulties with lead, 8% with copper, and 3% with silver. A large majority of
respondents (86%) did not report any compliance difficulties. The majority of those reporting compliance
difficulties have discharge limitations lower than Federal standards.
1.4.5 Recycle, Recovery, and Bath Maintenance
One section of the PWB survey form was devoted to gathering information concerning pollution prevention and
recovery technologies that are applied for the purposes of recovering and recycling chemicals and improving the life-
span of process solutions. Eighty-one percent (81%) of the respondents reported use of a recycle, recovery or bath
maintenance technology, including ion transfer, electrowinning, ion exchange, diffusion dialysis, membrane
10
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electrolysis, evaporation, and solvent extraction. Exhibit 1-15 displays the technologies found amongst the
respondents. They include:
• Electrolytic regeneration of permanganate desmear baths using a porous pot (or similar ion transfer designs) is
employed by 28.2% of the survey respondents. This relatively inexpensive and simple technology is used for
bath maintenance (i.e., extending the useful life-span) of permanganate desmear baths. In the conventional
permanganate process, the permanganate ion is reduced by heat and contact with PWBs and is replaced by
chemical addition. Also, during operation of this bath, by-products (including the manganate ion) accumulate in
concentration causing a sludge to form and frequent disposal is necessary. The porous pot can be used to
maintain a sufficiently low concentration of contaminants and thereby reduce the frequency of disposal.
• Ion exchange is a versatile technology that is applied by PWB manufacturers for various, sometimes
overlapping purposes, including: water softening, chemical recovery, water recycle, solution maintenance, and
waste treatment. Forty-five percent (45%) of the respondents reported using ion exchange as a water
recycle/chemical recovery technology. Many of these respondents reported the same system as a component of
their waste treatment system. In general, most of the waste streams discharged from PWB processes are
compatible with ion exchange, and many facilities mix several similar rinse streams and treat them with a single
ion exchange unit (e.g., sulfuric acid dips, micro-etch, and copper electroplating rinses are frequently combined).
The ion exchange effluent may be discharged and the regenerant processed using electrowinning, thereby making
ion exchange both an end-of-pipe waste treatment and a component of a metal recovery system.
• Electrowinning is a common metal recovery technology employed by PWB manufacturers to remove metallic
ions from spent process fluids, ion exchange regenerant, and concentrated rinse water (e.g., drag-out rinses).
Twenty-eight percent (28.2%) of the survey respondents reported using electrowinning as a recovery technology.
• Several other technologies are used by survey respondents, but to a much lessor extent than the porous pot, ion
exchange or electrowinning. One respondent cited use of evaporation, which was employed to recover copper
sulfate electroplating solution. One respondent reported using diffusion dialysis for bath maintenance on a tin-
lead strip solution. Membrane electrolysis is used by one respondent as an on-line regeneration method for
cupric chloride etchant. The same respondent also reported using solvent extraction technology for on-site
regeneration of ammoniacal etchant (and drag-out recovery).
Exhibit 1-15. Recycle, Recovery and Bath Maintenance Technologies Used
45-,
H
M
D
+2
i— '
O
.2
=
a '-g
>
-------
• Nearly all respondents reported using off-site recycling for disposing of spent process baths. By far, the most
commonly reported spent process fluid that is sent off-site for recycling is spent etchant, particularly spent
ammoniacal etchant. Eighty-three percent (83%) of the respondents who completed the off-site recycling section
of the survey reported that they send spent ammoniacal etchant off-site for recycling. Spent ammoniacal etchant
is created at a rate of roughly 1 gallon per 30 surface square feet of inner- and outer-layer panels. The reason that
spent etchant is a popular waste for off-site recycling is due mostly to its high copper concentration, which is
typically 150 g/1 Cu (i.e., 15% Cu). Etchant that is sent off-site is processed to recover the copper and
regenerate the etchant for reuse.
• Spent process baths other than etchant are less frequently sent off-site for recycling by the survey respondents.
The next most commonly shipped waste product is tin and/or tin-lead stripping solutions. These solutions are
listed by 20% of the respondents who completed this section of the survey form. Like etchant, spent stripping
solutions have a high metal concentration that makes it a viable candidate for recycling. Also, stripping
solutions are generated in relatively high volumes, furthering the economics of off-site recycling.
• Flux, solder dross from the hot-air-solder-level (HASL) process, and other lead-bearing solutions are shipped off-
site for recycling by 20% of the respondents. However, the quantities of these materials that are shipped are
relatively small.
• Micro-etchants are shipped off-site for recovery by only 8% of the respondents. Spent micro-etchants typically
contain copper concentrations of 15 to 30 g/1 Cu (i.e., 1.5 to 3.0% Cu). Other respondents reported
electrowinning these solutions on-site, or treating them with conventional precipitation.
• Gold- and silver-bearing wastes are sent off-site by 15% of the respondents. Gold electroplating baths (usually
gold cyanide) have a long life-span, and not surprisingly, the reported volumes were all 100 gallons per year or
less. Solutions containing gold may include spent gold electroplating bath, or the contents of drip or drag-out
tanks on the gold plating line. Silver is present in film developing fluids that may be reclaimed on-site
(electrowinned), shipped off-site for metal reclamation, or combined with other waste streams and treated
conventionally.
• Ten percent (10%) of the respondents indicated that spent rack stripping solution is shipped off-site. Plating
racks are typically coated with a non-conductive substance to prevent electroplating from occurring on the rack
surface itself. Due to use, this coating may degrade and plating can accumulate on the rack, especially near the
clamps and contact points. This unwanted copper deposit is removed in a stripping solution such as dilute nitric
acid. The volume of spent stripping solution can be significant.
• Nearly ninety percent (90%) of those who provided data concerning the destination of their sludges indicated that
they ship the sludges to recycling facilities rather than landfills.
1.4.7 Wastewater Treatment
End-of-pipe treatment is, by definition, not pollution prevention (P2). However, it is an important aspect of
pollution control and it sometimes competes financially with pollution prevention options when facilities are
developing pollution control strategies. To make informed decisions about implementing P2 alternatives that
include consideration of all applicable costs and potential savings requires accurate data. Therefore, the topic of waste
treatment was included in the PWB survey project so that the true costs of treatment could be examined. The
applicable portion of the survey form requested respondents to describe the type of waste treatment system currently
in use at their facilities and to provide operating and cost data. The following is a summary of the end-of pipe
treatment information provided by the respondents.
• The primary purpose of the wastewater treatment systems employed is the removal of dissolved metals. This is
accomplished by the respondents through installation of conventional metals precipitation systems, ion
exchange-based metals removal systems, and combined precipitation/ion exchange systems.
• Forty percent (40%) of the respondents reported using ion exchange as their basic waste treatment technology.
1.4.8 PWB Industry Environmental Problems and Needs
Checklists were included on the survey to identify sources of information, environmental and health challenges, and
areas where insufficient information is available for the industry. The respondents were also allowed to fill-in items
that were not covered in the checklists. The results are summarized below.
• Environmental and Occupational Health Challenges. Of the environmental and occupational health
challenges on the checklist, the challenges most frequently cited were increasing cost of compliance (68.6%),
frequently changing regulations (55.8%), and reducing worker exposure to chemicals (41.8%) (Figure 1-16).
12
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Exhibit 1-16. Environmental and Occupational Health Challenges
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certified courses for pollution prevention (33.7%), fully or semi-additive process (30.2%), tin-lead alternatives
(29.1%), smear removal alternatives (23.3%) and direct imaging (15.1%).
Source of Technical Information. The survey indicates that PWB facilities draw on a variety of sources
when seeking information (Exhibit 1-18). The sources of information that were identified most frequently by
the respondents were in-house engineer (50.0%), vendors (48.8%), and professional journals (39.5%).
13
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2.0 Laws and Regulations Affecting Pollution Prevention
and Recycling for PWB Manufacturers
2.1 Introduction
Implementing a sound environmental protection strategy for a PWB facility may involve using a range of reduction
and waste management methods that work in unison, including waste reduction, recycling, treatment, and disposal.
Decisions regarding each facility's strategy are usually guided by a number of factors, including a desire to meet
environmental regulations, reducing liability and operating costs, maintaining/improving the company's image and
reducing risks to workers, the public, and the environment. Of these factors, compliance with environmental
regulations is often the overriding factor. Understanding the influence of regulations and the need to move toward
more environmentally sound pollution control practices and to encourage source reduction practices, Congress passed
the Pollution Prevention Act of 1990 (PPA). The PPA declared it a national policy to prevent or reduce pollution at
the source whenever feasible. This section of the report helps to understand the impact of the PPA and other federal,
state, and local regulatory initiatives that promote source reduction and recycling.
2.2 Federal Laws and Regulations Affecting Pollution Prevention and
Recycling
Several key federal laws and regulations affect decisions regarding implementation of pollution prevention, with the
most influential being the Pollution Prevention Act of 1990, Emergency Planning and Community Right-to-Know
Act (EPCRA, also known as SARA Title III), the Resource Conservation and Recovery Act (RCRA, which covers
regulation of hazardous wastes), and the Clean Water Act (CWA, which covers regulation of wastewater discharges).
The following overview of these laws identifies provisions that pertain to PWB manufacturing pollution prevention.
A summary of this information is presented in Exhibit 2-1.
Exhibit 2-1. Summary of Federal Legislation Affecting Pollution Prevention and Recycling
Pollution Prevention Act of Formalized a national policy and commitment to waste reduction, functioning
1990 (PPA) primarily to promote the consideration of pollution prevention measures at the
federal government level.
Resource Conservation and Congress declared that the reduction or elimination of hazardous waste generation at
Recovery Act (RCRA), the source should take priority over other management methods such as treatment
including the Hazardous and and disposal. Hazardous waste generators are required to certify on their hazardous
Solid Waste Amendments waste manifests that they have programs in place to reduce the volume or quantity
(HSWA) to RCRA and toxicity of hazardous waste generated to the extent economically practicable.
Materials that are recycled may be exempt from RCRA regulations if certain
conditions are met.
Emergency Planning and EPCRA requires certain companies to submit an annual report (Form R) of the
Community Right-to-Know amount of listed "toxic chemicals" entering the environment. With passage of the
Act (EPCRA, also known as PPA, new reporting requirements were added to the Form R. Source reduction and
SARA Title III) waste management information must be provided for the listed toxic chemicals.
Clean Water Act (CWA) CWA regulations pertain to wastewater discharges. Most industries must meet
discharge standards for various pollutants. Specific methods of control such as
pollution prevention are not specified; however, many facilities use pollution
prevention as a means of reducing the cost of compliance with federal regulations.
State and local authorities generally have the responsibility to implement the
provisions of the CWA. These authorities must enforce the Federal guidelines as a
minimum, but may choose to enforce more stringent requirements. Some localities
include pollution prevention planning requirements into discharge permits.
2.2.1 Pollution Prevention Act of 1990
Pollution prevention is a relatively new theme in environmental laws and regulations. In 1990, Congress passed the
Pollution Prevention Act to promote the consideration and adoption of source reduction and recycling in both
regulatory and non-regulatory settings. This statute is a foundation for future regulations and Agency initiatives,
rather than a specific set of rules. The law obligates EPA to develop and implement a strategy to promote source
reduction that includes:
15
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reviewing existing and proposed programs and new regulations to determine their effect on source reduction
coordinating source reduction activities among Agency programs and other federal agencies
streamlining public access to environmental data and foster the exchange of source reduction information
establishing pollution prevention training programs for Federal and state environmental officials
facilitating adoption of source reduction by businesses
identifying and make recommendations to Congress to eliminate barriers to source reduction
Since the passage of the Pollution Prevention Act of 1990, EPA has implemented a diverse set of programs and
initiatives to meet their obligations defined by the law. Key to EPA's approach is an array of partnership programs
that are collectively referred to as Partners for the Environment. Through these efforts, EPA is utilizing voluntary
goals and commitments to achieve environmental results in a timely and cost-effective way. This is being
accomplished by building cooperative partnerships with a variety of groups, including small and large businesses,
citizen groups, state and local governments, universities, and trade associations.
Examples of these collaborative efforts include programs such as 33/50, Waste Wi$e, Climate Wise, Green Lights,
Energy Star, WAVE, the Pesticide Environmental Stewardship Program, Indoor Air, Indoor Radon, Design for the
Environment, the Environmental Leadership Program, and the Common Sense Initiative.
The Pollution Prevention Act of 1990 reinforced EPA's environmental management options hierarchy, where the
highest priorities are assigned to source reduction, which is analogous to pollution prevention. This involves the
judicious use of resources through, for example, product and process change, reuse of input materials during
production, reduced water consumption, and energy efficiency.
The Pollution Prevention Act of 1990 is essentially a formalized national policy and commitment to waste
reduction. However, even before passage of the PPA, some early consideration was given to waste reduction
activities. Of the previous legislation, those most affecting P2 are the RCRA, EPCRA and the CWA.
2.2.2 Resource Conservation and Recovery Act (RCRA)
EPA regulates the management and control of all hazardous wastes from their point of origin to final disposal.
These regulations are primarily the direct result of two congressional mandates: subtitle C of the 1976 Resource
Conservation and Recovery Act (RCRA) (PL 94-580) and the 1984 Hazardous and Solid Waste Amendments to
RCRA (PL 98-616). EPA has issued regulations, found in 40 CFR Parts 260-299, which implement Subtitle C.
However, in many states, RCRA requirements are implemented through EPA-authorized State hazardous waste laws,
which may be more stringent than Federal requirements. A facility should always check with the state when
analyzing which requirements apply to their activities.
This section reviews some elements of the RCRA regulations that pertain to management of wastes from PWB
manufacturing. In particular, RCRA rules regarding hazardous waste identification, requirements for generators, and
aspects of recycling are covered. Also, note that all definitions in this section are intended to pertain solely to
RCRA.
Identification of Hazardous Wastes. Each PWB facility has the responsibility for determining whether a
waste it generates is hazardous and what classification, if any, applies to the waste. Part 261 of 40 CFR addresses
the identification and listing of hazardous wastes. The facility must examine the regulations and undertake any tests
necessary to determine if the wastes generated are hazardous. Wastes can be classified as hazardous either because
they are listed by EPA through regulations that appear in the CFR or because they exhibit certain characteristics.
Listed wastes are specifically named, for example, wastewater treatment sludges from electroplating operations
(F006). Characteristic hazardous waste are wastes that "fail" a characteristic test, such as the RCRA test for toxicity.
When determining the status of a particular material, it is important to be familiar with the regulatory definitions of
certain terms. Some of the important terms are defined in Exhibit 2-2.
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Exhibit 2-2. Definitions of Terms Related to Waste Management/Recycling
Term
Definition
solid waste
hazardous waste
spent material
by-product
sludge
scrap metal
excluded scrap metal
Any discarded material that is not excluded under RCRA (exclusions are found in 40 CFR
261.2 and 261.4(a)) or by a variance granted under RCRA (procedures forvariances are
covered in 40 CFR 260.30 and 260.31).
A solid waste that meets any of the RCRA hazardous waste criteria (described in 40 CFR
261.3) and is not excluded from regulation as a hazardous waste (exclusions are found in 40
CFR261.4(b)).
Any material that has been used and as a result of contamination can no longer serve the
purpose for which it was produced without processing (40 CFR 261. l(c)(l)).
A material that is not one of the primary products of a production process and is not solely
or separately produced by the production process (40 CFR 261.1(c)(3)).
Any solid, semi-solid, or liquid waste generated from a municipal, commercial, or industrial
wastewater treatment plant, water supply treatment plant, or air pollution control facility
exclusive of the treated effluent from a wastewater treatment plant (40 CFR 260.10).
Bits and pieces of metal parts (e.g., bars, turnings, rods, sheets, wire) or metal pieces that
may be combined together with bolts or soldering (e.g., radiators, scrap automobiles,
railroad box cars), which when worn or superfluous can be recycled. (See 40 CFR
261. l(c)(6)). A material is "recycled" if it is used, re-used, or reclaimed.
Includes home (40 CFR 261.1(c)(ll)), prompt (40 CFR 261.1(c)(12)) and processed scrap
metal. (See 40 CFR 261.1(c)(10)).
Exhibit 2-3. Federal Regulatory Determinations*
Waste Type/Description
Regulatory Status under Federal RCRA
Unused/off-specification circuit boards:
Manufacturers of computer circuit boards send unused/off-
specification printed circuit boards off-site for reclamation.
As a matter of policy, whole unused circuit boards are
classified as commercial chemical products and if recycled
are excluded from the definition of solid waste. (See 40
CFR 261.2 Table 1).
Used whole printed circuit boards:
Old electronic equipment may be disassembled and the
usable parts salvaged. Salvaged circuit boards may be sent
for reclamation.
As a matter of policy, unprocessed, spent printed circuit
boards are classified as scrap metal and if recycled are
exempt from the definition of hazardous waste. (See 40
CFR 261.6(a)(3)(ii)). Whole used circuit boards which
contain mercury switches, mercury relays, nickel-cadmium
batteries, or lithium batteries do not meet the definition of
scrap metal. However, EPA does not intend to regulate
under RCRA circuit boards containing minimal quantities
of mercury switches, mercury relays, and/or batteries that
are protectively packaged to minimize dispersion of metal
constituents and that are part of a materials recovery
program. (See 63 FR 28629).
Shredded circuit boards:
Circuit boards are often shredded, for various reasons, prior
to reclamation. The process of shredding circuit boards
produces small fines from the whole board which are
dispersible and do not meet the RCRA regulatory
definition of scrap metal.
Shredded circuit boards being recycled are excluded from
the definition of solid waste provided that they are: 1)
stored in containers sufficient to prevent a release to the
environment prior to recovery; and 2) free of mercury
switches, mercury relays, and nickel-cadmium and lithium
batteries. (See 40 CFR 261.4(a)(14)).
Circuit board trimmings:
Manufacturers of computer circuit boards send board
trimmings from the production process off-site for
reclamation.
As a matter of policy, circuit board trimmings are
classified as characteristic by-products. If reclaimed, they
are excluded from the definition of solid waste. (See 40
CFR 261.2 Table 1).
Solder dross:
Generated by the periodic skimming of molten solder
baths used in the production of printed wiring boards to
remove contaminants acquired through use of the molten
solder baths.
As a matter of policy, solder dross is classified as a
characteristic by-product. If reclaimed, it is excluded from
the definition of solid waste. (See 40 CFR 261.2 Table
1).
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Spent solder baths (pot dumps):
Solidified pieces of tin-lead solder baths used in the
production of printed circuit boards.
As a matter of policy, spent solder baths are classified as
scrap metal and if recycled are exempt from the definition
of hazardous waste. (See 62 FR 26013).
Sweeps:
This term refers alternatively to a powdered material that is
a residue of thermal recovery of precious metal-bearing
secondary material (often ash that is crushed into
paniculate form in a ball mill or similar device) or
paniculate material that is collected from firms handling
precious metals, such as jewelers and metal finishers.
As a matter of policy, sweeps are classified as a by-
product. If hazardous solely by exhibiting a characteristic
and being reclaimed, they are excluded from the definition
of solid waste. If they are derived from a source material
that meets the description of a listed hazardous waste, the
sweeps are regulated as a solid and hazardous waste. (See
62 FR 26013).
Baghouse dust:
Circuit boards are often sent to precious metal recovery
furnaces for reclamation.
As a matter of policy, baghouse dust from precious metal
recovery furnaces is regulated as a sludge. If hazardous
solely by exhibiting a characteristic and being reclaimed,
they are excluded from the definition of solid waste. If
they are derived from a source material the meets the
description of a listed hazardous waste, the sweeps are
regulated as a solid and hazardous waste. (See 62 FR
26014).
Photoresist skins:
Dry film resists are typically stripped in hot potassium
hydroxide, which does not fully dissolve the resist
material. The solids (photoresist skins) are filtered out to
prevent clogging of spray nozzles, prevent redeposition on
panels, and prolong the life of the stripper.
The determination as to whether or not photoresist skins
are hazardous waste will depend on the analysis of the
individual facility by the State or Regional regulatory
authority.
Etchant:
Commercial alkaline etchant is distributed for use to
manufacturers of printed circuits. After a period of use,
the alkaline etchant is reduced below acceptable levels and
becomes "spent." The spent material is then returned to
the manufacturer of the alkaline etchant, where copper is
recovered and the remainder of the etchant is then used as a
raw material to produce additional alkaline etchant.
The determination as to whether or not spent etchant
generated at a particular facility is hazardous waste will
depend on the material, how it is managed, and the
recycling process used. Generators should contact their
State or Regional regulatory authority for assistance with
making this determination.
*State laws may vary from Federal rules with regard to the classification of PWB wastes. Facilities are urged to
contact their applicable state agency for the most recent information. State Agencies can be located using the
Internet web site of the Printed Wiring Board Resource Center (http://www.pwbrc.org).
Although the RCRA regulations are fairly specific, there are some instances where clarification is necessary.
Clarification or interpretations are often provided by EPA in direct response to requests. These responses are
particularly useful when facilities are making determinations about specific types of wastes. Some of the
clarifications and interpretations provided by EPA that apply to wastes generated during PWB manufacturing are
summarized in Exhibit 2-3.
Requirements for Hazardous Waste Generators. Producers of hazardous waste (called generators) are
ultimately responsible for the proper identification, pre-transport storage, and packaging and tracking of the waste.
The generator first determines whether the waste is hazardous according to the criteria outlined above though,
alternatively, the generator may simply declare the waste hazardous and treat it accordingly. If the waste is known to
be nonhazardous, the generator need not test it. The responsibility for the accuracy of the determination of whether
the waste is hazardous or not lies with the generator.
Generators of hazardous wastes are also responsible for notifying EPA and maintaining records of their activities,
using appropriate containers, labeling the containers, and ensuring proper disposal. The law requires most generators
of hazardous waste to use a manifest system to ensure the proper transport and disposal of the wastes. The manifest
system records the movement of hazardous wastes from the generator's premises to an authorized off-site treatment,
storage, or disposal facility. The generator must maintain original manifests for three years, and must report to EPA
if the manifest is not returned to him within 45 days. An exception report must be completed for any non-returned
manifests. Annual reports documenting shipments of all hazardous wastes originating during the report year also are
18
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required. All information submitted by a generator is available to the public to the extent authorized by the Freedom
of Information Act and EPA rules related to that Act.
Recycling Aspects of RCRA. Certain recycling activities can be implemented by PWB facilities that may
remove materials from RCRA regulation that otherwise would be considered hazardous wastes. Recycling can be
accomplished in several ways, for example: (1) using or reusing materials in an industrial process to make a
product, provided the materials are not being reclaimed (see definition of reclaimed material in Exhibit 2-2); (2) using
or reusing the material as an effective substitute for commercial products; or (3) returning materials to the original
process from which they are generated, without first being reclaimed (where the material is returned as a substitute
for raw material feedstock).
Materials managed by these types of recycling are not classified as solid waste and therefore are out of the scope of
RCRA Subtitle C regulation. However, materials recycled in other ways are considered solid wastes subject to
Subtitle C, including: (1) materials used in a manner constituting disposal or used to produce products that are
applied to the land; (2) materials burned as a fuel or for energy recovery; (3) materials that are speculatively
accumulated; and (4) inherently waste-like materials (these materials include listed hazardous wastes that are always
subject to RCRA regulation).
To assist the regulated community in determining whether a material that they recycle is a solid waste, EPA has
released regulatory determinations that address specific production processes and wastes. By comparing their own
situations to those in the determinations, industry personnel can develop a clearer understanding of the regulations
and improve their waste management practices.
RCRA regulatory determinations that pertain to recycling at PWB facilities are summarized in Exhibit 2-3. These
determinations address the following materials: etchant, photoresist skins, solder dross, pot dumps, off-spec boards
and trimmings, and used printed circuit boards. Generators should check with their state regulating offices to
determine if the Federal interpretations apply.
2.2.3 Clean Water Act Wastewater Regulations
Wastewater discharges from PWB manufacturing operations are governed by regulations developed under the Clean
Water Act. Of particular importance are the categorical regulations that cover electroplating (40 CFR 413) and metal
finishing (40 CFR 433). These regulations contain specific performance standards for contaminants discharged from
PWB manufacturing processes. The wastewater regulations have been divided into several layers of categories: those
for existing and new sources; and those for direct and indirect discharges. Direct dischargers are regulated by the
National Pollutant Discharge Elimination System (NPDES), under which EPA or its state equivalent issues a
separate permit to each discharger containing specific discharge limitations, reporting requirements, and compliance
schedules. NPDES permits are renewable every five years. Indirect dischargers must conform to national
pretreatment standards, both general and specific, which are enforced by the local government under EPA oversight
authority.
While local governments must enforce the Federal discharge limits as a minimum, they have the authority to impose
discharge standards that are more stringent than the Federal limits. As will be discussed, the enforcement of more
stringent local limits is today more common than that of the Federal limitations.
For regulating purposes, electroplating plants, including PWB manufacturing facilities, have been divided into
several categories. Facilities are first divided into captive and job shops. A captive shop owns more than 50 percent
(annual area basis) of the materials undergoing metal finishing. A job shop owns 50 percent or less. PWB
manufacturing job shops are referred to in the regulations as independent printed circuit board manufacturers
(IPCBM). Facilities have also been labeled as existing sources or new sources, depending on when they began their
operations. New sources are those facilities that began their operations after August 31, 1982.
Most of the PWB facilities responding to the P2 Survey are indirect dischargers whose applicable federal regulations
are found in 40 CFR 413 (Electroplating Regulations) or 40 CFR 433 (Metal Finishing Regulations). These
regulations are shown in Exhibits 2-4 and 2-5. The Part 413 regulations apply to independent PWB manufacturing
facilities that were in existence since July 15, 1983. All other facilities are covered by Part 433 regulations.
The electroplating pretreatment standards for existing dischargers (Part 413) include an alternative mass-based standard
for printed wiring board manufacturing facilities. The standard is expressed in units of milligrams per square meter
19
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of boards processed per operation. An operation is any "electroplating" step (e.g., electroless copper plating, copper
sulfate plating) that is followed by a rinsing step. These standards can only be used upon prior agreement between a
PWB facility and the regulatory authority. One purpose of mass-based standards is to encourage the implementation
of pollution prevention. For example, a facility that has a concentration-based copper limitation has less of a
regulatory compliance incentive to install a drag-out tank and counterflow rinse than a facility with a mass-based
limitation. That's because a facility with a concentration limit has to treat the wastewater to the same low
concentration level regardless of the incoming flow rate and concentration. Alternatively, the facility with the mass-
based standard may reduce the wastewater flow and mass of copper entering the treatment system and not have to
achieve as low of an effluent concentration.
The CWA also has provisions for requiring best management practices (BMPs) in discharge permits. BMPs are
typically baseline practices that are low in cost and easily implemented. Examples of BMPs include: good
housekeeping, preventative maintenance, employee training, waste segregation, and use of specific P2 measures such
as drip guards.
Exhibit 2-4. Pretreatment Standards for the Electroplating Category
(40 CFR 413.84(b), (c),and (d))
Facilities Discharging <10,000 gpd
Pollutant Daily Maximum, mg/1 Max. 4 Day Avg, mg/1
Cadmium 1.2 0.7
Lead 0.6 0.4
Cyanide (amenable) 5.0 2.7
Total Toxic Organics 4.57 ™
Facilities Discharging >10,000 gpd
Pollutant
Cadmium
Chromium
Copper
Lead
Nickel
Zinc
Cyanide (total)
Total Toxic Organics
Daily Maximum, mg/1
1.2
7.0
4.5
0.6
4.1
4.2
1.9
4.57
Max. 4 Day Avg,
0.7
4.0
2.7
0.4
2.6
2.6
1.0
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Facilities Discharging > 10,000 gpd — Alternative Mass-Based Standards
Daily Maximum, mg/m2
Pollutant of Operation Max. 4 Day Avg, mg/1
Cadmium 107 65
Chromium 623 357
Copper 401 241
Lead 53 36
Nickel 365 229
Zinc 374 232
Cyanide (total) 169 89
Total Metals 935 609
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Exhibit 2-5. Pretreatment Standards for the Metal Finishing Category (40 CFR 433.15(a))
Pretreatment Standards for Existing Sources (PSES)
Pollutant Daily Maximum, mg/1 Max. Monthly Avg, mg/1
Cadmium 0.69 0.26
Chromium 2.77 1.71
Copper 3.38 2.07
Lead 0.69 0.43
Nickel 3.98 2.38
Zinc 2.61 1.48
Silver 0.43 0.24
Cyanide (total) 1.2 0.65
Total Toxic Organics 2.13 —
Note: Pretreatment standards for new sources (PSNS) are identical to PSES except for the cadmium limitations which are 0.11 mg/1 and 0.07
mg/1 for the daily maximum and monthly average.
2.3 State Pollution Prevention Laws
A number of states have passed laws that incorporate aspects of pollution prevention into RCRA and EPCRA
reporting requirements. Generally, these laws require industrial facilities that generate hazardous waste to develop a
source reduction and waste minimization plan, including an implementation schedule, and to track and report waste
reduction progress. A list of states with mandatory pollution prevention laws are presented in Exhibit 2-6. The
following are some examples of provisions from state laws:
• Arizona, California and Minnesota have similar P2 requirement. The Arizona law applies only to facilities that
must file the annual Toxic Chemical Release Inventory Form R required by EPCRA Section 313 or during the
proceeding 12 months generated an average of one kilogram per month of an acutely hazardous waste.
Minnesota's law has similar applicability. The California law only applies to facilities that generate more than
12,000 kilograms of hazardous waste or 12 kilograms of extremely hazardous waste in a calendar year. Each of
the three programs requires facilities to perform pollution prevention planning that identifies waste sources and
specific technical steps that can be taken to eliminate or reduce the generation of hazardous wastes. Each
program requires that facilities submit progress reports with the length of time between reports ranging from
one to two years.
• Texas has established a similar program; however, they have implemented a two-tier P2 system with source
reduction as the primary goal and waste minimization as the secondary goal. The program has wide
applicability in that it applies to all hazardous waste generators, exempt for conditionally exempt small quantity
generators. Planning, tracking, and reporting requirements of the Texas law are similar to those of the Arizona,
California, and Minnesota laws.
• A number of states have implemented voluntary pollution prevention programs. The foundation of these
programs is generally educational outreach and technical assistance mechanisms.
2.4 Local Pollution Prevention Requirements
The Clean Water Act gives qualified local POTWs the authority to administer pretreatment programs, including
regulation of industrial dischargers. These POTWs also have the authority to implement regulations that are more
stringent than federal guidelines, such as 40 CFR 433. Many local agencies have used this authority to reduce the
impact of industrial discharges on the operation of the POTW, reduce the concentration of toxic pollutants in POTW
sludges and/or to reduce the mass of pollutants discharged by the POTW. This is typically accomplished by
lowering the permissible concentration limits of industrial discharges below the federal standards. One local
program, administered by the Palo Alto Regional Water Quality Control Plant (RWQCP), also incorporates P2
requirements into pretreatment discharge permits. This is one of the first examples of the use of such requirements
in place of more traditional pollutant concentration limitations.
In response to its own stringent copper discharge limit, the RWQCP had to reduce the copper content of wastewaters
received at the plant. This effort is focused upon all sources of copper, including stormwater runoff, as well as
residential, commercial and industrial activities. Since most of the industrial copper in the Palo Alto area is
discharged by metal finishing operations, particularly those associated with computer parts manufacture, the
21
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industrial portion of the copper source reduction efforts focused on printed circuit board manufacturing and other
metal finishing operations.
Based on their new requirements, RWQCP formed a Metals Advisory Group, made up of volunteers from local
industry, environmental awareness groups, the general public, and local officials. In collaboration, this committee
made a decision to implement a unique plan to meet the discharge standards. The plan involved giving metal
finishing and printed wiring board (PWB) manufacturers the choice between mass-based discharge limits or
concentration limits that carry an additional P2 requirement. The mass-based limits could be met in any manner that
the industrial discharger chose to implement. The mass-based limits were established on a facility by facility basis
using data collected through RWQCP-conducted P2 studies. If a discharger selected the concentration limits (e.g.,
0.4 mg/1 Cu), they had to implement a specific set of P2 items that were referred to as Reasonable Control Measures
(RCMs). The RCMs were established through a study performed at six volunteer metal finishing and PWB shops.
The RCMs for PWB manufacturing facilities included:
Minimize drag-out (e.g., spray rinsing, drag-out tanks, air knives, splash guards, drip bars, changing drip times)
Counterflow rinsing (i.e., two stage with spray option)
Positive flow control (e.g., conductivity, timer, contact switch)
Extend bath life (e.g., purification, filtering, anode purity, change bath chemistry)
Pre-treat spent baths (e.g., electrowinning)
Control bath make-up (e.g., deionized water, control bath make-up and additions)
Minimize drag-in (i.e., prevent bath contamination)
Optimize wastewater treatment
There were a total of 13 metal finishing and PWB shops in the RWQCP service area in 1995. One facility made an
unrelated decision to move out of the service area. Of the remaining 12 shops, eight facilities chose the
concentration-based limits and installation of the RCMs.
22
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Exhibit 2-6. State Pollution Prevention Programs
State Program Statute
Mandatory P2 Programs
Arizona AZ Rev. Stat. Ann. 49-961 to-73
California CA Health & Safety Code 25244.12 to .24
Georgia GA Code Ann. 12-8-60 to -83
Louisiana LA Rev. Stat. Ann. 30.2291 to .2295
Maine ME Rev. Stat. Ana, tit. 38, 2301 to 2312
Massachusetts MA Ann. Laws ch. 211, 1 to 23
Minnesota MN Stat. Ann. 115D .01 to . 12
Mississippi MS Code Ann. 49-31-1 to -27
New Jersey NJ Stat. Ann. 13: 1D-35 to -50
New York NY Envtl Conserv. Law 27-0900 to -0925
Oregon OR Rev. Stat. 465.003 to .037
Tennessee TN Code Ann. 68-212-301 to -312
Texas TX Title 30, Ch335
Washington WA Rev. Code 70.95C.010 to .240
Voluntary P2 Programs
Alaska AK Stat. 46.06.021 to .041
Colorado CO Rev. Stat. Ann. 25-16.5-101 to -110
Connecticut CT Gen. Stat. Ann Appendix Pamphlet, P. A. 91-376
Delaware 7 DE Code Ann. 7801 to 7805
Florida FL Stat. Ann. 403.072 to .074
Illinois IL Ann. Stat. Ch. 111 , 7951 to 7957
Indiana IN Code Ann 13 -9-1 to -7
Iowa IA Code Ann. 455B.516 to .518
Kentucky KY Rev Stat. Ann. 224.46-310 to -325
Ohio HB 147, HB 592
Rhode Island RI Gen. Laws 37-15.1-1 to . 11
South Carolina SC Code Ann. 68-46-301 to -312
Wisconsin WI Stat. Ann. 144.955
Source: Dennison, Mark, Pollution Prevention Strategies and Technologies, Government Institutes, Inc. Rockville, MD, 1996.
23
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3.0 Prevailing and Alternative Printed Wiring Board
Production Methods and Materials
3.1 Overview of PWB Manufacturing Processes
This section of the report addresses printed wiring board production methods and materials that are of particular
concern with respect to waste generation and pollution prevention and control. This information will help the reader
to relate the pollution prevention and control survey data to specific production steps. A brief overview of PWB
manufacturing processes is presented in this section. This is followed by a more detailed discussion of rigid
multilayer board manufacturing (Section 3.2), the most prevalent method of fabricating PWBs. The detailed
discussion also contains information on alternative production methods and materials that may reduce waste
generation and/or involve less hazardous materials. Section 3.3 presents information on waste generation rates,
alternative processes and potential P2 technologies applicable to PWB manufacturing steps.
Printed wiring boards are categorized in several ways. When overall complexity is being considered, they are often
categorized in terms of layer-counts, or the number of circuit layers present on a single PWB. PWBs fall into three
layer-count categories: multilayer, double-sided and single-sided. The manufacturing steps for these different types of
boards are shown in Exhibit 3-1. Multilayer PWBs contain more than two layers of circuitry (i.e., at least one layer
is imbedded in the substrate between the top and bottom layers of the board). A multilayer PWB may contain 20 or
more layers of circuitry, but more common layer counts are 4-10 layers. A typical motherboard for a Pentium
personal computer is usually a 6- or 8-layer board. Double-sided boards have two interconnected layers and the
manufacturing process is a subset of the multilayer process. Single-sided PWBs have only one layer of circuitry.
Single-sided manufacturing is a small subset of the multilayer process with a considerable number of wet and dry
process steps eliminated.
PWBs are also categorized by substrate, or base material, type and fall into three basic categories. Rigid PWBs are
typically constructed with glass-reinforced epoxy-resin systems that produce a rigid board at thicknesses of less than
0.1" (0.062 is the common rigid PWB thickness although there is a trend toward thinner PWBs). Flexible (or flex)
circuits are manufactured on polyimide and polyester substrates that remain flexible at finished thicknesses. A third
category, rigid-flex, are a combination or assembly of rigid and flex boards laminated together during the
manufacturing process often to produce three dimensional circuits.
There are two basic types of manufacturing methods, although hybrid methods exist. Most common is subtractive
processing in which copper is selectively removed from a PWB; what remains forms the circuitry. What is referred
to as the subtractive process does include additive steps (such as copper electroless and electrolytic plating) but the
process of forming the circuit on the substrate is performed by subtracting (etching) copper. Additive processing
refers to a process whereby the circuit is formed by selectively plating metal on a substrate thereby creating a circuit
layer. In the fully additive process, no subtractive (etching) process occurs. Hybrid methods referred to as partially
additive and semi-additive are essentially subtractive methods, but the amount of copper etched from the boards is
much less than with the standard subtractive process.
Rigid Multilayer Manufacturing. This process is covered in detail in Section 3.2.
Rigid Double-Sided Manufacturing. Not unlike single-sided, double-sided PWB manufacturing is a subset
of the multilayer process. The inner-layer image transfer, lamination, and hole cleaning are eliminated. The
through-hole metallization process is required.
Rigid Single-Sided Manufacturing. Several process steps, including through-hole metallization, are not
performed in this process. Furthermore, since no process step is unique to single-sided manufacturing, manufacturers
of multilayer and double-sided boards often include single-sided manufacturing as part of their product mix.
The most common sequence of single-sided production is drill, print-and-etch, surface finish, and final fabrication.
No inner-layer processing, through-hole plating, or hole-cleaning is performed.
Flexible PWB Manufacturing Overview. A flexible circuit is manufactured on materials that allow for
bending or flexing of the PWB to create a three-dimensional effect or to allow for movement of a device to which the
circuit is attached. Flex circuits can be designed to be flexed into shape once or a few times or to withstand
24
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thousands of flexing cycles. Flex circuits are found in printers, disk drives, automobile electronics, and a wide range
of other common products.
Although similar to rigid manufacturing in many respects, the flexible circuit manufacturing process includes some
unique processes and materials, and in general, is not integrated into a rigid PWB facility although data suggest a
trend toward integration. Therefore, few rigid PWB facilities have expanded into flexible circuit manufacturing. On
the other hand, manufacturers of flexible circuits often produce rigid boards as well, often as part of rigid-flex
assemblies. Flexible circuits may be single-sided, double-sided or multilayer, although the dimensional stability of
flexible circuit substrates generally complicates multilayer manufacturing.
Image transfer, drilling (if any), and through-hole plating (if any) processes are similar but not identical to their rigid
counterparts. Flex substrates are thin and unlike standard rigid materials. Thicknesses of a few mils are common
compared to rigid material thickness of up to 31 mils for inner-layers and 62 mils for double-sided. Additionally,
tooling and surface finishing processes for flexible circuits are quite different when compared to rigid. A cover sheet
of similar material to the base film is laminated over the circuit of flexible PWBs whereas rigid PWBs are coated
with soldermask. The coversheet is pre-punched to expose appropriate areas of the circuit for component soldering or
device connections. Solder coating is performed with hot air solder leveling or hot oil reflow. Many flex circuits are
nickel-gold coated.
3.2 Rigid Multilayer PWB Manufacturing
The remainder of Section 3 describes the individual processes that are used for rigid multilayer board manufacturing,
the most common method of making PWBs. Each major step of the process is described using a "use cluster"
approach. A use cluster is defined as a set of chemicals, processes, or technologies that may substitute for each other
to perform a specific function. This approach is used by EPA to assess the potential health and environmental risks
of alternative chemicals, processes, or technologies (ref. 2).
For purposes of this discussion, the fabrication of rigid multilayer PWBs has been subdivided into nine process steps
(see Exhibit 3.1). These steps form a generic process flow, with many processes and potential alternative processes
within each function. Each process is described below, identifying the most common processes, common
alternatives, and the general technology trends.
Exhibit 3-1. Typical Process Flow for Rigid Board PWB Manufacture
Typical Single-Sided Rigid PWB Manufacturing Sequence
Typical Double-Sided Rigid PWB Manufacturing Sequence
Typical Multi-Layer Rigid PWB Manufacturing Sequence
Circuit
Design/Data
Acquisition
*
Inner-Layer
Image
Transfer
*
Laminate
Layers
-H
Drill Hole
Pattern
on Board
-^
Clean Holes
(Desmear)
*
Make
Holes
Conductive
1
25
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3.2.1 Circuit Design/Data Acquisition
Nearly all PWB design and layout is performed with Computer Aided Design (CAD) software, a relatively recent and
dramatic development in the history of PWB manufacture (Exhibit 3-2). CAD packages for personal computers
completely eliminated by the early part of this decade older methods of PWB layout. With the advent of CAD
systems came a dramatic change in the materials provided to PWB facilities that specify the manufacturing and a new
department, the CAM department, now exists in all PWB facilities to handle the incoming data.
Exhibit 3-2. Process Flow to Design and Produce Film with Data
Circuit
Design/Data •
Acquisition
I
-^
Inner-Layer
Image
Transfer
f ,
Disk
I
Computer
Aided
Design (CAD)
I
Direct
Modem Link
I
f
Internet
I
Computer Aided
Manufacturing
(CAM) Processing
Certain design aspects of PWBs affect the quantity and characteristics of wastes generated during manufacturing. The
designer, through manufacturing specifications, has some control over the environmental impact the circuit will
create. For example, specifying a tin-lead surface finish may generate more hazardous waste than using an organic
solderability preservative.
Circuit layout also has some bearing on waste generation. For example, using blind/buried vias on multilayer
boards makes more efficient use of the available circuit "real estate" and may eliminate some layers. This layout
decision should be balanced against the additional wet processing required to make those holes conductive (i.e., more
layers travel down the plating line and generate plating waste). A software package is currently being developed to
take these manufacturing and environmental impact factors into account. With this software, "What if scenarios can
be run to compare the waste generated by one type of circuit and manufacturing process versus alternatives (ref. 9).
26
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3.2.1.1 CAM Processing
Modern PWB facilities must transform CAD generated data into customized tools for the manufacture of the part,
namely photo-tools, drill files and profile routing files. These functions are performed in what is usually called the
CAM department.
Data files are transferred to PWB manufacturing facilities on magnetic media, via modem or via the Internet. These
image files (native CAD files or, more often, "Gerber" files, so named for the company that created the format for
its vector plotters) along with drill and rout files are analyzed and graphically displayed by CAM software for sales,
quoting, and manufacturability purposes. Thereafter, the data are manipulated and edited to create the image, drill and
rout files for necessary for photo-tool creation and fabrication. Step-and-repeat patterns, thieving patterns, stretching
or shrinking to offset characteristic manufacturing dimensional shifts, registration and tooling marks, and other
editing is performed to create the highly customized photo-tools. Higher-end CAM packages will also perform
design-rule checking and other manufacturability analyses.
3.2.1.2 Photoplotting
CAM files are transferred to photoplotters for film imaging. Modern laser photoplotters can image a layer of
circuitry in a few minutes or less. Silver-based high-contrast film, secured on a flat bed or a rotating drum, is
passed under a laser source and the image created by the CAM software is reproduced on film. Developing is
performed in a three- or four-chambered conveyorized developer that includes developer, fix, rinse and drying steps.
