PB83-199190
Industrial Process Profiles for Environmental
Use: Chapter 30. The Electronic
Component Manufacturing Industry
PEDCo-Environmental, Inc.
Cincinnati, OH
Prepared for
Industrial Environmental Research Lab,
Cincinnati, OH
Apr 83
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
NTfc>
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PB33-1^31
EPA-600/2-83-033
April 1983
INDUSTRIAL PROCESS PROFILES
FOR ENVIRONMENTAL USE;
CHAPTER 30
THE ELECTRONIC COMPONENT
MANUFACTURING INDUSTRY
by
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
Contract No. 68-03-2924
Project Officer
John 0. Burckle
Energy Pollution Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
>;? : n 1983
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TECHNICAL REPORT DATA
(Heat nod liutnienoni on the mene be fan complenngl
REPORT NO
EPA-600/2-83-033
1. RECIPIENT'S ACCESSION NO.
nag 7
199190
I TITLE AND SUBTITLE
Industrial Process Profiles for Environmental Use:
Chapter 30, The Electronic Component Manufacturing
Industry
. AUTHOH(S)
5 REPORT DATE
April 1983
B. PERFORMING ORGANIZATION CODE
B. PERFORMING ORGANIZATION REPORT NO
PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo Environmental Research Laboratory
11499 Chester Road
Cincinnati, OH 45246
10. PROGRAM ELEMENT NO
N-104
11. CONTRACT/GRANT NO.
68-03-2924
12 SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
US Environmental Protection Agency
Cincinnati, OH 45268
13. TVPE OF REPORT AND PERIOD COVERED
Final
14 SPONSORING AGENCY CODE
EPA/600/12
15 SUPPLEMENTARY NOTES
Project Officer: John 0. Burckle
16 ABSTRACT
This report is one of a series constituting the catalog of Industrial Process Profiles
for Environmental Use. Each industry sector is addressed as a separate chapter of the
study. The catalog was developed for the purpose of compiling relevant information
concerning air, water, and solid waste emissions from industries which employ similar
technologies, have common types of environmental impacts, and supply their products for
further processing or consumption to the same general population of customers. Each
industrial process is examined from the standpoint of its function, feed materials,
operating conditions, utility requirements, and waste streams. A completed IPPEU report
constitutes a multimedia data base of the environmental impacts of an industry's
production operations based upon information available in the open literature. As such,
it is preliminary in nature and should be viewed as the first step in development of a
comprehensive analysis of environmental impacts. This report addresses the following
segments of the electronic component manufacturing industry: semiconductors, SIC 3674;
capacitors, SIC 3675; resistors, SIC 3676; transformer and inductors, SIC 3677; printed
circuit boards, SIC 3679052; electron tubes, SIC 36711, 36713; and cathode ray tubes, SIC
36712, 3671385.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS
c. COSATi Field/Croup
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
10 SECURITY CLASS IThuRiponi
UNCLASSIFIED
21 NO OF PAGES
233
2O SECURITY CLASS (ThUpaftj
UNCLASSIFIED
22. PRICE
EPA P«m 2220-1 (Hi*. 4-77) pncvioui EDITION is OMOLBTI
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NOTICE
THIS DOCUM.ENT HAS BEEN REPRODUCED
FROM THE BEST COPY FURNISHED US BY
THE SPONSORING AGENCY. ALTHOUGH IT
IS RECOGNIZED THAT CERTAIN PORTIONS
ARE ILLEGIBLE, IT IS BEING RELEASED
IN THE INTEREST OF MAKING AVAILABLE
AS MUCH INFORMATION AS POSSIBLE.
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii
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CONTENTS
Figures vi
Tables viii
1. Introduction 1
2. Semiconductors 7
Industry description 7
Industry analysis 24
Process No. 1, wafer cutting, smoothing, and polishing 27
Process No. 2, chemical cleaning and polishing 30
Process No. 3, epitaxial growth 32
Process No. 4, circuit fabrication 37
Process No. 5, diffusion 41
Process No. 6, metal interconnection 44
3. Capacitors 50
Industry description 50
Industry analysis 61
Tantalum wet and dry slug capacitors
Process No. 1, anode fabrication 68
Process No. 2, formation reactions 69
Process No. 3, forming 70
Process No. 4, acid/carbon slurry dips 71
Process No. 5, assembly (dry slug) 72
Process No. 6, assembly (wet slug) 73
Tantalum foil capacitors
Process No. 1, electrochemical oxide formation 74
Process No. 2, assembly 75
Glass encapsulated capacitors
Process No. 1, assembly 76
Process No. 2, terminal cleaning 77
Process No. 3, glass cutting 78
Aluminum electrolytic capacitors
Process No. 1, oxide formation 79
Process No. 2, assembly 80
iii
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CONTENTS (continued)
Page
Mica capacitors
Process No. 1, dielectric fabrication 81
Ceramic capacitors
Process No. 1, ball milling 82
Process No. 2, ceramic formation 83
Process No. 3, baking/printing 84
Process No. 4, assembly 87
4. Resistors 89
Industry description 89
Industry analysis 100
Process No. 1, resistive element formation 102
Process No. 2, impregnation and coating application 106
Process No. 3, assembly and lead attachment 108
Process No. 4, protective cover formation 110
5. Transformers and Inductors 114
Industry description 114
Industry analysis 120
Process No. 1, core fabrication 125
Process No. 2, coil winding 130
.Process No. 3, impregnation and coating 132
Process No. 4, encapsulation 135
6. Printed Circuit Boards 137
Industry description 137
Industry analysis 143
Process No. 1, board preparation 147
Process No. 2, board cleaning 149
Process No. 3, surface preparation 151
Process No. 4, catalyst application 153
Process No. 5, electroless plating (flash) 154
Process No. 6, image transfer 158
Process No. 7, electroplating 162
Process No. 8, etching 170
Process No. 9, multilayer board lamination 175
7. Electron Tubes 178
Industry description 178
Industry analysis 183
Process No. 1, tube mount assembly 187
Process No. 2, glass mount assembly 189
Process No. 3, gettering/final assembly 190
iv
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CONTENTS (continued)
8. Cathode Ray Tubes
Industry description
Industry analysis
Process No. 1, aperture mask manufacturing
Process No. 2, aperture mask degreasing
Process No. 3, glass panel wash
Process No. 4, photoresist application
Process No. 5, phosphor application