The film generated in this step usually serves as the photo-tool for the image transfer process.
The film developing step does produce a small silver-bearing waste stream. The film itself contains approximately
0.0016 ounces per square foot and 80% of this silver winds up in the spent developer, fixant, and rinse (ref 10).
Metallic replacement or electrolytic plating can be used to recover silver from the waste chemistry. With metallic
replacement, the solution is passed through a steel wool cartridge where the iron in the steel wool reacts with the
silver and replaces it. A silver sludge settles to the bottom of the cartridge. An electrolytic recovery system (referred
to as electrowinning and discussed in Section 5) recovers silver by plating the silver in the solution onto cathodes.
Photo-tools are ultimately discarded after the tool has served its purpose. Some facilities collect this film and ship it
offsite for silver recovery although the small yields do not encourage such a practice.
A company has developed a new film that consists of a thin layer of bismuth chemically deposited onto a polyester
base (ref. 11). The bismuth is then sandwiched by another polyester sheet that acts as a protective cover to prevent
scratching. The bismuth layer, initially opaque, has the property of becoming clear when heated. Gerber Scientific
Instruments has designed a laser photoplotter for this material that can also expose standard silver halide film. The
PRISM-IR photoplotter uses a 10W Nd:YAG infrared laser for the bismuth film, combined with a red laser diode for
silver film. This film requires no developing step, therefore, no waste stream is generated.
Registration systems, which maintain layer-to-layer alignment, usually include a film punch. The photo-tool is
imaged with targets (added to the image files in the CAM department) that match fixtures in exposing frames
employed in the image transfer step. The targets are punched in manual or automatic film punches. The film is
then inspected for flaws, repaired if necessary, and is then ready to perform as a photo-tool.
3.2.2 Inner Layer Image Transfer
The purpose of this process step is to transfer a circuit image to the copper-coated base laminate of the PWB
(Exhibit 3-3). Two basic strategies exist: subtractive and additive. The predominate method is subtractive which is
accomplished through a series of steps known collectively as "print-and-etch." Additive methods of multilayer
circuit manufacture are briefly covered in Section 3.1.
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Exhibit 3-3. Inner Layer Image Transfer
3.2.2.1 Conventional Print-and-Etch
Print-and-etch is a series of process steps that accomplish the goal of image transfer from the photo-tool to the
copper foil layer of the base material. The "print" step includes the coating of the copper-foil-clad base material with
a light-sensitive, organic photoresist. The photoresist (so named because in addition to being light sensitive, the
coating will subsequently "resist" the etchant during a later step in the print-and-etch process) polymerizes when
exposed to a light source of appropriate energy. The phototool, placed over the photoresist, acts to allow only an
image of the circuit to be exposed, protecting the other areas of the photoresist layer. After exposure, the photoresist
layer is developed; the exposed, polymerized areas remain, the unexposed areas (those which were under opaque areas
of the photo-tool) are washed away, revealing the copper layer underneath.
The "etch" portion of print-and-etch removes exposed copper areas selectively from the panel, but cannot attack the
copper residing under the photoresist. Thus, the image of the circuit is transferred from the photo-tool to the copper
layer.
PWB Laminate. The PWB base material consists of a dielectric core that has been coated or impregnated with
resin. The dielectric material is usually woven glass fibers or paper. Different combinations of these two materials
and the substitution of various resin systems can alter the electrical, physical, performance, and cost characteristics of
the material. The type of material employed for a specific part depends on the function of the PWB, design
requirements, and how it will be manufactured. Some materials perform better in certain environments (e.g.,
extreme heat or high humidity), others are more suitable for a particular manufacturing process (e.g., punching),
while others are chosen for their electrical properties (e.g., dielectric constant). FR4 is the designation given to the
most widely used material for the printed wiring board industry. It is constructed of multiple plies of resin
28
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impregnated woven glass cloth. GI type material, also known as polyimide, is an example of a high temperature
type material. Its resin system allows it to sustain temperatures of 200°C vs. FR4's 120-135°C.
Copper foil is rolled or electrolytically deposited on the base laminate. PWB facilities generally purchase sheets of
copper-clad base laminate in sizes of 3x4 feet or larger.
Survey data relative to base materials used by respondents are located in Appendix A.
Material Preparation. The core material is sheared to panel size then cleaned mechanically, chemically, or by a
combination of both. The purpose of this cleaning step, referred to as "pre-clean" or "chem-clean," is to remove
surface contamination, including any anti-tarnish coating present and to condition the surface copper topography to
promote the subsequent adhesion of photoresist.
Mechanical scrubbing methods include abrasive brush scrubbing and pumice scrubbing. Brush scrubbing removes a
thin layer of surface copper, thus ensuring a clean surface, but tends to impart stress to thin core material by
deforming it during the scrub. Brush scrubbing can also produce a surface not compatible with fine-line circuit
designs. Pumice or aluminum oxide scrubbing imparts less or no stress to the material and produces a favorable
surface for photoresist lamination, but is known to be ineffective at removing anti-tarnish coatings applied by
laminate manufacturers. Thus, pumice scrubbing is often accompanied by chemical cleaning.
Chemical cleaning is usually accomplished in a conveyorized spray chamber. Two chemistries are sprayed onto the
surface of the panel. The first is usually a proprietary product designed to remove anti-tarnish coatings. The second
is a micro-etchant such as potassium persulfate, which is applied to further clean the surface and leave a desirable
surface finish. A third chamber may include a mild anti-oxidizer.
Pre-treated material does not require cleaning and is discussed in Section 3.2.2.2.
The decision of which cleaning method to use is driven by a number of factors. Pumice scrubbing is claimed by
some as the process that produces the best surface for photoresist adhesion (a critical consideration; poor photoresist
adhesion is almost always fatal). But pumice scrubbing requires rather expensive and maintenance-intensive
equipment. While rinsewater generated in the pumice scrubbing operation is usually free of metal (the surface copper
is deformed during pumice scrubbing, not removed), pumice scrubbing is usually preceded by a chemical clean step
designed to remove the anti-tarnish coating that laminate manufacturers apply and this step does produce a copper-
bearing waste stream. Chemical cleaning produces a copper-bearing waste stream from each of the process tanks, but
the micro-etchant chemisty is found in many processes and its associated copper recovery and treatment regimen is
likely to already be in place in the shop. Mechanical scrubbing produces copper dust in its waste rinsewater stream
which is easily removed by simple filtration. Mechanical stress imparted to thin core material during scrubbing and
the difficulty of maintaining a precise topography as brushes wear tend to limit mechanical scrubbing of very thin
materials.
Imaging. The imaging process includes three steps: photoresist application, exposing (or "printing") and
developing. Photoresists are available as a dry film, currently the most common, and liquid resists. Dry film resists
are usually sold in rolls ranging from 2 in. to 60 in. wide and 125 ft. to 1,000 ft. long. Resist thickness varies
depending on the application. Resists less than 1 mil can resolve very fine lines. Resist thickness of 1 to 1.5 mils
is common for imaging innerlayers. Thicker resists (1.5 to 2.0 mils) are used as plating, rather than etch, resists.
The greater thickness allows the metal to plate up the sidewalls of the film without mushrooming over the top.
This mushrooming effect will cause downstream problems during the resist stripping and etching steps (ref. 12).
The photoresist is applied with heat and pressure to the surface of the panel. This can be done with a hot-roll or cut-
sheet laminator. A cut-sheet laminator cuts the resist slightly less than the panel dimensions thereby generating
fewer resist trimmings than a hot-roll laminator. The photo-polymer film layer is sandwiched between a separator
sheet that is automatically peeled away by the lamination equipment and a mylar cover sheet that is peeled away by
hand when the panel is ready for development. This top coversheet also serves to protect the resist from scratches,
keeps contaminants from the surface and prevents the phototool from adhering to the resist. Modern dry film resists
for common print-and-etch functions are fully aqueous and are developed in a simple carbonate solution.
Although less common, liquid photoresists offer certain distinct advantages over dry film, and some disadvantages.
Liquid resist coating equipment is more expensive than dry film lamination equipment, but offers greater production
29
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rates (250-300 panels per hour vs. 150 panels per hour with dry film) (ref. 13, 14). Liquid resist is more tolerant of
surface topography, but requires a higher level of surface cleanliness. Since the coating does not include a cover
sheet (the phototool rests directly on the photosensitive coating), resolution of fine lines is improved. Liquid resist
is applied either by roller coating or by curtain coating. Roller coating allows double-sided coating and the
equipment is less expensive than curtain coating. Development is performed in similar or identical chemistry as dry
film.
The printing of the image is accomplished with a film or glass phototool being placed between the panel to image
and a light source. A vacuum is drawn to remove air and to ensure the phototool is held securely against the panel
before the light source is turned on. Hinged-glass frame fixtures have become common to expose panels. Pins can
be set in the glass and when used in conjunction with holes punched in the film achieve precise layer-to-layer
registration. One drawback with glass is its natural rigidity which can cause off-contact exposure (ref. 12). An
alternative to glass is a polyester blanket which achieves a very good vacuum, but as the polyester conforms around
the edge of the panel and contacts the bottom glass, it can isolate portions of the blanket from the vacuum source.
"Bleeders" or "shims" must be used to maintain a constant source of vacuum to the surface of the panel (ref. 15).
Some facilities remove the mylar cover sheet from the photoresist prior to exposing when the traces are very fine.
The removal of 1 more mil of separation between the photoresist and the phototool decreases the chances of light
diffusion under the phototool. Also, there is less light scattering, which results in more light hitting the panel and
better resolution of the image. Finally, any foreign particles that collect on the coversheet will be removed along
with the coversheet. Using this method has enabled lines and spaces as fine as 1.5 mil (ref. 16).
Developing is performed in a sodium carbonate solution (1% to 2%). The same general developing chemistry can be
used for both dry film and liquid resist. The spent developer stream is of considerable volume, usually the largest
spent process fluid stream a PWB facility faces. Although copper is not usually present in the alkaline spent
developer, this stream, along with the spent resist stripper, is the source of photo-resist solids, or skins. Resist
solids from the developing of photo-resist does not generally fall into the category of F006 wastes because the
process is not (usually) "in line or contiguous with an electroplating operation." Developing precedes plating steps
and is separated from them by rinsing and drying steps, which is the basic consideration in determining the status of
the solids (see section 2.2.21). The more complicated status of resist solids generated during resist stripping
operations is discussed in Section 3.2.7.1.
Alternative image methods are discussed in Section 3.2.2.2.
Etching. Etching is required for any of the process alternatives within the subtractive process. Panels entering the
etch process have been coated with an etch resist, usually a dry film photo-resist. The resist layer selectively
protects the circuit areas from etchant, whereas the remaining copper foil is etched away.
Exhibit 3-4. Common Primary Etchants Used in PWB Manufacturing
Type Applications Advantages Disadvantages Cu Capacity
Cupric
Chloride
Ammoniacal
Sulfuric-
peroxide
For use with
organic resists
Organic or
metallic resists
Organic or
metallic resists
Ease of regeneration
Ease of copper recovery
Continuous operation
Ease of control
Simple waste treatment
Ease of regeneration
Constant etch rate
Incompatible with metallic resists
Regeneration is more difficult
Higher machine costs
Employee safety concerns while
handling concentrated chemicals
15-20 oz
18-24 oz.
4-5 oz
Etchant sprayed onto the surface of the panel removes the exposed copper, but cannot significantly dissolve the
copper residing under the resist. In this way, a copper circuit is formed. Etching is performed with conveyorized
equipment that typically includes a main spray chamber, an etchant flood rinse, and several cascading water rinses.
Long conveyorized units that include developing, etching, and film stripping are common only in large production
shops. Acidic cupric chloride and alkaline ammoniacal are the most common etchants (sulfuric-peroxide, a common
microetchant, is also employed as a primary etchant). Chromic acid and ferric chloride, dominant in the past, are
now rarely found. A complex array of issues surround the choice between the remaining chemistries, and the
decision is tied to downstream and upstream process material choices as well as economic considerations.
30
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For example, cupric chloride is generally incompatible with the metallic resists (tin or tin-lead) which are commonly
applied to outer layers, but may be selected for inner layers based on performance (for fine-line etching), waste
minimization (ease of on-site regeneration and copper recovery), or other issues. In this example, two etching
systems are required, cupric chloride for inner layers and ammoniacal for outer layers. Being a one-step conveyorized
process, etching is not often a production bottleneck and two etching systems may be difficult to justify. For this
reason, many small shops employ the more versatile ammoniacal etchant for both inner and outer layers.
Cupric chloride etchants consist of cupric chloride (CuCl2) and hydrochloric acid. The simple etch reaction is driven
by copper's two oxidation states:
Cu + CuCl2 -> Cu2Cl2
The reaction with cupric chloride etchant is reversible chemically by chlorination, oxidation with peroxide or other
oxidizer, or electrolytically. Several regeneration systems have been developed that reoxidize cuprous chloride and
maintain total copper content at desirable levels (usually in the 15 to 20 ounce/gallon range) (ref. 69). Chlorination,
the most common method, is performed in a closed-loop arrangement in which spent etchant is circulated through
the chlorinator and back to the etcher sump. Copper oxide waste is produced. Since this etchant is acidic, no attack
on the alkaline-sensitive dry film resists occur. Cupric chloride has a similar etch rate to ammoniacal but is not, as
mentioned above, compatible with many metal resists.
Ammoniacal etchant is popular due to ease of use and general compatibility with most etch resists. Ammoniacal
etchant systems are comprised mainly of ammonium hydroxide and ammonium chloride. Other ingredients are
present to a lesser degree and serve a variety of functions. As with cupric chloride etchant, the etching reaction is
driven by the cupric (Cu++) ion:
Cu + (Cu(NH3)4)+2 -» (2Cu(NH3)4)+1
Ammoniacal etchants are maintained for continuous operation with a feed-and-bleed arrangement based on baume or
specific gravity measurements. In this arrangement, a pump is connected to a baume-activated switch. When the
baume of the etchant in the sump rises due to the increasing copper concentration, the pump is switched on. Copper
rich etchant is removed from the sump while fresh etchant is introduced. In this way, a steady concentration of
copper (critical in maintaining a steady etching rate) is maintained. In the absence of regeneration, the spent
ammoniacal etchant stream is usually the largest waste stream shipped off-site by PWB shops.
Sulfuric-peroxide (i.e., sulfuric acid and hydrogen peroxide) is commonly used as a micro-etchant. This chemistry
was reported in use by a small percentage of respondents as a primary etchant. Sulfuric-peroxide has a much lower
copper-holding capacity than other etchants (approximately 4-5 oz/gal Cu vs. 15-24 oz/gal Cu or more for
ammoniacal and cupric chloride) but is easily regenerated on-site and is compatible with metallic etch resists.
The survey results relating to etchants are presented in Exhibit 3-5. 81% percent of the survey respondents use
ammoniacal etchant for inner-layer etching, while 18% use cupric chloride. Sulfuric-peroxide for inner-layer etching
was in use by 2 respondents. 5 of the 10 largest facilities reported using cupric chloride. The disproportionate use
of this etchant amongst larger facilities may be due, in part, to their ability to economically justify two etching
systems (4 of these 5 facilities used ammoniacal etchant exclusively for outer-layer etching).
Outer-layer etchant use data are discussed in Section 3.2.7.2.
31
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Exhibit 3-5. Etchant Use
90
80
70
50
o
o 40
I 30
20-
10-
Use Etchant for All or Part of
Inner-Layer Production
Use Etchant for All or Part of
Outer-Layer Production
Cupric
Chloride
Ammoniacal
Other
Resist Stripping. The photoresist is stripped after etching. Stripping may be part of the conveyorized etching
process with another spray chamber or done as a batch process in a stripping tank. A wide array of resist strippers
exists. A hot potassium hydroxide (KOH) solution is one, but this process is inappropriate for spray operation
because the resist is removed in strips and not dissolved. Monoethanolamine (20% by volume in an alcohol solvent)
is the chemistry of choice for most applications. Other proprietary formulations abound. Photoresist developer and
stripper wastes depend on the carrying capacities of the chemistries, the thickness of the resist, and the area to be
developed or stripped. See the Photoresist Stripping subsection in Section 3.2.7.1 for a discussion of the regulatory
status of resist skins.
Oxide. Oxide treatment is used in PWB manufacture to promote copper-to-epoxy adhesion in multilayer
manufacture. The batch oxide process line usually contains four or five process tanks and three or four rinse systems
(Exhibit 3-6). The process tanks consist of a hot alkaline cleaner, a microetch, and the oxide bath itself, which may
include a dilute pre-dip for drag-in protection. The microetch may be persulfate- or peroxide-based. Oxide
chemistries are usually proprietary—a common oxidizer is sodium chlorite with sodium hydroxide. Other
ingredients vary from vendor to vendor. The oxide bath must be quite hot, usually 140 to 150°F or hotter. The
process takes 15 to 30 minutes to complete.
Exhibit 3-6. Typical Oxide Line
, Drag-Out
Rinse
Rinse
•Mjeroeteh
Rinse
Rinse
Sulfuric,'
, Acid 'Dip'
Rinse
Rinse
Rinse
32
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One alternative is the conveyorized white oxide process that uses tin oxide as the adhesion promoter. Approximately
four microinches of tin metal are plated by displacement on the copper surface in this self-limiting process (ref. 17).
Another alternative is a proprietary acid-based oxide replacement (ref. 18). This solution is most effective when used
in conjunction with a new "drum-side treated foil," but it reportedly produces good results with conventional foils as
well. This new foil has topography with more surface area than ordinary copper foil, which allows for greater
deposition of the adhesion promoter. The proprietary oxide replacement is a sulfuric/peroxide-based system that is
applied horizontally with conventional spray equipment. The process time is less than 10 minutes and the process
bath temperature is 95-100°F. In addition to the increased productivity, some environmental benefits exist:
• Sulfuric peroxide is used as a microetch in many facilities and waste treatment may already be in place.
• Greater than 90% of the copper in the bath can be recovered with electrowinning or chilling whereas this is not
possible with the oxide solution.
• Sulfuric -peroxide baths are quite likely to be found elsewhere in the facility and the treatment and copper
recovery strategy already in place. Hypochlorite-based chemistry requires a distinct waste treatment strategy.
• The shorter process line and process time reduces the amount of rinse water used and wastewater generated.
The survey data indicate that all facilities producing rigid multilayer boards use the conventional oxide step for at
least some of their multilayer product and 13% also purchase double-treated material for some of their product. Of
the three exclusively flex manufacturers, one does not perform the oxide step at all, one does not use the oxide step
for 98% of multilayer product, and the third uses double-treated material on all of its multilayer product.
3.2.2.2 Image Transfer Options
Pre-treated Material. A minority of facilities reported using laminate that is pre-treated by the laminate
manufacturer with an oxide coating. This material, often referred to as "double-treat" material, comes ready to use.
No scrubbing or chemical cleaning is needed, although some facilities will run the panels through tacky rollers prior
to lamination. Eliminating the need for oxide treatment reduces chemical and water usage as well as process steps.
This is attractive to smaller, quick turnaround shops.
Pre-treated material is not appropriate for several applications including blind and buried via processes, during which
the oxide coating would be removed during the via metallization process. Furthermore, rework of pre-treated panels
is often severely limited; for example, stripping photoresist and reapplying is a fairly common rework scenario that
is not advisable with pretreated material simply because the stripping process includes a cleaning step prior to the
reapplication of the photoresist and this step will remove the oxide coating. Automated Optical Inspection (AOI)
performance can be negatively affected by the dark, nearly black surface of the oxided material. And finally, while
positively affecting waste generation at the PWB shop, the strategy of purchasing pre-treated material simply pushes
the oxide process and its attendant waste upstream to the laminate manufacturer.
Direct Imaging. Direct imaging is an alternative to using film or glass photo-tools. The panel is coated and
developed the same as when using a photo-tool, but the exposing step is done with a laser in place of a photo-tool.
Direct imagers are similar to photoplotters, except the photoresist-coated panel is imaged by laser rather than film
(so similar are the two the direct imaging machines are usually designed to perform either task). The high capital
costs, performance issues, and the fact that direct imaging takes longer than conventional exposing in most cases
have historically impeded the penetration of this technology. However, advancements in photo-resist technology and
improvements in laser technology are renewing interest in direct imaging.
In addition to the cost savings in film and developer chemistry, finished product yields may increase as well due to
improved alignment between layers. Film photo-tools suffer dimensional instability from the environment where
they are created, used and stored. Changes in temperature and humidity can cause characteristic and troublesome
stretching and shrinking of film photo-tools. The dimensional instability of film is, in many cases, s the largest
contributor to the overall registration tolerance of the manufacturing process. With direct imaging, only the
positional tolerance of the imager (usually claimed to be less than 1 mil over 24 inches) contributes to
misregistration. Furthermore, direct imaging eliminates the defects introduced by imperfections (dust, scratches) in
the photo-tool that occur during photo-plotting or thereafter during handling and use.
Electrodeposited Photoresist. Recently a company has developed a positive acting, cathodically
electrodeposited photoresist. Electrodeposited (ED) photoresists offer an alternative for imaging very fine lines and
spacing while using the print and etch process. Lines and spacing at 2 mils have successfully been etched with ED
33
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resist. Conductive surfaces are completely and uniformly covered with resist by submerging them in an aqueous,
micellular dispersion of the resist. Using a rectifier, the panel is charged to either a negative or positive potential
and attracts the polymer micelles in the resist bath. The panels come out of the bath with a clear resist coat; there is
no color pigmentation. The resist is non-tacky so phototools can be placed directly on the panel. The elimination
of the coversheet, normally found with dry film resists, improves line and space resolution. The image is developed
with an aqueous acid that differs from the standard resist developing chemistry.
This ED resist coating has some advantages over dry film photoresists: Dry film will tent over surface imperfections
(e.g., pits and scratches) rather than conform to them, which could allow etching chemistry to etch out the
underlying copper. Also, dry film is relatively thick (1 mil or greater) compared to ED resist (0.3 to 0.5 mils thick).
This makes it more difficult to develop out the channels between closely spaced circuitry. Another useful feature of
ED resists is the ability to make landless vias. Dry film tents over holes therby sealing off the hole barrel during
etching but it requires a pad, or annular ring, to anchor the film to the surface surrounding the hole. ED resist coats
the barrels of holes, as well as the surface, and eliminates the need for a pad (ref. 19).
3.2.2.3 Blind/Buried Via Multilayer Manufacturing
These two technologies are specialty type multilayer manufacturing which have been devised to make more efficient
use of circuit "real estate." Both methods are considerably more expensive to manufacture and are not recommended
as a casual solution to circuit routing problems due to dense layouts. Buried vias are drilled through innerlayers and
do not exit to either outer layer. Blind vias start at one surface layer but terminate prior to penetrating all of the
layers.
Because of the surface preparation steps required prior to making holes conductive, pre-treated material cannot be used
for blind or buried vias.
Buried Vias. The manufacturing process differs in that the innerlayer material must be drilled (Section 3.2.4) and
the holes made conductive (Section 3.2.6) prior to exposing and lamination (Section 3.2.3). It is processed as a tent
and etch outer layer (Section 3.2.7.1). This is performed for each pair of layers with buried vias. Then, they are
then laminated together and afterwards, processed normally starting at drilling.
Exhibit 3-7. Process Flow for a Buried Via Processing
Complex sets of buried vias can greatly complicate the manufacturing process. For example, if the buried vias are
designed to penetrate more than two layers, multiple or sequential lamination is required and the first four steps in
Exhibit 3-7 are repeated one or more times.
Blind Vias. There are two methods for manufacturing blind vias, each with their own advantages and
disadvantages. The first is to print, etch, laminate, and drill the innerlayers with the blind vias. After metallizing
the holes, the next set of blind vias (or the remaining layers if there are no more blind vias) are laminated to the first
assembly. This is also known as "sequential lamination" since the panel goes through multiple laminations for each
set of blind vias (Exhibit 3-8). It is a reliable method for plating holes since the vias are plated as through-holes
rather than as blind holes, but sequential lamination requires several time-consuming lamination cycles and increases
the square footage usage of the metallization line, which increases waste generation.
34
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Exhibit 3-8. Blind Via Process Using Sequential Lamination
Repeat for other
blind vias or to
laminate rest of
panel.
The alternative method to create blind vias is to use controlled depth drilling (Section 3-9). With this method, all of
the innerlayers are laminated in one step, similar to standard multilayer manufacturing. The panels are then drilled
with through-holes. Blind vias are drilled with precise controlled depth drilling. The panel is then sent to hole
cleaning and the through-holes and vias are made conductive as with the normal multilayer process.
The efficiency of the controlled-depth-drilling method is considerable when compared to the aforementioned sequential
lamination method, but process windows in both the drilling and plating steps are quite narrow. To accurately
penetrate a panel with CNC drilling equipment, at a precise depth, depends on several factors, including: an intimate
knowledge of the internal z-axis position of the layers in the multilayer panel; panel-to-panel and across-panel
consistency of the z-axis position of the layers; and the accuracy of the z-axis control of the drilling machine.
Plating blind holes is also challenging. Removing trapped air and providing fresh chemistry into the blind hole
during the plating time is necessary to prevent voids and thin plating. In short, reject rates are higher with this blind
via method.
Exhibit 3-9. Blind Via Process Using Controlled Depth Drilling
Clean Holes
3.2.3 Lamination
During the lamination process the thin-core innerlayers are subjected to heat and pressure and compressed into a
laminated panel. Sheets of material consisting of glass fibers impregnated with epoxy resin, known as pre-preg or
b-stage, are slipped between the layers and bond the layers together. Pre-preg is available in different styles with
varying amounts of resin and glass fibers, which allows the manufacturer to control the thickness between layers and
to provide the appropriate amount of resin flow between circuitry.
-------
Lamination steps are fairly consistent among manufacturers, although substitute lamination materials are available.
All of the materials, including the innerlayers and pre-preg, are tooled to the same registration system and are held in
place by tooling pins. Several panels can be pressed together in one set of heavy plates, creating what is known as a
"book." Next to each copper outer layer is some sort of protective coversheet. Sheets of aluminum or a thin plastic
sheet such as Paco-Thane® and a steel separator plate are used for this purpose. Foreign material must be kept from
the copper surface or it will become pressed into the surface of the panel causing pits and dents. Dust and other
contaminants can degrade the bondline between copper and the epoxy so cleanliness is essential. ,However, not all
manufacturers perform this process in a cleanroom environment.
Copper foil can be purchased that is laminated to an aluminum separator sheet. The sheets are laminated in a clean
room environment, which prevents any particle contamination on the copper surface. After the multilayer
lamination cycle the aluminum is peeled away, revealing the copper sheet underneath. Commercial products of this
nature are readily available (ref. 20).
Kraft paper, other fiber materials, or silicone rubber pads are used when the book is loaded into the press to evenly
distribute the pressure and temperature (ref. 21). Modern presses have platens that are enclosed in a vacuum chamber
to remove air and volatiles from the panels as the B-stage cures. If any air remains between layers, it will leave an
air pocket or bubble that may lead to delamination of the panel. Another benefit of vacuum lamination is that less
pressure is required, which reduces misregistration from the panels skewing under excessive force. Press cycles are
usually computer-controlled. The specific cycle is dictated by the substrate employed; for FR-4, temperatures of
350°F (176°C) and pressures of 150 to 350 psi are common. The entire cycle from heating, curing, and cooling can
take 2-3 hours for FR4 type material and as long as 5-6 hours with polyimide.
The heavy plates, steel separator plates, and silicone or rubber press pads are items that can be reused as long as they
are performing satisfactorily. The Paco-Thane® and Kraft paper are discarded after one use. If aluminum sheets are
used, they may be collected and sold for scrap or, depending on thickness, used in the drilling room as entry material.
Coolant water used by the press is either discharged or reused.
3.2.4 Drilling
Holes are drilled through the PWB to interconnect circuitry on different layers and to allow the insertion of
components (Exhibit 3-10). The etched innerlayer pattern will extend to the barrel of the hole and therefore will be
interconnected with the other layers when the hole barrel is made conductive in a later step. Most drilling is
performed with computer numerical control (CNC) equipment, but as hole sizes less than .012" have become more
common, other methods of making small holes are increasing in popularity. Two alternate methods are punching
and laser processing. Entry and back-up materials vary between manufacturers, since there are several alternatives.
These options are discussed below.
Dull drill bits can be sent for resharpening 2 to 4 times before being discarded. The backup material can be flipped
over and used a total of 2 times before being discarded. Paper types of entry material are disposed of, while
aluminum entry is collected and sold. The waste copper debris and fiberglass dust that is drilled or punched out of
the material is carried by vacuum away from the machinery and work area and into a holding tank.
By using new and stronger materials, drill bits can drill 200 to 1,000 times more holes as ordinary bits. Punching
holes eliminates the hole cleaning process and the need for entry material. Entry material and drill bits are
unnecessary to laser process holes.
36
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Exhibit 3-10. Drill Holes Process Step
3.2.4.1 Conventional CMC Drilling
Mechanical drilling is a mature technology that has reliably produced what have now become relatively large holes.
As hole sizes have gotten smaller, mechanical drilling limitations, such as drill bit diameter and aspect ratios have
emerged (ref. 22). Also, where drilling equipment technology surpassed that of drill bit metallurgical technology 10
years ago, that situation has now reversed. Older and poorly maintained equipment may not be able to drill small
holes. One reason is the inability of the spindle to generate high enough rotational speed. Another is that drill
runout and Z-axis slop are disproportionately large for these bits (ref. 25). Despite the smaller hole difficulties,
mechanical drilling is how the majority of manufacturers create holes. High-end CNC drilling equipment has "lights
out" features which allow automatic loading and unloading, broken bit detection, and tool cartridges that can hold
hundreds of tools for automatic replacement at programmed intervals.
Entry Material. The top layer that the drill enters before PWBs are drilled is called "entry material." The PWBs
are drilled in stacks that consist of a sheet of entry material, one or more circuit panels, and back-up or exit material.
Entry material is required to reduce or eliminate exit burring and to reduce drill wander, which is the tendency of the
drill to briefly skate on the surface before penetrating. A variety of entry materials exist, the most common being
paper-phenolic (10 to 24 mils thick), paper-melamine (10 to 24 mils thick), aluminum (7 to 15 mils thick), and an
aluminum-clad material consisting of a phenolic, melamine, simple paper, cellulose, or other core. Some entry
material is specifically made for small-hole drilling. One product consists of 1.5 mils of aluminum laminated to a
3.5 mil cellulose core. The alloy's softness allows for easy and accurate penetration while the cellulose softens the
impact of the drill bit (ref. 25). Entry material is discarded for recycle or disposal after use.
Back-up Material. The drill bit terminates its downward stroke with the point penetrating the back-up material
in order to complete the drilling of the bottom panel in the stack. Back-up materials are generally 0.062 or 0.093
37
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inches thick. Common materials are pressed wood products (pulp or fiber), paper-phenolic-clad with a wood product
core, or aluminum-clad with a wood product core. Since the drill penetrates only halfway through back-up material,
it is generally flipped over and used a second time before being discarded.
D rill Bits. Drill bit makers are now using materials such as diamond tipped bits and carbide alloys, which are
90% stronger than the older bits, to drill the smaller holes now being called out. Bits as small as 2 mils have been
produced. Ordinary drill bits become unacceptably dull after 1,000 to 5,000 hits, but diamond tipped bits purportedly
can drill one million holes if properly used. Drills are usually resharpened 2 to 4 times before being discarded. It is
estimated that 70% of holes drilled are drilled with resharpened bits (ref. 22).
3.2.4.2 Punching
Punch presses have been used for years to make holes by the millions for paper-phenolic PWBs used in consumer
items. It was discovered that punching could be used as a complement to the process of making high-density
multilayer boards. It solves the mechanical drilling problem with small holes and is less expensive than laser
processing. Punching is generally restricted to making small via holes on thin substrates (0.005" to 0.020").
Advantages to punching include:
• Better hole quality
• No hole cleaning process required
• No need for entry or backup materials (ref. 23)
3.2.4.3 Laser Processing
A few technologies exist for making holes using lasers. One company manufactures a unit that can drill 4 mil holes
and smaller in copper-clad and glass reinforced materials. Using a Nd:YAG laser, this unit can create up to 1,200
vias per minute (ref. 24). Another company uses a CO2 multimode laser that is capable of drilling FR4, BT resins,
and PTFE type materials at up to 1,200 holes per minute (ref. 23). A dual laser type system has also been
developed. A computer controls the alternating ruby laser to drill through copper and CO2 laser to clean out the
epoxy (ref. 25).
3.2.5 Hole Cleaning
Hole cleaning generally refers to a process called desmear and/or the closely related process of etchback. Desmear
removes the melted resin smear that results from the friction of the drill bit cutting through the material. If the
smear covers the copper that extends to the barrel of the hole, it would prevent interconnection between it and the
subsequently metallized hole. During etchback, in addition to removing resin smear, glass fibers are etched. The
result is that the copper on the innerlayers protrudes out into the barrel of the hole. This allows for what is known
as a "3-point" connection after metallization. Most of the demand for etchback stems from military specifications.
Exhibit 3-11 summarizes methods of hole cleaning and Exhibit 3-12 displays the survey results for this process
step. Detailed respondent data are found in Appendix A.
38
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Exhibit 3-11. Clean Holes Process Step
-*-
Laminate
Layers
-f
Drill Hole
Pattern
on Board
-4
Clean Holes
(Besmear)
Sulfuric Acid
1
Permanganate
1
Plasma
Besmear
1
Beburring and scrubbing are processes performed immediately before or after desmear or etchback. Buring drilling,
copper burrs may be raised on both sides of the panel by the action of the drill entering and exiting the material. The
burrs are sanded smooth on a deburring machine, which consists of a sanding wheel and a conveyor. In wet
deburrers, copper dust is carried off in a waste stream. Bry machines usually are outfitted with vacuum units.
Beburring is more correctly considered a surface preparation step rather than hole cleaning. Scrubbing is performed
as a surface preparation step prior to electroless copper (and during other stages, such as before solder mask).
Scrubbing may be performed similarly to deburring, except a much less aggressive surface abrasion occurs. Pumice
or aluminum oxide scrubbers, which direct a high-pressure spray of abrasive particles at the PWB, are also used for
surface preparation.
39
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Exhibit 3-12. Distribution of Besmear Methods
Sd
70
o 50
40
20
10
Permanganate Only
Sulfuric and
Permanganate
Plasma
Do Not Desmear
3.2.5.1 Desmear
During drilling, drill bits become heated resulting in the melting and smearing of the epoxy-resin base material
across the inner-layer copper surfaces within the hole barrel to which subsequent through-hole plating must connect.
If not corrected the smear would constitute a dielectric layer between the inner-layer copper surfaces and the plated
copper, and the circuit would be defective.
The desmear process is often grouped and sometimes confused with etchback because similar or identical chemistries
can be used to perform both functions. Desmear is simply the removal of smeared epoxy-resin by-products from
copper surfaces within the hole barrel to facilitate a connection with plated copper. Etchback is the significant
removal of epoxy-resin (including smear) and glass fiber from the hole barrel in an effort to expose a greater copper
surface and enhance the interconnection with the plating. The improvement and reliability of desmear chemistry has
made etchback unnecessary.
Currently the most widely used chemistry is sodium or potassium permanganate when significant etchback is not
required or specified. Permanganate-based systems remove a thin layer of epoxy-resin (typically less than 1 mil) and
smear and are quite adequate for desmear-only applications.
The permanganate desmear is a three step process consisting of epoxy sensitizing, permanganate etch, and
neutralizing (Exhibit 3-13). The sensitizer swells the epoxy and facilitates the subsequent removal. The
permanganate solution etches the epoxy by oxidizing the covalent bonds within the polymer network. This bath is
generally heated to 160°F or more with dwell times from 5 to 20 minutes. The neutralizing bath removes
permanganate from the oxidized hole and panel surface. If the neutralizing bath is not used, voiding and poor
adhesion can result during the metallizing of the holes.
40
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Exhibit 3-13. Permanganate Desmear Process
Permanganate
^ Rinse ^^ Desmear W^ Rinse ^^ Rinse
H
„. „. n.
Rinse ^^>, ~ Tr",v"'' ^^ Rinse ^^ Rinse
' ''
One problem with the permanganate solution is that alkalinity at high temperatures causes the permanganate to
decompose to manganate. As manganese dioxide builds in the bath, it accelerates the reaction of manganate to
manganese dioxide until a black sludge (MnO2) is formed that settles to the bottom of the tank. The epoxy etch rate
is steadily reduced until the solution becomes unusable (ref. 26). Frequent analysis and additions of permanganate are
necessary to counter this degradation in the etching rate. Electrolytic regeneration units are available to anodically re-
oxidize the manganate ion back to permanganate (MnO4_). These units consist of a porous pot, cathode, anode, and
rectifier.
3.2.5.2 Etchback
During etchback, in addition to smear removal, the glass fibers themselves are etched back from the hole wall. The
goal is to remove about 0.5 mil from the top and bottom of the innerlayer copper so that it will protrude out from
the hole wall. This creates three surfaces (also known as a three-point connection) for the copper to bond to during
the making holes conductive step. Glass etchants include hydrochloric acid, ammonium bifluoride, and hydrofluoric
acid (rarely used). Etchback with plasma can be achieved by varying the type and amount of reactive gases.
3.2.5.3 Plasma Desmear/Etchback
Using plasma to desmear eliminates an entire wet process line, reduces chemical disposal costs, and reduces water
usage and treatment costs. Labor costs are lowered as well since there are no baths to maintain. With plasma
etching the panels are placed in a vacuum chamber, and gas is introduced and converted to reactive plasma by a power
supply. The plasma reacts at the panel surface and volatile by-products (resin smear) are removed by the vacuum
pump.
The addition of relatively inert gases, such as nitrogen or argon, stabilizes the plasma and controls the rate of
ionization. Reactive oxygen species oxidize organic contaminants on the surface, creating volatile species that are
pumped away. Etch rates are increased by providing more reactive species in the form of fluorine such as F2, CF4 or
CHF2.
3.2.5.4 Desmear/Etchback Alternatives
There are several desmear/etchback process alternatives. The applications and advantages/disadvantages of each are
discussed in this section and summarized in Exhibit 3-14.
41
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Exhibit 3-14. Desmear/Etchback Methods
Process
Applications
Advantages
Disadvantages
Permanganate Smear removal
Concentrated
Sulfuric Acid
Plate Forward
Plasma
Besmear
Smear removal
4-layer power/ ground
plane multilayers
Smear removal/
etchback
Better control.
Ease of operation.
More easily controlled than
etchback. Smoother holes.
Eliminates chemical line and waste
treatment costs. No bath
maintenance.
Rapid chemical decomposition.
Frequent bath analysis and
maintenance
Lack of control. Operator safety
concerns with concentrated
chemicals. Generally requires
desmear.
Limited application.
High capital cost. Uneven etch
rate across panel.
Concentrated Sulfuric Acid. Concentrated sulfuric acid (usually 93%) is still in use, but generally requires a
permanganate step for final hole cleaning, making it a significantly longer and more expensive process than
permanganate alone. Handling the concentrated acid and operation of the line has proved to be a problem in many
shops. The amount of epoxy-resin removed is controlled by the dwell time in the sulfuric bath, which must be
precisely monitored. However, sulfuric acid does not etch glass and a second step is required to perform the glass
fiber etch.
Plate Forward. This process has a narrow field of use (4-layer boards with ground/voltage plane innerlayers), but
it represents a large portion of the multilayer market. To ensure the plating connection to the metallized hole surface
is reliable, panels are electroplated prior to electroless plating. In order to accomplish this, the innerlayer planes are
connected to the surface foil of the panel, which in turn is connected to the cathode bar. This plating step will
extend the copper from the hole edge out into the barrel of the hole.
Plating forward is more easily controlled than etchback and leaves the hole barrels relatively smooth, whereas with
etchback, hole interiors are roughened at an inconsistent rate. This process does not eliminate the desmear process
(ref. 27).
Condensed Besmear/Metallization Process. A method exists to combine desmear and two processes from
the plating through holes (PTH) electroless line into a single step. This process, which consists of a single process
tank and associated rinse tanks, will neutralize the permanganate, clean/condition the hole walls, and microetch the
surface. The reduction in process tanks lowers chemical maintenance costs, labor, and water usage, and simplifies
the treatment of wastes. Excellent results have been reported from Asian and European manufacturers employing
this technique (ref. 28).
3.2.6 Making Holes Conductive
To provide for the intended interconnection between layers, the holes must be coated or plated with a conductive
substance. The PWB substrate itself is not conductive, so a non-electrolytic deposition method is required.
Afterwards, electroplating is performed to plate the copper to the specified thickness.
Until recently, electroless copper has been used almost exclusively to metallize the holes. Direct metallization (DM)
processes were introduced in the 1970s, but reports of higher costs and inconsistent quality kept manufacturers from
experimenting with an unproven process (ref. 29). New interest in alternatives to electroless copper was ignited in
1992, when OSHA amended a standard for occupational exposure to formaldehyde, a probable carcinogen. With few
exceptions, electroless copper uses formaldehyde as the reducing agent.
Alternatives to electroless copper now include palladium-based systems, carbon/graphite-based systems, electroless
nickel, conductive polymer, and non-formaldehyde-based electroless copper. Based on the survey results, however, it
is apparent that the electroless copper process is still entrenched as the predominant method of making holes
conductive, although its use appears to be declining. Seventy-seven percent of all respondents reported using
electroless copper for through-hole metallization, with the remainder split evenly among graphite-, palladium-, and
42
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carbon-based systems. One user reported testing an electroless nickel-based system on a small percentage of their
product.
Design for the Environment (DfE) Printed Wiring Board Project participants are encouraged by this increase in the
use of alternative MHC technologies, especially because it occurred while awareness of the alternatives was being
increased by the MHC project. Additional increases in alternative MHC technology use can now be expected because
the CTSA results were presented in seven seminars around the United States in 1997, and because the final MHC
CTSA will be published in summer 1998.
The making holes conductive process step alternatives are shown in Exhibit 3-15. The advantages and disadvantages
of the alternatives are discussed in the following section and summarized in Exhibit 3-16. Survey data relative to
this process step are found in Appendix A.
Exhibit 3-15. Make Holes Conductive
Circuit
Design/Data •
Acquisition
-^
Inner-Layer
Image
Transfer
~M
Laminate
Layers
Drill Hole
Pattern
on Board
-M
Clean Holes
(Desmear)
43
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Exhibit 3-16. Comparison of Primary Alternatives for Making Holes Conductive
Process Advantages Disadvantages Waste Generated
Electroless 30+years of reliable use. Inherently unstable. Copper from microetchant
Copper EDTA complicates waste Complexed copper from
treatment. electroless bath.
Eight process baths.
Carbon- Short application time. High capital costs. Copper from microetchant.
based No formaldehyde. Five process tanks.
Less water consumption than
electroless copper.
Graphite- Short application time. None Identified. Copper from microetchant.
based No formaldehyde. Three process tanks. Four
Convey orized or vertical if anti-tarnish used.
processing.
Low water consumption and
treatment.
Palladium- No formaldehyde. None Identified. Copper from microetchant.
based Ten process tanks including
desmear.
Electroless No formaldehyde. None Identified. Six process tanks including
Nickel No microetchant. desmear.
Convey orized or vertical
processing.
3.2.6.1 Electroless Copper
Although electroless copper has been successfully used for more than three decades, limits on operator exposure to
formaldehyde and difficulties in removing the electroless copper from the waste stream caused manufacturers to seek
alternatives. Among the deficiencies are (ref. 30):
• Use of formaldehyde as reducing agent.
• The process is inherently unstable, requiring stabilizing additives to avoid copper precipitation.
• Environmentally undesirable complexing agents, such as EDTA, are used.
• The large number of process and rinse tanks causes high water consumption and energy use.
The electroless copper process consists of four basic operations: cleaning, activation, acceleration, and deposition
(Exhibit 3-17). An anti-tarnish bath is common after deposition. Virtually all facilities purchase a series of
proprietary chemistries from a single vendor that are used as the ingredients for the several process baths in the
electroless copper process line. Only the micro-etch, its associated sulfuric dip, and the anti-tarnish baths are likely
to be non-proprietary chemistries.
Cleaning. The cleaning segment begins with a cleaner-conditioner designed to remove organics and condition (in
this case swell) the hole barrels for the subsequent uptake of catalyst, followed by a microetch step. The cleaner-
conditioners are typically proprietary formulations, and mostly consist of common alkaline solutions.
A microetch step can be found on the electroless line, oxide line, pattern plate line and with chemical cleaning if that
is the cleaning method used. Three chemistry alternatives are available. Sulfuric acid-hydrogen peroxide (consisting
of 5% sulfuric acid and 1% to 3% peroxide) is most common, followed by sulfuric acid-potassium (or sodium)
persulfate (5% sulfuric, 8 to 16 ounces/ gallon persulfate), and ammonium persulfate. In each case, the microetch
bath is followed by a sulfuric acid dip, which serves to remove any remaining oxidizer. About 40 micro-inches of
copper are etched for the making holes conductive process. Based on a 3-4 ounce copper carrying capacity,
approximately 0.0183 gallons of microetch are used per square foot of product run. This figure does not include any
solution that may be dragged out when the panels are moved to the next tank. The sulfuric-peroxide alternative has
some attractive waste treatment and performance features (ref. 31):
• No spent etchant disposal. The etchant is replenished as it is used, and copper is removed with a recovery unit
in the form of copper sulfate crystals. These crystals form when the solution is cooled to room temperature or
44
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lower. Smaller shops may use a batch treatment where the solution is pumped to another tank to cool and
crystallize. After removing the copper crystals, the solution can be transferred back to the process line and
reused.
• Constant etching rate. The etching rate is dependent on temperature and hydrogen peroxide concentration, not
the copper concentration.
• Simple waste treatment. No chelators are present in sulfuric-peroxide microetchants.
• A high copper capacity of 3 to 4 ounces/gallon.
• Efficient copper recovery. Copper sulfate recovery is usually 90-95% efficient.
Persulfate microetchants must be treated in-house or shipped to a licensed disposal facility. The etching rate is
difficult to control since it declines as panels are processed and copper builds in the solution. Ammonium persulfate
is uncommon due to high waste treatment costs.
Activation and Acceleration. Activation, through use of a catalyst, consists of two process tanks. A pre-dip,
for the drag-in protection of the expensive activation (also called catalyst) bath, usually contains hydrochloric acid
and possibly tin or sodium chloride. The activation bath itself consists of hydrochloric acid, tin chloride, and
palladium chloride. The Sn+2 jon reduces the Pd+2 to Pd, which is deposited on the panel. The remaining Sn+2
and Sn+4 are selectively removed from the hole barrels by the accelerator (also called the post-activator). Fluoboric
acid is a common accelerator, as is sulfuric acid with hydrazine.
Copper Deposition. Electroless copper baths can be divided into two types: heavy deposition baths (designed to
produce 75 to 125 micro-inches of copper) and light deposition baths (20 to 40 micro-inches). Light deposition
must be followed immediately by electrolytic copper plating. The more common heavy deposition can survive the
outer layer imaging process, and copper electroplating occurs thereafter. The main constituents of the electroless
copper chemistry are sodium hydroxide, formaldehyde, EDTA (or other chelator), and a copper salt. In the complex
reaction, catalyzed by palladium, formaldehyde reduces the copper ion to metallic copper. Formaldehyde (which is
oxidized), sodium hydroxide (which is broken down), and copper (which is deposited) must be replenished frequently.
Exhibit 3-17. Typical Electroless Copper Plating Line
Hole
* Conditioner
Drag-Out
~ Rinse
Rinse
/T''••';''••'.;ViV 'S-wV-w.
• Rinse —^^ Microetch.
L
Rinse
Rinse
Sulfiiric
Acid Dip
Rinse
i
Catalyst
Rinse
Rinse
i
U
H.F
Rinse
Rinse
i
L
Copper
Electrizes s
> Copfe
/ £ i
( spare tajik)
Q
^ ~
D™g-0ut
Rinse
Rinse
,/v •{•«•»
Rinse
1
Anti-
tarnish
45
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Most heavy deposition baths have automatic replenishment schemes based on in-tank colorimeters. Light deposition
formulations may be controlled by analysis. Formaldehyde is present in light deposition baths in a concentration of
3 to 5 grams/liter and as high as 10 grams/liter in heavy deposition baths.
When light deposition is applied, the next process step must be electrolytic copper plate. This is either a full panel
plate (the typical 1 mil is plated in the holes and on the surface) or a "flash" panel plate, designed only to add enough
copper to the hole barrels to survive the imaging process. Flash-plated panels return to copper electroplating after
imaging to be plated up to the required thickness. This double plating step has made heavy deposition the more
common electroless copper process.
Process Waste Streams. The electroless copper line typically contributes a significant percentage of aPWB
shop's overall waste volume. Water use is high due to the critical rinsing required between nearly all of the process
steps. Copper is introduced into the wastewater stream due to drag-out from the cleaner-conditioner, micro-etch,
sulfuric, accelerator, and deposition baths. Much of this copper is complexed with EDTA and requires special waste
treatment considerations. Furthermore, waste process fluid generation is high. Micro-etch baths are exhausted when
2 to 4 ounces/gallon of copper is dissolved, and this bath life is usually measured in days. While the electroless
copper bath is relatively long-lived (usually several weeks or months), a considerable bailout stream (including
formaldehyde) is generated (several gallons of concentrated bath chemistry per day in production shops). This waste
must either be treated in-house or shipped off-site, which adds another cost to using electroless copper.
3.2.6.2 Carbon-based Alternative
Black Hole® is a carbon-black dispersion method for metallizing holes. The advantages of this type of process
versus conventional electroless plating are:
• Production rates are higher for Black Hole* since it is applied in about half the time required for electroless
copper
• Formaldehyde is not a constituent of any of the process formulations
• Copper is dragged into the wastewater stream from only the microetch bath
• Overall water use is reduced
Although it has become more common in larger shops, this process is still an uncommon choice for small shops
with sales of less than $5,000,000/year, which account for the majority of PWB facilities in the country. Capital
costs for the Black Hole® conveyorized process line are much higher than for an electroless copper tank line, and
represent a barrier of entry for small shops. Payback from production timesaving and waste reduction is likely to be
quite long for small manufacturers.
After being cleaned and conditioned, non-conductive surfaces absorb the carbon deposits. The carbon deposition step
is performed twice to ensure a good conductive surface. A microetching step follows to remove any carbon deposited
on copper surfaces. At this point the panels can proceed to imaging or be copper plated. Without copper plating,
the panels cannot be brush or pumiced scrubbed prior to exposing because carbon particles near the surface of the
panel may be brushed off (ref. 30).
3.2.6.3 Graphite-based Alternative
The available graphite-based processes are Shadow® and Shipley Graphite 2000. In these cases, graphite particles
suspended in a colloid are dispersed onto the surface and act as conductive pathway for electroplating. The four
specific process steps for the Shadow® process are (ref. 32):
• Cleaning/conditioning
• Graphite (Shadow®) application
• Microetch
• Anti-tarnish (optional)
Graphite application can be done on conveyorized equipment or with an immersion (vertical) process. One pass
through the graphite application step is sufficient to prepare holes for copper deposition. The vendor claims to be
able to run this process from cleaning to lamination in less than 10 minutes (ref. 33). Graphite particles adhere well
to the laminate surfaces and can tolerate mechanical scrubbing. The micro-etch solution is usually based on
persulfate. Some facilities do not use anti-tarnish coatings on the copper surface if the dry film lamination process
is done in-line, immediately following graphite application. Shadow® users include, buried and micro-via
46
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manufacturers with large layer counts up to 48 layers. Shadow® users process from 5,000 to 1,500,000 surface
square feet per month.
Cleaning and Conditioning. Panels can be cleaned using conventional methods or in the conveyor line.
Cleaning solutions used are similar to systems employed for electroless copper. As noted above, the cleaner-
conditioner step is designed to remove organics and condition hole barrels for the subsequent uptake of graphite.
Graphite. The graphite is applied in the form of colloidal graphite. The particles are suspended in a slightly
caustic colloidal solution (pH = 9). In the conveyorized process, surface activation is rapid, and solution that runs
off the boards can be reused. In an immersion (vertical) setup, conventional process tanks are used to apply graphite.
In this case, some efficiency is lost, but existing equipment can be used. Following the graphite application, the
panels must be dried to dry the graphite on dielectric surfaces. This step is critical for obtaining good copper
adhesion during subsequent copper plating. Drying is done with air knives, followed by a short bake (140 to 160°F).
The air knives used are run at close to room temperature; their principal function is to remove excess colloid from
the surface and hole walls. No rinse is required after this drying step.
Microetch. Microetch follows graphite application. (See the Cleaning section under 3.2.6.2 Electroless Copper
for a more detailed explanation of microetchants and available chemistries.) The drying step does a good job at
removing colloid material from the field area of the panel. However, simply drying the solution does not remove
graphite particles from exposed copper. The vendor recommends spraying a persulfate solution onto the panel
surface. A filter below the panels prevents graphite from entering waste streams.
Anti-tarnish. Following microetch, the exposed copper is subject to oxidation. Because of this, an optional
"anti-tarnish" step can be done. The system vendor recommends using a benzothiadzole-containing solution to
protect copper surfaces. Some PWB manufacturers skip this step, in which case it is recommended that image
transfer films be laminated onto the panels directly following micro-etch. Eliminating the anti-tarnish step should
reduce chemical use, cost, waste, and cycle time. Effects on reliability were not reported but some commercial
vendors use this approach (ref. 34).
Process Waste Streams. The quantity of wastewater produced by a typical horizontal conveyorized graphite
application system is less than 5 gallons/minute. Also, wastewater is only produced when the system is running,
rather than constantly, as in the rinse tanks used for electroless copper plating. In short, the graphite system seems
to reduce both waste streams and costs from PWB manufacturing. There are five principal environmental benefits
from using the graphite process instead of electroless copper. These include:
Reduction in chelated copper and metal waste
Elimination of formaldehyde
Reduced water use
Reduced treatment chemical use
Reduced sludge disposal
3.2.6.4 Palladium-based Alternatives
Palladium-based alternatives offer the common advantages of the absence of formaldehyde, reduction in water usage,
and the reduction in wastewater generated from the process. These alternatives can also be run with conveyorized
equipment to increase throughput and lower costs. The panels typically are run through a desmear process prior to
starting the palladium line.
The activator in these systems is palladium/tin. The accelerator removes stannous tin (Sn+2) or reduces it to a
metallic form (Sn). To improve conductivity and speed up the metallization of the hole, some systems have
modified the acceleration step so that copper is deposited with the palladium, taking the place of the tin (ref. 30). A
manufacturer has invented a modified palladium process called Crimson®, which has a conversion step after the
activator. The palladium is changed to palladium sulfide, which is claimed to be more conductive for subsequent
electrolytic copper plating (ref. 35).
Cleaner/Conditioner. During this "sensitizing" step, the holes are cleaned and a charged polymeric material is
applied to the inside dielectric surface of holes. This charged material then receives a catalyst during subsequent
processing. Chemical use and wastewater produced in the cleaning step of the palladium-based process is similar to
47
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volumes used for the carbon- and graphite-based processes. However, each step must be followed by a rigorous rinse
to prevent contamination of the following steps.
Microetch. Microetch, which is performed using hydrogen peroxide (H2O2) and sulfuric acid (H2SO4), removes
excess palladium sulfide from exposed copper surfaces without oxidizing the copper. This step enhances adhesion
between exposed copper and electroplated copper added later, without degrading adhesion between laminate materials
and plated copper. (See the Cleaning section under 3.2.6.2 Electroless Copper for a more detailed explanation of
microetchants and available chemistries.)
Pre-dip. A base salt version of the catalyst (which does not contain catalyst metal) is applied to the panels.
Activator. After pre-dip, the catalyst (activator) is applied. In this case, the catalyst is palladium/tin in a colloidal
solution. The catalyst adheres well to glass/epoxy laminates.
Accelerator. After the activator step, panels are rinsed with a caustic soda (accelerator or enhancer). The
accelerator removes stannous tin (Sn+2) or reduces it to a metallic form (Sn).
Acid Dip. The panels receive an acid dip and a final rinse, and are dried for lamination.
Process Waste Streams. There are two principal process waste stream considerations: first, formaldehyde is
completely eliminated from the process of making holes conductive; and second, the amount of water used (and
wastewater produced) is reduced when compared to conventional electroless plating. According to the manufacturer of
one palladium-based process, the cost of this process is competitive with electroless copper plating.
3.2.6.5 Electroless Nickel
Ultra-Plate® 300 is a commercial metallization process that plates an electroless nickel deposit. This process does
not use microetch, accelerator, or formaldehyde. Panels can be processed vertically or horizontally on conveyorized
systems. This flexibility reduces cost barriers for converting since existing PTH equipment can be used. Fewer
process tanks also reduce chemical usage, wastewater generation, and process time. With the Ultra-Plate® 300
process, the panels are sent to exposing after the palladium activator, and then are returned for selective electroless
nickel. Subsequently, an electrolytic copper bath is used to plate through the holes and pattern plate the circuit.
Neutralizer/Conditioner. This mildly acidic solution prepares the hole wall surface for subsequent steps and
acts as a neutralizer for the prior alkaline permanganate process tank.
Sensitizer/Activator. A 2-step process in which a palladium activator is deposited onto sensitized substrate
areas. The sensitizer promotes the absorption of the catalyst onto the hole wall surface.
At this point, the panels are laminated with resist, exposed, and developed. The panel surface can be scrubbed or
prepared as normal without detrimental effect.
Acid Cleaner. An acid copper cleaner is used to remove any residuals from the resist developing step.
Electroless Nickel. Electroless deposition is more rapidly initiated on palladium activated dielectric surfaces
than on copper. A very conductive, high purity, thin layer of nickel is deposited on the hole walls that provides a
low resistance path for subsequent electrolytic copper plating.
The electroless nickel process incorporates some steps from both the making holes conductive and outer layer image
transfer use clusters. Since the circuit image is already pattern plated at the end of electroless nickel sequence, the
process picks up at pattern plate etch resist in section 3.2.7.2.
Process Waste Streams. There are a number of items that impact the process waste stream when using
electroless nickel. Among them are:
Elimination of strong chelates
Elimination of formaldehyde and cyanides
Elimination of copper microetch
Elimination of accelerator
Reduced water use
48
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• Reduced treatment costs
3.2.6.6 Conductive Polymer
Conductive polymers have been commercially available for years, but only one (polypyrrole) has been adopted as an
alternative in making holes conductive. Polypyrrole, which was initially used in Europe, is very suitable for
horizontal, conveyorized application. The conductive polymer builds on the standard permanganate desmear
chemistry. As epoxy smear is removed from the holes, insoluble manganese dioxide is formed. The board is treated
with a solution of pyrrole monomer, which is oxidized by the manganese dioxide to form the conductive polymer
polypyrrole. The manganese dioxide is reduced to soluble manganese salts and is washed off. The full process line
includes a microetch, cleaner/conditioner, catalyst, conductive polymer, and microetch, followed by a copper
electroplate (ref. 35).
3.2.6.7 Non-Formaldehyde-Based Electroless Copper
At least two formaldehyde-free electroless copper systems exist. The first uses the standard electroless line with
hypophosphite as the reducing agent in place of formaldehyde. The copper deposition is run in two modes:
electrolessly as normal, then, while in the same tank, current is turned on to continue the copper deposition.
Afterwards, the panels pass to an acid copper electroplating tank to complete the process.
The second system uses the standard electroless process through catalyst application. The panels are then laminated,
imaged and developed. The imaged panel is then placed in the electroless copper bath that deposits copper on the
catalyzed surface and in the holes. The bath contains biodegradable complexing agents, and a boron compound acts
as the reducing agent (ref. 35).
3.2.7 Outer Layer Image Transfer
This large cluster includes outer layer imaging, copper plating, etch-resist plating or application, etching, and etch-
resist stripping (Exhibit 3-18). The cluster includes copper electroplating, a function not normally associated with
image-transfer. Although arguably an independent function, copper electroplating is performed in a sequence
determined by the overall image transfer strategy. Furthermore, with copper sulfate being the overwhelming choice
of PWB shops, a cluster of alternatives does not actually exist (pyrophosphate baths, the other chemistry, have
vanished). With the exception of process material improvements such as dry film photoresist, plating chemistries
(copper sulfate vs. pyrophosphate, in particular), or the substitution of tin-only etch-resist for tin-lead, this cluster
has remained essentially unchanged for many years. It also forms the core of double- and single-sided processing;
thus many of the processes described here predate multilayer manufacturing.
Two major subtractive options, starting with copper clad laminate, are available to the PWB manufacturer. The
majority of manufacturers in the U.S., Southeast Asia, and Europe use the print, pattern plate, and etch sequence.
While copper pattern plating is a uniform process shop-to-shop, the etch-resist metal plated over the copper is not,
and forms an interesting and important second-level cluster. Etching is theoretically a cluster of two chemistry
options, but with most metallic etch-resists, only ammoniacal is possible. In Japan, the majority of manufacturers
use the second method of panel plate, print, and etch. Copper is plated to full thickness over the entire panel prior to
imaging. The photoresist imaged during the "print" process serves as the etch-resist precisely as in inner layer image
transfer.
49
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Exhibit 3-18. Outer Layer Image Transfer
It can be seen that the panel plate, print, and etch process (also referred to as "tent-and-etch" because the drilled holes
are tented over and protected from the etchant by dry-film photoresist) eliminates process steps required in the more
common pattern-plate process. There is no etch-resist plating (the photoresist serves as the etch-resist) or metal
stripping; therefore, the tin or tin-lead problem is obviated. Furthermore, cupric chloride etching is an option when
dry-film photoresist is the etch-resist. Unfortunately, it is the inefficiency of panel plating, along with certain
technical limitations of this process, that prevent its widespread use. Most of the copper on a typical circuit panel is
etched away; thus, most of the plated-on copper of this process is promptly removed during etching, unlike the
copper added during pattern plating. Furthermore, the panel-plated copper can cause difficulty in etching, particularly
fine-line etching. The thicker the copper to be etched, the greater the undercut. This problem has dampened the
enthusiasm for tent-and-etch. On the other hand, layout design changes can easily rehabilitate tent-and-etch. One
method referred to as "pads-only outer layers" eliminates difficulty of fine-line etching on outer layers (along with
eliminating the need for solder mask) at the expense of requiring two extra layers of inner layer circuitry.
It should be pointed out that some of the etch resist options listed here are not true options, but rather alternative
methods that may be required by customer specification or for end-product performance. Although tin and tin-lead
perform identically as etch-resists, if reflow is the specified finish type, tin-lead plating must be used. Manufacturers
need to decide if the small percentage of jobs requiring a reflow finish justify keeping a tin-lead plating tank, along
with the worker exposure to lead and waste treatment difficulties that come with it.
3.2.7.1 Image, Pattern Plate, and Etch
Outer layer imaging is quite similar to inner layer imaging (see 3.2.2.2 Conventional Print-and-Etch for more
detail). The panel is thicker and has drilled holes, but it is essentially processed through the same sequence of
50
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operations. Some shops, especially smaller ones, may use the identical photoresist product for both inner and outer
layers for convenience. Photoresist thickness, not critical for an etch-resist, takes on significance as a plating resist.
Most facilities use a thinner resist for inner layers (0.001 inches) and are forced to use thicker resist for outer layers
(typically 0.0015 or 0.002 inches). Generally, the resist thickness should equal or exceed the thickness of the metals
to be plated onto the pattern to avoid copper or tin-lead "mushrooming" over the top of the resist. Resists other than
dry film are extremely uncommon for outer layer imaging.
Exposing may be done with first-generation photoplotted phototools or with diazo, a reddish transparent film that
allows for manual registration. With a diazo phototool, an operator can see through the dark areas of the film (the
circuit pattern) and can align the phototool to the hole pattern, eliminating the need for tooling regimes. Although
not practical for production shops, manual registration with diazo phototools is not uncommon in prototype shops.
When pattern plating is to follow, outer layer phototools are positive images of the circuit. The circuit image is
developed away exposing the underlying copper. The photoresist remaining on the panel is the plating resist for the
pattern plate process.
Pattern plating is so named because only the circuit pattern and hole barrels are plated (Exhibit 3-19). Only the thin
electroless copper layer has been deposited in the hole barrels up to this point in the process and it is far short of the
typical 0.001-inch specification for copper thickness. None of the copper plated during this process is etched away,
but rather, remains on the circuit and is part of the finished product. The copper is protected from the etchant by a
metallic etch resist that is plated on during the next process step. The ordinary outer layer will have about 33% of
the panel plated to a thickness of 1.5 mils of copper. This 1.5 mil target is to ensure a minimum thickness of 1 mil
in the holes. The result is 0.6866 ounces of copper being plated per square foot of product run for a typical panel.
This result does not account for the copper contained in the solution that is dragged with the panel.
Although a few copper electroplating chemistries exist, nearly all PWB facilities use basically the same copper
sulfate bath composition. The bath is typically made with 10 ounces/gallon of copper sulfate, 25 to 40
ounces/gallon of sulfuric acid, and a small amount of hydrochloric acid to provide a chloride concentration of 30 to
90 mg/1. This bath has an extremely long life (measured in years) and is generally easy to maintain and control.
Proprietary organic additives, usually referred to as brighteners, distinguish one vendor's bath from another. The pre-
plate line consists of an acid cleaner (dilute phosphoric acid is a common constituent), a microetch, and a sulfuric
pre-dip.
High-performance copper plating is reliably performed at a current density range of 20 to 35 amperes/ft2.
Manufacturers generally plate from 0.0013 to 0.0017 inches of copper to ensure that all hole barrels meet the
minimum of 0.001 inches in all areas of the panel. Dwell times depend on current density and target thickness, but
generally range from 30 minutes to somewhat more than one hour. Although a source of copper in the wastewater
stream, the copper sulfate plating process lends itself to recovery schemes. A drag-out tank, immediately following
the plating bath, can be electrowinned (an electrolytic recovery process), which recovers copper in metallic form and
reduces drag-out to the subsequent flowing rinses. Some facilities have employed ion exchange to create a closed-
loop. In this arrangement, wastewater is processed and reused as rinse water and the cation regenerant can be returned
to the copper sulfate bath.
Exhibit 3-19. Typical Pattern Plate, Etch-Resist, Photoresist Strip Process Line
Acid
,-,.
Cleaner
Drag-Out
_r
Rinse
„.
Rinse
„.
Rinse
, r. . ,
aEcroetcn
^v.;>v
Rinse ""^^- Rinse
Sulfunc
Acid Dip
1
L Sulfuric ^^
Acid Dip "^
^ Rinse
_^^^ Coppei _^^^
~^^ Electroplate ~^^"
Drag-Out
Rinse
;.'* /Ste&u .
-|^^* Rinse Hjjj^^
Rinse f
Tin
EleoOroplate
n-
Rmse
*.*>&*'&'
Rinse
Resist
Strip
Drag-Out
Rinse
_.
Emse
51
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Pattern Plate Etch Resist. Immediately after copper pattern plating, an etch resist is plated over the copper.
The three most common etch resists are tin, tin-lead, and nickel-gold; however, other metals may be used depending
on the customer's specifications. Tin is typically used on boards requiring solder mask over bare copper (SMOBC)
finish since it serves no other purpose than acting as an etch resist. It is removed from the panel surface in a
stripping step after etch. While the regulatory status of tin varies from locality to locality, it is safe to say that tin
receives less scrutiny than lead. Some manufacturers have been able to eliminate tin-lead plating altogether since the
majority of work is SMOBC. Manufacturers that serve military clients must maintain their tin-lead baths since
some military specifications continue to call for tin-lead reflow finish.
Tin-lead is plated to a thickness of 0.0002 to 0.0005 inches. Assuming a thickness of 0.00035 inches and plating
33% of the panel, approximately 0.3028-ounce of tin-lead are plated per square foot of a typical panel. Tin-lead can
be plated with one of the following baths:
Tin-lead fluoborate. This common bath consists of fluoboric acid, tin and lead fluoborate, and proprietary
organic additives. Stannous tin (Sn+2) is maintained at 2 to 4 ounces/gallon and lead at 1 to 2 ounces/gallon.
Methane sulfonic acid (MSA). MSA-based chemistry is not in wide use in the PWB industry due, in part, to
the cost of MSA. The MSA-based bath is, however, generally considered to be more compatible with the
environment and is less corrosive. Another advantage MSA has over the tin-lead fluoborate bath is that some local
government regulations impose restrictions on the release of fluoborates to municipal wastewater treatment plants
(ref. 35).
Tin is plated for etch resist purposes only, and a 0.0002-inch thickness is adequate. 0.2308 ounces of tin per square
foot will be plated on a typical panel where 33% of the panel is exposed for plating. There are three possibilities for
tin baths. A tin fluoborate bath exists, and some facilities have phased out tin-lead by simply replacing the tin-lead
anodes in the fluoborate bath with tin anodes and allowing the lead concentration to gradually fall. Second, the tin
sulfate bath consists of 20% sulfuric acid and enough stannous sulfate to provide 2 to 3 ounces/gallon of stannous
tin. Last is an organic sulfonic acid (OS A) -based (usually MSA) tin bath. Most of the advantages of OS A-based
chemistry are shared with the simple tin sulfate bath, and OSA chemistry has not found wide use in the PWB
industry.
Nickel-gold is also pattern plated electrolytically as an etch-resist and surface finish. The nickel-gold plating line
consists of a nickel pre-dip, the nickel plating bath, gold pre-dip, and the gold plating bath. The nickel plating
chemistry of choice is nickel sulfamate or nickel sulfate. Nickel is relatively concentrated in either bath (e.g., 17
ounces/gallon in typical nickel sulfate formulations). Unlike many other process baths, many facilities use decades-
old nickel plating formulations and do not purchase proprietary chemicals. Nickel is plated to any specified
thickness, usually in the range of 50 to 500 micro-inches. Gold is then immediately plated over the nickel. Acid
gold cyanide formulations are most common and are similar, but not identical, to the hard gold baths designed for
edge connector plating. Sulfite-based alkaline baths are also in use. Gold is generally plated to a thickness under
100 micro-inches, and for many applications 10 to 30 micro-inches will suffice. The area to be plated on a typical
gold panel is less than tin and tin-lead plated boards. The border areas are taped off in an effort to preserve gold and
prevent it from being plated on areas where it is not necessary. On a typical square foot, 0.023 ounces of nickel and
0.05 ounces of gold will be plated. Both the nickel and gold plating baths are quite long-lived; barring unusual
events, each may be maintained for several years.
Electrolytic soft gold is the surface finish of choice for certain performance considerations, including high corrosion
resistance, low contact resistance (although wear resistance is poor), and long shelf-life. Electrolytic pure gold may
be called for on circuits requiring wire bonding.
Metals such as rhodium or gold may be plated selectively over certain areas of a circuit, then masked off, and a
conventional etch-resist is plated over the remainder. Rhodium is the metal of choice for maximum wear resistance.
The survey results indicate that 52% of respondents use tin-lead plate for at least a portion of their production
(Exhibit 3-20), but tin-lead was used on only 23% of the aggregate production of the entire group of respondents.
Tin-only plating was performed by 49% of the respondents and represented 43% of the aggregate production. It is
clear from these data that many facilities are maintaining both tin-only and tin-lead plating operations, but are
moving an increasing portion of their production to tin-only (Exhibit 3-21).
52
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Exhibit 3-20. Outer Layer Etch Resist
60 -,
W 40
M
C
30-
20-
10-
Tin
Tin-Lead
Dry Film
Nickel Gold
Others
Exhibit 3-21. Percentage of Total Production with Various Types of Etch ant Resistance
<:
C=H 40
-3 Q^
-S 30
S o.
0>
» 20
8 -U
0 15
PH
G 10
.2 "
,,-
/
/"
,/
, ,
/
Tin Tin- Dry Nickel Others
Lead Film Gold
Etch Resist
Photo resist Stripping. Dry film strippers break down the bond between the resist and the panel and cause it to
detach. The chemical is usually alkaline and may be mixed with a solvent, such as ethylene glycol butyl ether or
diethylene glycol butyl ether, which is needed to strip semi-aqueous resist. The solution is heated from 45 to 60°C
(ref. 36). Stripping is accelerated at higher temperatures, but it also accelerates the attack on the tin or tin-lead
coating, which is soluble at high pH. The stripping rate decreases as panels are processed and resist particles build
up in the solution. Some facilities use a filter to remove the particles from the solution before they have a chance to
dissolve, in an attempt to extend the life of the bath.
An EPA Resource Conservation and Recovery Act (RCRA) determination on photoresist solids has been issued that
states they are to be considered a hazardous waste (see discussion in section 2.2.2). If the stripping process is in-line
with an electroplating operation (not physically separated from the plating operation and the panels are not rinsed and
dried prior to stripping), then the spent stripper solution itself becomes an electroplating wastewater. Thus, the
resist skins would be considered an F006 waste. The belief is that the physical separation of the operations, along
53
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with the rinsing and drying of the panels, will serve to prevent hazardous contaminants from the electroplating tank
or etcher from entering the stripping solution.
Resist skins from a tent-and-etch type process, which does not use a plated etch resist, would not be considered a
hazardous solid waste as long as the boards are rinsed prior to being stripped (most etchers are equipped with rinse
chambers). However, if tent-and-etch panels were stripped in the same tank as electroplated panels and those skins
had already been determined to be hazardous waste, then the resist skins would be F006 waste.
Outer Layer Etching. Etching is described in greater detail in section 3.2.2.2, Conventional Print-and-Etch.
Notable in outer layer etching is that cupric chloride etchant is not typically used for outer layers, due to its
incompatibility with metallic resists.
Tin and Tin-lead Stripping. For solder mask over bare copper boards, the tin or tin-lead is only used as an
etch resist and is stripped from the panel after etching. Tin-lead is left on boards and this step is skipped if the finish
type is tin-lead reflow. Nitric acid, ammonium bifluoride, and peroxide-based systems are available as stripping
solutions. If lead is present on the surface, the spent process fluid is a major source of waste lead. Tin-lead stripper
is consumed at 0.0168 gallons per square foot of a typical panel. This figure does not account for the volume lost
through drag out. When the saturation point of the stripper has been reached, this solution is usually is sent off-site
for treatment/disposal.
3.2.7.2 Panel Plate, Print, and Etch ("Tent-and-Etch")
With the exception of the additional panel plating, this process follows the steps of innerlayer print and etch. Panel
plating is less efficient than pattern plating since the entire panel is being plated rather than just the circuit. Most of
what is panel plated is subsequently etched off. Either cupric chloride or ammoniacal etching systems can be used.
Fewer steps and less process time are the advantages to using tent-and-etch.
The major disadvantage to tent-and-etch is the difficulty in etching through both the plated-on and base laminate.
Circuit features are becoming smaller, and most facilities are required to produce line widths of less than 10 mils.
To etch through 2 to 3 mils of copper, which is what the copper thickness can be after panel plating, the etching
undercut will amount to a significant portion of the trace width. Another drawback is that panel plating can only be
done where the surface finish will be bare copper or SMOBC. A surface finish of tin-lead, gold, or selective plating
of a particular metal requires the use of pattern plating.
3.2.8 Surface Finish
For most parts, the functions of the surface finish are to prevent copper oxidation, facilitate solderability, and prevent
defects during the assembly process. A number of metallic alternatives exist along with organic solderability
preservatives (also known as OSPs or pre-fluxes). A variety of deposition techniques exist, including hot air
leveling, electroplating, immersion, and electroless plating. The shelf life of immersion, electroless plated, and OSP
coating alternatives are less than that of leveled or tin-lead reflowed boards (ref. 35). Other surface finishes are
dictated by the environment in which the part will reside or by specific performance criteria.
54
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Exhibit 3-22. Surface Finish Processes
Solder-mask-over-bare-copper (SMOBC) with hot-air-solder-leveling (HASL) has been the preferred surface finish for
over 15 years (ref. 38). Nickel-gold, another popular finish, can be applied electrolytically as an etch resist,
replacing tin and tin-lead, or electrolessly as a substitute for HASL. Other electrolytic plating metals include
rhodium, palladium, palladium-nickel alloys, and ruthenium. Non-electrolytic deposition processes include tin
immersion, tin-lead displacement plating, electroless nickel, electroless gold, immersion gold, immersion silver,
immersion bismuth, and the previously mentioned OSPs.
3.2.8.1 Solder Mask Over Bare Copper (SMOBC), Hot Air Solder Level
(HASL)
This method predominates for several reasons. Copper is a surface that lends itself to rigorous cleaning, which is
essential for solder mask adhesion. If the solder mask were placed over tin-lead traces, the tin-lead would liquefy
during soldering and may cause the mask to blister and peel. The hot air solder leveling process generally produces
less wastewater and introduces less lead into the wastewater stream than tin-lead plating and reflow. The overall
process begins with a solder-mask pre-clean, usually a mechanical or pumice scrub. Solder mask is then applied,
followed by hot air solder leveling, nomenclature screening, and finally, gold edge plating if necessary.
Increasing circuit density, however, is causing some to look for alternatives to this difficult to control process.
Maintaining planarity of fine-pitch surface mount pads across both sides of the panel is a challenge. Another is
55
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solder bridging on fine pitch pads. This tends to happen when pads are lined up in the same direction of travel as the
panel as it is pulled from the solder pot. Increasing the pressure of the air knives may blow off the solder bridges,
but it also reduces the thickness of the solder coat on all of the other features.
Solder Mask. The purpose of solder mask is to physically and electrically insulate those portions of the circuit to
which no solder or soldering is required. Increasing density and surface mount technology have increased the need for
solder mask to the point that, with the exception of "pads only" designs, nearly all parts require it. Manufacturers
have had some autonomy in selecting masks. Many specifications do not call out a specific product or product type,
and this has allowed the manufacturer to choose masks based on processing as well as performance issues.
Three basic types of masks are commonly applied: thermally cured screen-printed masks, dry film, and liquid
photoimageable (LPI). Thermal masks have predominated for decades but are gradually being replaced by LPI,
despite being the lowest cost alternative. Dry film has some specific advantages, such as ease of application, but its
use seems poised to decline as well in the face of improving LPI formulations.
Hot Air Solder Level (HASL). The HASL process consists of a pre-clean, fluxing, hot air leveling, and a
post-clean. Pre-cleaning is usually done with a micro-etch. However, the usual persulfate or peroxide micro-etch is
not common in the process. Dilute ferric chloride or a hydrochloric-based chemistry is favored for compatibility
with the fluxes that are applied in the next step.
Fluxes perform the following functions:
• Provide oxidation protection to the precleaned surface
• Affect heat transfer during solder immersion
• Provide oxidation protection during HASL
Higher viscosity fluxes provide better oxidation protection and more uniform solder leveling, but reduce overall heat
transfer and require a longer dwell time or higher temperature. A balance in flux use must be struck between better
protection with high viscosity fluxes and superior heat transfer with lower viscosity fluxes (ref. 38).
Hot air level machines consist of a transport mechanism that carries the panel into a reservoir of molten solder
(460°F, 237°C), then rapidly past jets of hot air. All areas of exposed copper are coated with solder and masked areas
remain solder-free. Boards are then cleaned in hot water, the only step in the SMOBC process where lead may enter
the wastewater stream, albeit in very small quantities. Once cleaned, the panels may again enter the screening area
for optional nomenclature screening, or proceed directly to the routing process.
Copper, flu, and other impurities build in concentration in the solder pot as panels are processed through the hot air
leveler. These impurities can be removed to some degree by performing a procedure known as dressing. From the
hot operating temperature, the temperature is reduced to 385°F (196°C) and the machine sits idle for 8 to 12 hours.
The impurities will float to the surface of the solder where they are scooped out and placed in a dross bucket. This
material can be returned to the vendor for reclamation of the metals. Some manufacturers go for years without
changing the solder; they dross and make additions. When the time comes to change over the solder, vendors will
issue credit on the purchase of new solder as long as the old solder is returned to them for processing.
The acid pre-clean will have some copper in solution and can be treated conventionally. The waste flux is collected
and is sent off-site for treatment.
3.2.8.2 Reflowed Tin-lead
The reflow process uses the tin-lead plated as an etch resist to create the final surface finish. It is quite common in
lower technology single-sided boards. Some military specifications require reflow and specifically exclude the use of
SMOBC/HASL. The desire to remove lead from the plating process and tin-lead performance issues has lead to a
decline in use. The performance concerns include difficulty in cleaning, a poor surface for solder mask, and the fact
that it will liquefy during wave soldering, which may cause the mask to lift, among other downstream defects. Any
spent flux generated during the reflow process is collected to be shipped off-site for treatment.
Four methods exist for tin-lead fusing (ref. 35):
• Infrared reflow uses IR rays to melt the tin-lead. This method is widely used since it can be conveyorized and
gives consistent results. In-line are fluxing rollers, a pre-heat area, and the area of the oven where the actual
melting of the tin-lead occurs, which is followed by cleaning and drying.
56
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• Hot oil reflow has been around for years. The panel is fluxed and submerged in a pot of hot oil long enough to
melt the tin-lead. It is not currently preferred due to its lower productivity vs. IR reflow, and because of the fire
and safety hazards.
• Vapor phase reflow uses the principle of condensation heating. The panel is immersed in a saturated vapor,
which condenses on the board, causing heating and subsequent tin-lead melting. The heat transfer liquids are
very costly.
• The hot air leveling machine can be used to melt the tin-lead as well. It is dipped in the molten solder, the same
as a SMOBC-type board, and air knives blow off the excess solder.
3.2.8.3 Nickel/Gold
Nickel-gold finishes may cover an entire circuit or be selectively plated onto certain areas of a circuit. Nickel-gold
formulations can produce hard gold, with the addition of cobalt or another metal being co-deposited in small
amounts, or they can produce soft gold, by utilizing pure gold.
Hard Gold. Hard gold is electrolytically plated. The most common application of hard gold is edge connectors,
but hard gold may also be plated over circuit areas as well. Automated edge plating machines are common since
manual plating is quite labor-intensive. Typically, a plater's tape is applied to the board masking off all of the
circuit above the edge connector. The panel is then processed through a nickel-gold plating line, with just the edge
connectors immersed in the plating fluid. Nickel is plated first, Watts or sulfamate nickel is common. Cyanide gold
is the most common gold electroplating chemistry.
Soft Electrolytic Gold. Soft gold is a pure gold coating over a nickel deposit. It may be electroplated over the
entire circuit or selectively over certain portions of a circuit (excluding edge connectors, which require hard gold).
Selective electroplating requires a combination of masking and bussing (providing current to the portion of the
circuit being electroplated). Selective gold applications include contact points (which may require hard gold), press
pads, wire bond sites, or portions of a board that may reside in a corrosive environment. Selective gold plating can
be labor-intensive and is not frequently specified for production lots (all gold plating is often substituted; the labor
savings offset the extra gold required).
Electroless Nickel/Immersion Gold. The electroless nickel/immersion gold process is another method of
applying soft gold. Electroless plating can be conveniently performed after etching because no bussing is required.
Therefore, these all-gold boards can be processed with a standard tin etch-resist and processed identically as SMOBC,
except the gold plating step replaces the HASL step. This process has advantages over SMOBC/HASL and
electrolytic gold plating. When compared to SMOBC/HASL, electroless all-gold circuits have a much longer shelf
life. The flat surface profile of the electrolessly plated surface-mount pad and overall excellent solderability make
electroless nickel/gold ideal for surface-mount technology. When compared to electrolytic gold, electroless has the
advantage of full copper encapsulation because plating is performed after etching, not before, as with electrolytic gold
plating. Selective gold plating is made somewhat easier by the electroless plating method since no electrical bussing
is required. Cost is the main disadvantage. Immersion gold and electroless nickel process baths are short-lived
compared to electrolytic formulations, and maintenance and control of these baths is more difficult. The main
application of electroless nickel-gold coatings is chip-on-board technology, where component leads are ultrasonically
or thermosonically bonded to gold pads rather than soldered.
3.2.8.4 Immersion Bismuth/Immersion Silver
Two non-precious metal coatings have been developed that are less expensive and require fewer steps than their
precious metal counterparts. No base nickel is necessary, which eliminates that step. However, both immersion
technologies require that the surface is cleaned and microetched to remove surface oils and improve topography for
subsequent deposition. Testing has shown that these two immersion metals provide better solderability than organic
coatings (ref. 39).
Immersion Bismuth. Bismuth resists oxidation and provides solderability similar to that of unoxidized copper.
The bismuth coating does not form any intermetallic alloy with copper and readily diffuses throughout the solder
joint during soldering since it melts at nearly the same temperature as tin-lead.
Immersion Silver. Immersion silver is deposited in conjunction with an organic coating. After surface
preparation the panels are transferred to the immersion silver. Since bare silver surfaces tarnish and oxidize, the
organic component is added as a protective coating for the silver.
57
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3.2.8.5 Organic Solderability Preservatives (OSPs)
The OSP coatings are applied to bare copper after solder mask (they can be applied to the finished board after
routing). Their function is to protect the copper from oxidation and to provide long-term solderability. The coatings
can usually be applied in immersion, spray, or flood mode (ref 35). OSPs offer an environmentally friendly
alternative, low capital equipment expense, lower maintenance costs compared to HASL, and are safer for employees
to handle. However, HASL has a very long and reliable track record, which is a deterrent to change. For such a
change to occur, PWB facilities and their customers need to be convinced that OSPs are a viable alternative. Some
may be forced into trying OSPs as designs call for finer pitch surface mount pads. HASL is notorious for depositing
uneven and unlevel amounts of solder on surface features, while OSP-coated features have good pad coplanarity.
Care must be taken, however, while handling and storing OSP-coated boards. The surface is not very durable and is
susceptible to scratches that will expose the copper underneath and allow oxidation to occur.
A cost comparison completed at a large facility concluded that the OSP process costs one-third that of HASL.
Among the costs associated with HASL are:
High equipment maintenance costs
Cost and maintenance of safety equipment for HASL operators
Hazardous waste disposal of the tin-lead frames after the panels are routed
High electricity costs to keep the solder pot heated
Labor cost involved with the masking and subsequent cleaning of gold edge contacts
Added cleaning necessary to pass surface insulation resistance (SIR) testing when using dry film
While companies converting to OSPs report success, they indicate that facilities must be prepared for process
alterations. New "optimum" operating parameters will need to be established. During assembly, for example,
different flux formulations, pre-heat temperatures, and solder pot temperatures may be necessary. They recommend a
coordinated effort between the PWB shop, assembly shop, and the customer to educate one another on process issues
and what is or is not an acceptable final product.
3.2.9 Final Fabrication
Non-plated features are added to the board during the final fabrication process. These may include tooling holes,
cutouts, and countersink holes. Numeric controlled routers run profiling programs that are output from the CAM
systems with all of the features needed according to specifications.
Finally, the circuit is either completely routed from the panel or partially depanelized. Partial depanelization is
common with production lots or when board assembly will be performed by machine. Most of the circuit is routed
out of the panel, but tabs remain to hold the circuit in place. This allows the assembly machine to populate
multiple boards at once. Afterwards, the circuits can be snapped or broken out of the panel. Such panels are often
referred to as "breakaways," "snaps," or "arrays."
An alternative to breakaways is to have the panel V-scored. This allows more circuits to be placed on a panel since
no spacing is necessary for the routing bit. An array of circuits is routed as if it were a single image. The V-scoring
machine has a thin rotating scoring blade that will rout across the top of the panel 30-40% of the thickness of the
panel. This is repeated on the bottom side. Some scoring machines have two blades and both sides can be scored in
one pass. The remaining 20-40% of the panel not routed will hold the panel together through assembly and can then
be easily broken apart.