Process No. 6, glass funnel preparation
Process No. 7, shield degreasing
Process No. 8, electron gun assembly
Process No. 9, final tube assembly
Process No. 10, picture tube reclaim
192
192
196
198
200
202
203
205
208
209
210
211
212
Appendix Wastewater treatment and control
214
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FIGURES
Page
Value of Total Shipments (Primary, Secondary, and Miscel-
laneous) - Electron Tube and Semiconductor Industries 3
2-1 FET Bar Structure 9
2-2 N-channel Enhancement-Mode MOSFET Formation 9
2-3 World Total Semiconductor Production 14
2-4 Worldwide Shipments by U.S. Companies of Discrete
Semiconductors 15
2-5 World Discrete Semiconductor Market for Worldwide Suppliers 16
2-6 Transistor and Diode Production Flowsheet 25
2-7 Integrated Circuit (1C) and Light Emiting Diode (LED)
Production Flowsheet 26
3-1 Capacitor Sales: A Comparison of Growth Over the Past
Decade 56
3-2 Tantalum Wet and Dry Slug Capacitor Production Flowsheet 62
3-3 Tantalum Foil Capacitor Production Flowsheet 63
3-4 Glass Encapsulated Capacitor Production Flowsheet 64
3-5 Aluminum Electrolytic Capacitor Production Flowsheet 65
3-6 Ceramic Capacitor Production Flowsheet 66
4-1 Sales of Major Resistor Types, 1977-1979 92
4-2 Resistor Production Flowsheet 101
5-1 Transformer Production Flowsheet 124
vi
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FIGURES (continued)
Number Page
6-1 Additive Printed Circuit Board Production Flowsheet 144
6-2 Subtractive Printed Circuit Board Production Flowsheet 145
6-3 Semi-additive Printed Circuit Board Production Flowsheet 146
7-1 Receiving-type Electron Tube Production Flowsheet 184
7-2 Transmitting Electron Tube Production Flowsheet 185
8-1 Color Television Picture Tube Production Flowsheet 197
8-2 In-place Waste Treatment for Hexavalent Chromium Wastes
from a Picture Tube Manufacturing Process 204
8-3 In-Place Waste Treatment for Phosphor Wastes from a
Picture Tube Manufacturing Process 207
A-l Wastewater Treatment System - Semiconductor Manufacture 215
A-2 Wastewater Treatment System - Printed Circuit Board Manu-
facture (Segregated Waste Streams). 220
vii
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TABLES
Page
Electronic Components Industry - 1977 Statistics 2
U.S. Sales of Semiconductor Devices 13
Company Size Distribution by Total Employment for Semi-
conductors and Related Devices 17
2-3 World Discrete Market Share Estimates 19
2-4 Some Manufacturers of Discrete Semiconductors 20
2-5 Number of Companies Producing Various Semiconductors and
the Quantity of Shipments of Each Type 21
2-6 Characteristics of Raw Waste Streams from Semiconductor
Device Manufacturing 23
2-7 Semiconductor Machining Waste for a Typical Plant 29
2-8 Indirect Epitaxial Growth Techniques 34
2-9 Semiconductor Process Waste for an Isolated Plant 36
2-10 Semiconductor Process Wastes for the Circuit Fabrication
Process 40
2-11 Common Diffusion Sources for Open Tube Systems 42
2-12 Metal Interconnection Etch Rinse for an Isolated Plant 47
3-1 Capacitor Sales Over Past 10 Years 55
3-2 Forecast for Capacitor Sales 57
3-3 Number of Companies Manufacturing Various Capacitor Types 58
3-4 Size Breakdown of Capacitor Producers Based on Total Em-
ployment 59
3-5 Major Monolithic Ceramic Manufacturers 60
viii
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TABLES (continued)
Page
Analysis of Process Uastewater from a Ceramic Capacitor
Ink Manufacturing Operation 85
4-1 Industry-wide Consumption of Resistors Shipped by U.S. and
Foreign Manufacturers for the U.S. Market 93
4-2 Number of Companies Producing Each Resistor Type 95
4-3 Resistor Manufacturers by Employment Range Classification 96
4-4 Major Manufacturers of Fixed Resistors 97
4-5 Major Manufacturers of Variable Resistors 98
4-6 Market Shares of Major Resistor Suppliers 99
4-7 Characteristics of Alloys Used in Wire-wound Potentio-
meters and Resistors 104
5-1 High Permeability Materials and Alloys 117
5-2 Shipments of Electronic Transformers, Inductors, and Coils 118
5-3 Market Estimates for Coils, Transformers, and Chokes 119
5-4 Companies Manufacturing Various Products Under SIC 3677 121
5-5 Distribution of Company Size in SIC 3677 by Total Employ-
ment 122
5-6 Transformer and Inductor Manufacturers 123
5-7 High-Permeability Nickel-Iron Alloys 127
5-8 Cobalt-Iron Alloys 128
6-1 Printed Circuit Board Sales 140
6-2 Characteristics of Raw Waste Streams from Printed Circuit
Board Manufacturing 142
6-3 Typical Electroless Copper Plating Baths 156
6-4 Additives Used in Photosensitive Resists 161
6-5 Plating Bath Constituents 163
ix
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TABLES (continued)
Number Page
6-6 Common Operating Conditions for Plating Baths 166
6-7 Diatomaceous Earth Filtration Performance Data 168
6-8 Ion Exchange Performance Data 168
6-9 Characteristics of FeCl3 Solutions 171
6-10 Composition of Typical Persulfate Etch Solutions 171
6-11 Composition of Typical Chromic-Sulfuric Acid Etch Solutions 172
6-12 Composition of Typical Cupric Chloride Etch Solutions 172
6-13 Composition of Typical Alkaline Etch Solutions 173
7-1 Receiving-Type Electron Tube Manufacturers and Product
Shipments 181
7-2 Transmitting and Special-Purpose Electron Tube Product
Shipments 182
8-1 Companies Producing CRT's for Televisions 195
8-2 Summary of Raw Waste Data from an Aperture Mask Manu-
facturing Operation 199
8-3 Summary of Raw Waste for Television Picture Tube Manu-
facture 201
A-l Performance of Chemical Precipitation and Sedimentation -
Semiconductor Manufacture 217
A-2 Performance of Fluoride Treatment Systems - Semiconductor
Manufacture 218
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SECTION 1
INTRODUCTION
In recent decades electronic equipment has become an Integral part of
modern technological society. Computers, sophisticated communications systems
and Industrial and military hardware, entertainment equipment, and other
electronic devices are In widespread usage. This equipment 1s manufactured
from many Individual electronic components, which in turn may be made from any
of thousands of different substances. This report to the U.S. Environmental
Protection Agency (EPA) is a preliminary assessment of the potential environ-
mental impacts associated with the production of these components in the
United States.