Drilling and routing produces dust from the material that is being drilled or cut. Most of the material is the glass
and resin core. However, copper is laminated to the core, and in the case of routing, there may be tin-lead or another
metal plated to the surface. A toxicity characteristic leaching procedure (TCLP) can be performed on a sample of
router dust to determine how the dust needs to be treated. In most cases it can be treated as non-hazardous industrial
waste. If the lead concentration in the dust were greater than 5 mg/L, the router dust would be considered hazardous
and would have to be managed in compliance with Resource Conservation and Recovery Act (RCRA).
The "frames" that remain after the boards are routed from the panel may have a tin-lead or gold coating. These
frames are collected and sold as scrap.
3.3 Waste Generation and Pollution Prevention Methods
A summary of waste volume estimates for common PWB manufacturing processes is presented in Exhibit 3-23.
Potential substitute processes that may reduce the quantity of waste generated or the hazardous characteristics of the
58
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waste are presented in Exhibit 3-24. Potential bath maintenance and recovery options applicable to common PWB
manufacturing processes are identified in Exhibit 3-25. Detailed information relative to these technologies can be
found in Section 4.
Exhibit 3-23. Selected Waste Volume Estimates from PWB Processes
Process
Waste
Volume
(based on 1000 board ft2
of 4 layer boards)
Etching, Inner and Outer Layers
Dry Film Resist Developer
Dry Film Resist Stripper
Tin-Lead Stripper
Soldermask Developer
Microetch; Inner and Outer Layers
Sulfuric Acid Dips
Electroless Copper
Board Trim
Spent Etchant
Spent Developer
Spent Stripping Solution
Spent Stripping Solution
Spent Developer
Spent Micro-Etchant
Spent Sulfuric Acid baths
Waste Electroless Cu Bath
Waste Copper-Clad Material
140 gallons
200 gallons
6 gallons
17 gallons
60 gallons
16 gallons
12 gallons
26 gallons
187.5 square feet
49.2 Ibs Cu
Assumptions:
0 Ammoniacal etchant used for both inner- and outer-layers, 70% of copper foils etched, 1 oz copper used on all layers, and 20 oz/gal
carrying capacity of etchant.
1 Fifty percent of film developed (30% outer, 70% inner), developer carrying capacity of 3 mil-ft2/gal, and 1 mil film is used throughout.
2 Fifty percent of film stripped (70% outer, 30% inner), stripper carrying capacity of 100 mil-ft2/gal, and 1 mil film is used throughout.
3Thirty percent metal area, tin-lead resist is 0.3 mil thick and stripper capacity of 15 oz/gal of metal.
4 Thirty percent of mask developed, 1 mil thickness, 10 mil-ft2 carrying capacity.
SOxide, electroless Cu, and pre-pattern plate microetches (50%, 100%, and 30% of surface area etched, respectively) considered. Many
facilities may employ additional baths.
6 microinches average etch and 4 oz/gal carrying capacity.
7 Bath life of 1 gallon/500 ssf, 3 sulfuric dips (oxide, electroless copper, and pattern plate lines).
818x24 panels with .75-inch thief area and .25 inch spacing of 6 step-and-repeats, outer layer 2 oz copper (80% of trim area), inner layer 1
oz copper (50% of trim area).
Exhibit 3-24. Potential Substitute Processes for Common Multilayer PWB Manufacturing
Processes
Most
Common
Process
Substitute
Processes
Advantages
Disadvantages
Chemical
Clean
Photo-tool
creation
Oxide
Pumice
Scrub
Mechanical
Brush Scrub
Direct
Imaging
Use pre-
treated or
"double-treat"
material
Eliminates portion of chemical
preclean line (anti-tarnish remover and
anti-oxidant remover may still be
necessary)
Does not produce copper-bearing waste
from scrubbing operation
Eliminates chemical pre-clean line
Eliminates photo-tooling (film, film
punches, film developing)
Eliminates defects introduced by photo-
tools (film dimensional instability,
handling defects)
Eliminates oxide process line
Maintenance-intensive equipment
Imparts stress to thin layers-usually
not an option of very thin inner-layer
material
Introduces a waste stream bearing
copper dust
Very high capital costs
Current models are slower than
conventional photo-tool exposures
Material is more expensive
Simply moves oxide process upstream
to laminate vendor
59
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Permanganate
Besmear
Electroless
Copper
Pattern Plate
Copper
Pattern Plate
Tin-Lead
Solder Mask
Over Bare
Copper
(SMOBC)
followed by
Hot Air
Solder
Leveling
(HASL)
Plasma Eliminates desmear process line
desmear Completely "dry" process
Process control is more precise
Various Eliminates formaldehyde
metallization Some shorten process line from 7-8
alternatives process tanks for electroless Cu to 3-5
(see details in tanks for alternative
Exhibit 3-16) Some eliminate high concentrations of
EDTA and other complexing agents
Carbon and graphite-based alternatives
have only one copper-bearing process
tank and rinse stream—micro-etch
Panel-Plate Facilitates use of organic (dry film)
Copper etch resist as opposed to metallic
Shorter process-pattern plate pre-clean
line is eliminated along with tin-plate
line
Pattern Plate Eliminates lead from process
Tin No performance loss as etch resist.
Tin sulfate bath also eliminates
flouborates
SMOBC, Eliminates lead and maintenance and
E'less Nickel/ capital intensive HASL
Immersion When used with tin-only etch resist,
Gold manufacturing process becomes lead-
free
Provides excellent solderability, shelf
life
SMOBC, Eliminates lead and maintenance and
Organic capital intensive HASL
Solderability Opens new process sequence options
Preservative (OSP can be applied immediately after
(OSP) solder mask or later in the process)
Coating Lower overall costs
Slower, limiting use among production
shops
Higher capital investment
Far less mature—many early versions of
the alternatives had narrow process
windows
Some alternatives require
conveyorization which generally has
associated higher capital costs than
tank lines
Inefficient-most of copper plate is
subsequently etched away
Copper incidentally plated on surface
excludes use for fine lines due to
etching undercut.
Some specifications require tin-lead,
forcing facilities to maintain both lines
or a tin-lead line only; Issue is of
considerable importance to small and
very small shops
More expensive
Considerable additional process
chemistry and time
OSP coating is soft, scratches easily,
which can lead to defects
Requires some co-ordination with
assembly houses
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Exhibit 3-25. Potential Bath Maintenance and Recovery Options Applicable
to Common PWB Processes
Common
Process
Sequence
(wet processes Tank
only) Name
Common
Tank
Chemistry
Process Waste
Common Bath Maintenance
&
Recovery Options
Inner Layer Image Transfer
Chemical Anti-tarnish
Clean* Remover
Mixed strong
acids
Rinsewater contains
Cu
Spent bath contains
1-10 g/L Cu
Bath: Consider use of bath maintenance
technology such as diffusion dialysis or acid
sorption.
Microetch Persulfate-based Rinsewater contains
or Cu
Peroxide/ Spent bath contains
sulfuric 20-40 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Peroxide sulfuric can be chilled, causing
copper sulfate to crystallize for recovery and
sale. Decanted solution can be reused.
Persulfate baths can be reduced, then
electrowinned to recover copper.
Sulfuric Acid 5% sulfuric
Rinsewater contains
Cu
Spent bath contains
1-2 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Acid purification for bath life extension
(usually economical for large shops). Cu
concentrations usually too low for Cu recovery
using electrowinning.
Imaging*
Etching
Resist Strip
Anti-tarnish Weak acid
(citric)
Film develop,
fix
Resist Sodium
developer carbonate
Etchant Acidic cupric
chloride or
alkaline
ammoniacal
Stripper Potassium-
hydroxide/
solvent
Rinsewater contains None identified.
Cu
Spent bath contains
1 g/LCu
Spent developer, Small quantities of silver can be recovered with
fixant electrowinning or metal replacement
technologies.
Rinsewater generally Square footage analytical-based replacement
free of metals rather than time-based, which is frequently
Process solution employed for this bath.
contains dissolved
resist
Rinsewater contains Rinse: Cu-free etchant flood rinse to lower Cu-
Cu. rich dragout. Rinse can be recycled with ion
Spent etchant exchange.
contains 140 or Bath: Bath regeneration with chlorination is
more g/L Cu common with cupric etchant. Copper can be
electrolytically removed from ammoniacal
etchants, reinjected with ammonia and oxygen,
and reused. Other regeneration techniques
include membrane-based technologies
(electrodialysis).
Rinsewater contains Bath: Filtration can be used to remove solids
dissolved and solid and extend the bath life.
resist, but no metal
Spent stripper
contains dissolved
resist
61
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Oxide*
Microetch Persulfate-basedRinsewater contains
or Cu
Peroxide/ Spent bath contains
sulfuric 20-40 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Peroxide/sulfuric can be chilled, causing
copper sulfate to crystallize for recovery and
sale. Decanted solution can be reused.
Persulfate baths can be reduced, then
electrowinned to recover copper.
Sulfuric Acid 5% sulfuric
Rinsewater contains
Cu
Spent bath contains
1-2 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Acid purification for bath life extension
(usually economical for large shops). Cu
concentrations are usually too low for Cu
recovery using electrowinning.
Pre-Dip
Conventional
Oxide
Sodium
hydroxide
Caustic and
hypochlorite
No rinse; Little or None identified.
no Cu in bath.
Rinse contains Cu Consider new chemistries not based on
Spent process hyprochlorite.
solution contains
low concentration of
Cu
Clean Holes
Permanganate* Hole
Besmear Conditioner
Various organic Rinse with no Cu
solvents, amine Process solution
acids with no Cu
None identified.
Permanganate Potassium Rinsewater contains Bath maintenance technology (e.g., porous pot)
permanganate, little or no Cu extends bath life.
caustic Process solution
contains little or no
Cu
Neutralizer
Sulfuric acid
Rinse contains Cu
Process solution
contains 1-5 g/L C
None identified.
Make Holes Conductive
Deburr and Mechanical
Scrub Scrub
Electroless Cleaner
Copper*
Rinsewater contains
copper dust and
spent brush fibers
Triethan- Rinse contains some
olamine or Cu; Process
other caustic solution contains 1-
5 g/L Cu, also may
contain complexer
such as EDTA
Filter rinse to remove Cu particles.
None identified.
Microetch Persulfate-based Rinsewater contains
or Cu
Peroxide/ Spent bath contains
sulfuric 20-40 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Peroxide sulfuric can be chilled, causing
copper sulfate to crystallize for recovery and
sale. Decanted solution can be reused.
Persulfate baths can be reduced, then
electrowinned to recover copper.
Sulfuric Acid 5% sulfuric
Rinsewater contains
Cu
Spent bath contains
1-2 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Acid purification for bath life extension
(usually economical for large shops). Cu
concentrations usually too low for Cu recovery
via electrowinning.
Pre-dip Hydrochloric No rinse; Spent bath None identified.
acid contains 1-2 g/L Cu
62
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Catalyst
Accelerator
Electroless
Copper
Anti-tarnish
Hydrochloric
acid, stannous
chloride and
palladium
Fluoboric acid
or sulfuric acid-
based
Copper sulfate,
caustic,
formaldehyde,
EDTA, other
Some
formulations
include CN
Weak acid
(citric)
Rinse contains Cu,
Pd, Sn; Process
solution contains <1
g/L Cu, <1 g/L Pd
and ~5 g/L Sn
Rinse contains Cu
and Sn
Bath contains 2-5
g/L Cu and Sn
Rinse contains Cu
and formaldehyde
Bath contains Cu (3-
7 g/L)
Rinsewater
containing Cu
Spent bath
containing 1 g/L Cu
Rinse: Recycle with ion exchange.
Bath: Long-lived bath can be extended further
by maintenance of pre-dip.
Rinse: Can be recycled with ion exchange.
Switch to sulfuric -based chemistries that can be
electro winned for Cu recovery.
Rinse: Can be recycled with ion exchange.
Bath: Cu from solution can be recovered with
activated foam canisters.
Switching to an alternative metallization
method removes some Cu sources, eliminates
formaldehyde, and reduces water consumption.
Rinsewater contains Cu.
Spent bath contains 1 g/L Cu.
Outer Layer Image Transfer
Imaging Developer
Sodium
carbonate
Rinsewater generally
free of metals
Process solution
contains dissolved
resist
Square footage analytical-based replacement
rather than time-based, which is frequently
employed for this bath.
Pattern Plate Cleaner
Copper*
Ethylene glycol
None identified.
Microetch Persulfate-based Rinsewater contains
or Cu
Peroxide/ Spent bath contains
sulfuric 20-40 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Peroxide/sulfuric can be chilled, causing
copper sulfate to crystallize for recovery and
sale. Decanted solution can be reused.
Persulfate baths can be reduced, then
electrowinned to recover copper.
Sulfuric Acid 5% sulfuric
Rinsewater contains
Cu
Spent bath contains
1-2 g/L Cu
Rinse: Recycle using ion exchange.
Bath: Acid purification for bath life extension
(usually economical for large shops). Cu
concentrations usually too low for Cu recovery
via electrowinning.
Copper Sulfate Copper sulfate, Rinsewater contains
sulfuric acid Cu.
Bath contains 10-20
g/LCu
Rinse is excellent candidate for
dragout/electrowin setup for copper recovery.
Remaining Cu-bearing rinse can be recycled
with IX.
Pattern Plate Tin-lead Stannous Rinsewater contains
Etch Resist* fluoborate Sn and Pb
Lead fluoborate Bath contains 20-30
Boric acid g/L of Sn and Pb
Fluoboric acid
Rinse: Since bath is not heated, simple drag-
out configuration is not effective. Point source
ion exchange to remove metal or to recycle
water is effective in removing lead from
entering general waste streams to conventional
treatment.
63
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Strip
Photoresist
Stripper
Potassium-
hydroxide/
solvent
Rinsewater contains
dissolved and solid
resist, but usually
no metal
Spent stripper
contains dissolved
resist
Bath: Filtration can be used to remove solids
and extend the bath life.
Etch Copper Etchant
Acidic cupric
chloride or
alkaline
ammoniacal
Rinsewater contains Rinse: Cu-free etchant flood rinse to lower Cu-
Cu. rich dragout. Rinse can be recycled with ion
Spent etchant exchange.
contains 140 or
more g/L Cu Bath: Bath regeneration with chlorination is
common with cupric etchant. Copper can be
electrolytically removed from ammoniacal
etchants, rernjected with ammonia and oxygen,
and reused. Other regeneration techniques
include membrane-based technologies
(electrodialysis).
Strip Etch Tin, Tin-lead
Resist strip
Various
chemistries
used, including
nitic-based and
ammonium
biflouride
Rinsewater contains Switch to tin-only plating to
Sn and Pb ; bath from this waste .
contains 50-100 g/L
Sn and Pb.
Bath may contain
small but significant
amounts of arsenic
and other tin/lead
anode impurities.
eliminate lead
Surface Finish
Solder Mask Developer
Hot Air Solder Acid Cleaner
Level*
Flux
Solder
Immersion
Sodium
carbonate
Hydrochloric
acid
L-Glutamic
acid HCL,
Polyalkylene
glycol, other
Tin-lead
Rinsewater generally Square footage analytical-based replacement
free of metals rather than time-based which is frequently
Process solution employed for this bath.
contains dissolved
resist
Rinsewater contains None identified.
Cu
Bath contains 1 g/L
Cu
None identified.
Dross, rinsewater, Dross is generally recyclable
trace amount of bar vendor).
dissolved Pb; some
metallic Pb and Pb
salts may also enter
rinsewater stream
off-site (to solder
* See Table x-x for common process substitutions
64
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4.0 Wastewater Generation and Fundamental Waste
Reduction Practices
4.1 General
Section 4 presents a discussion of wastewater data provided by survey respondents. It also covers fundamental waste
reduction practices used in the PWB manufacturing industry. These practices were identified from the survey and a
review of literature. Implementation of these practices is considered the first step in an effective pollution control
program. These pollution prevention (P2) methods are relatively inexpensive to implement and they reduce the need
for the more expensive recovery, recycle and treatment technologies which are discussed in Sections 5 and 6.
The fundamental waste reduction practices are categorized into the following three groups:
• Good Operating Procedures
• Drag-Out Reduction and Recovery Methods
• Rinse Water Use Reduction
Descriptions of these practices, along with summaries of relevant survey responses, can be found in Sections 4.3
through 4. 5.
4.2 Wastewater Survey Data
This section of the report contains a discussion of wastewater data provided by survey respondents, including
discharge type, flow rates, and costs for raw water and sewer use charges. Additional wastewater data, including
discharge limits, compliance difficulties, and treatment methods employed by survey respondents, are found in
Section 6.
4.2.1 Discharge Types
For the purpose of this survey, the discharge type refers to the destination of wastewater discharges regulated by
categorical effluent standards. The three possible selections in the survey questionnaire were direct discharge (i.e., to
surface water such as a river or stream), indirect discharge (to a publicly owned treatment works or POTW), or zero
discharge (no process wastewater discharge from PWB manufacturing).
The survey data (see Exhibit 4-1) show that the majority of the respondents are indirect dischargers (69%). One
facility indicated they are at zero wastewater discharge. That particular facility is a small PWB shop operated by the
US Navy (ID# 36). Based on the information in their survey form, it appears they achieve zero discharge by
implementing good operating procedures and using an evaporative technology, and shipping concentrated residual
wastes off-site for disposal.
4.2.2 Discharge Flow Rates
Wastewater discharge data are summarized in Exhibit 4-1, columns 6 to 9. Average daily flow rates for respondents
range from 400 gpd (ID# 36) to 400,000 gpd (ID# 740500). The mean and median flow rates of respondents were
64,459 gpd and 35,000 gpd, respectively. The vast majority of water used in PWB facilities is used for rinsing. The
quantity of rinse water used is dependent on numerous factors, including types of boards manufactured, production
rate, cost of water and sewer use, drag-out rate, use of pollution prevention measures (e.g., extended draining time),
the rinsing configuration (e.g., single rinse vs. counterflow rinse), and water use control method (e.g., continuously
running rinses vs. those controlled by conductivity controllers). Some of these factors are examined in this section.
The values in column 8 express water use in terms of production. These values are calculated as the average flow
rate in gallons per square feet of "wetted surface." The wetted surface area was calculated based on the total surface
area of all layers of boards manufactured. Because these adjusted production-based flow rates account for multiple
processing and rinsing steps, they are a good method of comparing water use among respondents.
Not suprisingly, the data indicate that overall water usage was related to the product mix of the shop, particularly the
layer-count mix. Therefore, an adjusted, production-based flow rate was calculated. Comparing the adjusted
production based flow rates, the range of water use among respondents is extremely wide; 8% of respondents reported
water usage of over 250 gallons/layer-ft2, whereas 69% reported water use of less than 75 gal/layer-ft2.
A very sharp distinction can be drawn between the water use of larger and smaller shops. The largest 25 facilities in
65
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terms of production had water usage rates less than one-third that of all respondents. Since facilities that did not have
formal data were encouraged to estimate their water usage, it is possible that some of the very high usage rates
among the smaller shops are a result of poor estimation of either the production rate or water usage. Following this
line of reasoning, it is also possible that the rates shown in Exhibit 4-1 for the largest 25 facilities are a more
accurate estimate of true water usage by this industry sector.
There is a relationship between the adjusted production-based flow rates and the cost of water and sewer use. For
facilities that have very high combined water and sewer costs, the adjusted production-based flow rates are very low.
Variation of water and sewer use costs among survey respondents is likely due in part to geographical location, with
higher costs in coastal and arid regions.
Exhibit 4-1. Water Use and Wastewater Discharge Data
Resp.
ID
Prod.
(board ft2/yr)
Direct
In-direct
Zero
Avg Flow
(gpd)
Max. Flow
(gpd)
Flow
(gal/
layer-ft2)
Cost of Water
(S/Kgal)
Cost of Sewer
(S/Kgal)Cost of Water & Sewer
(S/Kgal) 36930A-X27,00000.951.452.40955099-
X120,000140,000nrnrl2.4055595-X20,00022,500nrnr44486-
X100,000130,0001.620.792.41955703-X98,000108,0001.700.552.2513-
X30,00033,000 37-X10,00012,000
1.51.352.85154,000X13,50017,000516.2386,800X3,0004,00060.44.63.48.
003610,000X4008002.85410,625X80,000120,000477.5
5111,000X9,50011,700114.61.51.352.854112,000X230,000275,000618.30.71.1
21.82671015,000X10,56021,12012.01.503.505.002215,000X10,00018,00058.8
5715,000X40,00050,000
2.335.304816,000X12,00030,000102.61.342.363.701216,788X17,00024,0001
19.73.183.181717,000X18,00021,00076.3 1917,500X275,000310,000677.
61.2534.252818,000X40,00051,000260.32.352.795.144718,000X25,00032,000
44.52.661.44.065218,000X21,00032,00034.7
1120,000X32,50052,00061.12.242.875.114222,000X25,00040,00051.8
4522,500X25,00030,00049.60.002025,000X3,5005,00022.5
3525,000X31,00039,00076.93.23.817.013925,000X95,000115,000125.10.00
2726,480X25,00028,00051.7
2628,500X77,00080,000291.50.003129,500X60,00090,00056.31.230.792.02
1830,000X40,00042,00049.61.31.552.853330,000X45,00070,000197.955.00
4030,000X60,00090,00075.8
3433,000X70,00085,00076.31.290.51.795035,000X39,00050,00069.1
4435,625X35,00040,00077.43.53.501036,000X30,00033,00041.8
66
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1636,000X200,000171.30.860.41.2694774540,000X13,00018,00028.61.501.50
3.004340,000X51,62872,28899.91.330.331.664465742,358X6,000180,0008.31.
982.294.274644,000X45,00060,00044.8
2345,000X130,000157.8213.002155,000X113,000175,000
2.80.63.402971057,OOOX74,000124,00091.2nrnr
50210060,OOOX35450.08nrnr
5564,500X168,900168,900192.31.212.613.825669,000X50,00065,00043.811.
005370,000X35,00040,00035.10.003271,064X215300
1.742.864.603248275,000X31,00054,00036.41.94nrl.942575,000X110,000130,
00036.9112.002975,000X34,000150,0007.833.002550390,000X5,0006,5009.
9nrnr 3693096,OOOXOOnrnr 49120,000X64,00085,00099.0
965874175,000X21,00027,00016.91.721.032.75953880180,000X35,00045,00013.9
1.332.603.9333089200,000X16,00025,00011.61.322.283.60X3200,000X20,000
30,0006.2nr4.004.003470240,OOOX20,00030,0009.20.060.0643841250,OOOX38,
00050,0009.93.542.576.11279250,000X5,2005,5004.37.565.8213.3814250,000
30250,000X2.52.50237900273,000X105,000125,00015.61.430.612.042737
01280,000X25,00030,0008.61.411.352.7641739300,000X57,12565,00017.90.801.
602.40959951320,000X20,00030,0007. Inrnr
42692360,000X100,000125,00023.90.03nr0.03358000500,OOOX9,00012,0000.9nr
nr
43694500,000X30,00040,00011.61.000.781.7837817540,000X6,00011,0002.41.2
00.211.4142751540,000X140,000160,0007.01.603.104.70X2600,000X48,00062,4
004.21.612.704.31133000600,OOOX160,000200,00013.72.732.335.06X1936,OOOX
160,000185,0005.21.632.924.557405001,800,000X400,0001,000,0009.62.223.085.30
9465871,900,000X200,000250,0004.30.580.731.3130232,300,000X145,000160,000
2.23.785.249.02318383,000,000X280,000420,0002.31.851.903.754628003,750,000
X26,00031,0001.813.803.4017.201073005,000,000X250,000300,0006.31.501.963.46
Mean64,459—
8.20* 1.602.283.18Median35,000—12.42*2.162.604.07
*For largest 25 shops.
Low water use rates can be achieved through the implementation of simple water conservation techniques and/or by
using technologies such as ion exchange that recycle water. ID# 462800 has achieved the lowest production-based
flow rate without the use of any sophisticated recycling technology. Rather, it uses flow controllers, rinse timers,
and reactive or cascade rinsing.3 Xhe data also indicate that facilities that have implemented the ion exchange
technology within their processes have a lower average flow rate than those that have not implemented this
technology.4
Xhe data also indicate that the use of water conservation methods does not always result in low water use. Xhe four
facilities with the highest production-based flow rates do not use ion exchange recycling, but they all indicated that
they employ counterflow rinsing, plus some other methods of water conservation. In such cases, it is probable that
water is simply being wasted by having unnecessarily high flow rates in the rinse tanks (e.g., flowing water during
periods of non-production).
4.3 Good Operating Practices
Good operating practices are organizational and procedural activities that reduce the generation of waste. Generally,
these are not equipment-oriented methods of waste reduction, although the implementation of some good operating
practices can result in significant capital expenditures when implemented plant-wide. Many of the good operating
practices identified will provide product quality improvements and operating cost reductions in addition to reducing
waste generation. Also, they will generally improve the working environment of a shop, including health and safety
aspects. Exhibit 4-2 contains the survey results for good operating practices.
Exhibit 4-2. Good Operating Practices
3 Water conservation methods such as these were covered in Section 6 of the PWB survey form. The responses to these questions are
summarized in Section 6 of this report.
4 Based on six facilities (ID#'s 25503, 3470, 43694, 37817, Tl, 31838) that have installed ion exchange and have an average adjusted
production-based flow rate of 5.4 gal/ssf, vs. an average for all facilities of 12.4 gal/ssf.
67
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Drag-Out Reduction or Recovery Method No. of PWB Respondents Using Method% of PWB
Respondents Using Method Maintain records of analysis and additions8193.1Perform in-house regular
process bath analysis8091.9Dump process baths based on analysis rather than schedules7485.0Control
inventory levels and access7282.7Have preventive maintenance program for tanks6372.4Conduct
employee education for pollution prevention6271.2Look for opportunities to reduce energy
consumption6170. IHave a formal policy statement regarding pollution preventions360.9Have a formal
pollution prevention program4855. IHave overflow alarms in process tanks4046.0Have a leak detection
system2023 .ORecycle non-contact cooling water* 11.1
* Added by respondent under "Other."
4.3.1 Employee Awareness and Education
Employees are often the fundamental cause of waste generation and, conversely, they are in the best position to
employ pollution prevention and control. Without employee cooperation, even the best efforts of management will
be ineffective or futile (ref. 23). Of the 87 PWB facilities responding to the survey, 62 (or 71.2%) indicated that
they conduct employee education for pollution prevention.
Employee awareness and education begins with a clear company policy with regard to the environment and plans for
pollution prevention and control. The policy must be conveyed to the employees and reinforced in various ways in
order to create a sufficiently positive attitude toward meeting the company's environmental goals.
There are three stages to instilling a pollution prevention attitude in employees and providing them with the
knowledge needed to perform successfully. These are prior to job assignment, during job training, and on-going
education throughout employment (ref. 40). This training should include the following elements:
How, why, and where waste is produced and how to minimize it (e.g., good rinsing practices)
Preventive maintenance methods that reduce waste generation (e.g., tank/liner inspection and repair)
Company rules for handling process chemicals and making process (tank) additions
Procedures for handling spills/leaks
How to operate pollution prevention and control technologies in their working area
Where to go for assistance with a non-routine problem
Capabilities and capacities of waste treatment processes
Environmental regulations and how they relate to the processes the employees operate
Why pollution prevention is important (cost, regulations, health and safety, improved working environment,
improved environment)
• How related waste management operating costs (e.g., chemicals, water, waste treatment, hazardous waste)
impact employee wages
The advantages of establishing company rules and employee training will be reduced or eliminated unless the
program has a method of measuring success and can deal with those who refuse to participate. Success should be
quantified, whenever possible. This means companies should collect chemical use and waste generation data,
maintain records, and periodically evaluate the records. Data collection and record keeping are discussed in Section
4.3.2.
One PWB company that was experiencing high HC1 use (HC1 bath serving as a microetch on a preclean line)
implemented an education program that kept employees informed about process specific chemical and water costs.
On their high production line, some incidents of misuse represented a cost of $2,000 to $5,000. By immediately
informing the employees after each incident of high water/chemical use was detected, the incidents were brought
under control in a matter of months and eventually were eliminated (ref. 41).
Bonuses, awards, plaques, and other forms of recognition are often used to provide motivation, and to boost
employee cooperation and participation. In some companies, meeting waste minimization goals is used as a
measure for evaluating the job performance of managers and other employees (ref. 42).
4.3.2 Chemical Tracking and Record Keeping
The major sources of pollution from plating operations are process chemicals. Process chemicals become pollution
through both use and misuse, resulting in wastewater generation, spills/leaks, spent solutions, sludge, and air
emissions. To be fully effective, a pollution prevention and control program must track and record chemical
68
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purchases, chemical use, and waste generation. The following is a list of chemical and waste data that merit
consideration for record keeping (ref. 3):
Chemical purchases
Chemical inventory
Bath analyses
Process bath reformulations and chemical additions
Partial tank discharges (i.e., decanting, bleed and feed) and total tank discharges (i.e., batch dumps)
Water use per rinse tank or process line
Total wastewater flow
Wastewater treatment chemical use
Spent process solution analyses
Waste treatment sludge analyses
Specific incidents of high chemical use
To increase the utility of the chemical use and waste generation data, corresponding production data should also be
collected and recorded. These data can be used to identify variability of chemical use and waste generation that are due
to production changes rather than operational practices. As discussed in Section 4.3.1, chemical use data should be
shared with employees in an effort to educate them.
Several survey questions were related to chemical tracking and record keeping. Records of analyses and additions are
kept by 93.1% of the shops. This item had the highest response for good operating procedures. In-house bath
analysis is second with 91.9% of the shops. Controlling inventory levels and access is performed by 82.7% of the
PWB shops.
4.3.3 Chemical Purchasing, Storage, Usage, and Handling
Proper purchasing, storage, usage, and handling of chemicals increases the percentage of raw materials that reach
their intended process without spills, leaks, or other types of losses that could result in waste generation. Some
basic guidelines for good operating practices include (ref. 40):
Purchasing:
• Standardization of materials (i.e., using the minimum number of materials in all operations). Many times the
decision to use one material over another is based on operator preference, rather than on a technical or economic
requirement. Written specifications can improve purchasing and reduce waste.
• Avoid over-purchase of materials.
• Avoid collecting free samples of process chemicals from vendors. Only accept amounts needed for testing
purposes.
Storage:
• Utilize a dedicated/protected storage area.
• Space containers in storage areas to facilitate inspection.
• Label all containers.
• Stack containers according to manufacturers' instructions to prevent cracking and tearing from improper weight
distribution.
• Separate incompatible materials in storage, such as cyanides and acids.
• Raise containers off the floor in the storage area to inhibit corrosion from sweating concrete.
Handling/Use:
Establish written procedures for process (tank) formulation and additions.
Use specifically assigned personnel to formulate baths and make tank additions.
Perform routine bath analyses and maintain bath analysis logs and tank formulation/addition logs.
Use process baths to the maximum extent possible (do not employ a dump schedule).
Implement multiple use of certain materials.
Implement statistical process control (SPC) to improve the efficiency of chemical use.
Survey results show that process bath dumps based on analysis rather than a schedule is performed by 85%
respondents. Overflow alarms in process tanks are used by 46% respondents.
69
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4.3.4 Preventive Maintenance
In general, preventive maintenance is an important element in operating and maintaining a PWB facility. With
regard to pollution prevention, preventive maintenance can minimize chemical losses due to leaks and can reduce the
potential for a catastrophic loss due to a tank failure. Specific areas where preventive maintenance can reduce
pollution generation include:
• Periodic inspection of tanks and tank liners with replacement or repair of damaged or corroded units
• Regular replacement of seals on chemical pumps and filter systems
• Inspection and repair of racks, particularly focusing on loose coatings that can hide drag-out and copper nodules
that can dissolve in process tanks
• Regularly checking tank bottoms for panels, fixtures and other materials that have fallen and will corrode
4.3.5 Leak/Spill Prevention and Control
Chemical losses from leaks and spills can equal or outweigh the losses due to routine production operations. If
small leaks from pumps, filters or tanks go unnoticed or ignored over a long time, the overall loss can be very
significant. Catastrophic losses, such as a tank failure caused by corrosion, will cause more immediate results.
Several methods for reducing the potential of chemical losses from these sources were identified from the literature
and survey. These include:
• Conduct preventive maintenance of pumps, filters, tanks, etc., as discussed in Section 4.3.4.
• Employ a controlled method of adding make-up water to process tanks (do not permit use of unattended hoses).
• Install overflow alarms on all process tanks and especially on tanks that are heated and require regular
evaporative replacement.
• Install double-walled tanks and for added protection; install a sight tube that will indicate if a leak of the inner
wall has occurred.
• Implement company rules for tank additions and other chemical transfers.
• Construct secondary containment with segregation that would permit reuse of spilled material. For example,
install berms around process tanks, external filter systems, and pumps.
• Install pH, ORP, moisture sensors, and/or conductivity sensors with an associated alarm system in bermed
areas, sumps, drain lines, or around treatment tanks.
Of the PWB facilities responding to the survey, 72.4% indicated that they have established a preventive maintenance
program for tanks, and 23% use a leak detection system; 46% have installed overflow alarms in process tanks.
4.4 Drag-out Reduction and Recovery Methods
For the typical PWB shop, the drag-out of process solutions and the subsequent contamination of rinse waters are the
major pollution control problems. This section explains the basic principles of drag-out theory and explores the
function and applicability of the various drag-out minimization techniques in use today.
By reducing drag-out before it gets into the waste stream, less water is required to maintain clean rinses, water and
sewer charges are reduced, and treatment costs are lowered by treating reduced volumes of water.
4.4.1 Drag-Out Reduction Principles
The viscosity of a plating process solution can be described as its resistance to flow or removal by another liquid (in
this case, rinse water), caused by molecular attraction forces. The difference between high and low viscosity can be
demonstrated with paint and water. A much thicker film will form on a knife dipped in paint than on one dipped in
water. Paint, therefore, has the higher viscosity because of its cohesive and adhesive qualities.
Surface tension is another physical phenomenon that has a significant effect in the PWB shop. According to kinetic
theory, molecules of a liquid attract each other. At the surface of a solution, such as a copper plating bath, the
molecules are subjected to an unbalanced force because the molecules in the gaseous phase are so widely dispersed.
As a result, the molecules at the surface are under tension and form a thin, skin-like layer that adjusts to create a
minimum surface area. The property of surface tension causes liquid droplets to assume a spherical shape.
With the PWB chemical processes, the volume of solution that clings to a panel depends partly on surface tension.
The force of surface tension appears to be most significant at the bottom edge of the part as it passes through and
leaves the process solution. This force and the resultant volume of drag-out appear to be greatly affected by the
orientation of the panel relative to the surface of the liquid (ref. 43).
70
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The third factor that influences drag-out volume is the temperature of the process solution. Temperature is
interrelated with viscosity and surface tension. As the temperature of a process solution is increased, its viscosity,
surface tension, and, therefore, drag-out volume are reduced. A possible exception is when panels are withdrawn too
rapidly from a hot process solution, evaporation concentrates the film and impedes drainage. This problem,
however, can be overcome by reducing withdrawal time and using a fog spray rinse on the panels as they emerge
from the process solution (ref. 44).
4.4.2 Drag-Out Reduction Techniques
Devices and procedures exist to successfully reduce drag-out. These techniques usually are employed to alter
viscosity, chemical concentration, surface tension, velocity of withdrawal, and temperature. Also used are drag-out
tanks and similar equipment for capturing lost plating solution and for returning it to the bath (ref. 45). Exhibit 4-3
shows the PWB facility survey results for drag-out reduction methods. Also shown in Exhibit 4-3 are the results of
a similar survey conducted for the metal finishing industry during 1993-1994 (ref. 3). A comparison of survey
results shows that most drag-out reduction methods are more common to one industry segment or the other. Several
methods are found with similar regularity in both sectors. Some key differences between the industry sectors that
affect P2 choices are discussed in this section.
Most drag-out reduction methods are inexpensive to implement and are repaid promptly through savings in plating
and other PWB processing chemicals. An additional saving many times the cost of the changes is realized through
decreased operating costs of a pollution control system. The reduced drag-out will decrease the need for treatment
chemicals and, subsequently, the volume of sludge produced.
For some process solutions, return of drag-out may be impractical. In the case of process baths that become steadily
contaminated by use, the return of drag-out would simply increase the frequency of dumping (ref. 45).
Exhibit 4-3. Drag-Out Reduction and Recovery Methods Data — Survey Results
Drag-Out Reduction or Recovery Method
Allow for long drip times over process tanks
Have drip shields between process and rinse tanks
Practice slow rack withdrawal from process tanks
Use drag-in/drag-out rinse tank arrangements
Use drag-out tanks and return contents to process
baths
Use wetting agents to lower viscosity
Use air-knives to remove drag-out
Use drip tanks and return contents to process baths
Use fog or spray rinses over heated process baths
Operate at lowest permissible chemical concentrations
Operate at highest permissible temperatures
No. of PWB
Respondents
Using Method
29
23
20
13
13
12
10
4
4
o
J
1
% of PWB
Respondents
Using Method
76.3
60.5
52.6
34.2
34.2
31.6
26.3
10.5
10.5
7.9
5.2
% of Plating
Shops Using
Method*
60.4**
56.9
38.1**
20.8**
61.0**
32.4
2 2**
27.0**
18.9**
34.6
17.9
* Results published in reference 1.
"Data are for manually operated methods, which are the predominant type for the plating operations surveyed during the NCMS/NAMF
project.
4.4.2.1 Minimizing Drag-Out Formation
Drag-out of various processing baths into subsequent rinses is a significant source of pollution in a PWB shop. The
amount of pollutants contributed by drag-out is a function of factors such as the design of the racks carrying the parts
to be plated and plating procedures. As previously discussed, several interrelated parameters of the process solution,
including the concentration of process chemicals, temperature, viscosity, and surface tension, also impact pollution
levels.
Many devices and procedures can be used successfully to reduce drag-out. These techniques are usually employed to
alter those important and interrelated process solution parameters.
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Controlling Plating Solutions. As a rule, as the chemical content of a solution is increased, its viscosity
increases. Increased viscosity contributes not only to a large volume of drag-out, but also to a higher chemical
concentration of drag-out. The consequent need for more rinse water creates additional pollution control problems.
Process baths can often be operated at significantly lower concentrations than those recommended by chemical
manufacturers. This practice received the lowest response rate on the survey; only 8% reduce bath concentrations to
lower drag-out rates.
For years wetting agents have been used in process solutions as an aid to drag-out reduction. Survey results indicate
that wetting agents are used by 32% of the PWB survey respondents. A wetting agent, usually a surfactant, reduces
the surface tension of a liquid causing it to spread more readily on a solid surface. A typical plating bath solution
has a surface tension close to that of pure water at room temperature or about 0.0050 Ib/ft. The addition of very
small amounts of surfactants can reduce surface tension considerably-to as little as 0.0017 to 0.0024 Ib/ft. (ref. 43).
Further additions of the wetting agent will not lower the surface tension appreciably beyond this point (ref. 46).
Kushner (ref. 43) estimates that the use of wetting agents will reduce drag-out loss by as much as 50 percent,
although no test data or other quantitative information are presented. For plating baths, he recommends the use of
non-ionic wetting agents, which are not harmed by electrolysis. PWB facilities contemplating the use of a wetting
agent for drag-out reduction should conduct experiments to determine their potential benefit before implementation.
In addition, facilities should investigate the compatibility of a wetting agent with the bath chemistry before use.
Some process baths can only tolerate certain products (ref. 49).
Workpiece Withdrawal. The velocity at which work is withdrawn from the process tank has a major effect on
drag-out volume. The faster an item is pulled out of the tank, the thicker the drag-out layer will be, because
viscosity forces do not have a chance to operate and a much larger volume of liquid will cling to the surface (ref. 46).
For this reason, an automatic machine that performs smooth, gradual withdrawal will usually drag-out less solution
per item racked than will manually operated equipment.
In a study by the U.S. EPA, slowing the rate of withdrawal significantly reduced the amount of drag-out. The drag-
out on a microetch bath was reduced by 45 percent (12.1 ml/ft2 to 6.7 ml/ft2) by adjusting the withdraw rate of an
automatic unit from 100 ft/min to 11 ft/min (see Exhibit 4-4). A 50 percent reduction was achieved on an
electroless copper bath (6.0 ml/ft2 to 3.0 ml/ft2) by reducing the withdraw rate from 94 ft/min to 12 ft/min (see
Exhibit 4-5) (ref. 48). Less drastic changes to the withdrawal rate can be implemented without sacrificing waste
reduction by combining and optimizing the effects of reducing part withdraw rates and increasing the draining time
over the tank. The additional processing time needed to achieve a substantial reduction in drag-out loss is typically
small in comparison to the overall production time. For the case study, the additional 16 to 17 seconds of
withdraw/drain time was considered negligible in comparison to the total production time of 60 min. through the
sensitize line. Also, minor modifications to other parts of the process can usually be made to off-set any increases
due to waste minimization changes.
Exhibit 4-4. Summary of Micro-Etch Results
Experimental Conditions
Baseline
Modification 1
Withdraw
Rate
(ft/min.)
100
11
Time of
Withdraw
(sec.)
1.7
14.9
Drain
Time
(sec.)
3.4
2.5
Total
Time
(sec.)
5.1
17.4
Drag-Out
(ml/ft2)
12.1
6.7
slower rate of withdraw
Modification 2
longer drain time with
intermediate withdraw rate
40
4.3
12.1
16.4
7.1
Exhibit 4-5. Summary of Electroless Copper Results
Experimental Conditions
Withdraw
Rate
(ft/min.)
Time of
Withdraw
(sec.)
Drain
Time
(sec.)
Total
Time
(sec.)
Drag-Out
(ml/ft2)
72
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Baseline 94 1.8 5.2 7.0 6.0
Modification 1 12 13.9 3.2 17.1 3.0
slower rate of withdraw
Modification2 40 4.3 11.9 16.3 2.9
longer drain time with
intermediate withdraw rate
The survey indicates that 20 facilities (or 52.6% of the respondents) practice a slow rack withdrawal to reduce drag-
out formation.
Drag-out can also be reduced by altering the position of panels as they are withdrawn from a process solution.
Panels racked with an angular orientation will drain much faster than those racked perpendicular to the solution.
4.4.2.2 Direct Drag-Out Return
Commercially available equipment for the recovery of plating bath chemicals includes types that apply such
principles as ion exchange, reverse osmosis, electrodialysis, and evaporation. These devices usually are applied to a
single operation, such as copper electroplating, where they concentrate the salts in the rinse water, return them to the
plating bath, and recycle the purified water to rinse tanks (ref. 3).
Although effective, these recovery technologies are capital intensive. Before the purchase of such equipment, PWB
manufacturers should evaluate use of simple methods of drag-out recovery that require much less capital and are
simpler to operate. After implementing these methods and establishing new drag-out conditions, PWB facilities can
consider the applicability of additional recovery through commercially available units (ref. 3). This section describes
methods that directly return the drag-out to the process tank. In the following section (Section 4.3.2.3), methods are
described to recover the drag-out in tanks and then return it to the process bath.
Draining/Rinsing Over the Plating Tank. After a rack or basket is removed from a process tank, the drag-
out drains from the item and it returns directly to the bath, as long as the item is held over the tank. This simple
method of direct drag-out return can be maximized on a hand-line by installing a bar over the process line on which
the operator can hang a rack or hook. On automatic machines, the unit can be programmed to increase dwell time
above the process tank. Dramatic results from this simple method of waste minimization have been documented
(ref. 48). Allowing a longer time above the process tank for the solution to drip from the panels is used by 76% of
the survey respondents. Simple and effective, it is the most commonly practiced drag-out reduction procedure cited
by the survey respondents.
Allowing the drag-out to dry on the panel can cause staining, peeling, passivation, or it may prevent complete
rinsing. To increase the drag-out removal rate over the process tank, rinsing with small amounts of water can be
employed. The amount of water that can be used will depend on the water balance for a given process tank. The
water balance is affected mostly by evaporation. Process solutions operated at temperatures greater than 120°F often
have sufficient surface evaporation such that rinsing can be performed over the tank. However, using this method
may reduce or eliminate the potential benefit from other drag-out recovery methods (e.g., use of a drag-out tank).
Rinsing over the tank can be performed by flood rinsing (e.g., hose), spray rinsing, or fog rinsing. The use of flood
rinsing is not practical except for very high temperature baths with high drag-out rates. Spray rinsing uses less
water than flood rinsing. With the proper selection of spray nozzles, this can be a very efficient method of direct
drag-out return. Nozzle selection should consider flow rate, spray velocity, and spray pattern. Air-assisted sprays are
also utilized, which are generally more efficient than plain water sprays. Sprays can be hand-held or mounted on the
tank rim. For automatic plating machines, the sprays can be controlled to operate only when the part exits the bath
by installing photosensitive cells that detect part movement.
Fog rinsing is used at exit stations of process tanks. A fine fog is sprayed on the work, diluting the drag-out film
and causing a run-back into the process solution. Fog rinsing is applied when process operating temperatures, high
enough to produce a high evaporation rate, allow replacement water to be added to the process in this manner. Fog
rinsing prevents dry-on patterns by cooling the panels, but it may preclude the use of a drag-out tank as a recovery
option. For fog rinsing to be effective, work must be withdrawn from the process tank at a slow rate. From the
PWB facility survey, fog rinsing is used by only 10.5% of the respondents.
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Fog/spray rinsing over the bath has potential drawbacks and problems. Fog/spray rinsing may be messy, or worse,
may cause splashing on nearby workers. Nozzles require frequent maintenance (i.e., unplugging) and must be
occasionally repositioned to point in the correct direction.
Other Methods of Direct Drag-Out Return. The following are miscellaneous methods of direct drag-out
return that are not discussed elsewhere in the report.
A drain board or drip shield is a tilted surface placed between process and rinse tanks that catches the drips from racks
or barrels as they are transferred between tanks, thus preventing the drag-out from falling to the floor. The solution
on the drain board returns to its original tank by gravity flow. The drain surface can be plastic or metal. For acid
solutions, the best materials are vinyl chloride, polypropylene, polyethylene, and Teflon®-lined steel. Stainless
steel should be used for hot alkaline solutions. It is important that the drain surface be positioned at an angle that
allows the process solution to return to the bath (i.e., rather than the subsequent rinse) (ref. 6). Drain boards or drip
shields are used by 60.5% of the survey respondents and is the second most frequently used method of drag-out
reduction or recovery.
Another direct drag-out return method, the air knife, is a device that blows an intensive air stream at a rack as it exits
the bath causing the drag-out to be blown off. The use of air knives is limited due to the potential to dislodge parts
from racks and the drying effect of the air stream, which may cause staining, passivation, etc. Concerning the
second limitation, Altmayer suggests that if the air is humidified to near saturation, drying will not occur (ref. 49).
Air knives are used by 26.3% of the facilities responding to the survey. In a PWB shop, air knives are commonly
found at the end of convey orized equipment where low pressure air is used to blow or dam excess fluid off of the
surface of horizontally transported panels.
4.4.2.3 Drag-Out Recovery and Return
Drip Tank. A drip tank is an ordinary rinse tank that, instead of being filled with water, simply collects the drips
from racked panels after chemical processing and before rinsing. The drip tank is useful with work that involves
continuous dripping over a period of time. When a sizable volume of solution has been collected in the drip tank, it
can be returned to the process bath. Because drag-out is not diluted with water when using a drip tank, this technique
is especially applicable to lower temperature process solutions (ambient to 120°F).
Using a drip tank will restrict the use of an additional rinse tank, when floor space is limited. An additional rinse
tank, used as a drag-out tank or in a counterflow arrangement, is usually much more beneficial than a drip tank since
a drip tank only recovers the drag-out that freely flows off the part/rack. The determining factors are the volume of
drag-out, part configuration (i.e., drainability), and the evaporation rate in the process tank. Drip tanks are used by
10.5% of the survey respondents.
Drag-Out Tank. The drag-out tank is a rinse tank that initially is filled with pure water. As the PWB chemical
processing line is operated, the drag-out rinse tank remains stagnant and its chemical concentration increases as more
work is processed. Air agitation is often used to aid the rinsing process because there is no water flow within the
tank to cause turbulence. The presence of a wetting agent is also helpful, according to Kushner (ref. 43). After a
period of operation, the solution in the drag-out tank can be used to replenish the losses to the process bath. If
sufficient evaporation has taken place, a portion of the drag-out tank solution can be added directly to the process
bath (e.g., using a transfer pump). Thirty-four percent (34%) of the survey respondents indicated that they use drag-
out tanks.
As a rough estimate, drag-out recovery will reduce drag-out losses by 50 percent or more (ref. 3, 10). The efficiency
of the drag-out tank arrangement can be increased significantly by adding a second drag-out tank. Use of a two-stage
drag-out system usually reduces drag-out losses by 70 percent or more. In some cases, multiple drag-out tanks (e.g.,
three to five tanks) can be used to completely close the loop and return essentially 100 percent of drag-out (ref. 3).
The drag-out rate and evaporation rate are the key parameters that determine what percentage of the drag-out can be
recycled back to the process tank. Various mathematical formula have been used to estimate the recovery rate (ref.
50,51). Exhibit 4-6 presents estimates for common conditions that can be used in lieu of the more complex
equations.
Exhibit 4-6. Drag-Out Tank Recovery Rates for a Range of Common Conditions
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Number of
drag-out
tanks
1
2
3
4
5
E/DO=1
50.0
66.7
75.0
80.0
83.3
Drag-out
Evaporation to
E/DO=2
66.7
85.7
93.3
96.8
98.4
Recovery Rate,
drag-out ratio
E/DO=3
75.0
92.3
97.5
99.2
99.7
%
(1 to 5)
E/DO=4
80.0
95.2
98.8
99.7
99.9
E/DO=5
83.3
96.8
99.4
99.9
100
The transfer of solution between drag-out tanks and the process tank and the addition of fresh make-up water to the
system can be accomplished in several ways. Ryder (ref. 52) recommends that transfers to the plating tank be
accomplished using a small pump (magnetic drive, seal-less types), which is activated by a "dead-man" switch. The
dead-man switch only permits solution transfer while the switch is depressed. If the operator leaves, the solution
transfer automatically stops, which prevents catastrophic tank overflows. For adding make-up water, Ryder suggests
using a level-controlled valve (local float controlled) in the first rinse. When the solution level in the first rinse is
lowered (i.e., after solution is transferred to the plating bath), the float switch is activated and fresh water is added to
the final rinse. Ryder further suggests the use of a water control valve on the inlet water line for shut-off during
non-operating periods.
The use of an automatic drag-out return system was described by Roy (ref. 53). In this system, chemical metering
pumps were used to return drag-out from the rinse tank to a plating tank. The pumps were controlled by a level
sensor in the plating tank.
With multiple rinse tank arrangements, the transfer of solution from rinse tank to rinse tank can be accomplished in
the same manner as a flowing counterflow rinse system. These are discussed in Section 4.5.
It should be noted that although drag-out reduction can be a very effective means of pollution prevention, it may also
present the PWB manufacturer with a new set of problems. In particular, reducing drag-out reduces the purging of
bath contaminants. The contaminants are contributed to process baths mainly by a breakdown of process chemicals
and low concentration constituents in the fresh water (e.g., hardness). Other sources include: cross contamination
due to transporting dripping racks over tanks, corrosion of bus bars, racks, anodes, tanks, etc., and airborne
contaminants. This contamination may also lead to another problem-staining of the panels after the drag-out rinse.
To minimize the impact of contaminants, platers must do one or both of the following: (1) treat the raw rinse water
prior to use with ion exchange and/or reverse osmosis technologies, or (2) perform bath maintenance. Bath
maintenance technologies are discussed in Section 5.
Drag-out tanks can be placed in series to completely recover process chemicals and rinse water, as suggested by the
estimates in Exhibit 4-6. This is achieved by balancing the introduction of rinse water with the evaporation rate of
water from the process tank. One author suggests that aqueous developer and stripper processes can be operated in a
similar manner. In these cases, rinse water flow is balanced with developer/strip solution feed systems rather than
with evaporative losses. The author suggests that two chemical supply tanks be used, one serving as a makeup tank
and one as the on-line supply tank. The rinse water should be directed back to the makeup tank. Periodically, based
on level, a concentrated carbonate or hydroxide solution can be added to convert the rinse water to develop or strip
solution. The solution is mixed and transferred back to the supply tank. Conductivity controllers can be used to
ensure proper concentrations (ref. 41).
It is interesting to note that drag-out tanks are used more frequently by metal finishing facilities than by PWB
facilities (61% vs. 34%) (see Exhibit 4-3). A higher sensitivity to contaminant build-up may, in part, explain this
disparity. In addition, PWB process lines are long and room considerations are often cited as a limiting factor for
drag-out tanks. For example, a typical electroless copper line may include over 20 tanks (including counterflowing
rinses) without any drag-out tanks at all. Nevertheless, several tanks in this line are excellent candidates for drag-out
recovery, including the heated cleaner-conditioner and the copper-rich micro-etchant baths. The electroless copper
bath itself is an example of a poor candidate for drag-out recovery. This bath accumulates contaminants from
chemical decomposition and requires frequent additions, which are usually accommodated with bailouts.
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Drag-out tanks can be combined with counterflow rinsing to provide both chemical recovery and flow reduction.
Combinations of rinse configurations are discussed in Section 4.5.3.5.
Drag-In/Drag-Out Rinsing. Drag-in/drag-out rinsing (also referred to as double-dipping) involves rinsing in the
same solution before and after plating. This can be achieved by using a single rinse tank or two hydraulically
connected rinse tanks, usually located on opposite sides of the process tank. In the latter case, which is most
applicable to automatic plating machines, the rinse water is recirculated between the two rinse tanks using a transfer
pump to maintain equal concentrations of chemicals in the tanks.
The advantage of a drag-in/drag-out arrangement is that plating chemicals rather than pure rinse water are transferred
into the process tank by incoming racks and panels. This increases the recovery efficiency of the recovery rinse.
The drag-in/drag-out system finds application with plating baths that have a low to moderate evaporation rate and
especially with baths that tend to increase in volume (i.e., equivalent to a negative evaporation rate). This condition,
referred to as "solution growth," occurs when the volume of drag-in (water from the preceding rinse) can be greater
than the sum of drag-out and evaporation. The recycle ratio, which determines recovery efficiency, is calculated as
the volume of recycled rinse plus the volume of drag-out divided by the volume of drag-out. The recycle ratio,
therefore, is greater with a drag-in/drag-out system than a common recovery tank. If the evaporation rate is low, the
difference between the recycle ratios for common recovery and drag-in/drag-out systems is significant. When
evaporation ratios are high, the difference is less. Generally, the use of a drag-in/drag-out arrangement will increase
the recovery rate by 25 to 40 percent (ref. 3). As with drag-out tanks, the drag-in/drag-out arrangement can result in
bath contaminant buildup. It also creates an extra labor step and will lengthen the process time.
4.5 Rinse Water Use Reduction
Although the plating industry as a whole has significantly reduced water use during the past 10 to 15 years, many
plating operations can further reduce water use by improving the efficiency of their rinsing operations. The
advantages of reducing water use include:
• Lowering operating costs by reducing the size of water bills.
• Reducing the quantity of treatment chemicals used (treatment chemical use is mostly dependent on the mass of
contaminants, but a portion of treatment chemical use is related to hydraulic loading; see Section 6 which covers
end-of-pipe treatment.
• Potentially improving the removal efficiency of waste treatment systems.
• Reducing the needed size of future end-of-pipe treatment systems and certain types of recovery technologies.
A summary of the survey data relative to methods for reducing rinse water use is presented in Exhibit 4-7.
Exhibit 4-7. Rinse Water Use Reduction Methods Data
Drag-Out Reduction or Recovery
Method
Use counterflow rinses
Use flow controllers
Use spray rinses
Track water use with flow meters
Reactive or cascade rinsing
Use rinse timers
Recycle or reuse rinse water
Use conductivity or pH controllers
Use part sensors to activate rinse*
Use squeeze rollers to remove water*
Use spring-loaded valves to activate rinse*
No. of PWB
Respondents
Using Method
31
30
27
25
20
19
11
10
4
1
1
% of PWB
Respondents
Using Method
81.2
78.9
71.1
65.7
52.6
50.0
28.9
26.3
10.5
2.6
2.6
% of Plating
Shops Using
Method
68.2
69.8
39.0
11.6
23.9
11.3
~
16.0
~
~
-
* Added by respondent under "Other."
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Central to the reduction of rinse water use is the required quality of water used in rinsing. Simply reducing the flow
rate of water in a rinse system, without regard to water quality, may cause loss of product quality or appearance or it
may cause the contamination of the next tank in the plating sequence. Various rinse water quality criteria are
presented in the literature.
Various methods of water use reduction have been identified in the literature and throughout the survey. These
methods have been categorized into three groups: (1) optimizing the rinse tank design; (2) controlling the rate of
rinse water use; and (3) using alternative rinsing configurations. The following is a discussion of each group.
PWB facilities practiced all rinse water use reduction methods more frequently than plating shops. While
counterflow rinses and flow controllers were common in both types of shops, rinse timers, spray rinsing, flow
meters and reactive/cascading rinses were far more prevalent in PWB shops. One explanation could be the presence
of conveyorized equipment in nearly all PWB facilities such as etchers and resist developers, both of which
commonly employ spray rinsing chambers, and etchers, are commonly equipped with cascading rinse chambers.
Such equipment may also be equipped with flow meters.
4.5.1 Optimal Rinse Tank Design
The key objectives with regard to optimal rinse tank design are to attain fast removal of drag-out from the part and
complete dispersion of the drag-out throughout the rinse tank. When these objectives are achieved, the time
necessary for rinsing is reduced and the concentration of contaminants on the part when it leaves the rinse tank are
minimized for a given rinse water flow rate. The following are rinse tank design elements that help to achieve fast
drag-out removal and complete mixing. These methods can be combined to develop an optimal rinse tank design for
a given workload.
• Select the minimum size rinse tank in which the parts can be rinsed and use the same size for the entire process
line.
• Locate the water inlet and discharge points of the tank at opposite positions in the tank to avoid short-circuiting.
• Use a flow distributor/sprayer to feed the rinse water evenly.
• Use air agitation, mechanical mixing, or other means of turbulence.
• Use spray rinsing.
• Use ultrasonics, where applicable.
4.5.2 Controlling the Flow Rate of Rinse Water Use
Water use reduction can be achieved by coordinating water use and water use requirements, regardless of the type of
rinse tank arrangement employed (e.g., single overflow, counterflow). When these two factors are perfectly matched,
the rinse water use for a given work load and tank arrangement is optimized. Four methods of coordinating water use
and water requirements were identified during the survey and literature search. Each of these methods is discussed in
the following subsections. Some methods are applicable to a range of chemical processing operations while others
are more relevant to specific conditions (e.g., small manual operations, large automated machines). Some of the
methods can be combined to optimize water use.
4.5.2.1 Flow Restrictors
Flow restrictors are inexpensive devices that are connected in-line with the tank's water inlet piping to regulate the
flow of water through the pipe. They are typically an elastomer washer that flexes under pressure such that the
higher the water pressure, the smaller the hole available for flow passage. Therefore, they maintain a relatively
constant flow under variable water pressures. Flow restrictors are available in a wide range of sizes (0.1 gpm to
more than 10 gpm). The smaller sized restrictors are most commonly used with multiple counterflow rinse tank
arrangements and the larger ones are commonly used with single overflow rinses. Some restrictors aerate the water
as it passes through, in a manner similar to a kitchen faucet (venturi effect).
Flow restrictors are applicable to nearly all rinse systems. A possible exception is a rinse tank equipped with a
conductivity controller (see Section 4.5.2.3). With conductivity controllers, the instantaneous water flow rate is
unimportant, since the controller stops water flow based on the low conductivity set point of the controller and the
conductivity of the water in the rinse tank. Therefore, restricting the flow will only increase the time needed to
dilute the rinse water to the conductivity set point and will not affect the total volume of water used.
Flow restrictors as a stand-alone method of rinse water control are only effective with plating lines that have constant
production rates, such as automatic plating machines. Even in such cases, to use water efficiently, the plater must
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have a means of stopping water flow during non-production periods. With variable production rates, flow restrictors
alone will not provide the necessary coordination of rinse water need and use. One method for improving this
coordination is to install a timer rinse control (see Section 4.5.2.4).
Generally, the size of a flow restrictor is selected to provide adequate rinsing for all parts. This means that the
maximum rinse water flow requirement is the governing factor and that on the average, the flow will be higher than
necessary for good rinsing. This fact is a sufficient reason for supplementing the control provided by a flow
restrictor.
Flow restrictors are widely used by the respondents to the survey (79%).
4.5.2.2 Manual Control of Water Flow
Manual control of water flow simply refers to manually opening and closing water valves to adjust flow or to turn
the water flow on or off. This method of control is obviously dependent on the operator and usually results in
inconsistent water use.
Combining manual control with flow restrictors reduces the variability of water flow; however, it does not address
the problem of water use during idle production periods. Manual control can be improved by installing a main water
valve for an entire plating line that stops water flow to all rinse tanks in that line.
4.5.2.3 Conductivity Controls
These units consist of a probe or sensor located in the rinse tank that senses the conductivity of the rinse water, a
transformer box that houses the solid state circuitry that controls the system, and a solenoid valve that opens and
closes in response to signals from the circuitry. In use, when drag-out is introduced to the rinse tank, the probe
senses a rise in conductivity above a set-point, which is picked up by the circuitry, and the solenoid water valve is
opened. The valve remains open until the probe senses a drop in conductivity below a set-point. The set-points are
operator-adjustable to permit use over a range of desired water qualities.
Conductivity rinse controls have been effectively used to reduce rinse water use. However, in some cases, they have
been removed from service due to maintenance problems (ref. 3). The results of the survey show a moderate level of
usage for conductivity controllers (26%).
The use of conductivity controllers does have some problems. First, operators who object to the appearance of a
controlled rinse, which may be less clear than a free-flowing rinse, have been known to override conductivity
controllers. Operators often override the units by placing the probe into a process tank or a bucket of process
solution (i.e., causes solenoid to remain open). This problem can be controlled by shortening the length of the
probe's cable or by running the cable through a PVC pipe (if using the latter method, be certain the piping
arrangement permits access to the probe for periodic cleaning). Second, the controllers do not sense non-ionic
contaminants and rinse tanks may become contaminated with particulates such as dust. Third, the units require
frequent preventive maintenance to remain operable.
A new electroless sensor controller (induction type) provides some advantages over the conventional type described
above. Due to the design of the new units, they are less likely to foul than the conventional controllers. The
hardware cost of the new units is substantially higher ($1,140 vs. $290 forthe conventional type) (ref. 54).
4.5.2.4 Timer Rinse Controls
Timer rinse controls consist of a push-button switch and timer mechanism and a solenoid valve. These units operate
in a manner similar to conductivity controllers; however, rather than regulating rinse water flow on the basis of rinse
tank water quality, the timer controls simply turn water on and off based on a pre-set time period.
In operation, a plater lowers parts into the rinse tank and pushes a button (alternatively, a momentary or
photoelectric switch could be used that is activated by lowering a rack). The button or switch activates a timer and
opens the solenoid valve for a preset time period. After that time period has expired, the solenoid valve
automatically closes.
The timer setting is selected through trial and error. It is best to select a time period that provides consistently clean
rinse water, without excessive waste. Once set, the time period is not changed unless the general trend of production
changes. Timers are being used by 50% of the survey respondents.
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4.5.2.5 Flow Meters and Accumulators
These devices by themselves do not reduce water use. However, they make the PWB manufacturer aware of water
use rates and are useful in identifying excessive water use.
Flow meters and accumulators are most useful when installed on fresh water lines feeding individual rinse tanks or,
at a minimum, on pipes feeding individual process lines (e.g., electroless copper). Meter readings taken over an
extended time period will show trends in water use. Using these data, facility management can identify specific
locations where excessive water use occurs and can correct the problem before long-term wastage has resulted.
4.5.3 Rinsing Methods
4.5.3.1 Counterflow Rinsing
PWB facilities have long reduced water use by employing several rinse tanks connected in series. Fresh water flows
into the rinse tank located farthest from the process tank and overflows, in turn, to the rinse tanks closer to the
process tank. This technique is termed counterflow rinsing because the work piece and the rinse water move in
opposite directions. Over time, the first rinse becomes contaminated with drag-out and reaches a stable concentration
that is lower than the process solution. The second rinse stabilizes at an even lower concentration and uses less rinse
water than if only one rinse tank was in place. The more counterflow rinse tanks (three-stage, four-stage, etc.), the
lower the rinse rate needed for adequate removal of the process solution.
Counterflow rinsing systems are not without drawbacks. The negative aspects of counterflow rinsing include the
cost of additional rinse tanks, loss of valuable production space, and an increase in production time/labor.
The rinse rate needed for adequate cleaning is governed by an exponential equation that depends on the concentration
of process chemicals in the drag-out, the concentration of process chemicals that can be tolerated in the final rinse
tank, and the number of counterflow rinse tanks. The mathematical rinsing models are based on complete rinsing
(i.e., removal of all drag-out from the part/fixture) and complete mixing (i.e., homogeneous rinse water). These
conditions are not achieved or even approached unless there is sufficient residence time and agitation in the rinse
tank. More typically, each added rinse stage reduces rinse water use by 50 percent.
Eighty-one percent of the survey respondents employ counterflow rinsing. This is a greater percentage than for any
other method of reducing rinse water usage.
4.5.3.2 Cascade, Reactive, and Dual Purpose Rinsing
Cascade rinsing refers to the practice of reusing rinse water multiple times in different rinse tanks for succeeding less
critical rinsing. Reactive rinsing is similar, but it refers to cases where a chemical reaction takes place because of
using the rinse water for multiple purposes. Various cascade rinsing schemes are employed in the PWB industry.
Poskanzer provides an example for an electroless line that is described in Exhibit 4-8 (ref. 55, 56). In this example,
there is a double counterflow rinse after each process step. In four cases, the discharge from a rinse tank is reused in
another rinse system. The author suggests that this scheme will reduce water use by 40% to 50% for the electroless
copper line.
Dual purpose rinsing refers to the practice of using the same rinse tank for rinsing following more than one process
tank. It provides essentially the same results as cascade and reactive rinsing but uses a fewer number of rinse tanks.
Often, the employment of dual purpose rinsing means transporting a dripping rack/part over a considerable distance.
This can result in dripping onto floors and/or the accidental contamination of other tanks. An exhaustive evaluation
of dual purpose rinsing is presented by Mohler (ref. 57). Mohler presents methods and guidelines for ascertaining the
accumulated concentration of chemicals in counterflow, dual-purpose rinses in order to determine the feasibility and
economics of this technique.
Use of any of these methods must closely consider the combined chemistry in the rinse tank to prevent undesirable
reactions that may impact worker safety (e.g., harmful vapor) or work quality (e.g., precipitation of solids).
Reactive or cascade rinsing is used by 66% of the survey respondents to reduce water usage.
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4.5.3.3 Chemical Rinsing
The technique of chemical rinsing has been used by the metal finishing industry for many years. Lancy and Pinner
have described the application of chemical rinsing to plant effluent treatment, known in the industry as integrated
waste treatment (ref. 3). Aside from the environmental benefits, this type of rinsing also prevents the majority of
heavy metal solids formed in the chemical rinse from reaching the succeeding water rinses by removing these
materials in an external settling vessel. Removal of these solids is accomplished by flowing the chemical rinse
solution to a treatment reservoir. The overflow from the reservoir is pumped back to the rinse tanks, forming a
complete closed-loop system. Integrated treatment gained some popularity in the 1970's, but is believed to be in
little use today, mostly due to high maintenance requirements.
In general, the long pre-treatment process lines and the high sensitivity to contamination limit the opportunity for
chemical rinsing in a PWB shop.
4.5.3.4 Spray Rinsing
Spray rinsing is employed in various manners to reduce drag-out losses and rinse water use. Spray rinsing over
process tanks (Section 4.4.2.2) provides direct recovery of drag-out. Spray rinse tanks can be used as drag-out tanks,
single rinses, or multiple rinses.
A common use of spray rinsing is to substitute a spray rinse tank for an overflow rinse tank. Depending on the
racking configuration, spray rinsing generally uses from one-eighth to one-fourth the amount of water that would be
used for equivalent dip rinsing (ref. 3).
Combined spray and dip rinse tank designs are employed where the bottom portion of a rinse tank acts as a dip tank
and the upper portion a spray rinse. A weir is located at approximately the middle of the tank which maintains the
solution level in the tank. In operation, the rack is lowered into the dip rinse, raised above the solution level, and
sprayed with fresh water. This combination rinse can be nearly as effective as a counterflow rinse, but takes up the
floor space of one tank.
The design of spray rinses must consider the size and shape of the part. Spray nozzles are available in many sizes
and spray patterns, and should be selected appropriately. Usually, the pressure in the waterline is sufficient to
operate an effective spray rinse; however, higher spray velocities can be obtained by pumping.
A special application of the spray rinse is a patented unit that contains five to seven progressively cleaner rinse
solutions in separate compartments (ref. 58). The solutions are successively pumped (up to 20 gpm) to a spray rinse
tank and drain back to the unit. During each cycle, only the water use in the first spray is discarded or processed for
recovery. The subsequent sprays are collected for reuse in the following cycles. The advantage of this unit is that it
provides the effect of multiple counterflow rinsing with use of a single rinse tank. The floor space requirement of
the unit is 7.5 square feet (five stage rinse unit) or 11.0 square feet (seven stage rinse unit).
The survey indicates that 71% of the respondents are using spray rinsing, making it the third most frequently used
method for reducing water use.
The prevalence of spray rinsing in PWB facilities is due in part to presence of conveyorized spray rinsing found in
resist developers and etchers. For these machines, there is essentially no automated alternative to spray rinsing.
Furthermore, in the case of resist development, the effects of relatively high pressure spray are required to adequately
remove developer and resist residues from the surface of the copper panel.
Specific spray patterns are often required in PWB processes. Many systems use water pressure to produce the desired
pattern. A more efficient and cost effective alternative is to use an off-line tank with a recirculating sump. A pump
can create the pressure needed to establish the desired pattern, while using a fraction of the water for a conventional
spray system.
Combined spray and immersion (i.e., overflow) rinse systems are employed at some PWB facilities to reduce water
use. One facility uses a pulsed spray system in the first rinse tank following a process tank and a conventional
overflow rinse arrangement in the second rinse tank. Flow from the second rinse tank is used as makeup in the first
rinse tank. With this system, drag-out dwell times are set at 20 sec., the sprays at 20-30 sec. (with 5 sec. side to
side activated pulse), and overflow rinse at 20 sec. to 2 min. This system has reduced water use on the affected lines
by 70% from that used with simple overflow rinses (ref. 59).
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4.5.3.5 Combined Drag-Out Loss/Rinse Water Reduction Rinsing
Arrangements
Some PWB facilities combine drag-out tanks and overflow rinsing in the same rinse systems. For example, a four
rinse system could consist of two drag-out tanks connected in series and two free-flowing rinses connected in series
(counterflow). Alternatively, the system could consist of three drag-out tanks in series and a single overflow rinse or
a drag-in/drag-out arrangement and two counterflow rinses. Various rinsing configurations can also be combined
with chemical recovery technologies, as discussed in Section 5. The optimal rinse configuration will depend on
numerous factors including:
The evaporation rate in the process tank
The drag-out rate
The rinse water quality requirement (final rinse)
Process chemical costs
Alternative technology recovery costs
Water costs
Wastewater treatment/sludge disposal costs
In general, when more of the available rinse tanks are used as drag-out tanks, the process chemical and wastewater
treatment operating costs are lowered and water use costs are increased. The reverse is true when more tanks are used
for counterflow rinsing than for drag-out recovery tanks.
The optimal configuration can be determined through mathematical means, which must be supported by data
collection (i.e., drag-out and evaporation measurements, production rates, etc.) for producing accurate results. As an
alternative to using the rinsing equations to perform the calculations, a modeling program can be employed. A
commercially available software program permits an analysis considering up to five rinse stations and the use of
supplemental evaporative recovery (ref. 60). This program permits the user to add recovery rinses, change tank
volumes, experiment with process chemistries, add evaporators, and change workload to find the combination that
makes the most environmental and economic sense (ref. 61).
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5.0 Process Solution Maintenance and Chemical
Recovery Technologies
5.1 Introduction
This section describes technologies used in the PWB industry for maintaining process solutions in operable
condition and recovering process chemicals from spent baths and rinse waters. The information contained in this
section was compiled from the PWB facility survey results, a literature search, and through contacts with vendors.
Often, bath maintenance, chemical recovery, and waste treatment technologies are competing pollution control
measures. For example, some process solutions can be used on a bleed-and-feed basis (fresh chemical solution is
introduced into a process to replace a portion of used solution, thereby maintaining the process bath within an
operable chemical range), with the bleed stream going to waste treatment. Alternatively, a continuous bath
maintenance technology may exist that keeps the bath operating within tolerable limits by removing contaminants,
or, a recovery technology may be applied to the bath after it exceeds tolerable limits to recover reusable components.
The decision to select bath maintenance, recovery, or waste treatment is often clouded by a lack of technical and cost
information. The purpose of this section is to organize and present the technology information that was collected
during the project so that it can be used in the decision process.
Survey data relative to recovery, recycle, and bath maintenance technologies are found in Appendix A. The data from
the 1995 and 1997 surveys are contained in separate tables, because the number and wording of survey questions
differed between the two surveys (i.e., in 1997, the scope of the survey was reduced in order to increase the response
rate). Exhibit 5-1 is a summary of the two surveys. Shown are the percentage of respondents that use various
recovery, recycle, and bath maintenance technologies.
Other information regarding recovery, recycle, and bath maintenance is contained in Exhibit 3-25. This exhibit
indicates the specific types of wastes generated by the various processing steps of multilayer PWB manufacturing and
the P2 technologies that can be applied.
The remainder of this section contains information on recovery, recycle, and bath maintenance technologies gathered
from the survey, from literature, and through contacts with vendors. Due to the diversified nature of information
collected during the project, some technologies receive greater attention than others. When available, the discussions
include both technical and cost information.
Off-site recycling, which is not considered a pollution prevention method by EPA but is widely used by the PWB
industry, is discussed in Section 5.4.
Exhibit 5-1. Recovery, Recycle, and Bath Maintenance Technologies Used
S3 40
"o
c 35
£
H 30
1 20
OJ
OH
J 10
^0
£ 5
0
/
n-, r
1 | 1 1!
•S 8 M 9 43 ^
1 1 1 1 i
1 * § 62
« S '•§ 1 13
3 ^ « o ;3
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82
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5.2 Solution Maintenance
Chemical solution maintenance includes a range of pollution prevention options that preserve or restore the chemical
integrity of PWB process solutions, thereby extending their useful lives. The majority of PWB process solutions
are used and then discarded. Some exceptions exist, such as etchants that are shipped off-site for recovery due to their
economic value. However, due to rising costs for chemicals, energy, and treatment/disposal and increasingly more
stringent environmental requirements, solution maintenance has become a greater priority to PWB facilities and the
technologies they employ have increased in sophistication. Today, many firms are willing to expend significant
amounts of capital and operating funds for equipment and methods that primarily reduce the disposal frequency of
their baths.
In addition to extending bath lives, solution maintenance often improves the average operating efficiency and
effectiveness of a process solution and, therefore, has a positive impact on PWB production rates and quality.
PWB process solutions are subject to a variety of forces that cause them to become unusable. The key contributing
factors are: (1) depletion or chemical breakdown of bath chemicals; (2) etching of copper foil and plate; (3)
contamination from impurities in make-up water, chemicals, anodes, etc.; (4) corrosion of racks, bussing, tanks,
heating coils, etc.; (5) drag-in of non-compatible chemicals; and (7) errors in bath additions.
Solution maintenance replaces the practices of: (1) using a chemical solution until it is degraded and replacing it
with fresh solution, or (2) decanting a portion of a degraded solution and replacing it with fresh solution (bleed and
feed). In both cases, the spent solution is usually either batch treated, combined with other process wastes and
treated in a central wastewater system, or transported to a recovery/treatment/disposal facility. On-site treatment is
not always possible because concentrated wastes may upset treatment facilities designed primarily for treating dilute
rinse waters. In some cases, facilities are able to reuse spent solution for either: (1) a less critical process
application or (2) as a treatment reagent (e.g., spent acid cleaner used in place of sulfuric acid for pH adjustment).
The former of these uses is regarded as a pollution prevention option by EPA. The latter method may reduce the
overall use of chemicals at a shop, but because it involves treatment, it is not considered "pollution prevention" by
EPA.
The remainder of Section 5.2 contains descriptions of PWB bath maintenance technologies that are either commonly
in use or have been proven to work under certain production conditions.
5.2.1 Basic Bath Maintenance (Filtration, Carbon Treatment, and
Electrolysis)
Basic bath maintenance methods were not specifically covered by the survey. However, some respondents indicated
that they successfully employ methods such as filtration, carbon treatment, and electrolysis; therefore, a short
discussion is included in this section.
Many process solutions, especially electroplating baths, can be maintained indefinitely by monitoring for organic
and inorganic contaminants, making chemical adjustments when necessary, and utilizing filtration, carbon treatment,
and electrolysis.
Filtration is the most commonly applied method of bath maintenance. It is used to remove suspended solids from
plating and process solutions. Suspended solids in plating solutions may cause roughness and burning of deposits.
Various equipment are used for filtration, with the most common being cartridge filters and precoat (diatomaceous
earth) filters. Sand or multimedia filters are also employed. Cartridge filters are available with either in-tank or
external configurations, with the former used mostly for small tanks and the latter for larger tanks. Most cartridges
are disposable; however, washable and reusable filters have been recently commercialized.
Carbon treatment of plating baths is a common method of removing organic contaminants. The carbon adsorbs
organic impurities that are present as a result of oil introduction or the breakdown of bath constituents. It is used on
both a continuous and batch basis. Various application methods are available, including carbon filtration cartridges
(contain up to 8 oz of carbon and are restricted to use on small applications), carbon canisters (up to 10 Ibs of
carbon), precoat filters, and bulk application/agitation/filtration (ref 63).
Electrolysis, also referred to as dummy plating, is an electrolytic treatment process in which metallic contaminants
in a metal finishing solution are either plated out (low current density electrolysis) or oxidized (high current density
electrolysis).
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Electrolysis is applied to a range of plating and other process solutions. The contaminant metals that are most
frequently removed by dummy plating are copper, zinc, iron, and lead. Electrolysis is usually performed using a
corrugated steel sheet cathode, with an anode to cathode spacing of approximately 4 in. The optimal current density
will depend on the metal contaminants being removed. The normal range is 2 to 8 A/ft2. The duration of treatment
is typically 2 to 5 amp-hr/gal. Agitation is essential for speedy removal of contaminants, and air agitation should be
used if the type of bath permits (ref. 64, 65, 66, 67).
Electrolysis can be performed on a batch or continuous basis, with batch treatment being the most common. Batch
treatment is usually performed in the process tank and requires down-time. Continuous treatment is usually
performed in a side-tank and cathodes are typically sized to permit 0.05 amp/gal of solution (ref. 65, 67). The
solution is preferably returned to the process tank through a filter (ref. 68).
Basic bath maintenance recommendations for common plating solutions used in PWB facilities are presented in
Exhibit 5-2.
Exhibit 5-2. Basic Bath Maintenance for Common Plating Solutions
Process
Bath
Common Contaminates
(tolerable levels)
Basic Bath Maintenance
Acid Copper Organic: residues from cleaners, resists.
Sulfate Inorganic: chloride (60-80 mg/1), chromium
(25 mg/1), iron (500 mg/1), tin (300 mg/1),
antimony (25 mg/1), nickel, lead, and
arsenic.
Copper Organic: residues from cleaners, resists and
Pyrophosphate oil.
Inorganic: chloride (40 mg/1), sulfur (0
mg/1), iron (50 mg/1), nickel (50 mg/1), and
lead (10 mg/1).
Solder Plate Organic: peptone or additive breakdown.
(tin-lead) Inorganic: chloride (2 mg/1), sulfate (2
mg/1), copper (15 mg/1), iron (400 mg/1),
nickel (100 mg/1), and lead.
Acid Tin Organic: additive breakdown or resists.
Sulfate Inorganic: chloride (5 mg/1), copper (5-10
mg/1), iron (120 mg/1), nickel (50 mg/1),
cadmium (50 mg/1), and zinc (50 mg/1).
Nickel Organic: additive breakdown or resists.
Sulfamate Inorganic: sulfates, copper (10 mg/1),
chromium (20 mg/1), aluminum (60 mg/1),
lead (3 mg/1), iron (250 mg/1), nickel (50
mg/1), cadmium (50 mg/1), tin (10 mg/1),
calcium (0 mg/1), and zinc (10 mg/1).
Filtration: continuous (3-10 u filter, 4 turnovers per
hour).
Carbon treatment: needed approximately every 1,500
amp-hr per gal.
Electrolysis: 10 A/ft2 for 6 hr.
Filtration: continuous (3-5 u polypropylene filter, 4
turnovers per hour).
Carbon treatment: minimum frequency of 6 mths.
Electrolysis: 5 A/ ft2 for 2-6 hr. once per week.
Filtration: continuous (3-10 u polypropylene filter, 4
turnovers per hour).
Carbon treatment: frequency of 4-12 mths.
Electrolysis: 3-5 A/ ft2 for 2-4 hr. once per week for
copper removal.
Filtration: continuous (3-10 u polypropylene filter, 4
turnovers per hour).
Carbon treatment: frequency of 4-12 mths.
Filtration: continuous (5-10 u polypropylene filter, 4
turnovers per hour).
Carbon treatment: as needed, use 3-5 Ib carbon per
100 gal.
Electrolysis: 5 A/ ft2 for 2-6 hr. once per week for
copper removal.
5.2.2 Etchant Regeneration
Spent etchant is the largest waste stream shipped off-site for most PWB shops. It also represents the most
significant quantity of copper waste. Exhibit 5-3 shows a summary of copper waste source data for a particular PWB
shop. For this facility, approximately 93% of the total amount of copper discharged was from the inner layer and
outer layer etching processes.
Approximately 60% of the copper on the PWB is dissolved and removed by the etching process. When the copper
content of the etchant increases beyond a certain level, the etchant cannot continue to effectively remove the copper
from the board, and is considered spent. Spent etchant is stored in drums or a tank and is ultimately shipped off-site
for reclamation.
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Even in situations where the copper is recovered and the etchant is regenerated by the waste hauler, this waste stream
may be an environmental hazard. Transportation of the spent etchant and its ultimate disposition may pose
environmental risks and result in increased liability for the PWB facility. The costs of managing spent etchants and
the danger they pose to the environment can be reduced dramatically with an on-site regeneration system. Recycling
etchant onsite is an attractive alternative when considering the costs associated with shipping spent etchant,
purchasing replacement fresh etchant, and the labor spent on manifesting and regulatory reporting. Recycling also
permits the sale of recovered copper, reduces drum handling, and reduces the storage of hazardous waste.
Exhibit 5-3. Amount of Copper Wasted for Various Streams as a Percent of Total Discharge
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
OH
&
o
o
93.7%
Ammoniacal
Etch (Both
I/O Etch)
3.0%
Sodium
Persulfate
Bath&
Etch
2.3%
Copper
Containing
Rinses
0.3%
Low
Copper
Containing
Baths
0.6%
Electroless
Copper Bath
and Bailout
0.1%
Electroless
Copper Rinse
Source: ref. 36.
Ammoniacal etchants (ammonium chloride or ammonium sulfate) are the most commonly used in PWB facilities,
followed by cupric chloride etchants. Some etchant regeneration systems may only work on one type, although, one
system described below can process both etchants.
The following sections describe etchant regeneration systems. Most of the information in these sections is
summarized from DfE case studies (ref. 69, 72, 74).
5.2.2.1 Ammoniacal Etchant Regeneration
The MECER System regenerates ammonium chloride, recycles rinse water, and recovers copper using a process of
solvent extraction and electrowinning (Exhibit 5-4). The regeneration and recovery occurs in several stages: 1) a
portion of the copper is removed from the spent etchant so that it can be used for further etching; 2) copper is
removed from the rinse water so that it can also be reused; 3) copper is re-extracted and transferred to the electrolyte;
and 4) in the electrowinning unit, copper is recovered from the now copper-enriched electrolyte to produce high
quality, saleable copper metal sold for approximately $1.00/lb (or about 90% of the COMEX copper price) (ref. 69).
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Exhibit 5-4. Ammoniacal Etchant Regeneration System
Regenerated Etchant
i
Etching
Rinsing
! Re
f
Fresh Rinse Water
Spent Etchant
Spent Rinse Water
generated Rinse Wa
r -^*
Sulfi
Organic Solution,
Extraction 1
1
Extraction 2
ter 1
""T
Stripping
Organic Solution
iric Acid Electrolyte
i
Effluent
i Copper
-i *
Electro winning
T
Units are sized based on the total throughput of the etching line, best estimated by a shop's current consumption rate
of replenisher. Ten different size systems are available depending on the facility's annual replenisher volume,
ranging from 14,300 gal/year to 380,000 gal/year (ref. 69).
One respondent to the survey uses this type of etchant regeneration system (ID# 946587). They purchased one unit
in 1990 for regeneration of cupric chloride etchant (inner layer etching) and a second unit in 1994 for regeneration of
ammoniacal etchant (outer layer etching). These were successful installations; however, the respondent indicates
that: "We have invested extensive engineering resources to improve equipment process control." They indicate that
the primary maintenance item is the replacement of anodes, cathodes, and membranes, which is done annually at this
site for a cost of $10,000.
The Elo-chem Regeneration Module and Copper Recovery System by Atotech regenerates a proprietary ammonium
sulfate etchant, which has a slower etch rate than ammonium chloride. The Elo-chem system consists of two
separate regeneration circuits: an etchant recycling module and a copper recovery module. Etchant is regenerated
utilizing atmospheric oxygen and ammonia to restore the copper in the spent etchant to the ionic form needed for
etching. The regeneration occurs as a batch process. When a density meter indicates a high copper concentration,
spent etchant is pumped to a tank with an electrolytic copper recovery cell. Etchant that has already been processed
is reinjected with ammonia and oxygen before being sent back to the etcher. At the electrolytic cell, copper is
deposited on the cathodes and is removed in sheets. This etchant has a 15-20% slower etch rate, and a proprietary
rate accelerator is needed to keep the etch rate from falling any lower (ref. 69, 70).
The Elo-chem system is applicable to both large and small facilities. The same equipment is used for all size
facilities, and multiple plating cells are added to accommodate facilities with larger production capacities. The
average copper recovery capacity of the system is 5.4 Ib/hour, with a maximum hourly capacity of 6.6 Ib. One
customer who runs a prototype board shop (using fewer than 10,000 gallons of etchant/year), describes this as the
"ideal" system for their operation. They expect the system can eliminate the time and resources associated with
shipping spent etchant off-site, reduce the space required for storage of fresh and spent etchant, decrease chemical
purchase costs, eliminate safety issues associated with handling drums, and improve etching process control.
Ammonia gas, a proprietary rate accelerator (added at 0.25 liter/plating hour), and small quantities of ammonium
sulfate crystals (from an industrial chemical supplier) are needed to operate the system; actual quantities required
depend on the carry-over losses. This system does not recycle or remove copper from rinse water (ref. 69).
5.2.2.2 Cupric Chloride Etchant Regeneration
The FSL Electrolytic Regeneration system from Finishing Services Limited regenerates etchant and plates out the
copper. Users say their spent etchant has been reduced by 95%, and the volume of hydrochloric acid needed has
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dropped by 70-80%. Another saving is the elimination of oxidizer purchases (chlorine or peroxide). The copper
plated out of the etchant can be sold as scrap. No changes are made to the rinse water stream.
The smallest FSL Regeneration system available is a module that removes 2.2 pounds of copper per hour; by
joining these modules together, FSL can supply a system large enough to accommodate hundreds of pounds of
copper per hour. As system capacity increases, however, so does the size of the system (ref. 69).