The electronic components industry is large and complex, and many seg-
ments are experiencing rapid changes in technology. Hundreds of individual
component types are manufactured. Table 1-1 presents statistical data on the
industry. Total sales of primary products in 1977 were over $14 billion, and
overall the industry has been growing at a fast pace. The largest single
segment of the industry, with $4.5 billion in sales, is semiconductors and
related devices. This is also a rapidly growing category; the value of
shipments increased 92 percent between 1972 and 1977. However, some segments
of the industry face a much different outlook. Older product types are being
replaced in many applications by newer solid-state technologies. This is
illustrated in Figure 1-1, which shows comparative data on the value of total
shipments for the semiconductor and electron tube industries from 1963 to
1977.]
Although there are changes taking place in the types and quantities of
specific components being manufactured, there should continue to be strong
growth for the industry in the future. This will be especially true of micro-
electronic components, already one of the most rapidly growing industries in
the United States. Although the microprocessor was invented only ten years
1
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TABLE 1-1. ELECTRONIC COMPONENTS INDUSTRY - 1977 STATISTICS
1
Product
Electron tubes, all
types
Semiconductors and re-
lated devices
Capacitors
Resistors
Colls and transformers
Connectors
Others3
Total
Number of
establishments
146
545
118
101
294
133
3,119
4,456
Employment
Number of
employees
36,700
114,000
28.900
21,300
20,700
26,000
126,000
373,600
1972-1977
Increase, %
12
17
5
4
-13
44
25
11
Leading states
NY, PA, CA
NY, TX, AZ, CA
PA, NC, SC, CA
PA, IN, CA
NY, IL, CA
NY, PA, IL, CA
MA, NY, IL, CA
Primary shipments
$ million
1,257
4,532
736
583
606
986
5,574
14,274
1972-1977
Increase, %
6
92
62
33
57
88
74
67
Printed circuit boards, modular components, magnetic recording media, antennas, microwave devices,
filters, crystals, etc.
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6000
5000
4000
3000
0")
2000
1000
i i I
ELECTRON TUBES
SEMICONDUCTORS
A I
/ » 11 —
i i i i i i i i i i i i i
1963 1965 1967 1969 1971 1973 1975 1977
YEAR
Figure 1-1. Value of total shipments (primary, secondary, and
miscellaneous) - electron tube and semiconductor industries.1
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ago, these chips are now used in an incredible variety of manufactured goods.
Microelectronic devices that were no more than an expensive curiosity a few
years ago are now commonplace. There will be increasing use of these com-
ponents for applications in our homes, industries, schools, and transportation
equipment in the future.
The potentially hazardous and toxic nature of some substances used to
make electronic components, coupled with the continued growth forecast for the
industry, suggests that such emissions from these emitting production process-
es be controlled to achieve continuous compliance with established standards.
In 1977 there were nearly 4,500 manufacturing establishments spread throughout
i p
the country, an increase of 50 percent over a five-year period. • In addition,
nearly 400,000 persons were directly employed in these facilities in 1977;
this represents 1.9 percent of the total U.S. manufacturing work force. '3
As indicated, there are hundreds of individual electronic components.
Many are manufactured with similar processes. For the purposes of this
analysis, EPA has requested that the following segments be analyzed:
SIC Code
1. Semiconductors 3674
2. Capacitors 3675
3. Resistors 3676
4. Transformers and inductors 3677
5. Printed circuit boards 3679052
6. Electron tubes 36711, 36713
7. Cathode ray tubes 36712, 3671385
The analyses in this report are in the format of the Industrial Process
Profiles for Environmental Use (IPPEU). This format was developed by EPA's
Industrial Environmental Research Laboratory for the purpose of cataloging
relevant information concerning air, water, and solid waste emissions from
industries which employ similar technologies, have common types of environ-
mental impacts, and supply their products for further processing or consump-
tion to the same general population of customers. Each industrial process is
examined from the standpoint of its function, feed materials, operating condi-
tions, utility requirements, and waste streams. A completed IPPEU report
constitutes a multimedia data base on the environmental impacts of an indus-
try's production operations based upon information available in the open
literature. As such, it is preliminary in nature and should be viewed as the
-------
first step in development of a comprehensive analysis of environmental Impacts.
Major pollution problems are Identified, and any gaps in the data base are
readily apparent. The final report thus serves to direct fact-finding research
and development needed to reduce environmental problems. It should also
provide sufficient data to allow a focus on problems that have the most ad-
verse effect on public health and welfare.
Rapid technological changes are taking place in the industry, and many
operations are proprietary in nature. Because the IPPEU report 1s based only
upon Information found in the open literature, few details were found of many
aspects of some production processes. This preliminary report summarizes the
available data. It was prepared by PEDCo Environmental, Inc., of Cincinnati,
Ohio; PEDCo was assisted in this effort by Centec Consultants of Reston,
Virginia. Mr. John 0. Burckle was Project Officer for EPA's Industrial Envi-
ronmental Research Laboratory in Cincinnati.
Sections 2 through 8 present the IPPEU analyses of the Individual seg-
ments of the electronic components industry. Each section is divided into two
parts: an Industry Description, which presents an overview of the raw materi-
als, products, and companies associated with each component type; and an
Industry Analysis, which presents specific information on production processes
and discharges. An appendix presents additional information on wastewater
control and treatment in the industry.
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REFERENCES FOR SECTION 1
1. U.S. Department of Commerce. 1977 Census of Manufactures: Electrical
Components and Accessories. June 1980.
2. U.S. Department of Commerce. 1972 Census of Manufactures: Electrical
Components and Accessories.
3. U.S. Department of Commerce. 1977 County Business Patterns: U.S. Sum-
mary.
4. U.S. Environmental Protection Agency. Industrial Process Profiles for
Environmental Use. Chapter 1: Introduction. PB-266274. January 1977.
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SECTION 2
SEMICONDUCTORS
INDUSTRY DESCRIPTION
A semiconductor material is one whose electrical conductivity falls
between that of a conductor and that of an insulator. In the electronic
components industry, the term semiconductor covers a wide range of devices
whose main functioning parts are composed of a semiconductor material; these
include transistors, diodes, thyristors, and integrated circuits. These solid
state devices have no moving parts and are used for information processing,
display purposes, power handling, and conversion of light to energy.
Semiconductor components now manufactured are many times smaller than the
equivalents of even a few years ago. They meet today's needs for high compo-
nent density in many electronic applications. Generally, semiconductor devices
are mounted on printed circuit boards as part of a larger circuit. Discrete
devices are used for relatively simple circuitry, where processing needs do
not place unusual demands on semiconductor electrical characteristics. Many
semiconductor components can be integrated into a single processor chip to
meet greater density demands. The following paragraphs present an overview of
the major types of semiconductor components.
Transistors consist of a small block of semiconductor material with three
or more electrodes. Similar to electron tubes in use (i.e., amplification and
rectification), transistors are constructed of various semiconductor materials
and additional impurities ("dopants") such as boron, aluminum, gallium, or
indium. The semiconductor materials are referred to as "P-type" or "N-type"
depending on their ability to accept or donate electrons to the atomic struc-
ture. There are three broad categories of transistors: bipolar, field ef-
fect, and unijunction.
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Bipolar (or multijunction) transistors have a base and two junctions
(emitter, collector) with terminals attached to each. Junctions of bipolar
transistors are formed by either alloying donor or acceptor material to a
thin, doped semiconductor pellet; by diffusion of dopants into a doped silicon
or germanium wafer; by formation of the junctions during crystal growth; or
by a combination of crystal growth and diffusion.
Field-effect transistors (FET) are also three-layered devices but are
voltage-actuated rather than current-actuated. Conduction is by the flow of
majority carriers through a conduction channel controlled by voltage applied
between the gate and source terminals. One type of FET is the junction field-
effect transistor (JFET), which consists of a bar of doped silicon with semi-
conductor materials diffused into it. A typical JFET structure is shown in
Figure 2-1. Another type of FET, the metal-oxide-semiconductor field effect
transistor (MOSFET), differs in both structure and control mechanism. Two
separate low-resistivity regions (source and drain) are diffused into a high-
resistivity substrate. The surface is then covered with an oxide layer to
insulate the channels from the gate and a silicon nitride layer to protect the
oxide layer from sodium ion contamination. This type of MOSFET is shown in
Figure 2-2. MOSFET applications include RF amplifiers, mixers, oscillators,
audio and wide band amplifiers, variable attenuators, choppers, and current
limiters.1
Unijunction transistors (UJT) have one junction and a stable negative
resistance characteristic between the emitter and base 1 terminals when a
positive bias voltage is applied between base 1 and base 2 terminals.
Diodes are semiconductor devices with two terminals that find uses anal-
ogous to electron tube diodes. They include semiconductor rectifier diodes,
zener diodes, varactors (voltage variable capacitors), tuning diodes, and
silicon diode capacitors. Semiconductor rectifier diodes may be made from
germanium, selenium, copper oxide, and, most commonly, silicon. One type
called a point-contact diode consists of a sharp-pointed fine wire attached to
a semiconductor crystal. These have superior high-frequency characteristics
and some types can even operate at microwave frequencies. Junction rectifier
diodes operate at a much lower frequency than point-contact diodes, but have
higher power dissipation capabilities. Zener (or breakdown) diodes are two-
layered devices that exhibit a sharp rise in current flow when an applied
8
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METALIZED SOURCE
CONNECTION
N-TYPE SILICON
SUBSTRATE
METALIZED DRAIN
CONNECTION
METALIZED GATE
CONNECTIONS '
DIFFUSED P-TYPE
REGIONS
Figure 2-1. FET bar structure.
1
P-TYPE SUBSTRATE
N-TYPE SOURCE
N-TYPE DRAIN
SILICON NITRIDE
N N
.SILICON
DIOXIDE
METALIZED SOURCE
CONNECTION
METALIZED GATE
METALIZED DRAIN
CONNECTION
Figure 2-2. N-channel enhancement-mode MOSFET
formation.1
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reverse-bias voltage Is increased to the region of the breakdown voltage.
When forward-bias voltage is applied, the zener diode functions as an ordinary
rectifier. They are used for voltage regulation, overvoltage protection, and
to provide a reference voltage.
Thyristors (also called silicon controlled rectifiers [SCR's]), silicon
controlled switches (SCS's), and triacs are semiconductor switching devices
that have three or more junctions. These devices act to rectify a main AC or
DC current by normal diode action, but conduct only when an external signal or
voltage applied at the gate terminal exceeds a certain amount. It ceases to
conduct if that voltage is reduced below threshold or if the gate current is
switched off.
Integrated circuits (IC's) are electronic subassemblies consisting of a
number of elements placed together on a semiconductor chip. These elements
are primarily diodes and transistors yet are often used to perform activities
associated with components. They can be used in almost any electronic appli-
cation that involves small AC or DC signals. IC's can be divided into two
broad categories, digital (or switching) circuits and analog (or linear)
circuits. Digital circuits are further classified by the system logic; for
example, TTL (transistor-transistor logic), DTL (diode-transistor logic), ECL
(emitter-coupled logic) and RTL (resistor-transistor logic). MOS (metal-
oxide-semiconductor) digital circuits are more sophisticated and are subdivid-
ed. Linear IC's can be classified as operational amplifiers, voltage regu-
lators, audio amplifiers, television modules, radio tuners, IF amplifiers, and
2
others.
Raw Materials
Raw materials for the manufacture of semiconductors can be categorized
into groups that include semiconductor base materials, dopants, passivating
345
and insulating materials, and metals: ' '
0 Base materials - Silicon is the most widely used base material (sub-
strate) in the semiconductor industry, finding applications in 90 to
96 percent of all products. The silicon must be of extremely high
quality; impurities are as low as one part per billion. Germanium
is used primarily in the production of discrete devices such as
diodes. First used in this regard in the early 1950's, it is still
manufactured to supply and maintain existing equipment, but has been
10
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Products
replaced by silicon in most recent applications. Gallium arsenide
(GaAs) and gallium phosphide (GaP) are used primarily in the pro-
duction of light emitting diodes (LEO's). Use of gallium arsenide
in photovoltaics for space and terrestrial applications is also
increasing.
Dopants - Dopants are added to the semiconductor to increase conduc-
tivity. The commonly used dopants for silicon are boron, phosphorus,
arsenic, and antimony. Phosphine gas (PH3) or phosphorous oxychlo-
ride (POC13) are usually used for phosphorus diffusion. Boron tri-
chloride (8013) or diborane (62*14) gases are usually used for dif-
fused junction formation with boron. Boron trifluoride (BF3) may
also be used, as well as pure boron powder. Other dopants include
arsine gas (Asfy), arsenic hexafluoride (AsFg), arsenic, antimony,
aluminum, gallium, gold, beryllium, germanium, magnesium, silicon,
tin, and tellurium.
Passivating and insulating materials - The two most commonly used
materials are silicon dioxide (Si02) and silicon nitride (Si3N4).
A silicon dioxide layer may be deposited by using silicon dioxide,
vaporized silicon and oxygen gas, or by silane (SiHa) and nitrous
oxide (N20) gases. Silicon nitride may be deposited by chemical
vapor deposition using dichlorosilane (SiH2Cl2) and ammonia
Metals - Metals are sputtered or evaporated onto the surface of the
wafer to provide electrical contacts. These metals include alumi-
num, gold, chromium, tin, palladium, nickel, titanium, copper, and
platinum, as well as various combinations. Some metals may be
electroplated onto the wafer's metal surface to provide the external
contacts. These include gold, tin, copper, silver, and chromium.