The payback from installation of the system is dependent on the operating parameters of each facility, such as
throughput and current costs associated with off-site shipments of spent etchant. Savings include a reduction in the
volume of hydrochloric acid used, elimination of oxidizer purchases (chlorine or peroxide), and savings associated
with the reduction or elimination of spent etchant. Costs include capital investment for the equipment, electricity
costs, minor costs from addition of chemicals to replace drag out, evaporation, and carry-over. Based on past
experience, the manufacturer estimates a payback of 1.5 to 3 years. There is no change in the rinse water stream (ref.
69).
One of the survey respondents has installed an FSL unit (ID #946587) (see detailed data in Appendix A).
Membrane electrolysis can also be used for cupric chloride regeneration, although no U.S. commercial units were
identified. With membrane electrolysis, an electrical current is passed through electrolytes that are separated by an
ion specific membrane. Two reactions typically occur as the result of using membrane electrolysis: (1) ions of a
given species are electrically driven across a selective membrane, and (2) chemical changes (e.g., oxidation/reduction)
occur at the electrodes.
Cupric chloride regeneration using membrane electrolysis is accomplished by reoxidizing the cuprous chloride to
cupric chloride, and by removing the dissolved copper. The etching solution is fed into an anode compartment and
becomes the anolyte. A solution of 15 to 20% sulfuric acid is maintained in the catholyte compartment. An
electrical current is passed through the electrolytes that are separated by a cation specific membrane that permits
positively charged ions to pass from the anolyte to the catholyte. The oxidation of monovalent copper to bivalent
copper occurs at the anode (ref.71). A commercialized system in Europe that that employs a PVC-based membrane
was identified in the literature. A PWB facility in the UK reported a two-year pay-back from use of the technology
(ref. 72).
5.2.2.3 Combined Cupric Chloride/Ammoniacal Etchant Regeneration
ARS Resource Recovery from ARS can handle both types of etchant. In addition, the system can simultaneously
process acid copper plating baths, electroless copper dumps, and other copper bearing rinse water streams (ref. 73).
Copper is recovered by liquid ion exchange in the form of copper sulfate. This can be sold as liquid copper sulfate,
electrowon into copper metal, or crystallized into copper sulfate crystals (ref. 69).
ARS has recently installed its first integrated etchant regeneration and copper recovery system at one of the largest
PWB manufacturing facilities in the country. At start-up, the system will allow this facility to process, on-site, its
flows of cupric chloride spent etchant and ammoniacal spent etchant. In the future, the facility plans to use the
system for recovery of copper from all copper dumps in the facility (ref. 69).
The initial system was designed for a large, high volume PWB manufacturer; however, ARS is currently developing
the integrated regeneration technology to meet the needs of mid-sized companies. A payback period of about 2 years
is estimated by the manufacturer, but depends on the facility-specific conditions (ref. 69).
5.2.2.4 Microetchant Regeneration
Microetching is a common process used as a preclean step in many stages of PWB manufacturing. Microetching
removes anywhere from 10-70 microinches of copper to rid the panels of oxidation prior to the subsequent process,
such as pattern plate, solder mask application, or hot-air-solder-leveling (ref. 74). Most facilities use a sulfuric-
acid/hydrogen-peroxide solution as the microetchant, which can be maintained using electrowinning or
crystallization.
Several approaches to using electrowinning for microetchant maintenance have been successfully employed. In one
option, the working etch solution is continuously circulated through a separate electroplating cell where the
dissolved copper is plated out on stainless steel cathodes or copper wire mesh. With this technique, the dissolved
copper concentration can be maintained with a minimum amount of hydrogen peroxide breakdown. Additional
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proprietary stabilizers help to keep the peroxide decomposition to a minimum. For every 1 ampere hour of plating,
approximately 1.0 to 1.3 milliliters of 50% hydrogen peroxide is consumed, in addition to the peroxide consumed in
the etching process. One variation of this option that is under investigation is to employ a special cell with a
membrane that separates the hydrogen peroxide from the plating cell. This may reduce the decomposition rate of the
hydrogen peroxide.
Another facility reportedly uses a high surface area electrowinning system equipped with dimensionally stable
anodes. This facility had been decanting 138 gallons of spent microetch solution per week from the electroless
copper line and 35 gallons/week from the black oxide line. This spent solution was being sent off-site for recycling.
In order to conserve sulfuric acid and prolong bath life, they installed the electrowinning unit (ref. 74). Their setup
uses dimensionally stable anodes and cheap scrap laminate as the cathode onto which the copper is plated. The
pumps are hard-piped for batch transfer from the microetch process bath to the electrolytic plate-out cell. The facility
chose only the electroless copper and the black oxide lines for microetchant regeneration because other preclean
processes do not have high copper concentrations, due to a high rate of copper drag-out.
Their continuous-batch plate-out system reportedly allows for better process control because the copper concentration
remains more stable, which in turn provides for a more stable etching rate. In addition, the copper ion concentration
in the microetch is lowered to 25 - 45 g/1, from an average of 45-80 g/1 by the old decant method. The reduced
copper concentration has the effect of decreasing the average amount of copper dragged into the subsequent rinse and
then into waste treatment by about 50%. More importantly, the spent microetch is no longer decanted from these
processes each week and sent off-site (ref. 74).
Several survey respondents use electrowinning for microetchant bath maintenance (ID #s 36930, 31838, 14, 34, and
53). Data relative to these installations can be found in Appendix A.
Additional information on electrowinning is presented in Section 5.3.2.
With the crystallization process, copper is recovered in the form of sulfate pentahydrate by cooling the solution to
room temperature or below. The process can be carried out in batch or continuous modes. The former approach is
more applicable to smaller shops that deal with lower volumes of solution. With the batch process, the copper laden
solution is transferred to a separate tank and permitted to cool. When the copper sulfate crystallizes, it is decanted
and returned to the operating tank and reused until the copper concentration reaches saturation. The crystallization
process can be controlled by agitation and cooling rate. Larger operations use a two tank system with continuous
transfer of solution into a highly agitated crystallization tank where it is cooled to 60 to 70°F, followed by
crystallization in the second tank. Solution from the second tank flows continuously to the operating tank (ref. 75,
76, 77).
Facilities contemplating use of the crystallization maintenance method should investigate the availability of local
markets for this material. It may be more difficult to find a recycler that accepts this material than the metallic
copper recovered by electrowinning.
One survey respondent (ID#273701) has purchased and installed two crystallization units. Their first unit was
purchased in 1988 and used on the final etching line. This unit processes 1,200 to 1,500 gal/day of solution that is
fed to the unit at 50 g/1 Cu. In 1993 they purchased a second unit that is used on the electroless copper line. The
respondent is satisfied with the performance of both units. Additional details concerning these installations can be
found in Appendix A.
5.2.2.5 Microetchant Reuse
Cascading reuse is another potential method of reducing the quantity of microetchant used in a PWB shop. With this
method, microetchant is used in one process until its efficiency is reduced; it is then reused in another process that
has a lower chemical requirement.
This concept was implemented by a company that had previously been using electrowinning to plate-out copper
from spent sulfuric acid-potassium persulfate microetchant, then disposing of the solution. This particular chemistry
could not be regenerated, due to the buildup of sulfates that resulted from the breakdown of the microetch
components (a hydrogen peroxide-based microetchant, on the other hand, can be regenerated using this technology
because the breakdown product is simply water). Therefore, in this case, electrolytic recovery served to remove
copper before the solution goes to the wastewater treatment unit, but not to regenerate microetchant. The company
-------
was initially motivated to conserve microetch solution because their electrolytic plate-out unit frequently failed to
meet capacity needs for processing spent solution. Excess waste had to be placed in drums until capacity was
available.
Because the amount of copper that must be removed from the board varies among the different process lines, a
microetch considered spent for the purposes of one process line may still be useful for microetching in a line
requiring a lower etch rate. For example, at this facility the microetch step for an electroless copper line must
remove 40 to 60 microinches of copper from the PWB, whereas the preclean step for pattern plating requires a
microetch rate of 4 to 6 microinches. Using this process knowledge, they designed a continuous-flow system
consisting of new plumbing and pumps to reuse microetch solution (ref. 78).
The reuse system is shown in Exhibit 5-5. The continuous-flow system begins with a single tank of microetch
solution, prepared daily. This day tank is formulated to the specifications for the electroless copper line's preclean
step, during which 40 to 60 microinches of copper must be removed from the panels. The microetchant is then used
in the following sequence (ref. 78):
• Microetch for Electroless Copper Plating. A photocell provided by the electroless copper equipment
vendor measures copper ion concentration in the microetch bath and automatically feeds fresh microetchant from
the day tank to the bath when the copper concentration reaches a threshold of 10 g/1. Before this automated
system was installed, the bath was dumped three times per week, the copper concentration in the bath ranged
from 0 to 13 g/1, and the etch rate ranged from 14 to 60 microinches. The autofeed arrangement maintains
copper concentration between 9 to 11 g/1, allowing for better process control and a more stable etch rate of 33 to
57 microinches. Although the flow of microetch could be triggered manually (i.e., without using a photocell),
frequent analysis would be required to feed fresh solution into the microetch bath for electroless copper at the
appropriate time. The benefits would not be as substantial (ref. 78).
• Microetch for Pattern Plating. As additions are made to the microetch tank for the electroless copper
line, the excess overflows and is gravity-fed to the microetch prior to pattern plating. This preclean process
needs to remove only 4 to 6 microinches of copper. Therefore, a weaker solution (one that has a higher copper
concentration and less oxygen available) can be used. Because the etch rate is determined by temperature,
concentration, and dwell time, the latter has been adjusted to achieve the desired etch rate based on the copper
concentration of the incoming solution (ref. 78).
• Electroless Copper Rack Strip. The excess from the microetch bath for pattern plating flows, in turn, to
a tank used for electroless copper rack stripping. During the electroless plating process, copper is deposited on
the wire racks that hold parts to be plated, as well as on the inside of the plating tank. It is not necessary to use
fresh microetch solution because etch rate is not a critical parameter in cleaning racks and tanks. Microetch
solution can be reused from other processes to remove copper build-up (ref. 78).
• Electroless Copper Tank Strip. When the rack-strip tank is full, the microetchant is then pumped to a
holding tank. Each weekend, the solution is pumped back into the electroless copper tank to remove copper
build-up from its walls (ref. 78).
• Electrolytic Recovery. After cleaning the electroless copper tank, the microetchant is pumped to the
electrolytic plate-out cell, where copper is plated out and sold to a recycler at $0.80/lb (ref. 78).
• Wastewater Treatment. The remaining spent microetchant, consisting of sulfates, sulfuric acid, residual
copper, and water, is sent to wastewater treatment (ref. 78).
89
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Exhibit 5-5. Continuous Flow Microetchant Reuse System
Electroless Copper
Microetch
Electroless
Copper Platingl
Line
Day Tank
1
L^PumpfJ
Pattern Platin
Pattern Plate
Microetch
Electroless Copper
Tank Strip
T
_f
i IT
3
4
H
PumpL
Holding
Tank
Electroless
Copper
Rack Strip
5.2.3 Permanganate Desmear Maintenance
Ion transfer is a relatively inexpensive and simple technology used for bath maintenance of permanganate desmear
baths by 32% of the survey respondents. In the conventional permanganate process, the permanganate ion is reduced
by heat and contact with PWBs, and is replaced by chemical addition. Also, during operation of this bath, by-
products (including the manganate ion) accumulate in concentration, causing a sludge to form, and frequent disposal
is necessary. The ion transfer technology (also referred to as porous pot) can be used to maintain a sufficiently low
concentration of contaminants, and thereby reduce the frequency of disposal. One survey respondent indicated that
use of the technology has resulted in up to a 90% reduction in chemical use for the applicable bath.
The common porous pot design consists of a rectifier, a ceramic pot that houses a cathode (protecting the cathode
from direct contact with the process solution), and an anode, which surrounds the pot and is in direct contact with the
bath. At startup, the pot is immersed into the bath (with the top remaining above the solution, preventing it from
flowing into the cathode compartment) and filled with an electrolyte, usually sodium hydroxide. With the bath
shielded from the cathode, the primary reaction that occurs is the anodic re-oxidation of the manganate ion back to
permanganate. Using the porous pot, a bath-life extension of ten-fold or more can be realized.
Capital costs for this technology are low to moderate, and some respondents reported leasing the equipment from
chemical vendors rather than purchasing it. Of those who did purchase the equipment, the price range was $2,500 to
$14,000. The lease price ranged from $200/year to $900/year. Generally, the reported installation and operating
costs were also low.
The survey data pertaining to this technology are shown in Exhibits 5-6 and 5-7. From the 1995 survey, ninety-two
percent (92%) of the respondents who operate ion transfer units indicated they are satisfied with the technology. A
somewhat lower percentage of respondents (67%) indicated that in the future they would buy the same technology
from the same vendor if faced with a similar situation.
The 1997 survey data were similar. All installations were operating successfully and maintenance levels were as
expected or lower.5
The porous pot technology is reported to be a relatively low maintenance item. The units require periodic cleaning,
which one facility suggests should be done on a weekly basis (ID# 6710). Several respondents indicated that special
attention should be given to cleaning the electrical contacts. The primary maintenance problem with this technology
appears to be replacement of broken ceramic pots. One facility (ID# 3023) reported " porous pots are fragile and are
broken frequently." Replacement pots cost approximately $100 each for certain models. One respondent also
indicated that the metal frame of the unit corroded (ID#36930).
The 1995 and 1997 survey data are presented in separate exhibits because the survey questions were somewhat different.
90
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Two facilities indicated that the concentrated caustic used in the pots presents a worker safety problem. One of those
facilities (ID# 3023) indicated that handling of the pots has resulted in several worker accidents.
Exhibit 5-6. Porous Pot Technology Data (1995 Survey)
Equip. Install Non- Down
Resp. Year Cost Cost Labor Labor Use Time Future
ID Application Purch. ($) ($)* (hr/yr) ($/yr) Code % Satisfied? Decision
41739
44486
959951
273701
237900
6710
955099
953880
29710
36930
3023
44657
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
Potassium
Permanganate
1993
1992
1992
1990
-
1989
1990
1992
1992
1991
1989
1990
0
0
14000
600
0
750
0
0
900
4000
2500
200
25
100
5000
200
0
125
0
100
100
200
1250
0
10
52
0
0
0
20
550
8760
30
100
208
15
45
200
0
0
0
875
0
400
0
1000
250
46
1
1
1
1
1
1
1
1
1
1
1
1
0
0
1
0
2
0
1
2
0
5
1
0
Yes
Yes
Yes
Yes
Partially
Yes
Yes
Yes
Yes
Yes
Yes
Yes
1
-
1
1
3
4
1
1
1
1
1
2
*The lower install costs are presumably annual lease costs.
Use codes: 1 = in use; 2 = not in use; 3 = not in use, future use expected
Future decision codes: (in response to survey question, "indicate a future course of action should you be required to fill a similar need"): 1 =
buy the same technology from the same vendor; 2 = purchase same technology from different vendor; 3 = purchase different technology; 4 =
do nothing.
91
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Exhibit 5-7. Porous Pot Technology Data (1997 Survey)
Facility
ID
14
23
42
31
28
37
44
56
45
50
35
41
Application
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate
Potassium permanganate bath on
desmear line (has resulted in an
85-90% reduction in chemical
use and treatment for that bath).
Potassium permanganate
Reasons
1,2,3,5,6
7
2,3,4,5
2,3, 5,6,7
1,3,5,6
3,5
1,2,5
4,7
2,5,7
2,3
2, 3, 4, 7
2,4
Meet
Need?
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Maintenance
A
A
L
A
A
A
L
A
A
A
A
A
Overall
Satisfy?
nr
5
3
4
3
5
4
5
5
nr
5
nr
Future
Decision
S
S
S
S
D
S
S
S
S
S
S
S
nr = no response
Reasons technology was purchased:
1 = to meet or help meet effluent limits
2 = to reduce process chemical purchases
3 =to reduce quantity of waste shipments off-site
4 = to increase production rate
5 = to reduce worker exposure to hazardous waste
6 = to recover a metal for resale
7 = to recover a chemical for reuse
Has the technology met the need for which it was purchased?
Y = yes
N = no
P = partially
Rate the level of maintenance required:
A = about what was expected
M = more than expected
L = less than expected
Overall satisfaction with the technology:
1 = very dissatisfied
5 = very satisfied
To fulfill a similar need in the future, which technology would
you purchase?
S = same technology
D = different technology
S = none
5.2.4 Common Acid Regeneration
Several technologies are in use by industry to regenerate common acids, including sulfuric, hydrochloric, and nitric
acids. Although these technologies are not commonly used by PWB shops, they are employed to a moderate extent
by the metal finishing industry. The two most commonly used technologies, diffusion dialysis and acid sorption,
are discussed in this section.
Recycling spent solution is not always as easy as hooking up a unit and adding fresh solution periodically. It may
require extensive experimentation and teamwork. Understanding the chemistries involved in the process is the key to
regenerating bath solutions successfully (ref. 74).
5.2.4.1 Diffusion Dialysis
Diffusion dialysis is an ion exchange membrane technology that competes directly with acid sorption (Section
5.2.4.2) as a purification/recovery method for acids that have become contaminated with metals (e.g., cleaning,
stripping, and etching baths). This technology has been commercialized for less than 10 years, which is reflected by
the fact that only one of the survey respondents indicated that they have employed diffusion dialysis.
The diffusion dialysis process separates acid from its metal contaminants via an acid concentration gradient between
two solution compartments (contaminated acid and deionized water) that are divided by an anion exchange membrane.
Acid is diffused across the membrane into the DI water whereas metals are blocked due to their charge and the
selectivity of the membrane. A key difference between diffusion dialysis and other membrane technologies, such as
electrodialysis or reverse osmosis, is that diffusion dialysis does not employ an electrical potential or pressure across
the membrane. Rather, the transport of acid is caused by the difference in acid concentration on either side of the
membrane. As such, the energy requirements for this technology are low.
The process uses ion exchange membranes that are assembled in a membrane stack. The membrane separates two
liquids: (1) acid contaminated with metal, and (2) deionized water. The physical laws of diffusion and
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electroneutrality cause material in high concentration, to move to an area of low concentration without an imbalance
of electrical charge. Because of the presence of the anion membrane, the metals in the concentrated solution are
unable to pass from the concentrate to the DI water. However, anions in the concentrate (e.g., chlorides, sulfates,
nitrates, phosphates) are permitted passage. Also, hydrogen ions, although positively charged, diffuse along with the
disassociated acid (anions). The passage of hydrogen, which is key to the success of this process, is due to the small
size of the hydrogen molecules and their mobility. The passage of the positively charged hydrogen ions satisfies the
law of electroneutrality, preventing an imbalance of ionic charge on either side of the membrane (ref. 79, 80).
Diffusion dialysis, like other membrane technologies, is not 100 percent efficient; not all of the acid will be
recovered and some leakage of metal will occur. In the laboratory, the process has yielded acid recovery efficiencies
as high as 99%, with 98% metal removal. In the manufacturing environment, the practical limits are 80% to 95%
acid recovery, with 60% to 90% of the metal contaminants removed. Also, the recovered acid may be of insufficient
concentration to permit direct reuse. In such cases, vacuum evaporation may be needed to increase its concentration
(ref. 81), although the economics of a concentration step are questionable. One source indicates, based on 1.5 years
of experience with diffusion dialysis, that it is more efficient and economical than acid sorption for certain
applications (e.g., recovery of mixed acid pickling baths) (ref. 80).
The diffusion dialysis membrane material is relatively resistant to chemicals commonly used in the PWB shop.
However, contact with solvents could cause swelling of the membrane, and strong oxidizing agents can deteriorate
the membrane material (ref. 82). The process is tolerant of feed solution temperatures up to 50°C (ref. 82).
One survey respondent reported the use of this technology (ID #955099). Their unit is successfully used for
maintenance of a solder strip solution. The unit was purchased for $10,000 in 1994, and requires approximately 50
man-hours per year to maintain. However, use of the technology in PWB facilities has been reported elsewhere (ref.
D, F). One facility successfully applies diffusion dialysis to a methane sulfonic acid (MSA) solder electrostrip to
continuously remove metals. As a surface finish, this facility uses solder-mask-over-bare-copper with hot-air-solder-
leveling. This outer layer finish prevents copper oxidation and facilitates solderability during the assembly process.
Before panels can then undergo nickel/gold tab plating (also called finger plating, connector plating, or microplating)
for electrical conductivity and environmental resistance, the tin/lead solder must be stripped from the panel. In the
stripping process they use methane sulfonic acid (MSA) and apply a reverse electrical current to dissolve tin and lead
from the boards.
In the past, the facility changed the acid every 30,000 ends (one pass of a circuit panel), or approximately every 6
weeks, depending on production schedules. MSA is an expensive acid (~$21/gal.), and accounted for an average of
$17,000/year in raw material costs. Spent solution was sent off-site for disposal at a cost of approximately
$5,600/year. The facility recognized an opportunity to conserve acid, prevent hazardous waste generation, and lower
employee exposure to corrosive materials using a relatively simple and efficient in-process recycling technology
called diffusion dialysis.
At this shop, the diffusion dialysis recycling unit is hard-piped to the MSA tab stripping bath. The company first
evaluated a 5 gallon/day recycling unit in an off-line pilot test. They assessed parameters such as acid recovery and
metal rejection rates, as well as the stripping rate of the recovered acid. The facility then proceeded to evaluate the
system on-line. After working with the vendor to fine-tune metal rejection and acid recovery rates, they were able to
maintain a constant solution level in the stripping bath. Based on the projects costs and savings, the payback on the
investment was approximately 6 to 7 months (ref. 74).
The same facility is investigating the use of diffusion dialysis for maintaining their nitric acid/ ferric nitrate tin/lead
etch-resist strip solution. The nitric acid solution is used to strip the tin/lead layer, and the ferric nitrate component
is necessary to remove the intermetallic layer that forms when the tin and copper diffuse into each other. These
solutions also contain wetting agents, copper etching inhibitors, and anti-tarnishing agents (ref. 74).
The investigation involves the use of diffusion technology to separate the stripped metals from the stripping
solution, rendering it reusable. This would be a continuous, on-line recycling system similar to that used for their
MSA recovery. The major roadblock to this process is the presence of an iron component in the proprietary
stripping solution. They anticipate that the diffusion dialysis process will reject from the spent solution all metals,
including the iron, which is essential to the stripping process. However, the facility believes it may be possible to
determine the rate of loss of iron from the diffusion dialysis process and replace the iron with a concentrated
replenisher. The difficulties here include adjusting for the losses of the other components, since rejection of organics
and non-metal inorganic materials varies, depending on the charge and size (ref. 74).
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In order to make these determinations, the facility contacted its solder strip chemical vendor and arranged a meeting
with the company's process engineers, representatives from its chemical vendors, and the diffusion dialysis
equipment vendor. Together they designed an off-line pilot system to test the acid reclaim efficiencies and metal
rejection rates at various ratios of virgin to spent solder strip. The facility is awaiting further test results from its
chemical vendor on parameters such as solder stripping rates, intermetallic removal, copper etching inhibition, and
anti-tarnish capability. Based on the findings, the chemical vendor will be able to determine the additive package of
chemical constituents that would replace the components lost from the diffusion dialysis process (ref. 74).
5.2.4.2 Acid Sorption
Acid sorption is a purification technology applicable to dilute to moderately concentrated acid solutions, such as
cleaning and stripping baths. The term sorption, which includes both adsorption and absorption, is a general
expression for a process in which a component moves from one phase to another, where it is accumulated,
particularly for cases in which the second phase is a solid (ref. 435). Acid sorption is not a widely used technology
by the PWB industry, although it has been commercially available in North America for approximately 15 years.
As an acid bath maintenance technology, acid sorption competes with diffusion dialysis (Section 5.2.4.1).
Acid sorption is one of several processes where resins are used to absorb chemicals present in surrounding solutions
and the chemicals are subsequently desorbed with water. These reversible sorption processes include ion exclusion
(cation resin), ion retardation (special resin), and acid retardation (anion resin). Of particular interest in PWB
manufacturing is acid retardation. This is a separation process where an acid is separated from its salts by using a
column containing a strongly basic anion exchange resin of a specific porosity and particle size. This separation
occurs because at high concentration the acid crosses the Donnan potential barrier (Donnan invasion) and is taken up
by the resin, whereas the salts are excluded from it. The acid is thus "retarded" and the salts pass through the resin.
This is not an ion exchange process, because the acid is desorbed from the resin with plain water.
The acid sorption or retardation process is employed to remove dissolved metal contaminants from acid baths. It is
most often applied to the purification of sulfuric acid anodizing baths, and sulfuric acid and hydrochloric acid pickling
baths. When these solutions are contaminated with dissolved metal, the free acid concentration decreases and the
anodizing or pickling efficiency drops. Additions of fresh acid are possible up to a point, but eventually, the bath
must be either purified or dumped.
Diagrams of the acid sorption process are presented in Exhibits 5-8 and 5-9. These diagrams illustrate the equipment
of a particular commercial acid sorption manufacturer. During the sorption step, the acid and metal salt mixture is
fed up through the resin bed. Acid is sorbed into the resin, while the remaining dissolved metal salts are rejected as
mildly acidic solution, leaving from the top of the bed. Depending on the metal salt, this solution may be waste-
treated or diverted to an electrowinning cell for recovery of the metal. During the desorption step, water flows down
through the resin bed. Acid is desorbed from the resin and displaced from the bottom of the bed. City water is
typically adequate for this step. The resin is stable under normal operating conditions for many years, without the
need for regular replacement or any special treatment.
94
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Exhibit 5-8. Acid Sorption Operating Cycle
t
Metal Salt
Byproduct or Waste
\
Water
Reservoir
1
Acid
Reservoir
^ Upstroke
(desorption)
Downstroke
(desorption)
Water
Reservoir
A
Acid
Reservoir
W Recovered Acid
Exhibit 5-9. Acid Sorption Flow Diagram
Acid Process
Tank
Purified Acid
\
1
Water
Reservoir
(cooled)
-^
\
\
City Water
Acid Sorption
Unit
Acid
Feedstock
Waste or
Byproduct
i
Acid
Reservoir
95
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Acid sorption does not recover all of the acid in a treated bath. Rather, it recovers only a percentage (typically 80%
to 90%) of the "unused" or free acid (i.e., that acid which is not chemically bonded to the dissolved metal).
Typically, 40% to 70% of the total acid is free acid. Therefore, if a shop's current method of operation involves
dumping and treating spent acid baths and replacing the bath with fresh solution, then acid sorption can be expected
to reduce their total acid usage by approximately 30% to 65% (ref. 83, 84).
In addition to reducing acid usage, there are several benefits from using acid sorption. These include: (1) reduces
neutralization treatment reagent usage (e.g., caustic or lime); (2) reduces interruptions in production (i.e., when used
on a continuous basis as opposed to batch purification); and (3) reduces process control variability caused by
fluctuations in bath composition (i.e., when used on a continuous basis).
5.2.5 Electroless Copper Ethylenediamine-tetraacetic Acid (EDTA)
Recovery
EDTA is the most widely used chelating agent with electroless copper. Its purpose is to keep the cupric ions in
solution and prevent them from precipitating as copper hydroxide. It does present some problems downstream at the
waste treatment level. While using precipitation to recover the copper is possible, the EDTA remains and will have
an attraction to copper from other waste streams. If an ion exchange system is used, standard cation and chelating
ion exchange resins cannot effectively remove dissolved copper with EDTA present. A method has been developed
to recover the EDTA from spent electroless copper baths and solve these treatment problems.
EDTA is recovered by acidifying the solution and creating H4EDTA, which is insoluble. Before this can be done,
however, the copper must be removed. This is done through the introduction of HCHO and NaOH to the electroless
solution, which causes the bath to become unstable, and the copper precipitates. The copper is then removed
through filtration. The remaining filtrate contains sodium sulfate (or nitrate), sodium hydroxide, sodium formate,
EDTA, formaldehyde, stabilizers, and additives. This is acidified with concentrated HCL or H2SO4 to reduce the pH
to about 4. CO2 gas is released, due to the presence of carbonate in the solution. After the gassing stops, more acid
is added to bring the pH to 2.1 or below, and the EDTA is precipitated.
Although this H4EDTA can be recycled to prepare a new electroless copper bath, this is not typically done.
Electroless chemistry is usually supplied from the manufacturer with some of the components pre-mixed in the
appropriate ratios. One of the components is EDTA (ref. 75).
5.2.6 Dry Film Stripping Solutions
Membrane filtration, including microfiltration and ultrafiltration, is a potentially viable technology for the recovery
of developer solution associated with photoresists. Membrane filtration is a cross-flow filtration method as opposed
to "dead-end" barrier filtration. With the latter method, all of the feed solution is forced through the membrane by an
applied pressure. With a high solids-fed stream, the pores of a dead-end filtration device plug. With crossflow
filtration, the fluid to be filtered is pumped across the membrane, parallel to its surface. By maintaining a high
velocity across the membrane, the retained material is swept off the membrane surface. This mode of operation
typically requires multiple passes and consumes a greater amount of energy than dead-end filtration. However, for
high solids applications, crossflow filtration is the only practical method (ref 3).
PWB facilities are interested in reducing the wastes from stripping processes because of the labor and cost of on-site
treatment and/or preparing the materials for shipment off-site. A recent research project collected samples of waste
developer, developer rinse, stripper, and stripper rinse (ref. 85). Tests of the spent stripper showed that it contained
nearly the same concentration of ethanolamine (key stripper ingredient) as does fresh solution. Ultrafiltration was
investigated as a means of generating a reusable product from the spent stripper. Earlier tests by other researchers
were unsuccessful due to the use of antifoam in stripper, which tends to coat and foul the ultrafiltration surface. The
current tests were performed on spent stripper containing no antifoam. The ultrafiltration unit successfully separated
the spent stripper into a reusable product that represented 80% of original waste volume and 74% of the active
ingredients in virgin stripper. The remaining 20% waste contained 100% of the solids, 83% of the copper, and 50-
70% of the organics and dissolved solids. In a parallel board facility test, recycled stripper was used in a production
situation (74% ultrafiltration filtrate and 26% virgin stripper) and proved to have the same stripping speed of purely
virgin solution. Future test will focus on determining the number of times that stripper can be recycled.
The survey did not specifically request information on filtration of dry film stripping solutions. Therefore, the
extent of use of this technology was not determined.
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5.3 Chemical Recovery Technologies
Various technologies are used by PWB facilities to recover chemicals from spent baths and rinse waters. In most
cases, the recovered chemicals are sent off-site for reclamation, rather than reused in the PWB shop. The two most
common recover technologies are ion exchange and electrowinning. These technologies are often used in
combination where ion exchange separates and concentrates the dissolved copper from rinse waters and
electrowinning is used to recover the copper in metallic form from the concentrated solution. Due to the prolific use
of these technologies, they are covered in greater detail in this report than other chemical recovery technologies.
5.3.1 Ion Exchange
5.3.1.1 Technology Description
Ion exchange is a chemical reaction wherein an ion from solution is exchanged for a similarly charged ion attached to
an immobile solid particle (i.e., ion exchange resin). Ion exchange reactions are stoichiometric (i.e., predictable
based on chemical relationships) and reversible. The resins are normally contained in vessels referred to as columns.
Solutions are passed through the columns and the exchange occurs. Subsequently, when the capacity of the resins is
reached, the ions of interest, which are attached to the resin, are removed during a regeneration step where a strong
solution containing the ions originally attached to the resin is passed over the bed.
The strategy employed in using this technology is to exchange somewhat harmless ions (e.g., hydrogen and
hydroxyl ions), located on the resin, for ions of interest in the solution (e.g., copper). In the most basic sense, ion
exchange materials are classified as either cationic or anionic. Cation resins exchange hydrogen ions for positively
charged ions such as copper, nickel, and sodium. Anion resins exchange hydroxyl ions for negatively charged ions
such as sulfates, chromates, and cyanide.
The basic ion exchange column consists of a resin bed that is retained in the column with inlet and outlet screens,
and service and regeneration flow distributors. Piping and valves are required to direct flow, and instrumentation is
required to control regeneration timing. The systems are typically operated in cycles consisting of the following
steps (ref. 3):
1. Service (exhaustion) - Water solution containing ions is passed through the ion exchange column or bed
until the exchange sites are exhausted.
2. Backwash - The bed is washed (generally with water) in the reverse direction of the service cycle in order to
expand and resettle the resin bed.
3. Regeneration - The exchanger is regenerated by passing a concentrated solution of the ion originally
associated with it through the resin bed; usually a strong mineral acid or base.
4. Rinse - Excess regenerant is removed from the exchanger; usually by passing water through it.
The ion exchange process has been commercially available for many years, but early use was primarily for water
deionization or softening. Use of the process for PWB pollution prevention and control is a more recent application,
and widespread interest in it has grown rapidly over the past 10 years.
5.3.1.2 PWB Manufacturing Applications
Ion exchange is common in PWB facilities for several reasons. Among them are:
• Several PWB rinse water streams are readily compatible with ion exchange. Simple copper-bearing, low-organic
streams from micro-etchant, acid dip, and copper electroplating rinses can usually be sent directly to ion
exchange with no pretreatment. With carbon filtration and pH control of the incoming stream, additional rinse
streams become ion exchange candidates.
• The preponderance of copper as the contaminating metal allows facilities to take advantage of the powerful ion
exchange/electrowinning combination. Together, these two technologies combine to separate, concentrate, and
recover copper from rinse streams.
• Ion exchange offers facilities the ability to close-loop some rinses and reduce the need for downstream treatment.
• Due to the large number of rinses potentially amenable to ion exchange and the ability of ion exchange to
produce compliant effluent, some shops (particularly small ones) can employ metal-scavenging ion exchange as
a primary end-of-pipe system.
• Reducing the quantity of copper entering the waste treatment system greatly reduces the quantity of wastewater
treatment sludge generated, which is typically shipped off-site as hazardous waste.
97
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Generally, ion exchange is limited to dilute rinse water streams, although scavenging resins can be used to treat more
concentrated wastes under certain circumstances. As concentrations increase, ion exchange becomes impractical due
to the increasing frequency of regenerations and the declining difference between the concentration of the regenerant,
which is a constant (typically 5-10 grams/liter), and the concentration of the stream being treated.
Drag-out recovery tanks are used in conjunction with ion exchange systems, whenever feasible, to reduce the load on
the ion exchange system. In operation, the drag-out tanks return the bulk of the plating chemicals directly to the
plating bath, and an ion exchange unit connected to a subsequent flowing rinse captures only the residual chemicals.
The needed size of the ion exchange unit and its regeneration frequency are therefore reduced.
Metal Scavenging Applications. When the sole objective of using ion exchange is to remove metal from a
wastestream, a metal scavenging configuration is employed (Exhibit 5-10). This system uses only one type of ion
exchange resin, either selective anion or cation, depending on the charge of metal or metal complex being targeted for
removal (e.g., a cation-type resin is used for most copper removal applications). Because this system does not have
both cation and anion resins, the rinse water will not be fully "deionized" and cannot be reused as rinse water for
common rinsing purposes. The primary advantage of metal scavenging is the large capacity (in terms of rinse water
treated) vs. a deionizing configuration, since only divalent cations are exchanged, and common monovalent cations
such as sodium and potassium are bumped off the resin and passed. Thus, regeneration cycles are longer, lowering
chemical and other operating costs.
Exhibit 5-10. Ion Exchange Recovery-Metal Scavenging Configuration
Evaporation
Drag-Out/Recovery
Drag-Out
, 1
If
Drag-Out
Tank
—
\
Ri
City
Water
IX Regeneration
Acid Acid
f LJ
Metal-Depleted
Electrolyte Reused
for Regeneration
or Sent to Disposal
V T
11
o o
Discharged to
Treatment or
Sewer (after pH adjust)
Scrap Metal
to Recycle
Electro winning
Certain PWB wastestreams are commonly treated with the metal scavenging configuration. Most common are
copper, tin-lead, and gold rinse systems. Various copper rinses are commonly processed with this technology,
including etch, microetch, and copper electroplating. Resins are regenerated using sulfuric acid. In the case of tin-
lead, ion exchange scavenging is employed to remove lead from rinse water, which is then often discharged.
Regeneration may be performed on-site with methane sulfonic acid (MSA), or the resin, when exhausted, can be
shipped off-site for processing/disposal. Point source ion exchange treatment of tin-lead rinses may be performed to
protect downstream units from lead-bearing streams. Ion exchange may also outperform the primary waste treatment
system, and this configuration may cost-effectively maintain compliance where lead discharge limits are more
98
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stringent than copper limits. Gold rinses are often ion exchanged for the purpose of gold recovery. When exhausted,
gold-bearing resin is usually processed offsite to ensure efficient recover of the gold.
Deionization. When the objective is to recover metal and recycle rinse water (i.e., closed-loop), a deionization
configuration is employed. This configuration uses a combination of cation and anion exchange columns in series
to remove all ions from the rinse water (Exhibit 5-11). This strategy may be employed when continuous discharge
is impractical due to stringent limits, or where the benefits of water reuse outweigh the cost of installing and
operating a water recycling ion exchange unit.
Exhibit 5-11. Ion Exchange Recovery-Metal Recovery/Deionized Water Cycle
Drag-Out/Recovery
^Evaporation
T Drag-Oul
I lf~
Drag-Out
Heated
Process
Tank
r
I
*
Drag-Out
Tank
Ri
u
City
Water
IX Regeneration
Acid Acid NaOH NaOH
Metal-Depleted
Electrolyte Reused
for Regeneration
or Sent to Disposal
<
CH
O
Returned to
Rinse Tanks
Anion
Regenerant
Scrap Metal to Treatment
to Recycle
Electrowinning
A good candidate for deionization is the electroplating copper rinse system. With this application, rinse water
containing copper is sent to the cation and anion exchange columns, and deionized water is returned as fresh rinse
water to the rinse system. The anion regenerant, usually NaOH, can usually be pH treated and discharged. The
cation regenerant stream is interesting due to its similarity to the plating bath make-up--sulfuric acid and copper
sulfate. While it is possible to return the regenerant to the plating bath, thereby closing the loop for most of the
process, this is generally not done for two important reasons: (1) the performance of the PWB through-hole plating
in various stress tests is quite sensitive to small variations in bath chemistry, making additions of regenerant
inadvisable, and (2) the copper sulfate plating bath is operated at too low of a temperature to create sufficient
evaporative headroom for the regenerant additions. The regenerant is an ideal electrowinning candidate, and this is the
most common treatment option.
Deionization or metal scavenging can be accomplished using "point-of-source" ion exchange as shown in Exhibits 5-
10 and 5-11, or by using a central system similar to that shown in Exhibit 5-12. With this system, rinses are first
processed through a selective resin for cation removal, and subsequently processed through anion and cation resins for
complete deionization. They are then returned to the rinse system (ref. 36).
99
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Exhibit 5-12. Central Copper Recovery System Utilizing Ion Exchange and Electrowinning
Acid Copper Line
Vi1, '•*••'' '<• Microetch '';,„,, s.'.z-
Microtek' „. 1,0'kAad:,
•,•.', . •..•...,' Rinse • ..«•.• , >,
Acid
n.
Rinse
.f....:.:::....f.....::r......t...:.:.:....i
The three baths that are not connected
Electroless Copper Line ^. are 10% sulfuric acid baths that must be
pumped to the low Cu dump collection
tank.
Microetch ''.''KA' ':-* -'j': Acid
„. :10*'6Acjtt; „.
Rinse .' ;,'•; .;;. /•• Rinse
I •* ' ,:SlSlEj'"3l,r''iS?'.57'3T
1 Mf'S:KRif'::.i~ ,&V
xs;f; M"^>
/V.X.I.'T-,,;-,-."••-v.j* ;.:Xi^,Ufai;Jit3»<#(|f, • .
• ' T n T?-
r, -„. i«iSS¥pi&,s->Ajc;v 1 o Cu Rinse
Cu Rinse *;C»i«Sl®W; „ n ^
Collection Collection ^
£ ^. :'• .'.t/mf'1' /./•
T Regenerant
^ A k- Jl
Reused for
Rinsing
Selective
Cation
Exchange
Anion and Cation
Exchange
Process Residuals. The primary residuals from ion exchange recovery processes are the regenerants and
backwash solutions. The regenerants are concentrated wastes and the backwash is dilute. Both solutions are either
caustic or acidic, depending on the resin type and application. High metal-bearing regenerates (typically cation resin)
are sometimes reused directly in the bath, further processed to recover the metal (e.g., electrowinning), waste treated,
or sent to an off-site recovery facility. Low metal-bearing regenerants (typically anion resin) and backwash solutions
are typically treated on-site. Waste treatment processes generate sludge that is an EPA listed hazardous waste (F006).
The volume of regenerant produced will depend on the regeneration requirement (e.g., Ibs of acid per ft3 of resin) and
the concentration of acid used (typically 1 to 5%). The regeneration requirement will depend on the resin type,
application (metal or complex being recovered) and the configuration (cocurrent vs counterflow). Typical volumes of
regenerant are 20 to 50 gal/ft3 of resin. The volume of regenerant waste is sometimes reduced by reusing the last
portion of the regenerant, which will be less contaminated with metal and contains free acid. Backwash volumes
depend mostly on the equipment design and the application. Typically, backwashing generates 25 to 75 gal/fl3. The
100
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backwash is partly reused by some equipment vendors as make-up water for regenerant, in an effort to reduce the total
waste volume generated. Because backwash contains only dilute concentrations of pollutants it is typically not a
major concern and is treated on-site and discharged. However, for facilities working toward zero discharge, the
backwash volume could present a significant problem. Both backwash and regenerant can be processed by
evaporation to reduce the volume requiring disposal. However, this increases the capital and operating costs of the
system. Also, evaporation of hazardous wastes is sometimes regulated as a RCRA technology and may require a
permit to operate.
5.3.1.3 Survey Results
The survey results pertaining to ion exchange recovery are presented in Exhibits 5-13 and 5-14. Of the PWB
facilities responding to the survey, 44% are using ion exchange for chemical recovery. Some of the recovery
systems also serve as the primary end-of-pipe treatment. The latter mostly include central systems that recover
copper using ion exchange and electrowinning, but do not recycle water.
Exhibit 5-13. Ion Exchange Technology Data (1995 Survey)
Resp.
ID
Tl
502100
955703
36930A
36930
37817
25503
3470
31838
358000
43694
Application
Various Rinses
Plating, cleaning,
etching
Various rinses
Copper rinses
Copper rinses
Various rinses
Copper rinses
(etch, plate,
cupric chloride)
Various rinses
Various rinses
Mixed Cu rinses.
Also serves as
EOF treatment
Cu bearing rinses
(etch, microetch,
plate)
Year
Purch.
1991
1985
1990
1989
1989
1989
1991
1984
1994
1993
1990
Equip.
Cost
($)
90000
100000
75000
5000
15000
50000
45000
100000
24000
15000
60000
Install
Cost
($)
0
20000
25000
5000
5000
0
3000
200000
4000
5000
0
Labor
(hr/yr)
800
1500
7488
50
250
500
2200
3000
100
2500
4000
Non-
Labor
($/yr)
6300
2000
25000
1000
2000
1500
3600
35000
2000
1500
50000
Use
Code
1
1
1
1
1
1
1
1
2
1
1
Down
Time
0
0
0
0
0
0
1
0
0
10
1
Future
Satisfied? Decision
Yes
Yes
Yes
Yes
Yes
Partially
Yes
Yes
Yes
Yes
Yes
-
3
1
1
1
3
1
1
-
1
1
Use codes: 1 = in use; 2 = not in use; 3 = not in use, future use expected
Future decision codes: (in response to survey question, "indicate a future course of action should you be required to fill a similar need"):
1 = buy the same technology from the same vendor; 2 = purchase same technology from different vendor; 3 = purchase different technology;
4 = do nothing.