Processing materials - Other major processing materials include acid
and alkaline cleaners, resists (etchant resistive materials), flam-
mable solvents, chlorinated solvents, and etch solutions. These
include a broad range of formulations (many proprietary).
The semiconductor industry comprises establishments primarily engaged in
the manufacture of semiconductors and related solid-state devices such as
semiconductor diodes and stacks. This includes rectifiers, integrated micro-
circuits (semiconductor networks), transistors, solar cells, thyristors, light
sensing and emitting semiconductor (solid-state) devices, microprocessors, and
solid-state memory devices. The Bureau of the Census classifies semicon-
ductors and related devices into SIC 3674.
11
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Shipments of U.S. primary semiconductor products increased 92 percent
from 1972 to 1977. Integrated microcircuits and semiconductor networks
accounted for a significant portion of that increase. Total estimated 1980
sales of all semiconductors, including integrated circuits, were $6,360.5
million. A breakdown of products and total sales from one industry source is
presented in Table 2-1. Projected sales for 1983 are $11,074 million, which
represents an annual increase of 18.9 percent. However, one recent article
reported that the discrete semiconductor sales for 1981 are expected to in-
crease by only about 4 percent. The following year (1982) is expected to see
o
a 10 percent increase.
Integrated circuits comprise by far the greatest portion of the market.
Estimated 1980 1C sales were about 77 percent of the total semiconductor in-
dustry.7 By 1983 this share is expected to increase to about 82 percent. A
comparison of world production of IC's and discrete semiconductors is shown in
Figure 2-3.8 In 1980, power transistors accounted for about 21 percent of the
total shipment of discrete semiconductors, making this the biggest product
Q
area among discrete components. Optoelectronics (solar cells, photoconduc-
tive cells, LED's, photodiodes, phototransistors, couplers, and fiber optics)
comprised the second largest category, almost 19 percent of total shipments.
Optoelectronics, however, is expected to overtake power transistors as the
largest product category among discrete components in the next two to three
years.8 Figure 2-4 presents estimated worldwide shipments by U.S. companies
D
of various categories of discrete semiconductors from 1979 to 1983. A
o
breakdown of estimated world market share by type is shown in Figure 2-5.
On a worldwide basis, power transistors should continue to hold the largest
share, followed by rectifiers and optoelectronics.
Companies
The Bureau of the Census reports that approximately 545 companies are
engaged in the manufacture of semiconductors and related devices in the United
States. Table 2-2 shows the size distribution of companies by total employ-
ment. However, an August 1979 listing of plant locations compiled by the
Semiconductor Industry Association lists only 257 plants involved in the
production of semiconductor devices. Table 2-3 shows major world producers of
12
-------
TABLE 2-1. U.S. SALES OF SEMICONDUCTOR DEVICES,
$ mil lion?.a
Product
Total semiconductors
Discrete semiconductors
Diodes
Transistors
(includes bipolar MOSFET,
and junction FET)
Signal transistors
Thyristors
Integrated circuits
Standard logic facilities
(includes RTL, DTL, TTL,
ECL and C-MOS)
Microprocessors and micro-
computers (includes CPU's,
one-chip microcomputers,
LSI peripheral chips)
Dedicated LSI circuits
Memories (includes random-
access read-only, CCD's,
magnetic-bubble devices and
shift registers)
Linear IC's
Consumer product IC's
Optoelectronic devices
(includes photovoltaic
cells, photoconductive
cells, LED's, laser diodes,
photodiodes, phototran-
sistors, and optically
coupled isolators
Year
1978
3,937.6
1,035.6
370.2
533.9
251.0
114.5
2,694.5
813.1
210.9
95.5
850.3
594.7
130.0
207.5
1979
5,061.7
1,137.1
398.2
606.6
269.3
115.0
3,684.1
1,011.0
330.8
155.0
1,289.7
681.1
216.5
240.5
1980
6,360.5
1.202.2
421.9
640.4
283.3
122.4
4,876.3
1,192.8
532.4
210.5
1,922.2
746.4
272.0
282.0
1983
11,074
1,523
548
788
321
162
9,121
1,784
1,506
595
3,560
1,158
518
430
Annual
growth ,
%
18.9
7.1
6.8
7.8
5.2
9.0
22.3
15.3
31.9
31.1
Z7.4
11.1
25.4
13.3
a Dollars represent actual volume of sales unadjusted for inflation.
13
-------
16
14
ce
g
LL.
O
l/l
O
CO
10
SDISCRETES3
1977 1978 1979 1980 1981
YEAR
Figure 2-3. World total semiconductor production.8
14
-------
3000
2500-
2000-
1500 -
1000-
500-
1979 1980
OTHER
THYRISTORS
DIODES
1981
1982 1983
SMALL SIGNAL TRANSISTORS
RECTIFIERS
OPTOELECTRONICS
| | POWER TRANSISTORS
Floure 2-4. Worldwide shipments by U.S. Companies of discrete semiconductors
($ million).8
15
-------
(MILLIONS OF DOLLARS)
1980 - $4110
1985 - $5648
Figure 2-5. World discrete semiconductor market for
worldwide suppliers ($/million).8
16
-------
TABLE 2-2. COMPANY SIZE DISTRIBUTION BY TOTAL EMPLOYMENT FOR
SEMICONDUCTORS AND RELATED DEVICES^
Employment range
1 to 4 employees
5 to 9 employees
10 to 19 employees
20 to 49 employees
50 to 99 employees
100 to 249 employees
250 to 499 employees
500 to 999 employees
1,000 to 2,499 employees
2,400 employees or more
TOTAL
Number of companies
191
75
80
48
40
59
31
19
10
12
545
17
-------
Q
discrete semiconductor devices and their estimated share of the total market.
Table 2-4 gives a small sample of semiconductor manufacturers and their prod-
i a
6
uct lines. Finally, Table 2-5 gives a breakdown of the number of companies
producing each type of semiconductor.
Environmental Impacts
Air emissions from semiconductor device manufacturing Include acid fumes
and chlorinated organic solvent vapors. Acid fumes originate from solutions
used in most wet processes. Chlorinated organic solvent vapors are primarily
the result of surface cleaning and developing and stripping of resists.
Control of air emissions Involves collection of contaminated air streams using
hoods above processing baths and equipment, followed by wet scrubbing. Con-
taminant removal 1s based on segregation and treatment of similar air streams.
Total process water flow from semiconductor device manufacturing dis-
charged to POTW's (publicly owned treatment works) or surface waters on a
national basis is estimated to be 628 million liters per day. An average
plant's process water flow is estimated to be 2.44 million liters per day.
Due to the high purity requirements of the semiconductor manufacturing indus-
try, few plants recycle their water, although up to 80 percent recycle is
possible. The principal constituents of the liquid waste streams from semi-
conductor device manufacturing are suspended solids, fluorides, dichloroben-
zene, trichlorobenzene, trlchloroethane, and phenols. Values of pH in the
range of 2 to 3 are characteristic of the wastes as a result of the acid
cleaning and etching. A range of constituent concentrations found in end-of-
pipe raw liquid waste streams from semiconductor device manufacturing is shown
in Table 2-6. Waste stream suspended solids are comprised primarily of
metals from metal film deposition and semiconductor debris that is generated
during cutting and surface smoothing processes. Fluorides are primarily the
result of cleaning and surface etching processes utilizing weak and concen-
trated forms of hydrofluoric acid. The large amount of chlorinated hydrocar-
bons and, to a lesser extent, phenols present in the waste stream comes from
solvents and detergents used in the numerous chemical cleaning steps, as well
as resist developing and stripping.
The liquid wastes from semiconductor device manufacture may be controlled
using end-of-pipe treatment systems. Adjustment of pH with lime, ammonia, or
18
-------
TABLE 2-3. WORLD DISCRETE MARKET SHARE ESTIMATES
$ minion8
Company
Motorola
Philips
Texas Instruments
Toshiba
Siemens
Hitachi
Nippon
Matsushita
General Electric
RCA
Fairchild
AEG Telefunken
Others
Total Market
Year
1976
290
220
234
146
120
147
161
137
107
91
103
43
1,107
2,906
1977
315
234
227
152
135
152
182
132
109
98
99
71
1,253
3,159
1978
351
266
242
212
186
206
219
168
111
113
105
88
1,357
3,624
1979
419
290
260
242
206
284
195
134
126
124
116
107
1,567
3,990
19
-------
TABLE 2-4. SOME MANUFACTURERS OF DISCRETE SEMICONDUCTORS
8
ro
o
General Purpose Diodes
Zener Diodes
Field Effect Transistors (FFT's)
•Silicon Rectifiers (SCR's)
Selenium Rectifiers
Thyrlstors
Transistors. RF, Microwave
Transistors. Snail Slanal and Power
Silicon Rectifiers
Silicon Diodes
Power Transistors
VhTJS Transistors
Germanium Transistors
Gate Turnoff Transistors
nwn Power Transistors
Snail Signal Transistors
HI -Power Trlacs
Power Darlmqtons
&
X
X
X
I
X
X
,
Atlantic Senlconductor I
X
,
Codl Senlconductor |
X
X
Collmer Semlnconductor |
X
X
Falrchlld |
X
Power Semiconductor |
I
,
X
1
c
X
I
X
X
X
X
General Semiconductor (Gil) |
X
General Transistor (GTC) |
„
X
I
I
X
X
Intercomp Corporation |
1
X
I
X
I
X
X
§
c
5
S
C
I
•J
S
International Rectifier |
X
I
X
X
1
National Semiconductor 1
,
X
X
X
*•
c
1
X
Semtech |
I
X
M
I
X
X
X
X
X
,
95". SensUrnr |
X
Semlkron |
X
X
Solltron |
X
X
X
X
X
s
1
5
X
X
X
Unltrode Corporation ||
„
X
n
I
K
I
X
„
X
x
n
X
X
X.
e
S
X.
n
-------
TABLE 2-5. NUMBER OF COMPANIES PRODUCING VARIOUS SEMICONDUCTORS AND
THE QUANTITY OF SHIPMENTS OF EACH TYPE&
Product
SEMICONDUCTORS AND RELATED DEVICES
Integrated microcircuits (semiconductor
networks):
As reported In Census of Manufactures
As reported In Current Industrial Reports MA-36N, Selected
Electronic and Associated Products, Including Telephone
and Telegraph Apparatus
Hybrid integrated circuits, thick film; composed of material
deposited by silk screen process on a passive substrate
combined with discrete active or passive components
Hybrid integrated circuits, thin film; composed of material
deposited by vacuum deposition, sputtering, or similar
process on a passive substrate combined with discrete active
or passive components
Hybrid integrated circuits, multichip; circuits not incor-
porating film techniques. These are ususally combinations
of chips, active and/or passive. Discrete package devices may
be used for some, but not all of the circuits
Monolithic digital integrated circuits:
Bipolar:
DTL (diode transistor logic), excluding microprocessors
TTL (transistor transistor logic), excluding microprocessors
CML/ECL (current mode logic/emitter coupled logic), ex-
cluding microprocessors
I^L (integrated injector logic), excluding microprocessors
Microprocessors
Other bipolar digital integrated circuits, including diode
logic, complementary transistor logic, resistor transistor
logic, direct couple transistor logic, etc.