101
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Exhibit 5-14. Ion Exchange Technology Data (1997 Survey)
Shop
ID
14
22
43
19
21
55
34
49
29
54
54
30
44
52
38
32
53
45
47
36
20
26
46
39
13
Technology
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Ion
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
exchange
Exchange
Application
Point source metal bearing rinses
All copper rinse waters and process bath
dumps less than 2g/l copper and little or no
tin, lead or iron
(IX application not defined)
(not defined)
Etch rinse and micro etch rinses
(not defined)
Rinses after etchants, copper plate, and tin
strip
Rinse waters
Pattern solder copper, electroless Cu,
ammoniacal Cu, solder strip, acid Cu, Ni
sulfate, Au, and Ag
Horizontal etcher & chem clean line rinses
(total 9 gpm)
All copper bearing rinses with >60 ppb
copper content, except the three still rinses
in previous system (60 gpm)
Small systems used for closed loop rinse
after gold plating
Copper plating/etching rinses.
All metal bearing rinses
Ion Exchange (IX application not defined)
Ion
Ion
Ion
Exchange
Exchange
exchange
Ion Exchange
Ion
Ion
Ion
Ion
Ion
Ion
Exchange
Exchange
Exchange
Exchange
Exchange
Exchange
Rinse water from the etcher. The cleaned
water is then recycled to the rinse tank of
the etcher. "We are generating more
hazardous waste than without IX unit."
Sulfuric acid rinses
Various rinses in the electroless and oxide
lines
Acid cleaners, metal-bearing rinses
Plating rinses, plating bath, developer
rinses, board cleaning, general water rinses
Copper Plating Bath rinses
Cupric Chloride etch rinses
Used to remove copper from rinse waters
from microetch and precleaner rinses on our
oxide, Cu, etch, nickel, and gold plating
lines
Nickel drag-out, gold drag-out, microetch,
and spent shadow conditioner/cleaner.
Nickel bearing rinse waters
System just being installed
1,
6,
1,
6,
1
1,
1
U
1,
1,
1,
1,
6
1,
1,
1
5
3,
1,
2,
1,
1,
1,
1
1,
1
1,
Reasons
2, 3,5,
3,4, 5,
3
2,3,4,5
3,6
2, 3,5
6
6
2,3,5,6
3,6
,2, 3,4,
4, 5,7
3,5,6
3,6,7
3,4
3
2,3,5,6
6
4
Meet
Need?
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
P
P
Y
Y
Y
Y
Y
Y
Y
Y
Maint.
A
A
A
A
A
L
M
A
L
L
M
A
A
A
A
M
A
A
M
A
L
M
A
A
A
Overall
Satisfy?
nr
5
nr
4
5
4
3
4
5
5
4
4
5
4
3
3
2
5
4
4
4
3
3.5
4
nr
Future
Decision
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
D
Reasons technology was purchased:
1 = to meet or help meet effluent limits
2 = to reduce process chemical purchases
3 =to reduce quantity of waste shipments off-site
4 = to increase production rate
5 = to reduce worker exposure to hazardous waste
6 = to recover a metal for resale
7 = to recover a chemical for reuse
Has the technology met the need for which it was purchased?
Y = yes
N = no
P = partially
Rate the level of maintenance required:
A = about what was expected
M = more than expected
L = less than expected
Overall satisfaction with the technology:
1 = very dissatisfied
5 = very satisfied
To fulfill a similar need in the future, which technology would
you purchase?
S = same technology
D = different technology
S = none
102
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Based on the survey results, it appears that most installations of ion exchange by PWB facilities are successful. The
1995 survey results indicate that 90% of the facilities that use ion exchange as a recovery technology are satisfied
with its performance. Similarly, facilities responding to the 1997 survey that employ ion exchange rated the
technology a 4.0 on a scale of 1 to 5 (five being the best). In a similar survey conducted with the metal finishing
industry, ion exchange received an overall rating of only 3.2. The lower rating by the metal finishers may be due to
difficulties associated with using this technology with metals other than copper. For example, the metal finishers
using ion exchange for cadmium and zinc recovery rated the technology 2.0 and 2.6, respectively.
Equipment prices for ion exchange systems purchased by the survey respondents vary widely ($10,000 to $120,000
installed costs), due to major differences in system capacities (some larger systems are used to process nearly all
rinses waters generated) and levels of automation. Operating and maintenance requirements appear to be moderate to
high.
5.3.2 Electrowinning
Electrowinning is employed in PWB facilities to remove metallic ions from concentrated rinse water, spent process
solutions, and ion exchange regenerant. An electrowinning unit consists of a rectifier and a reaction chamber that
houses anodes and cathodes. In the simplest design, a set of cathodes and anodes are set in the reaction chamber
containing the electrolyte. When the unit is energized, metal ions are reduced onto the cathode. The rate at which
metal can be recovered (i.e., plated onto the cathode) from solutions depends on several factors, including the
concentration of metal in the electrolyte, the size of the unit in terms of current and cathode area, and the species of
metal being recovered.
Electrowinning is different from other recovery technologies (e.g., evaporation, ion exchange) in that an elemental
metal is recovered rather than a metal bearing solution. The recovered metal is usually not pure enough to be used as
anode material in plating processes. More often, it is sold as scrap metal.
Electrowinning is particularly applicable for removing metal from solutions containing a moderate to high
concentration of metal ions (>3,000 mg/1). Below 1,000 to 2,000 mg/1 of metal, the conventional electrowinning
process becomes very inefficient. Therefore, it is not thought of as a "compliance" technology (i.e., a technology
that will meet wastewater discharge standards). Rather its benefit is in recovering valuable metals that would
otherwise be converted to metal hydroxide sludge by the wastewater treatment system.
High surface area (HSA) electrowinning, developed during the 1970s and commercialized in the 1980s with the
reticulate cathode design, extends the applicability of this technology to low concentration solutions and in some
cases HAS electrowinning may serve as a compliance technology for specific wastestreams. HAS units employing
reticulate cathodes are designed as flow though tanks where the electrolyte passes through a series of cathodes. Each
reticulate cathode is made up of thread-like material that is woven into a sheet and given a metallized surface. During
use, the ions plate onto the surface of the cathode (up to 5 to 10 lbs./ft2). The cathodes are subsequently removed
and sold as scrap.
Commercial units employ a variety of strategies designed to increase plating efficiency at the relatively low metal
concentrations found in typical electrolytes available for electrowinning. This is usually accomplished by design
innovations that focus on causing motion of the electrolyte across the surface of the cathode or increasing the surface
area of the cathode (e.g., HAS). Solution movement reduces the effect of concentration polarization, a condition
where the thin film of electrolyte surrounding the cathode is depleted of metal ions. A high cathode surface area
permits efficient operation at low metal concentrations.
Electrowinning is applied to a wide variety of chemical solutions found in the PWB industry. Metals that are most
commonly recovered by electrowinning are copper, gold, and silver. For practical purposes, the degree to which a
metal can be recovered by electrowinning depends on its position in the electromotive series. In general, metals that
have more positive standard electrode potentials plate more easily than the ones with less positive potentials. As an
illustration, the more noble metals, such as silver and gold, can be removed from solution to less than 1 mg/1 using
flat plate cathodes, whereas with copper and tin, a concentration in the range of 0.5 to 1 g/L or more is required for a
homogeneous metal deposit.
5.3.2.2 Applications
Ion Exchange Cation Spent Regenerant. Ion exchange is employed in a variety of configurations in PWB
shops, ranging from closed-loop treatment of single rinse systems to a major component (particularly in small
103
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shops) of the waste treatment system handling combined rinse streams from a majority of the wet processes. The
metal-rich spent cation regenerant is an ideal and logical candidate for electrowinning. For most PWB ion exchange
installations, sulfuric acid is the cation regenerant of choice, which is a particularly favorable electrowinning
electrolyte.
The ion exchange-electrowinning combination (Exhibit 5-10) is most efficient with copper-bearing rinses that may
be combined from several sources (Exhibit 5-12) or accomplished at the location of a single process. Although ion
exchange may also be employed on tin-lead and gold rinse systems, cation resins primarily employed to remove lead
or gold are not usually regenerated on-site, due to the difficulty of the cycle or the expense of the required regenerant.
D rag-out Tanks. Since the efficiency of electrowinning falls off as the concentration of metal falls,
electrowinning of rinse water is, in general, less efficient that that of ion-exchange regenerant where ion exchange
serves to concentrate metal. Nevertheless, electrowinning is quite effective at greatly reducing the introduction of
metal into flowing rinses ultimately treated by the facilities main waste treatment system when employed on drag-
out rinses (Exhibit 5-15).
Exhibit 5-15. Electrowinning Technology Applied to a Drag-Out Tank
Work Flow
Drag-Out
.((S^ii-j-^'Oec^fr^^oficii'" 1^'fi'*f?a^¥.^^aiS;>)it''^'1' ,4*\>vf^w>^»'SS'tW*'^
>^3j>Jp|||i||.:^ ^ • : ^:i^;>>sVH;;S1ff/: ? ^li^-^'^i^ ' •
Continuously
Recirculated
Scrap Metal
to Recycle
Batch Dump or
Occasional Purge
to Treatment
Drag-out tanks are rinse tanks, initially filled with water. Parts are first rinsed in this tank; then proceed to the
flowing rinse system. In the most efficient configuration, a drag-out rinse is placed after a heated process tank, and
the contents of the drag-out tank are returned (recovered) to the process tank as evaporative loss make-up. The level
of the drag-out tank is made-up with fresh water, thereby maintaining the overall concentration of the drag-out tank
below that of the process tank. This simple arrangement is quite effective at reducing the mass of metal entering the
flowing rinses, but the efficiency of the drag-out tank is a function of the temperature (evaporation rate) of the
process fluid. Cool process fluids create little evaporative headroom, and little drag-out fluid can be returned.
A major source of copper-bearing drag-out in the PWB facility is the copper electroplating tanks. Today, the
overwhelming electrolyte of choice for PWB copper electroplating is copper sulfate. This bath is generally
maintained at SOT or below making it less than an ideal candidate for conventional drag-out recovery rinsing. Some
facilities have opted for a closed loop ion-exchange/electrowinning system to handle the flowing rinses of the copper
electroplating process. A second effective alternative is to employ a drag-out rinse tank connected to an
electrowinner, through which the drag-out tank solution is continuously circulated. In this configuration, the metal
concentration of the drag-out tank is maintained at a low level (determined by the introduction rate due to drag-in, the
metal removal rate of the electrowinner, particularly at low concentration levels, which can be greatly enhanced by
104
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the use of high-surface-area cathodes), thereby reducing the drag-out of metal to the flowing rinse. A properly sized
electrowinning unit can maintain the drag-out tank metal concentration well below 100 mg/L, compared to the 14-25
g/L copper concentration contained in the process fluid. The effect being, with the drag-out and electrowinning
configuration, the introduction of copper into flowing rinses will be reduced by two orders of magnitude when
compared to a standard flowing or counterflowing rinse system.
In the copper sulfate example, the drag-out tank gradually accumulates sulfuric acid, which is not an unfavorable
environment for PWBs and, therefore, only rarely will the tank need to be dumped. When applied to other plating or
preparation processes, the build-up of constituents (the electrowinning is only removing metal) from the process
fluid may require more frequent dumping of the drag-out tanks, lowering the overall efficiency of the system.
The drag-out electrowinning configuration can also be employed after tin-lead, nickel, and gold plating, with good to
excellent results. Recovery of gold from drag-out tanks is common for obvious economic reasons, although many
facilities also opt for ion exchange of gold rinse water, which is another effective method of gold recovery. Nickel
recovery from dragout tanks following nickel electrolytic plating is less common. Nickel plating baths are generally
heated to above 120°F, making conventional drag-out recovery effective. Also, many facilities only plate nickel on
connector edges (only a small portion of the PWB is immersed and the drag-out is much lower compared to copper
electroplating), and a significant percentage of PWBs may receive no nickel plating at all, making an investment in
nickel drag-out recovery less attractive. On the other hand, the value of nickel is 3 to 4 times that of copper, making
nickel recovery more economically attractive to facilities that do full panel nickel plating or otherwise generate
above-average nickel drag-out.
Tin-lead plating, like copper sulfate, is generally performed at low temperature, making the drag-out, electrowinning
configuration attractive. The move in the industry away from tin-lead to tin-only plating and the competition from
ion exchange of tin-lead flowing rinses has limited the use of electrowinning. Although the drag-out with
electrowinning configuration will perform nearly as effectively with tin lead as with copper, a few factors combine to
make the overall system somewhat more expensive and less attractive strategically. The tin-lead plating operation is
basically the only source of lead in the rinsewater of a PWB facility (other sources may contribute minute amounts).
Cation exchange essentially can remove nearly all lead from the rinses from this operation, thereby preventing any
lead from reaching the conventional waste treatment system. Elimination of lead from rinsewater available from ion
exchange may be viewed favorably to the reduction of lead achieved by electrowinning. Also, the common
electrolyte for tin-lead plating is flouboric acid, which necessitates the use of expensive, precious-metals-coated
anodes.
Tin is not usually recovered (as it is usually not regulated), except incidentally along with lead in ion exchange or
electrowinning systems.
Spent Process Fluids. It is possible to electrowin several spent process fluids to recover metal and/or to reduce
the burden on the general waste treatment system. While there are several spent process fluids found that are easily
electrowinned, it is not an extremely common practice due mainly to a combination of competing technologies or
treatment methods, and the cost of handling irregularly timed or one-time dumps of potential electrowinning
candidates.
A large process fluid waste stream that can be electrowinned is spent micro-etchant. The currently favored micro-
etchant chemistries are sulfuric-persulfate or sulfuric-peroxide. These baths contain 20-40 or more g/L of copper
when spent. Both are strong oxidizing solutions, and the spent bath is usually reduced with sodium meta-bisulfite or
other reducing agent before electrowinning. With very high copper concentrations and the favorable sulfuric acid-
based electrolyte, electrowinning proceeds at very high efficiencies, near copper's theoretical maximum plating rate
of 1.19 g/amp-hour. A unit capable of delivering 500 amps can easily plate a pound of copper out of such solutions
in a single hour, the proceeds from which can easily cover energy costs and, depending on the level of automation
and the amount of labor involved in the handling and preparation of the electrolyte, may also cover the operating
costs.
A study at one circuit board facility involving copper recovery from microetchant demonstrated that an 80 to 90%
electrowinning efficiency could be achieved, while reducing metal content to 1 mg/1 in the waste stream (ref. 7).
Two types of cathodes were used in an air-sparged electrolytic recovery cell during a two-step operation. Flat
reusable stainless-steel sheet cathodes were first used to reduce the copper concentrations of the solution from 20
grams per liter down to 500 milligrams per liter. The cathodes are removed and the copper is peeled off (up to 2 Ibs.
105
-------
of copper per cathode). The second step employs disposable high-surface-area cathodes that collect up to 3 Ibs. of
copper per cathode and reduce the copper concentration of the solution below 1 mg/1. After two years, the original
stainless-steel cathodes were still in use and nearly 1,000 Ibs. of copper has been collected. The process reportedly
reduced hazardous waste generation by more than 35 tons. Another benefit is a reported 50% reduction in the cost of
operating the wastewater treatment system.
Electrowinning of micro-etchant competes with common and simple treatment methods. In the case of sulfuric-
peroxide, chilling is very effective. Both sulfuric-peroxide and sulfuric-persulfate spent baths can be shipped off-site
for copper recovery. This option is often attractive to small shops that produce only a hundred gallons of spent
micro-etchant/year.
Another large process waste stream is spent sulfuric acid dips. These, too, are readily electrowinned. However, the
concentration of copper in these spent bath, however, is low, usually 1 g/L or less. While electrowinning can reduce
the copper concentration much lower, efficiency at this concentration is reduced and plating times per unit of copper
recovered much higher.
Spent electroless copper is also an electrowinning candidate, but more effective, easier methods are available. Spent
electroless copper is produced steadily by bail-out (to make room for frequent additions), and the bath itself is
relatively short-lived. Most facilities prefer to treat the bailout by passing it through activated foam canisters that
cause copper to plate-out on the media surface. The effluent from these cartridges is nearly metal-free.
Spent gold baths are commonly electrowinned, although credits for gold content can also be obtained by shipping the
spent bath for off-site recovery.
Other spent electroplating fluids (tin, tin-lead, copper, nickel) are not produced in large quantities. Copper sulfate
baths may last for several years, and the timing of the dump is based solely on analysis. Similar bath lives are
common for nickel and tin-lead, making an electrowinning recovery strategy for these baths uncommon.
Restrictions. Solutions containing hydrochloric acid, or the chlorine ion in general, are usually not processed
using electrowinning, since electrolysis of these fluids can result in the evolution of chlorine gas. Fluoboric acid
electrolytes, such as tin-lead fluoborate, generally require platinized anodes, affecting the cost-effectiveness of
electrowinning such solutions. Solutions containing chelated metals, reducing agents, and stabilizers are more
difficult for direct application of electrowinning.
Nickel recovery using electrowinning is possible, but it requires close control of pH and is therefore performed less
frequently than for metals such as copper and gold.
Exhibit 5-16. Electrowinning Technology Data (1995 Survey)
Resp.
ID
959951
955099
965874
42751
44657
36930
37817
Application
Lead-bearing
rinses from
resist strip and
solder drag-out
Microetch on
electroless
Gold rinse
Microetch
Photo fixer
Black oxide
line microetch
bath
All baths high
in cu cone.
Year
Purch.
1986
1990
-
1992
1994
1992
1989
Equip.
Cost
($)
21000
0
0
15000
800
20000
6000
Install
Cost
($)
0
0
0
2000
30
1000
200
Labor
(hr/yr)
2080
0
0
500
24
60
250
Non-
Labor
($/yr)
0
0
0
0
12.56
1000
1000
Use
Code
1
1
1
2
1
1
1
Down
Time
5
1
2
20
0
0
2
Satisfied?
Yes
Yes
Yes
No
Yes
Yes
Yes
Future
Decision
1
1
1
3
1
1
3
106
-------
Exhibit 5-17. Electrowinning Technology Data (1997 Survey)
Shop
ID
14
22
Application
Copper peroxide etchants
Recovers the copper from ion exchange
Reasons
1,2,3,5,
6
3,5,6
Meet
Need?
Y
Y
Maint.
A
A
Overall
Satisfy?
no
response
5
Future
Decision
S
S
regenerant
22 Recover Copper from bath dumps and other 1,3,5,6 Y A 5 S
sources that do not go to ion exchange
34 Microetches, rack stripper, ion exchange 1,3,5,6 Y L 5 S
regenerant
29 Cu IX regenerate, Pb IX regenerate, chelated 1,3,5 Y L 5 S
Cu regenerate, persulfate etches, and Ni
sulfates.
37 Spent cleaner\conditioner baths 1,3,6 Y A 5 S
54 All spent copper laden baths 1,6 Y M 5 S
44 Drag out rinses following copper plate 1,3,6 Y A 4 S
53 Sulfuric acid rinses, some micro-etches 1,3,5,6 Y A 2 S
56 Concentrated wastes from gold plating and 1,5,6 Y A 4 S
silver artwork developing
45 All copper bearing drag-out and spent baths 1,3,6 P A 4 S
are processed down to a low Cu cone. Using
EW and then go through a copper specific
resin for polishing to less than 2 mg/1 Cu.
Adjusted then sent to the local POTW. The
technology is sound, but our system needs a
few enhancements to make it more
productive.
51 Spent copper baths, spent fixer baths 1,3,6 Y A 3 S
36 Plating baths. Cost of running is greater 1,3 P M 2 D
than benefits much of the time.
46 Ion exchange regenerant 1, 6 P M 3 S
Use codes: 1 = in use; 2 = not in use; 3 = not in use, future use expected
Future decision codes: (in response to survey question, "indicate a future course of action should you be required to fill a similar need"):
1 = buy the same technology from the same vendor; 2 = purchase same technology from different vendor; 3 = purchase different technology;
4 = do nothing.
Reasons technology was purchased:
1 = to meet or help meet effluent limits
2 = to reduce process chemical purchases
3 =to reduce quantity of waste shipments off-site
4 = to increase production rate
5 = to reduce worker exposure to hazardous waste
6 = to recover a metal for resale
7 = to recover a chemical for reuse
Has the technology met the need for which it was purchased?
Y = yes
N = no
P = partially
Rate the level of maintenance required:
A = about what was expected
M = more than expected
L = less than expected
Overall satisfaction with the technology:
1 = very dissatisfied
5 = very satisfied
To fulfill a similar need in the future, which technology would
you purchase?
S = same technology
D = different technology
S = none
5.3.3 Evaporation
Evaporators are commonly used in the metal finishing industry for the recovery of plating solutions. However, this
technology is not widely applied by the PWB industry. Only 3.5% of the survey respondents indicated that they use
evaporative equipment. One respondent uses evaporative recovery to recover drag-out of their electroplating copper
solution (ID # 13 3 000). One respondent uses evaporation to reduce their volume of wastewater and achieve zero
discharge (ID #36). However, there is no recovery of chemicals or water. Another respondent uses evaporative
distillation to recover gamma butyrolactone (solvent) on their solder mask line.
107
-------
There are two primary types of evaporators: atmospheric and vacuum evaporators. Both are employed to concentrate
dissolved chemicals into a smaller volume by removing water. The concentrated dissolved chemicals are either
recovered or discarded off-site. An atmospheric evaporator is a relatively simple device that evaporates water at
atmospheric pressure and releases the moisture to the environment. A vacuum evaporator is a distilling device that
vaporizes water at low temperatures when placed under a vacuum. Vaporized waters are typically condensed and
reused. Additional details of the two types of evaporators are presented in this section.
5.3.3.1 Atmospheric Evaporators
Most commercial atmospheric evaporator units consist of a pump to move the solution, a blower to move the air, a
heat source, an evaporation chamber, and a mist eliminator. The evaporation chamber is where the solution and air
are mixed and is usually filled with packing material or finned panels to increase the air to water interface. The mist
eliminator removes any entrained liquid from the exit air stream. In operation, the temperature of the solution being
evaporated is elevated, and the heated solution is introduced into the evaporation compartment. Air from the room is
then blown through the compartment, where it accepts the water vapor and is then vented out of the chamber.
Commercial units are advertised to have evaporation rates of 10 to 90 gph, depending on the size of the unit and
operating conditions (e.g. solution temperature). Often actual evaporation rates are considerably less because the
atmospheric conditions within PWB manufacturing facilities do not match the ideal conditions under which the
manufacturers rate their systems. To meet higher evaporative requirements, it is feasible to utilize multiple
atmospheric evaporators in series. However, the use of atmospheric evaporators is generally limited by energy costs
to applications where the required evaporation rate is 50 gph or less.
Most commercial atmospheric evaporator units have the same principals of operation. To achieve chemical
recovery, solution from a heated plating tank is fed to and concentrated by the evaporator and returned to the plating
tank. This approach reduces the volume of solution in the plating tank, thereby "making room" for the recovery
rinse water/drag-out to be added to the plating bath. Often two or more recovery rinse stations are used to minimize
the overall rinse water requirements of the process and increase the recovery rate of plating chemicals. Less
frequently, atmospheric evaporation is applied to ambient or low temperature baths. In this case, the recovery rinse
water may be fed to the evaporator from a heated transfer tank, which increases the overall evaporative capacity of the
system. The latter application is often restricted by the maximum temperature that can be applied to the solution,
since heat sensitive components of the bath could be destroyed.
5.3.3.2 Vacuum Evaporators
Vacuum evaporators are applied to the recovery of a wide range of process solutions within the metal finishing
industry, but are not widely used by PWB manufacturers. They are especially applicable in situations where
atmospheric evaporators are either technically or economically impractical. This includes: (1) the recovery of heat
sensitive chemicals (e.g., cyanide plating baths); (2) the recovery of chemicals that are sensitive to air oxidation
(e.g., cyanide plating baths or the stannous tin bath); (3) low or ambient temperature plating solutions where there is
no appreciable surface evaporation; (4) the recovery of solutions that contain volatile components; and/or (5) where
high evaporation rates (e.g., >20 to 40 gph) are necessary to achieve recovery, and atmospheric evaporators become
too expensive (i.e., energy cost) to operate (ref. 299).
Vacuum evaporators depend on the fact that water, when introduced into a vacuum, tends to boil off, or vaporize.
The rate of vaporization is directly related to the level of the vacuum and the temperature of the solution. In
operation, heated solution is introduced into the vacuum chamber, the boiling point of the solution is reduced by the
vacuum and the resultant vapor (distilled water) is removed from the chamber. The vapor can be either discharged or
condensed for return to the process (e.g., as rinse water).
5.3.4 Other Recovery Processes
5.3.4.1 Silver Recovery from Photoplotting Film
Silver is used as the light-sensitive material that forms the image on photoplotting film. For the ordinary circuit,
almost 80% of the silver emulsion is developed into the chemistry and can be recovered by one of two methods.
With metallic replacement, the solution can be passed through a steel wool cartridge, where the iron in the steel
reacts with the silver and replaces it. A silver sludge settles to the bottom of the cartridge.
108
-------
The scrap film has the remaining amount of silver that is not developed. This film can be collected in bins and sent
out to a commercial reclamation facility. This process is not done on-site because of the complexity of the process.
5.3.4.2 Removal of Copper from Electroless Copper Baths
Copper contained in the spent electroless copper plating solution is difficult to recover using electrowinning, but can
be recovered for off-site recycle using a proprietary deposition technology or sodium borohydride reduction. With the
deposition technology, the copper solution is passed through canisters or modules that contain a sponge-like material
deposited with copper and palladium (ref. 36). The copper in the spent solution is autocatalytically reduced and
retained in the unit. One survey respondent indicted that they use this technology (ID #993585) and that they were
very satisfied with its performance.
With sodium borohydride reduction, a 0.5 to 1% by volume NaBH4 solution is added to a tank containing the spent
electroless copper bath. This causes the copper to precipitate and it can be removed by decanting. This process
generates a significant quantity of flammable hydrogen gas and therefore must be conducted under controlled
conditions (e.g., ventilated tank) (ref. 36).
5.4 Off-Site Recycling
Off-site recycling is a commonly used alternative for PWB manufacturers as a means of managing spent etchant
solutions and wastewater treatment sludges. Widespread implementation of this option reduces the quantity of
wastes being disposed of in landfills. The PWB survey gathered information regarding the types of wastes sent to
off-site recycling firms, quantities, destinations, and associated costs. These data are presented and discussed in this
section.
A summary of data related to off-site recycling of spent process solutions, including etchants, is presented in Exhibit
5-18. Nearly all respondents reported using off-site recycling for disposing of spent process baths. A summary of
data related to off-site recycling and disposal of wastewater treatment sludges is presented in Exhibit 5-19. Nearly
ninety percent (90%) of those who provided data concerning the destination of their sludges indicated that they ship
the sludges to recycling facilities rather than landfills.
5.4.1 Off-site Recycling of Spent Process Baths
By far, the most commonly reported spent process fluid that is sent off-site for recycling is spent etchant,
particularly spent ammoniacal etchant. Spent ammoniacal etchant is created at a rate of roughly 1 gallon per 30
surface square feet of inner- and outer-layer panels. On-site regeneration of ammoniacal etchant is not widespread.
One respondent reported installing solvent extraction technology for the purpose of on-site regeneration of
ammoniacal etchant and copper recovery. The reason that spent etchant is a popular waste for off-site recycling is
due mostly to its high copper concentration, which is typically 150 g/1 Cu (i.e., 15% Cu). Etchant that is sent off-
site is processed to recover the copper and regenerate the etchant for reuse. Eighty-three percent (83%) of the
respondents who completed the off-site recycling section of the survey reported that they send spent ammoniacal
etchant off-site for recycling. Costs associated with ammoniacal etchant recycling were provided in several different
types of units and varied widely, but in general, it was clear that etchant recycling represented a major portion of
overall recycling costs. One respondent (ID# 462800) reported an income from off-site recycling of their spent
cupric chloride etchant ($26,000 annually).
Waste products other than etchant are less frequently sent off-site for recycling by the survey respondents. The next
most commonly shipped waste product is tin and/or tin-lead stripping solutions. These solutions are listed by 20%
of the respondents who completed this section of the survey form. Like etchant, spent stripping solutions have a
high metal concentration that makes them viable candidates for recycling. Also, stripping solutions are generated in
relatively high volumes, furthering the economics of off-site recycling. For example, ID# 44486 reported shipping
49,911 Ib of tin strip and ID# T2 reported shipping 9,000 Ib of tin stripper. In comparison, these quantities are
equivalent to approximately 20% to 30% of their etchant volume sent off-site.
Flux, solder dross from the hot-air-solder-level process, and other lead-bearing solutions are shipped off-site for
recycling by 20% of the respondents. However, the quantities of these materials that are shipped are relatively small.
One exception was ID# 41739, who reported shipping 20,000 pounds of solder bath to an off-site recovery facility.
Tin-lead plating baths generally have a long life-span (several years) and disposal of the solution is an unusual event.
For this reason, it is believed that with this particular case, shipment was a one-time event. For example, the
facility may have replaced their tin-lead plating bath with a tin-only solution or needed to dispose of a bath due to
irreversible contamination.
109
-------
Micro-etchants are shipped off-site for recovery by only 8% of the respondents. Spent micro-etchants typically
contain copper concentrations of 15 to 30 g/1 Cu (i.e., 1.5 to 3.0% Cu). Other respondents reported electrowinning
these solutions on-site, or treating them with conventional precipitation.
Gold- and silver-bearing wastes are sent off-site by 15% of the respondents. Gold electroplating baths (usually gold
cyanide) have a long life-span, and not surprisingly, the reported volumes were all 100 gallons or less. Solutions
containing gold may include spent gold electroplating bath, or the contents of drip or drag-out tanks on the gold
plating line. Silver is present in film developing fluids that may be reclaimed on-site (electrowinned), shipped off-
site for metal reclamation, or combined with other waste streams and treated conventionally.
Ten percent (10%) of the respondents indicated that spent rack stripping solution is shipped off-site. Plating racks
are typically coated with a non-conductive substance to prevent electroplating from occurring on the rack surface
itself. Due to use, this coating may degrade and plating can accumulate on the rack, especially near the clamps and
contact points. This unwanted copper deposit is removed in a stripping solution such as dilute nitric acid. The
volume of spent stripping solution can be significant. Respondent T3 shipped 1,000 gallons of nitric acid rack
stripper off-site at a cost of more than $5 per gallon. By comparison, this volume is equivalent to 12.5% of the etch
volume shipped by the same respondent.
5.4.2 Wastewater Treatment Sludge
A very high percentage of respondents (88% of those providing data) indicated that they send their wastewater
treatment sludge to off-site disposal facilities rather than to landfills. This percentage appears to be particularly high
when compared to the 31% of plating facilities that use this method for disposal (based on results presented in ref.
3).
The average and median unit costs for off-site recovery of sludge are $0.48/lb and $0.21/lb, respectively. In general,
the lower costs experienced by some respondents compared to others were due to larger-size shipments and shorter
distances to the recycling sites, both of which reduce transportation costs. However, in some cases, differences in
unit costs may be the result of other factors. For example, ID#'s 133000 and 953880 ship similar quantities of
sludge the same distance to the same recycling company.6 The unit cost of the off-site recycling for the two PWB
manufacturers varies significantly ($0.17/lb vs $0.40/lb). One difference between the sludges shipped by these
respondents is the percent solids. ID# 133000 is shipping a much dryer sludge (60% solids compared to 35% solids
for ID# 953880). The dryer sludge will have a greater recovery value. By drying sludges PWB manufacturers can
also reduce transportation costs, since drying reduces the volume of the sludge. The sludge drying technology and its
impact on sludge volume are discussed in reference 1. One facility reported a reduction of sludge quantity from
418,441 Ibs/yrto 110,116 Ib./yrby installing a sludge dryer (ref. A).
A discussion of off-site recycling, including descriptions of processes used by recycling companies, is presented in
reference 1.
This particular recycling company operates recycling facilities in both Arizona and Pennsylvania. Due to the confidentiality procedures
employed during this project, it is not known if the two PWB manufacturers discussed send their waste to the same site.
110
-------
Exhibit 5-18. Off-Site Recycling of Spent Process Fluids
Resp.
ID
279
279
3023
3470
3470
6710
6710
25503
29710
29710
29710
29710
32482
33089
33089
36930
36930
37817
37817
37817
37817
41739
41739
41739
42692
42751
42751
43694
43841
43841
43841
44486
44486
44486
44486
44657
133000
237900
237900
237900
237900
358000
358000
462800
462800
462800
462800
502100
Waste
Description
cupric chloride
cupric chloride
ammoniacal
ammonia etch
gold plate bath
D001/D002
D002
cupric chloride
D002/D004
F005/D001
D001
D001
gold plating
ammoniacal etchant
tin/lead
etchant
microetch
flux
etchant
resins
acid sludge
D002
F007
D008
ammoniacal etchant
cupric chloride
ammoniacal etchant
ammoniacal etchant
D002
D001
class 55
NH etchant
peroxide/sulfuric
flux
acid Ni
D002/D008
etchant
ammoniacal etchant
acid
acid
acid
etchant
tin stripper
spent copper
acid rinse water
copper sludge
spent flux
sludge
Source
etch
etch rinses
etch
etch
plate
sulfuric/peroxide
ammoniacal etch
etch
etch
paint
solder wave
HASL
gold plate
etch
solder strip
etch
etching/cleaning
hot air leveler
etch
cadines
waste catch drains
ammoniacal etch
gold bath
solder bath
etch
inner layer etch
outer layer etch
etch
etch
oil/glycol
board scrap
Cu etch
tin strip
HASL
Ni plate
etch
etch
etch
nitric solder strip
solder strip
plating
etch
tin stripper
etch
etch
etch/microetch
hot air leveling
etch
Quantity
(per year)
11,000 gal
6,000 gal
199,450 gal
18,000 gal
60 gal
440 gal
8,000 gal
2,000 gal
98,000
1,536
2,721
1,482
100 j
60,000
6,000
60,000 |
6,000 i
200 {
23,000 i
15
200 j
17,000 |
25 i
20,000
lb
Ib
lb
lb
ial
lb
lb
?al
pd
?al
pd
ft3
ial
?al
?al
lb
52,883 gal
83,700 |
32,050 {
35,000 |
13,700 {
220 {
38,000
255,370
49,911
32,292
195
6,300 |
40,000 i
50,000 |
2,000 j
1,000 |
1,400 j
70,000 |
1,800 j
1,419,393
349,020
12,854
4,400
1,000 |
?al
?al
?al
?al
?al
lb
lb
lb
lb
lb
?al
pd
?al
pd
?al
pd
pd
ial
lb
lb
lb
lb
pd
Available
Cost
Data
5.54 $/gal
5.55 $/gal
0.50 $/gal
nr
nr
1.96 $/gal
1.52 $/gal
0.25 $/gal
nr
nr
nr
nr
nr
0.29 $/lb.
0.40 $/lb.
4,000 $/yr
9,600 $/yr
230 $/drum
nr
160 $/drum
230 $/drum
18,060 $/yr
3,000 $/yr
nr
nr
nr
nr
nr
38,000 $/yr
2,000 $/yr
7,000 $/yr
nr
18,135 $/yr
16,000 $/yr
683 $/yr
nr
0.20 $/gal
0.10$/gal
4.60 $/gal
5.00 $/gal
4.80 $/gal
0.11$/gal
3.18$/gal
26,000 $/yr'
0.05 $/lb
0.00 $/lb
0.91 $/lb
nr
Distance to
Name of Recycle
Recycle Company
Company (miles)
Phibro Tech
Phibro Tech
Macdermid
nr
nr
US Filter Rec.
Phibro Tech
Old Bridge
Macdermid
Safety-Kleen
Safety-Kleen
Safety-Kleen
Advanced Chem
US Filter Rec.
US Filter Rec.
Phibro Tech
nr
Entech Managt.
Dexter
Entech Managt.
Entech Managt.
Phibro Tech
Technic
Alpha Metals
Old Bridge
Norris Environ.
Phibro Tech
S. Cal Chem
Phibro Tech
Safety Kleen
SIMCO
Phibro Tech
Phibro Tech
Hydrite
PhibroTech
HubbardHall
Macdermid
S. Cal Chem
Norris
Norris
Norris
Old Bridge, NJ
Republic
Phibro Tech
Envirite
Phibro Tech
AKA Industrial
nr
40
40
75
nr
nr
40
350
3,300
768
100
100
100
120
225
225
400
nr
150
nr
150
150
400
800
800
400
1,000
1,200
30
500
1,500
1,000
200
200
90
200
nr
150
370
370
370
370
600
200
40
30
40
55
nr
111
-------
946587
947745
947745
953880
955099
955099
955099
955703
955703
955703
955703
959951
959951
959951
965874
36930A
Tl
Tl
T2
T2
T2
T2
T3
T3
D002
etchant
stripper
D002
etchant
CuSO4
solder
etchant
solder oil
tin strip
flux
gold
silver
ammonia
etchant
etchant
gold
ammoniacal etch
etchant
etchant
tin strip
nitric acid
etchant
nitric acid
Cu sulfate
plating
etching
rack strip
etch
ammoniacal etch
plating
HASL
etch
HASL
tin strip
HASL
tab plate
film processor
etch
etch
etching
deep gold
inner/outer etch
Cu chloride etch
ammoniacal etch
tin strip
rack strip
etch
rack strip
7,500 gal
3,960 gal
1,200 Ib
15,000 gal
65,000 gal
12,000 gal
22,000 Ib
45,000 gal
1,300 gal
5,000 gal
800 gal
50 gal
250 gal
15,840 gal
15,800 gal
4,200 gal
nr
nr
18,500 gal
33,000 gal
9,000 gal
660 gal
8,000 gal
1,000 gal
0.12$/lb
0.06 $/lb
0.29 $/lb
nr
nr
2.00 $/lb
l.lOS/lb1
0.18$/lb
0.40 $/lb
0.37 $/lb
0.40 $/lb
nr
nr
nr
0.30 $/gal
nr
nr
nr
3.68 $/gal
nr
3.45 $/gal
4.09 $/gal
nr
5.46 $/gal
Learonal
Phibro Tech
Encycle
Phibro Tech
Macdermid
Phibro Tech
Dexter
Phibro Tech
DK
Phibro Tech
Romic
Electrochemicals
Electrochemicals
Phibro Tech
Phibro Tech
Phibro Tech
Learonal
Phibro Tech
Phibro Tech
Phibro Tech
Encycle, TX
Encycle, TX
S. Cal Chemical
Great West. Chem
980
250
250
600
280
400
50
25
20
25
70
nr
nr
nr
600
400
nr
nr
7
7
450
450
10
10
1 Income from recycled process fluid.
nr = no response
112
-------
Exhibit 5-19. Off-Site Recycling/Disposal of Wastewater Treatment Sludge
Resp.
ID
279
29710
31838
36930
43694
237900
358000
955703
3470
965874
25503
42692
273701
36930A
33089
502100
959951
T2
44486
462800
Tl
41739
107300
740500
55595
42751
133000
947745
3023
946587
955099
32482
44657
953880
43841
6710
37817
T3
Quantity
dbs)
nr
nr
nr
nr
nr
nr
nr
nr
10,000
5,000
1,200
200,000
300
181
80,000
3,000
33,190
58,000
nr
12,854
260,000
42,000
400,000
1,700,000
140,000
250,000
160,000
9,600
320,000
308,000
220,000
14,000
8,200
120,000
10,000
18,000
1,000
10,000
Percent
Solids
(%)
nr
nr
nr
nr
nr
nr
nr
nr
75
15
95
40
50
50
35
75
50
25
nr
98
80
65
60
36
40
48
60
80
41
53
48
65
30
35
26
nr
95
80
Recycle
or
Dispose
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
unknown
unknown
D
D
D
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
Cost
($/yr)2
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
720
85,000
200
nr
48,000
nr
nr
nr
nr
0
35,000
6,000
60,000
275,000
22,880
39,375
27,000
1,875
68,000
63,150
50,000
4,000
3,000
48,000
7,800
25,000
1,500
20,000
Cost
($/lb)2
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
0.60
0.43
0.67
nr
0.60
nr
nr
nr
nr
0
0.13
0.14
0.15
0.16
0.16
0.16
0.17
0.20
0.21
0.21
0.23
0.29
0.37
0.40
0.78
1.39
1.50
2.00
Company
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
Norris Env
S. Water Treat. Co
US Filter Rec.
US Filter Rec.
US Filter Rec.
nr
Cyprus Miami
Encycle, TX
Foreman Metals
Phibro Tech
Encycle, TX
Encycle, TX
WRC
WRC
Envirite
WRC
WRC
Encycle, TX
WRC
WRC
WRC
WRC
WRC
WRC
WRC
WRC
NE Chemical Co
Encycle, TX
Distance
to Site
(miles)
nr
nr
nr
nr
nr
nr
nr
nr
nr
nr
30
300
nr
30
225
nr
nr
450
20
40
1,500
600
222
1,500
400
nr
300
250
375
1,000
500
nr
750
300
500
850
400
1,800
1 Unit is ft
2 Some variation in costs among respondents may be due to inclusion or omission of analytical fees (sometimes referred to as material profile
fees).
nr = no response
113
-------
6.0 End-of-Pipe Treatment
6.1 General
End-of-pipe treatment is, by definition, not pollution prevention. However, it is an important aspect of pollution
control and it sometimes competes financially with pollution prevention options when facilities are developing
pollution control strategies. To make informed decisions about implementing pollution prevention alternatives that
include consideration of all applicable costs and potential savings requires accurate data. Therefore, the topic of waste
treatment was included in the PWB survey project so that the true costs of treatment could be examined. The
applicable portion of the survey form requested respondents to describe the type of waste treatment system currently
in use at their facilities and to provide operating and cost data. These data are summarized and discussed in this
section.
6.2 Wastewater Characterization
Data that characterize the respondent's raw wastewater from their PWB processes are presented in Exhibit 6-1. The
data indicate that copper and lead are the most abundant of the regulated metals. Copper was reported to be present
by all respondents. Copper concentrations in the raw wastewaters ranged from 0.4 mg/1 to greater than 100 mg/1.
Factors affecting the copper concentration of raw wastewater may include: the effectiveness of rinse water controls
(which will determine the level of dilution); whether or not process solutions that have relatively high copper
concentrations (e.g., spent acids and micro-etches) are commingled directly with rinse water; the effectiveness of drag-
out reduction and recovery; and the presence of upstream recovery/recycle technologies, such as ion exchange and
electrowinning.
Sixty-two percent (62%) of the facilities that provided raw wastewater data reported the presence of lead.
Concentrations of lead ranged from less than 1 mg/1 to 20 mg/1. The primary sources of lead in a PWB
manufacturing process are drag-out from the tin-lead electroplating and stripping operations. Lead may also be
introduced in small quantities from reflow or solder-leveling operations. Respondents not reporting lead in their raw
wastewater may remove lead with a recovery/recycle technology (e.g., ion exchange) upstream, or may not perform
lead plating (or, therefore, stripping). Also, possibly due to a higher sensitivity to lead discharges than some other
metals, more aggressive drag-out reduction and recovery methods may be practiced for lead sources.
Forty-eight percent (48%) of the facilities that provided raw wastewater data reported the presence of nickel. Nickel
concentrations ranged from less than 1 mg/1 to 7.5 mg/1. The most common source of nickel in the raw wastewater
is nickel electroplating or electroless nickel plating, which serve as an undercoat for gold. Another common process
is the electrolytic nickel-gold plating of the connector edge ("tab plating") of certain PWBs (e.g., PC expansion
cards). Wastewater flows generated from these operations may be small in comparison to copper or tin-lead plating
operations, and drag-out from typical nickel-gold tab electroplating process baths is generally low. Not all PWBs
require tab nickel-gold plating, and few require full nickel-gold. For tab plating, a small portion of the board is
actually immersed in the bath, thereby limiting dragout. Respondents not reporting nickel in their wastestream may
perform little or no nickel plating, or they may aggressively recover nickel drag-out.