Metal oxide silicon (MOS):
Microprocessors
MOS memories
Other MOS devices
Monolithic analog integrated circuits
Transistors:
As reported in Census of Manufactures
As reported in Current Industrial Reports MA-36N, Selected
Electronic and Associated Products, Including Telephone and
Telegraph Apparatus
Signal (less than 1 watt dissipation)
Power (1 watt or more dissipation)
(continued)
Number of
companies
108
101
46
24
16
10
18
7
4
6
10
16
21
19
22
48
37
23
23
21
-------
TABLE 2-5 (continued)
Product
Number of
companies
Diodes and rectifiers:
As reported in Census of Manufactures 61
As reported in Current Industrial Reports MA-36N, Selected
Electronic and Associated Products, Including Telephone and
Telegraph Apparatus 41
Signal diodes and assemblies thereof (maximum current 0.5 amps) 13
Semiconductor rectifier/power diodes and assemblies thereof
(current rating greater than 0.5 amps) 28
Selenium rectifier 7
Microwave diodes (mixers, detectors, varactors, parametric,
harmonic generators, etc.) 17
Zener diodes (voltage regulator and voltage reference diodes) 23
Semiconductor devices, n.e.c., and parts for semiconductors:
As reported in Census of Manufactures 112
As reported in Current Industrial Reports MA-36N, Selected
Electronic and Associated Products, Including Telephone and
Telegraph Apparatus 118
Light sensitive and light emitting devices:
Solar cells 7
Light emitting diodes (LED) 8
Other 22
Other semiconductor devices:
Thyristors (SCR's, triacs, PNPN diodes) 14
All other semiconductor devices 15
Semiconductor parts:
Semiconductor devices and circuits:
chips (DICE) and wafers (DISCS) 26
All other semiconductor parts (headers, packages, heat sinks,
other accessories, etc.) 75
22
-------
TABLE 2-6. CHARACTERISTICS OF RAW WASTE STREAMS FROM
SEMICONDUCTOR DEVICE MANUFACTURING3
Parameter
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Cyanide
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Phenols
Oil and grease
Total suspended solids
Total organic carbon
Biochemical oxygen demand
Fluoride
1 ,2,4-trichlorobenzene
1 ,1 ,1-trichloroethane
Chloroform
1 ,2-dichlorobenzene
1 ,3-dichlorobenzene
1 ,4-dichlorobenzene
1 ,1-dichloroethylene
2,4-dichlorophenol
Ethyl benzene
Methyl ene chloride
Naphthalene
2-nitrophenol
4-nitrophenol
Phenol
Di-n-octyl phthalate
Tetrachloroethylene
Toluene
Trichloroethylene
Concentration
range, mg/ liter
<0. 001-0. 187
<0. 003- 0.067
<0.001-<0.015
<0. 001-0. 008
<0.001-1.150
<0. 005-2. 588
<0. 005-0. 01
<0.04-1.459
<0. 001-0. 051
0.005-4.964
<0. 002-0. 045
<0.001-0.013
<0. 001 -0.01 2
0.001-0.289
<0. 002-6.1
ND-20.8
ND-203
ND-80
9-202
ND-330
<0.01-27.1
<0.01-7.7
<0. 01 -0.05
<0. 01-186.0
<0.01-14.8
<0.01-14.8
<0.01-0.071
<0.01-0.017
<0.01-0.107
<0.01-2.4
<0.01-1.504
<0. 01-0. 039
<0. 01-0. 18
0.014-3.5
<0. 01-0. 01
<0. 01-0. BO
<0.01-0.14
0.007-3.5
Mean
concentration,
mg/ liter
0.021
0.018
0.002
0.003
0.129
0.570
0.005
0.145
0.004
0.502
0.021
0.005
0.015
0.093
0.630
5.058
31.61
55.676
52.768
62.0
4.643
1.395
0.015
15.972
1.450
1.341
0.029
0.012
0.021
0.244
0.214
0.024
0.061
0.519
0.01
0.122
0.018
0.322
Industry
wide pollutant
discharge,
kg/day3
13.2
13.2
1.9
1.9
99.9
540.7
3.8
61.5
5.7
655.6
6.9
3.8
11.3
46.5
812.6
2,778.3
30,470.6
17,094.2
38,848.1
35,909.0
257.5
928.2
15.7
499.3
174.0
156.4
9.4
9.4
6.3
276.1
19.5
27.6
15.1
203.5
6.3
363.0
33.9
177.1
Flowrate weighted.
NO - Not detected.
23
-------
sodium hydroxide is common. Segregation and treatment of Individual liquid
waste streams Is also practiced. There are also many commonly used In-line
technologies for reducing pollutant concentrations, for reducing wastewater
quantities discharged, for reclaiming potential pollutants for reuse, and for
reusing water Itself. Generally, in-line treatment 1s an effective method for
improving the performance of end-of-pipe treatment systems.
Solid wastes produced during semiconductor device manufacturing include
sludges generated during treatment of liquid process wastes and semiconductor
debris from polishing wafer surfaces. Suspended particulates typically con-
tain fine semiconductor material and abrasive particles. The semiconductor
materials include silicon wafer particles and small amounts of dopant.
Sludges primarily contain precipitated calcium fluoride and other precipitates
of spent processing chemicals. Sludges may be dewatered and disposed on-site
or contract hauled off-site. Metal and chemical recovery from sludges is also
practiced on or off-site.
INDUSTRY ANALYSIS
The following industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potential effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
As indicated in the Industry Description, there are a large number of types of
semiconductors and related devices. Some information was found in the litera-
ture on the production methods used for two categories of these components:
(1) transistors and diodes, and (2) integrated circuits (IC's) and light-
emitting diodes. Figures 2-6 and 2-7 are flowsheets showing the processes
used for these devices, as well as their interrelationships and major waste
streams.
24
-------
SEMICONDUCTOR1
INGOT
WAFER CUTTING,
SMOOTHING, AND
POLISHING 1
t
CHEMICAL
CLEANING AND
POLISHING 2
t
EPITAXIAL
GROWTH 3
t
CIRCUIT
FABRICATION 4
*
DIFFUSION 5
1
METAL
INTERCONNECTION
1
S
1
Bj
1
-------
C
,
SEMI CONDUCTOR
WAFER CUTTING,
SMOOTHING, AND
POLISHING .
CHEMICAL
CL FAN ING AND
POLISHING 2
J sp
EPITAXIAL
GROWTH 3
CIRCUIT
FABRICATION
METAL
INTERCONNECTION,
MOUNTED
WAFER
o WATER
A AIR
OSOLID
Note: Process No's. 3 and 4 are repeated up to
20 times for IC's and only once for LED's.
Figure 2-7. Integrated circuit (1C) and light emitting
diode (LED) production flowsheet.
26
-------
SEMICONDUCTORS PROCESS NO. 1
Wafer Cutting. Smoothing, and Polishing
1. Function - Semiconductor device manufacturers purchase ingots of
doped silicon material or "grow" their own crystals. In either event, the
ingot must be sliced into wafers prior to device manufacture. The slice may
be circular and range from 1.3 to 10.2 cm in diameter. It may also be trape-
zoidal or semicircular. After slicing, the wafer is rinsed and smoothed to
make both sides flat and parallel. Smoothing is followed by another rinse,
polishing, and a final rinse.
Wafer cutting is performed with reciprocating saws, wire saws, rotating
(circular) saws, or in some instances ultrasonic cutters. Reciprocating and
rotating (circular) saws use an abrasive material such as diamond, boron
carbide, silicon carbide, or garnet, which is a component of the saw blade
itself. These blades are often operated in the presence of a cooling or
lubricating slurry. Circular saw blades attain peripheral speeds of 1500 to
2300 cm/sec when silicon or germanium is cut. These high speeds require that
a coolant be injected into the cut to reduce exposure of the blade to exces-
g
sive heat. Reciprocating saws employ steel blades with a diamond abrasive
plating. Wire saws are usually composed of a copper metal alloy. This cut-
ting method often employs the use of an abrasive slurry to perform the actual
cutting. The ultrasonic method also achieves cutting through the use of
abrasive slurries.
Wafer smoothing consists of either lapping or grinding operations used to
remove up to 50 pm of material from the wafer surface. Lapping can remove
material from both sides simultaneously, resulting in surfaces which are
parallel to within 2.5 urn. Grinders using abrasives can be used to achieve
the wafer smoothing. Smoothing is often achieved with a dry abrasive.
Wafer polishing is similar to smoothing, except that it is performed to
remove wafer irregularities left behind after the smoothing operation has been
completed. Occasionally, hydrochloric acid or sodium hydroxide is used to
adjust the pH of the polishing compound. Hydrogen peroxide is added to
polishing compounds for germanium polishing.