Sixteen percent (16%) of the facilities that provided raw wastewater data reported the presence of silver. Only one
respondent reported silver in concentrations greater than 1 mg/1. Silver is present in the photographic developer and
fix solutions (and associated rinses) required to create film images. Silver is also used at some PWB facilities for
electroplating, but less commonly than for photographic purposes.
114
-------
Exhibit 6-1. Discharge Limitations and Compliance Difficulties
Respondent
ID
40CFR413
40 CFR 433
6710
36930A
36930
273701
358000
955703
33089
107300
502100
44657
43694
29710
T3
Tl
955099
37817
959951
947745
95880
42751
32482
44486
42692
41739
43841
T2
3470
740500
279
3023
237900
133000
25503
946587
462800
31838
55595
965874
Cu
max
mg/1
4.5
3.38
4.50
2.59
4.34
3.38
2.00
3.00
3.38
2.00
1.00
3.00
3.00
0.49
2.70
1.00
1.50
5.00
3.22
3.38
0.25
3.00
3.38
4.50
4.50
4.00
4.30
2.20
1.50
3.38
3.00
1.50
2.70
1.50
3.00
3.40
2.90
3.00
nr
3.38
Cu
avg
mg/1
2.7
2.07
0.37
1.59
2.60
2.07
1.50
2.07
2.07
1.00
1.50
2.07
2.07
0.41
2.70
0.03
-
3.50
0.45
2.07
-
2.07
2.07
2.70
2.70
0.40
2.60
2.07
2.07
1.70
2.02
-
1.00
-
2.07
-
1.91
1.50
nr
2.07
Pb
max
mg/1
0.6
0.69
0.60
0.53
0.58
0.69
-
0.69
0.69
0.30
-
0.60
0.69
0.43
0.40
0.20
0.20
1.00
0.60
0.69
0.19
0.69
0.69
0.60
0.60
0.60
0.57
0.69
0.20
0.69
-
0.20
0.40
0.34
0.69
0.50
0.39
0.69
nr
0.69
Pb
avg
mg/1
0.4
0.43
0.10
0.33
0.39
0.43
-
0.43
0.43
0.10
-
0.40
0.43
0.27
0.40
0.05
-
0.25
0.11
0.43
-
0.43
0.43
0.40
0.40
0.30
0.38
0.43
0.23
0.40
-
-
0.40
-
0.43
-
0.26
0.43
nr
0.43
Ni
max
mg/1
4.1
3.98
4.10
3.05
3.95
3.98
-
3.98
3.98
1.30
-
2.20
3.98
2.50
2.60
1.00
1.00
-
2.91
3.98
0.60
2.50
3.98
4.10
4.10
4.00
0.72
3.00
1.00
3.98
-
1.00
2.60
4.10
3.98
2.20
2.64
3.00
nr
3.98
Ni
avg
mg/1
2.6
2.38
0.09
1.83
2.91
2.38
-
2.38
2.38
1.00
-
-
2.38
1.50
2.60
0.04
-
-
0.43
2.38
-
2.38
2.38
2.60
2.60
0.50
0.23
2.38
2.38
1.60
-
-
0.25
-
2.38
-
1.69
1.50
nr
2.38
Ag
max
mg/1
1.2
0.43
1.20
0.33
1.16
0.43
-
0.43
0.43
-
-
0.43
0.43
0.02
0.70
0.50
2.00
-
0.85
0.43
0.13
1.00
0.43
5.80
-
1.00
0.03
0.43
0.43
0.43
-
2.00
0.70
0.23
0.43
0.80
-
0.43
nr
0.43
Ag
avg
mg/1
0.7
0.24
0.01
0.18
0.67
0.24
-
0.24
0.24
-
-
0.24
0.24
0.02
0.70
0.01
-
-
0.12
0.24
-
-
0.24
-
1.90
-
0.01
0.24
0.24
0.24
-
-
0.70
-
0.24
-
-
0.24
nr
0.24
CN
max
mg/1
1.9
1.20
1.90
0.92
1.83
1.20
-
1.20
1.20
-
-
1.20
1.20
0.76
1.00
-
1.00
-
1.90
1.20
0.74
1.20
1.20
1.90
1.00
1.00
1.82
1.00
0.50
1.20
-
0.50
0.50
0.60
1.20
0.40
1.23
0.80
nr
1.20
CN
avg
mg/1
1.0
0.65
0.01
0.50
0.96
-
-
0.65
0.65
-
-
0.65
0.65
0.41
-
-
-
-
0.17
0.65
-
0.65
0.65
1.00
-
0.01
0.96
0.65
0.65
0.65
-
-
0.50
-
0.65
-
0.65
0.40
nr
0.65
TTO
max
mg/1
2.13
2.13
2.13
1.63
2.05
-
-
0.58
2.13
2.13
-
2.13
0.58
1.34
2.13
2.35
5.00
-
2.13
2.13
0.74
2.13
-
1.30
2.13
-
2.13
2.13
2.13
2.13
-
1.00
2.13
2.13
0.58
-
1.40
2.13
nr
2.13
TTO
avg
mg/1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.00
-
-
-
-
-
-
-
-
2.13
-
-
-
-
-
-
-
-
-
-
-
-
-
nr
-
Bold type indicates compliance difficulty with discharge parameter.
nr = no response
40 CFR 413 maximum is based on a 4 day average concentration.
40 CFR 433 maximum is based on a monthly average concentration.
Total toxic organics (TTO) were reported in raw wastewaterby 20% of the respondents. The primary sources of
toxic organics are solder mask ink solvents and screen cleaners, certain film strippers, phototool cleaners, and tape
residue removing solvents.
6.3 Types of Processes/Systems Employed
Exhibit 6-2 summarizes the respondents' wastewater treatment equipment purchase data. The primary purpose of the
wastewater treatment systems employed is the removal of dissolved metals. This is accomplished by the respondents
115
-------
through installation of conventional metals precipitation systems,7 ion exchange-based metals removal systems,
combined precipitation/ion exchange systems, and aluminum chip reactor systems. The most common type is
conventional metals precipitation systems, which includes precipitation units followed by either clarifiers or
membrane filters for solids separation. Fifty-eight percent (58%) of the respondents reported having conventional
metals precipitation systems installed. Polishing filters are also commonly employed following precipitation/solids
separation. The use of clarifiers is the predominant method for separation of precipitated solids from the wastewater
(only 12.1% of the respondents with conventional precipitation technology reported using membrane filters).
Several respondents use reverse osmosis to further process the wastewater and a portion of the treated water is reused
for rinsing.
Thirty percent (30%) of the respondents reported using ion exchange as their basic waste treatment technology and
another 6% used ion exchange in conjunction with conventional metals precipitation units. Thirty-six percent (36%)
of the ion exchange systems included electrowinning. The use of ion exchange as a waste treatment technology is
more widespread in the PWB industry than in the plating industry, where it is found in approximately 6% of plating
shops (ref. 1). One reason ion exchange is more common as an end-of-pipe technology for PWB facilities is the
limited number of regulated ionic species present in PWB wastewater. For most shops, copper, lead, and nickel are
the only metal ions present in significant concentrations, all of which are amenable to ion exchange. Furthermore,
these metals are also easily electrowinned from ion exchange regeneration solutions, which makes the ion
exchange/electrowinning combination an effective metal recovery system for PWB shops. Facilities using ion
exchange tend to be small- to medium-size with the median sales level being $7.5 million, compared to $14.5
million for all respondents.
Six percent of the respondents employ an aluminum bed reactor system as their primary end-of-pipe treatment. With
this technology, the wastewater pH is lowered to approximately pH 3.2 and it flows through an aluminum chip bed.
Copper present in the wastewater is exchanged for aluminum on the surface of the chips. Eventually, the chips are
removed and sent off-site for disposal or recovery. This technology does not effectively remove chelated copper or
other regulated metals such as nickel or lead.
Column 8 of Exhibit 6-2 shows the satisfaction ratings given by the respondents for their treatment system or
system component. The ratings are based on a scale of 1 to 5, with 1 being a low level of satisfaction and 5 being a
high level of satisfaction.
Column 9 of Exhibit 6-2 indicates if the respondent reported that a failure, malfunction, or other event associated
with the end-of-pipe system resulted in a permit exceedance. Thirty-two percent (32%) of the respondents indicated
that they did experience a permit exceedance due to their system. Some respondents reported the nature of the permit
exceedance; these included: pH (7.9% of all respondents), Pb (10.5% of all respondents), Cu (10.5% of all
respondents), and Ag (2.6% of all respondents).
Exhibit 6-2. Wastewater Treatment Equipment Data
Resp.
ID
3023
3023
3023
3023
3470
6710
25503
29710
29710
29710
29710
32482
33089
System
Initial System
Upgrade 1
Upgrade 2
Upgrade 3
Initial System
Initial System
Initial System
Initial System
Upgrade 1
Upgrade 2
Upgrade 3
Initial System
Initial System
Type of
System
(not in use)
ion exchange
precipitation/membrane
resist strip treatment
ion exchange
precipitation/clarifier
ion exchange
unknown
ion exchange-copper
ion exchange-nickel
ion exchange-copper
precipitation/clarifier
precipitation/clarifier
Flow
(gpm)
100
40
54
-
0.5
22
9
120
12
3
50
2
9
Year
Pur-
chased
1984
1992
1994
1995
1993
1987
1991
nr
1991
1992
1993
1986
1987
Cost
($)
250,000
553,000
125,000
60,000
25,000
50,000
45,000
nr
70,000
46,000
237,000
120,000
4,000
Manufacturer
Chemtronics
Memtek
Memtek
JCL Associates
none
JWI
Remco
Baker Bros
Bio Recovery
Bio Recovery
Kinetco
Lancy
various
Rating1
3
4
4
4
3
4
4
4
5
5
4
4
2
Permit
Exceed
Yes or
No2
Y
-
-
-
Y
N
N
Y
-
-
-
N
Y
Conventional treatment is a series of unit operations that is commonly installed for metals removal by facilities in the metal finishing and
PWB manufacturing industry sectors. Metals removal is accomplished using hydroxide precipitation followed by separation of the
precipitated metals.
116
-------
33089
33089
37817
37817
41739
41739
42692
42751
42751
42751
43694
43841
43841
43841
43841
44486
44657
55595
107300
107300
107300
133000
133000
133000
133000
237900
273701
358000
462800
740500
946587
946587
947747
947745
953880
955099
955099
955703
955703
965874
36930A
Tl
Tl
Tl
T2
T2
T2
T3
T3
T3
Upgrade 1
Upgrade 2
Initial System
Upgrade 1
Initial System
Upgrade 1
Initial System
Initial System
Upgrade 1
Upgrade 2
Initial System
Initial System
Upgrade 1
Upgrade 2
Upgrade 3
Initial System
Initial System
Initial System
Initial System
Upgrade 1
Upgrade 2
Initial System
Upgrade 1
Upgrade 2
Upgrade 3
Initial System
Initial System
Initial System
Initial System
Initial System
Initial System
Upgrade 1
Initial System
Upgrade 1
Initial System
Initial System
Upgrade 1
Initial System
Upgrade 1
Initial System
Initial System
Initial System
Upgrade 1
Upgrade 2
Initial System
Upgrade 1
Upgrade 2
Initial System
Upgrade 1
Upgrade 2
filter press
new tanks, repipe
ion exchange
electro winning
precipitation/membrane
pre/post-treat upgrade
ion exchange
precipitation/clarifier
polishing filter
filter press
ion exchange
precipitation/filtration
filter press
equalization pit
filter bags
precipitation
precipitation/clarifier
precipitation/filter press
precipitation/clarifier
sludge dryer
equalization tank
precipitation
sludge dryer
clarifier
rinse water pump
precipitation/clarifier
ion exchange/electrowin
ion exchange
ion exchange/
precipitation
precipitation/clarifier
precipitation
clarifier
precipitation
clarifier
precipitation/filtration
precipitation/clarifier
polishing system
electro winning
ion exchange
ion exchange/electrowin
ion exchange
precipitation/clarifier
sludge dryer
chemical tester
precipitation/clarifier
sludge dryer
air scrubber
precipitation/membrane
nr
nr
-
-
10
-
50
-
70
100
-
-
20
55
_
-
_
nr
6
15
250
-
_
175
-
-
_
73
10
30
103
300
60
-
30
-
30
83
_
-
70
20
40
135
_
_
40
-
-
30
_
-
1989
1994
1989
1989
1989
1993
1987
1986
1994
1994
1990
1983
1985
1991
1993
1990
1986
1976
1980
1992
1993
1984
1993
1993
1990
1984
1994
1991
1990
1981
1987
1994
nr
1989
1984
1981
1990
1989
1990
1993
1989
1980
1990
1992
1989
1993
1994
1984
1987
1991
12,000
6,000
50,000
6,000
300,000
250,000
250,000
nr
16,000
24,000
60,000
65,000
13,000
400,000
1,000
25,000
200,000
1,200,000
nr
83,000
43,000
362,000
40,000
40,000
4,500
300,000
40,000
nr
240,000
20,000
250,000
50,000
nr
30,000
125,000
nr
nr
nr
nr
65,000
201,000
1,200,000
60,000
7,000
25,000
20,000
11,000
75,000
25,000
10,000
JWI
various
Eastern Ind Wtr
Retec
Memtek
Gabel Contracting
NCA
Napco
Conrec
JWI
Remco
BMP
JWI
Generic
Generic
unknown
Andco
in house
Durion/Chemtronics
Fenton
Fedco
Manchester
JWI
Graver Water
Durco
Strangle
self
Lisle -Metrix Ltd
Kisco
various
Memtek
Parkson
nr
Atlantes
Memtek
_
Serfilco
Baker Bros
Remco
Smith Engineering
nr
Dickson
OSI
Acrison
Atlantes
Leatherwood
Fenton
Memtek
Memtek
in-house
4
5
3
4
4
5
3
4
3
4
4
1
5
3
3
5
3
4
5
3
5
4
5
4
5
2
5
4
4
4
2
3
nr
5
4
3
3
5
5
3
3
1
2
4
3
3
4
4
5
5
N
Y
N
N
N
Y
N
N
N
N
N
N
N
N
N
N
Y
Y
N
N
N
Y
N
N
Y
Y
1 Satisfaction rating is based on a scale of 1 to 5, with l=lowest and 5=highest.
2 Indicates if a failure, malfunction, or other event associated with the end-of-pipe system resulted in a permit exceedance (Y = yes, N = no).
nr = no response
6.4 End-of-Pipe Treatment Capital Costs
End-of-pipe wastewater treatment capital costs are included in Exhibit 6-2. Capital costs ranged from $1.2 million
(purchased in 1980 for a flow of 135 gpm) to $4,000 (purchased in 1987 for a 9 gpm flow). For ion exchange
systems, costs ranged from $250,000 (purchased in 1987 for a 70 gpm flow) to $40,000 (purchased in 1994 for a 10
gpm flow).
117
-------
6.5 End-of-Pipe Treatment Operation Costs
Exhibit 6-3 displays the major operating costs associated with end-of-pipe wastewater treatment. For the three
largest facilities (in terms of sales) that provided data, these costs represent 0.29%, 0.37% and 0.35% of sales. The
data indicate that waste treatment operating costs, as a percentage of annual sales, are higher for small shops than for
large shops. Fourteen percent (14%) of the facilities reporting had costs in excess of 2% of sales with the highest
being 3.1%. All of these facilities had sales near or below the median sales level for all respondents. The median
cost for waste treatment as a percentage of annual sales was 0.83%, and the average was 1.02%. A plot of waste
treatment operating costs as a percentage of sales volume for all respondents is presented is Exhibit 6-4.
Exhibit 6-3. Wastewater Treatment Operating Costs
Production
Respondent (board ft2
ID per year)
36930A
955099
55595
44486
955703
6710
947745
44657
29710
502100
32482
25503
36930
965874
953880
T3
33089
3470
43841
279
237900
273701
41739
959951
42692
43694
358000
42751
37817
T2
133000
Tl
740500
946587
3023
31838
462800
107300
Median:
Mean:
nr
nr
nr
nr
nr
15,000
40,000
42,358
57,000
60,000
75,000
90,000
96,000
175,000
180,000
200,000
200,000
240,000
250,000
250,000
273,000
280,000
300,000
320,000
360,000
500,000
500,000
540,000
540,000
600,000
600,000
936,000
1,800,000
1,900,000
2,300,000
3,000,000
3,750,000
5,000,000
Average
Wastewater
Flow
(gpd)
27,000
120,000
20,000
100,000
98,000
10,560
13,000
6,000
74,000
nr
31,000
5,000
nr
21,000
35,000
16,000
20,000
20,000
38,000
5,200
105,000
25,000
57,125
20,000
100,000
9,000
30,000
6,000
140,000
48,000
160,000
160,000
400,000
200,000
145,000
280,000
26,000
250,000
Chemical
Chemical Costs Sludge
Costs ($/Kgal Costs
($/yr) of Flow) ($/yr)
1,600
141,000
nr
nr
15,500
6,768
13,212
6,460
37,444
nr
40,492
2,200
13,100
10,456
96,092
24,185
13,320
4,755
26,674
nr
87,012
11,800
71,374
48,561
172,429
20,320
20,624
nr
6,320
96,250
167,000
167,764
98,000
108,840
124,029
nr
23,875
143,850
0.23
4.52
-
-
0.61
2.47
3.91
4.14
1.95
-
5.02
1.69
-
1.92
10.56
5.81
2.56
0.91
2.70
-
3.19
1.82
4.81
9.32
6.63
8.68
2.64
-
0.17
7.71
4.01
4.03
0.94
2.09
3.29
-
3.53
2.21
3.24
5.00
0
50,000
nr
nr
nr
25,000
1,875
3,000
nr
nr
4,000
720
nr
nr
48,000
20,000
48,000
0
7,800
nr
nr
200
6,000
nr
85,000
nr
nr
39,375
1,500
nr
27,000
35,000
275,000
63,150
68,000
nr
0
60,000
Routine
O&M
(hrs/yr)
100
20,000
nr
nr
7,000
1,040
780
550
3,552
1,200
2,200
2,200
800
10,000
1,760
600
2,000
2,000
5,100
nr
6,000
3,500
3,120
nr
4,992
4,000
2,500
10,000
550
3,000
6,500
2,080
nr
8,050
6,834
nr
4,000
9,275
Repair
Time
(hrs/yr)
40
300
nr
nr
30
30
50
30
nr
100
100
40
50
100
100
240
100
200
100
nr
425
700
100
nr
100
40
250
2,500
45
250
500
500
nr
208
342
nr
150
1,571
Costs
($/Kgal of
Flow)
0.53
15.88
-
-
4.75
17.42
8.15
11.64
4.72
-
9.80
28.09
-
29.66
18.90
13.65
17.85
7.26
11.38
-
6.72
11.54
8.46
-
12.84
34.58
7.93
-
0.46
11.62
7.19
5.80
3.59
5.69
7.95
-
12.74
5.64
9.13
11.41
nr = no response
118
-------
Exhibit 6-4. Waste Treatment System Operational Costs as a Percentage of Annual Sales
^ 2 50 -
M ^.J\>
JU
*c3
GO
rt 7 7S
13 z-z;?
•'>>••'. •••,,,
A *•
• z " " ',
20 40 60 80
Annual Sales (Millions of Dollars)
100
120
6.6 Sludge Generation and Disposal
Wastewater treatment sludge data were presented previously (Exhibit 5-19) and discussed in Section 5.4.2.5. The
three largest facilities (in terms of production) that provided data generated sludge solids at a rate of 0.048, 0.003,
and 0.057 lb/ft2 of production. The variation evidently comes, in part, from product mix. The facility generating
only 0.003 lb/ft2 is exclusively a single-sided PWB manufacturer, whereas the other two have a product mix of
double-sided and multilayer PWBs, for which additional process steps increase waste generation, including sludge
production. Eighty-eight percent (88%) of those responding indicated they recycle their wastewater treatment sludge.
Costs associated with the disposition of sludge ranged from $2.00/lb to $0.13/lb. Annual costs and unit costs are
given in Exhibit 5-19.
119
-------
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122
-------
Appendix A - Survey Data
Data for Exhibits 1-1, 1-2, 1-3, 1-4, 1-5, 1-6
Respondent ID
Facility Size
Employees
Ft2 Production
Sales
6,710
29,710
33,089
947,745
279
32,482
36930A
44,657
37,817
25,503
502,100
T3
965,874
273,701
959,951
3,470
953,880
41,739
43,841
44,486
42,692
T2
955,703
955,099
36,930
358,000
462,800
237,900
43,694
133,000
42,751
31,838
107,300
55,595
Tl
946,587
740,500
3,023
10
11
12
13
14
15
16
17
18
19
20
21
22
23
nr
nr
15,000
9,000
15,000
26,500
18,000
22,000
14,000
25,000
37,000
24,000
38,000
22,500
54,000
30,000
30,000
31,800
56,000
36,000
50,000
30,000
112,500
100,000
nr
36,000
55,000
300,000
42,000
125,000
50,000
300,000
200,000
109,000
70,000
120,000
600,000
190,000
36,000
20,000
16,788
250,000
4,000
36,000
17,000
30,000
17,500
25,000
55,000
15,000
45,000
51
500
30
28
40
35
38
40
45
40
65
50
105
80
85
100
100
130
115
150
150
175
150
250
200
0
210
178
450
366
380
480
350
420
550
500
1,000
830
125
55
37
450
40
350
65
120
450
55
215
36
158
15,000
57,000
200,000
40,000
250,000
75,000
nr
42,358
540,000
90,000
60,000
200,000
175,000
280,000
320,000
240,000
180,000
300,000
250,000
nr
360,000
600,000
nr
nr
96,000
500,000
3,750,000
273,000
500,000
600,000
540,000
3,000,000
5,000,000
nr
936,000
1,900,000
1,800,000
2,300,000
50,000
800,000
350,000
792,000
78,000
2,800,000
50,000
3,660,560
337,500
4,683,453
45,916,206
1,500,000
2,000,000
2,500,000
2,800,000
3,000,000
3,038,042
3,600,000
4,000,000
4,500,000
6,000,000
6,000,000
7,000,000
7,000,000
7,500,000
9,000,000
9,000,000
11,000,000
14,000,000
15,000,000
16,000,000
16,000,000
16,000,000
17,000,000
18,000,000
20,000,000
22,000,000
24,000,000
36,000,000
40,000,000
45,000,000
50,000,000
50,000,000
51,000,000
84,000,000
100,000,000
105,000,000
10,000,000
4,000,000
58,000,000
4,500,000
6,000,000
12,000,000
67,000,000
4,000,000
20,000,000
3,500,000
19,000,000
123
-------
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Resp.
ID
36930A
955,099
55,595
44,486
955,703
10
11
13
17
22
27
38
42
49
52
53
8
47
45,000
75,000
28,500
26,480
18,000
75,000
250,000
29,500
71,064
30,000
33,000
25,000
10,000
6,800
25,000
30,000
12,000
22,000
40,000
35,625
22,500
44,000
18,000
16,000
120,000
35,000
11,000
18,000
70,000
10,625
64,500
69,000
15,000
158
237
80
83
55
216
1,200
240
195
125
150
103
35
15
12
140
300
750
37
65
85
150
180
106
32
200
115
25
49
110
33
180
170
4
337,500
750,000
225,000
227,500
1,200
2,321,203
52,000
1,611,578
260,000
17,000
500,000
240,000
20,000
900,000
215,900
3,200,000
145,000
78,000
120,000
248,400
1,100
1,300,000
193,700
104,000
70,000
719,468
720,000
2,000,000
19,000,000
23,000,000
6,000,000
6,000,000
3,800,000
26,000,000
130,000,000
24,000,000
61,000,000
8,000,000
19,000,000
12,000,000
3,000,000
1,000,000
900,000
20,000,000
32,000,000
72,000,000
2,500,000
6,000,000
10,000,000
18,000,000
20,000,000
6,250,000
2,500,000
8,000,000
2,000,000
7,700,000
17,000,000
17,000,000
6,000,000
Data for Exhibits 1-7, 1-8
Rigid
1
100
100
100
100
10
10
1
10
10
1
10
10
1
90
10
90
10
Flex Combination Single
60
60
5
1
5
1
40
1
1
1
1
1
1
1
1
1
40
1
1
1
5
1
5
1
1
5
5
1
1
1
1
1
10
20
5
10
10
60
1
5
10
1
Double
60
40
60
30
10
30
28
1
53
50
10
90
30
40
10
45
40
5
4-6
20
30
30
60
65
48
25
1
25
25
80
1
20
1
28
45
10
42
8-12
18
24
5
10
20
20
39
1
12
5
5
1
40
1
50
5
10
42
14-20
2
1
1
1
5
1
7
1
1
1
1
1
1
1
10
1
10
10
More
than 20
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
20
1
124
-------
29
6,710
34
37
947,745
44,657
12
20
31
29,710
502,100
54
32,482
18
44
25,503
36,930
51
45
43
965,874
953,880
50
33,089
T3
40
26
28
3,470
36
46
43,841
279
33
237,900
273,701
41,739
959,951
23
24
15
42,692
358,000
43,694
35
37,817
42,751
T2
133,000
55
56
25
16
14
39
Tl
48
32
10
100
10
10
100
100
10
1
10
100
1
10
90
10
95
5
100
10
10
10
100
100
10
100
98
10
10
10
100
85
10
100
100
10
100
98
100
100
10
10
1
100
100
1
99
100
100
100
1
10
10
10
10
10
10
100
10
1
1
1
1
1
1
1
1
95
1
1
95
1
10
1
5
85
1
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
1
1
2
1
1
1
1
10
1
1
100
1
1
1
1
60
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
5
1
1
5
1
1
1
1
10
1
1
1
1
1
1
1
1
1
1
1
1
1
12
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
40
1
1
1
1
1
1
1
1
1
1
1
2
5
5
5
10
75
1
1
50
1
5
10
5
70
1
13
1
1
15
5
3
20
10
1
10
8
5
13
1
10
75
3
1
5
32
8
1
1
30
3
1
74
5
80
1
1
4
1
1
1
1
1
1
1
10
1
1
5
10
89
65
50
80
20
5
60
45
55
70
15
50
20
3
84
12
65
85
55
48
80
30
5
73
82
83
51
20
50
25
97
5
70
50
80
40
40
70
62
30
23
50
20
10
40
60
49
40
3
2
1
10
10
90
1
1
1
40
5
28
25
10
2
23
30
1
30
20
22
45
3
70
3
70
27
1
30
34
1
50
60
17
10
11
22
60
24
1
1
65
25
27
12
39
39
1
35
50
o
J
30
1
20
43
5
49
50
17
35
10
40
28
1
1
40
15
45
1
2
18
1
2
60
10
5
15
5
51
1
2
25
1
14
7
1
10
15
1
10
32
1
1
1
13
10
15
1
1
29
1
1
1
20
20
1
1
15
1
13
1
50
12
25
1
10
60
45
60
40
50
1
1
40
80
3
1
1
2
1
1
10
1
1
1
1
1
1
1
2
1
4
1
1
1
1
1
1
2
1
1
1
1
9
1
1
1
1
1
1
1
1
1
1
1
5
1
2
1
20
5
5
1
1
20
10
28
10
10
1
1
20
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
1
125
-------
740,500
946,587
57
3,023
30
19
31,838
41
21
462,800
107,300
100
100
10
100
10
10
100
10
10
100
100
1 1
1
1
1
1
1
1
1
1
1
1
L 1
1 1
10
1
1 1
1
1
1
10
100
10 8
L
0
L
L
0
5
80
65
1
70
30
82
30
50
1
1
5
20
20
1
15
50
14
40
42
1
1
1
1
5
1
15
9
3
30
8
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Respondent ID Feet
Data for Exhibit 1-9
Palladium- Carbon-
Electroless only based
Graphite- Electroless
based Ni
Other
36930A
955099
55595
44486
955703
13
37
15
38
36
54
51
41
6710
22
48
12
17
19
28
47
52
11
42
45
20
35
39
27
26
31
18
33
40
34
50
44
10
16
947745
43
0
0
0
0
0
0
0
4000
6800
10000
10625
11000
12000
15,000
15000
16000
16788
17000
17500
18000
18000
18000
20000
22000
22500
25000
25000
25000
26480
28500
29500
30000
30000
30000
33000
35000
35625
36000
36000
40,000
40000
100 0 0 0 0
100 0 0 0 0
100 0 0 0 0
100 0 0 0 0
100 0 0 0 0
100
100
100
100
100
100
100
100
100 0 0 0 0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100 0 0 0 0
100
0
0
0
0
0
0
0
126
-------
44657
46
23
24
29710
502100
55
56
53
32482
25
29
25503
36930
49
965874
953880
33089
T3
3470
43841
279
30
237900
273701
41739
959951
42692
358000
43694
37817
42751
T2
133000
Tl
946587
3023
31838
462800
107300
Respondent ID
36930A
955099
55595
44486
955703
13
37
15
38
36
54
51
41
42,358
44000
45000
45000
57,000
60,000
64500
69000
70000
75,000
75000
75000
90,000
96,000
120000
175,000
180,000
200,000
200,000
240,000
250,000
250,000
250000
273,000
280,000
300,000
320,000
360,000
500,000
500,000
540,000
540,000
600,000
600,000
936,000
1,900,000
2,300,000
3,000,000
3,750,000
5,000,000
Feet
0
0
0
0
0
0
0
4000
6800
10000
10625
11000
12000
100
100
100
0
100
100
100
99
100
100
97
100
100
100
100
100
100
0
0
100
100
100
100
100
100
100
0
0
100
100
100
99
100
100
100
0
100
Data for
Tin
0
33
0
100
0
40
100
80
90
84
82
0
100
0
0
3
0
0
0
0
0
0
0
100
0
0
0
0
0
0
100
100
0
0
0
0
0
0
0
0
0
0
100
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Exhibits 1-10,
Tin-Lead
95
67
0
0
0
5
95
0
0
0
1
0
0
100
0
0
0
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1-11
Dry Film
0
0
0
0
100
50
20
10
2
10
16
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
Nickel Gold
5
0
0
0
0
5
2
18
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
Other
0
0
0
0
0
127
-------
6710
22
57
48
12
17
19
28
47
52
11
42
45
20
35
39
27
26
31
18
33
40
34
50
44
10
947745
43
44657
46
23
24
21
29710
502100
55
56
53
32482
25
29
25503
36930
49
965874
953880
33089
T3
3470
43841
279
30
237900
273701
41739
959951
42692
358000
15,000
15000
15000
16000
16788
17000
17500
18000
18000
18000
20000
22000
22500
25000
25000
25000
26480
28500
29500
30000
30000
30000
33000
35000
35625
36000
40,000
40000
42,358
44000
45000
45000
55000
57,000
60,000
64500
69000
70000
75,000
75000
75000
90,000
96,000
120000
175,000
180,000
200,000
200,000
240,000
250,000
250,000
250000
273,000
280,000
300,000
320,000
360,000
500,000
0
80
97
10
20
100
90
88
97
98
100
93
40
0
0
85
85
100
0
99
98
90
90
90
1
96
78
85
0
0
0
75
0
0
75
0
50
0
65
95
98
100
100
95
90
60
10
100
o
J
85
81
80
95
10
10
5
5
95
10
95
99
0
5
1
10
5
90
2
2
0
100
95
80
10
85
0
20
100
45
0
35
5
0
0
5
7
40
5
100
100
80
100
8
15
1
2
50
2
0
1
0
95
0
96
0
20
15
0
5
10
10
10
65
0
0
100
0
0
0
0
3
5
15
19
10
2
5
75
1
3
5
3
5
15
15
0
0
2
5
10
10
1
2
2
0
0
0
10
5
5
0
5
0
5
0
0
0
2
0
100
2
0
0
100
0
0
0
0
0
0
0
0
0
0
35
0
0
0
0
0
0
128
-------
43694
37817
42751
T2
133000
Tl
740500
946587
3023
462800
107300
Respondent
ID
36930A
955099
55595
44486
955703
13
37
15
38
36
54
51
41
6710
22
57
48
12
17
19
28
47
52
11
42
45
20
35
39
27
26
31
18
33
40
34
50
44
10
16
947745
500,000
540,000
540,000
600,000
600,000
936,000
1,800,000
1,900,000
2,300,000
3,750,000
5,000,000
Inner
Cupric
0
0
0
0
0
0
100
100
100
100
0
0 0 100
002
80 0 0
100 0 0
0 95 0
0 99 0
0 0 100
94 1 0
0 100 0
000
98 0 0
Data for Exhibit 1-12
Inner Inner Outer
Ammoniacal Other Cupric
100 0 0
100 0 0
000
100 0 0
100 0 0
100
100
100
100
100
100
100
100 0 0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100 0 0
0
0
20
0
5
1
0
5
0
0
2
Outer
Ammoniacal
100
100
0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0
98
0
0
0
0
0
0
0
100
0
Outer
Other
0
0
0
0
0
0
100
0
129
-------
43
44657
46
23
24
21
29710
502100
55
56
53
32
32482
25
29
25503
36930
49
965874
953880
33089
T3
3470
43841
279
14
30
237900
273701
41739
959951
42692
358000
43694
37817
42751
T2
133000
Tl
740500
946587
3023
31838
462800
107300
0
100
0
100
0
100
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
100
100
0
0
100
100
0
0
0
50
100
100
100
100
100
0
100
100
100
100
0
100
100
0
100
0
100
0
100
100
100
0
100
100
0
100
100
100
100
100
0
0
0
100
100
0
0
100
100
0
50
0
0
0
100
0
0
0
0
0
0
0
0
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
100
0
95
0
97
0
20
0
0
0
0
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
100
0
0
0
100
0
100
100
100
100
100
100
5
100
100
100
0
100
100
3
100
80
100
100
100
100
100
100
0
100
100
100
0
100
100
100
100
100
100
100
100
100
100
0
100
100
100
0
100
0
0
0
100
0
0
0
0
0
0
0
0
0
0
100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Data for Exhibits 1-13, 1-14
Respondent
ID
36930A
955099
55595
44486
955703
13
Direct
Discharge
X
X
Indirect
Discharge
X
X
X
X
Average
Zero Flow
Discharge (gal/day)
27,000
120,000
20,000
100,000
98,000
30000
Maximum
Flow
(gal/day)
0
140,000
22,500
130,000
108,000
33000
Cost of
Water
($/Kal)
0.95
3.10
1.00
1.62
1.70
Cost of
Sewer
(Steal)
1.45
9.30
24.40
0.79
0.55
130
-------
37
15
38
36
54
51
41
6710
22
57
48
12
17
19
28
47
52
11
42
45
20
35
39
27
26
31
18
33
40
34
50
44
10
16
947745
43
44657
46
23
24
21
29710
502100
55
56
53
32
32482
25
29
25503
36930
49
965874
953880
33089
T3
3470
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
10000
13500
3000
400
80000
9500
230000
10,560
10000
40000
12000
17000
18000
275000
40000
25000
21000
32500
25000
25000
3500
31000
95000
25000
77000
60000
40000
45000
60000
70000
39000
35000
30000
200000
13,000
51628
6,000
45000
130000
130000
113000
74,000
35
168900
50000
35000
215
31,000
110000
34000
5,000
0
64000
21,000
35,000
16,000
20,000
20,000
12000
17000
4000
800
120000
11700
275000
21,120
18000
50000
30000
24000
21000
310000
51000
32000
32000
52000
40000
30000
5000
39000
115000
28000
80000
90000
42000
70000
90000
85000
50000
40000
33000
18,000
72288
180,000
60000
175000
124,000
45
168900
65000
40000
300
54,000
130000
150000
6,500
0
85000
27,000
45,000
25,000
30,000
30,000
2
5
0
2
1
1.50
2
1
3
1
2
3
2
1
o
J
1
2
1
1
5
1
0
2
1
1.50
1
1.98
2
2
3
nr
nr
1
1
0
2
1.94
1
nr
nr
1.72
1.33
1.32
nr
0.00
1
3
0
1
1
3.50
3
2
3
3
1
3
4
0
0
1
2
0
0
0
2
0
1.50
0
2.29
1
1
1
nr
nr
3
0
0
o
5
nr
1
3
nr
nr
1.03
2.60
2.28
4.00
0.06
131
-------
43841
279
14
30
237900
273701
41739
959951
42692
358000
43694
37817
42751
T2
133000
Tl
740500
946587
3023
31838
462800
107300
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
38,000
5,200
105,000
25,000
57,125
20,000
100,000
9,000
30,000
6,000
140,000
48,000
160,000
160,000
400,000
200,000
145,000
280,000
26,000
250,000
50,000
5,500
125,000
30,000
65,000
30,000
125,000
12,000
40,000
11,000
160,000
62,400
200,000
185,000
1,000,000
250,000
160,000
420,000
31,000
300,000
3.54
7.56
1.43
1.41
0.80
nr
0.03
nr
1.00
1.20
1.60
1.61
2.73
1.63
2.22
0.58
3.78
1.85
13.80
1.50
2.57
5.82
2
0.61
1.35
1.60
nr
nr
nr
0.78
0.21
3.10
2.70
2.33
2.92
3.08
0.73
5.24
1.90
3.40
1.96
Discharge Limitations and Compliance Difficulties
Data Discussed in Section 1.4.5
Respondent
ID
40CFR413
40 CFR 433
6710
36930A
36930
273701
358000
955703
33089
107300
502100
44657
43694
29710
T3
Tl
955099
37817
959951
947745
95880
42751
32482
44486
42692
41739
43841
T2
Cu
max
mg/1
4.5
3.38
4.50
2.59
4.34
3.38
2.00
3.00
3.38
2.00
1.00
3.00
3.00
0.49
2.70
1.00
1.50
5.00
3.22
3.38
0.25
3.00
3.38
4.50
4.50
4.00
4.30
2.20
Cu
avg
mg/1
2.7
2.07
0.37
1.59
2.60
2.07
1.50
2.07
2.07
1.00
1.50
2.07
2.07
0.41
2.70
0.03
-
3.50
0.45
2.07
-
2.07
2.07
2.70
2.70
0.40
2.60
2.07
Pb
max
mg/1
0.6
0.69
0.60
0.53
0.58
0.69
-
0.69
0.69
0.30
-
0.60
0.69
0.43
0.40
0.20
0.20
1.00
0.60
0.69
0.19
0.69
0.69
0.60
0.60
0.60
0.57
0.69
Pb
avg
mg/1
0.4
0.43
0.10
0.33
0.39
0.43
-
0.43
0.43
0.10
-
0.40
0.43
0.27
0.40
0.05
-
0.25
0.11
0.43
-
0.43
0.43
0.40
0.40
0.30
0.36
0.43
Ni
max
mg/1
4.1
3.98
4.10
3.05
3.95
3.98
-
3.98
3.98
1.30
-
2.20
3.98
2.50
2.60
1.00
1.00
-
2.91
3.98
0.60
2.50
3.98
4.10
4.10
4.00
0.72
3.00
Ni
avg
mg/1
2.6
2.38
0.09
1.83
2.91
2.38
-
2.38
2.38
1.00
-
-
2.38
1.50
2.60
0.04
-
-
0.43
2.38
-
2.38
2.38
2.60
2.60
0.50
0.23
2.38
Ag
max
mg/1
1.2
0.43
1.20
0.33
1.16
0.43
-
0.43
0.43
-
-
0.43
0.43
0.02
0.70
0.50
2.00
-
0.85
0.43
0.13
1.00
0.43
5.80
-
1.00
0.03
0.43
Ag
avg
mg/1
0.7
0.24
0.01
0.18
0.67
0.24
-
0.24
0.24
-
-
0.24
0.24
0.02
0.70
0.01
-
-
0.12
0.24
-
-
0.24
-
1.90
-
0.01
0.24
CN
max
mg/1
1.9
1.20
1.90
0.92
1.83
1.20
-
1.20
1.20
-
-
1.20
1.20
0.76
1.00
-
1.00
-
1.90
1.20
0.74
.20
.20
.90
.00
.00
.82
.00
CN
avg
mg/1
1.0
0.65
0.01
0.50
0.96
-
-
0.65
0.65
-
-
0.65
0.65
0.41
-
-
-
-
0.17
0.65
-
0.65
0.65
1.00
-
0.01
0.96
0.65
TTO
max
mg/1
2.13
2.13
2.13
1.63
2.05
-
-
0.58
2.13
2.13
-
2.13
0.58
1.34
2.13
2.35
5.00
-
2.13
2.13
0.74
2.13
-
1.30
2.13
-
2.13
2.13
TTO
avg
mg/1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.00
-
-
-
-
-
-
-
-
2.13
-
-
-
132
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3470
740500
279
3023
237900
133000
25503
946587
462800
31838
55595
965874
1.50
3.38
3.00
1.50
2.70
1.50
3.00
3.40
2.90
3.00
nr
3.38
2.07
1.70
2.02
-
1.00
-
2.07
-
1.91
1.50
nr
2.07
0.20
0.69
-
0.20
0.40
0.34
0.69
0.50
0.39
0.69
nr
0.69
0.23
0.40
-
-
0.40
-
0.43
-
0.26
0.43
nr
0.43
1.00
3.98
-
1.00
2.60
4.10
3.98
2.20
2.64
3.00
nr
3.98
2.38
1.60
-
-
0.25
-
2.38
-
1.69
1.50
nr
2.38
0.43
0.43
-
2.00
0.70
0.23
0.43
0.80
-
0.43
nr
0.43
0.24
0.24
-
-
0.70
-
0.24
-
-
0.24
nr
0.24
0.50
1.20
-
0.50
0.50
0.60
1.20
0.40
1.23
0.80
nr
1.20
0.65
0.65
-
-
0.50
-
0.65
-
0.65
0.40
nr
0.65
2.13
2.13
-
1.00
2.13
2.13
0.58
-
1.40
2.13
nr
2.13
-
-
-
-
-
-
-
-
-
-
nr
-
Bold type indicates compliance difficulty with discharge parameter.
nr = no response
40 CFR 413 maximum is based on a 4 day average concentration.
40 CFR 433 maximum is based on a monthly average concentration.
Data For Exhibit 1-16
Environmental and Occupational
Health Challenges
% of PWB Survey
Respondents Citing
Challenge
% of Plating Survey
Respondents Citing
Challenge
Meeting air emission standards
Eliminating solvent use
Frequently changing regulations
Consistently meeting effluent and discharge limits
Increasing cost of compliance
Reducing worker exposure to chemicals
Inconsistent enforcement of regulations
Hazardous waste transportation liabilities
Lack of hazardous waste disposal sites
Management/worker acceptance*
Permit modification time*
Understanding local, state and federal regulations*
23.3
32.5
55.8
32.5
68.6
41.8
29.1
13.2
4.7
1.2
1.2
1.2
23.2
23.8
54.5
38.2
72.4
—
—
—
17.9
—
—
—
* Added by respondent under "other." This item may have been more frequently selected if it had been listed on the survey form.
— Indicates that item was not listed on the survey form.
Data For Exhibit 1-17
Items for Which Available
Information is Insufficient
Percentage of PWB Survey Respondents
Citing Information Need
Chemical recycling (such as etchant, developer
Water recycling
Certified courses for pollution preventior
Fully or semi-additive process
Tin-lead alternatives
Smear removal alternatives
Direct imaging
Solder mask disposal*
In-house waste treatment*
Treatment for resist stripper*
Air quality issues*
Low cost chemical and water recycling*
41.9
33.7
33.7
30.2
29.1
23.3
15.1
1.1
1.1
1.1
1.1
1.1
* Added by respondent under "other." This item may have been more frequently selected if it had been listed on the survey form.
133
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Data For Exhibit 1-18
% of PWB Survey % of Plating Survey
Source of Information Respondents Citing Source Respondents Citing Source
Vendoi
In-house engineei
Professional journals
Literature from trade organizations
In-house chemisi
Books
Other shops, competitors
Conferences
Other in-house employees
Consultanl
Internet*
From regulators-WWTP, OSHA, EPA81
48.8
50.0
39.5
32.6
35.0
35.0
33.7
24.4
27.9
18.6
1.1
1.1
63.6
20.0
66.1
-
22.6
51.1
-
53.6
4.4
51.4
-
-
* Added by respondent under "other." This item may have been more frequently selected if it had been listed on the survey form.
134
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