27
-------
2. Input Materials - Wafer cutting requires the input of specific
semiconductor material to be cut. Types of material include silicon, germanium,
gallium arsenide, gallium phosphide, and indium antimonide. Cutting blades
may contain diamond, boron carbide, silicon carbide, or garnet abrasives.
Wire or ultrasonic cutting systems will employ abrasive slurries containing
proprietary solutions. Wafer smoothing requires dry abrasives containing
diamond, alumina, zirconia, and chromic oxide. Polishing compounds may be
composed of diamond abrasive in an oil suspension. Other compounds may employ
water as a liquid carrier. Hydrochloric acid, aqueous sodium hydroxide, or
910
hydrogen peroxide may be added to polishing compounds to adjust for pH. '
3. Operating Conditions - The steps of cutting, smoothing, and mechanical
polishing are all carried out at conditions of ambient temperature and pressure.
4. Utilities - Tap water is used for cooling diamond tipped saws.
Deionized rinse water is required following milling operations. Electricity
is used to run the mechanical equipment such as saws, lapping machines, and
grinders.
5. Waste Streams - There are no air emissions reported for this process.
Wastewater includes cooling water from slicing operations that use dia-
mond tipped saws and from deionized water rinses following slicing, smoothing,
and polishing. The wastewaters contain semiconductor particles and abrasive
materials from smoothing and polishing. Machining waste stream characteris-
tics for an isolated plant are presented in Table 2-7.
There are no solid wastes other than scrap from cutting and grinding
operations.
6. Control Technology - Lime, ammonia, or caustic are typically used for
pH adjustment, followed by clarification for solids removal. The settled
solids are then collected, dewatered, and disposed on-site or contract hauled
for off-site disposal.
28
-------
TABLF 2-7. SEMICONDUCTOR MACHINING WASTE FOR A TYPICAL PLANT
(Flow - 10,409 liter/h)3
Pollutant
Concentration,
mg/liter
Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver-
Thallium
Zinc
Aluminum
Barium
Boron
Calcium
Cobalt
Gold
Iron
Magnesium
Manganese
Molybdenum
Palladium
Platinum
Sodium
Tellurium
Tin
Titanium
Vanadium
Yttrium
Phenols
Oil and grease
Total suspended solids
Biochemical oxygen demand
1,1,1-Trichloroethane
1,1-Dichloroethane
Chloroform
1,2-Dichlorobenzene
Methylene chloride
Phenol
Bis(2-ethylhexyl)phthalate
Di-N-Butyl phthalate
Pi ethyl phthalate
0.007
0.003
<0.001
<0.001
<0.001
0.046
0.001
<0.001
<0.001
<0.003
<0.005
<0.025
1.113
0.015
0.024
0.222
28.040
<0.001
<0.020
0.169
13.500
0.006
0.001
<0.080
<0.050
111.601
<0.020
0.023
0.006
0.091
<0.001
0.032
9.0
885
310
<0.01
0.01
0.02
<0.01
0.035
0.031
<0.01
<0.01
<0.01
29
-------
SEMICONDUCTORS PROCESS NO. 2
Chemical Cleaning and Polishing
1. Function - Chemical cleaning and polishing are key operations in
producing wafer surfaces free of imperfections which might interfere with
circuit or device fabrication. Both of these procedures are designed to
remove embedded particles and contaminants from wafer surfaces. This is
achieved through the use of degreasing solvents to remove organics or acids to
remove damaged surfaces. The operations may be assisted through ultrasonic
agitation of the bare substrate. Only bare silicon wafers are ultrasonically
cleaned. Wafers with semiconductor devices already fabricated on their sur-
g
faces will be too frail for such a technique. Following either degreasing or
acid treatment, the clean, polished wafers are rinsed in deionized water and
blow-dried with air or nitrogen.
2. Input Materials - A typical ultrasonically agitated cleaning bath
contains potassium chromate solution or other mildly alkaline solutions such
as sodium hydroxide, potassium hydroxide, hydrazine, ethylenediamine, sodium
silicates, or sodium hypochlorite. A complexing or chelating agent usually
consisting of an alcohol is used to effect dissolution. Alcohols used include
isopropanol, n-propanol, sec-butanol, and pyrocatechol. For silicon wafers,
acid baths are composed of various mixtures of nitric, hydrofluoric, and
acetic acids. For germanium wafers, acid baths are composed of a mixture of
hydrogen peroxide and hydrofluoric acid. The most commonly employed cleaning
baths for gallium arsenide and gallium phosphide are comprised of bromium-
methanol, sodium hydroxide-hydrogen perioxide, sulfuric acid-hydrogen perox-
ide-water, ammonium hydroxide-hydrogen peroxide-water, or glycerol-hydro-
chloric acid-nitric acid. High viscosity acid mixtures are preferred for
chemical polishing because the preferential reaction results in a leveling
action.
3. Operating Conditions - Ultrasonic cleaning is a very rapid process
requiring only a few minutes per wafer. Sound vibrations of 20 to 40 kHz are
imparted to the cleaning solution. Cleaning solutions are used at room tem-
perature although, in time, ultrasonic agitation will cause the temperature to
rise.
30
-------
The acid baths used in the chemical cleaning operations may be heated as
high as 86°C.
4. Utilities - Electricity is used to operate conveyor mechanisms on
automated production lines. In addition, ultrasonic agitation is electrically
operated. Deionized water is used for rinsing, while compressed air or nitro-
gen is required for drying.
5. Waste Streams - Air emissions consist of acid fumes from hot acid
baths.
Liquid wastes include add and alkaline contaminated rinse water, spent
cleaning solutions, and acid baths. Typically, spent cleaning solution bath
dumps are 4 to 7 liters in volume.
There are no solid wastes reported for this process.
6. Control Technology - Acid fumes may be collected by hoods over proc-
ess baths and sent through ducts to a wet scrubber. The scrubbed air is dis-
charged to the atmosphere, while the acid is contacted with water or some
other medium.
The acid contaminated effluent from the wet air scrubber 1s mixed with
spent acid baths, acid contaminated rinsewater, and alkaline cleaning solu-
tions, and finally pH adjusted with lime or sodium hydroxide. The liquid
effluent is then sent to a clarifier where acid and alkaline salts settle out
and are dewatered prior to contract hauling to disposal.
31
-------
SEMICONDUCTORS PROCESS NO. 3
Epitaxial Growth
1. Function - Semiconductor wafers are Inserted Into an epitaxial growth
furnace (oven) where they receive a polishing etch. A very thin layer (2 to
25 urn) of doped semiconductor is then grown on top of the polished wafer
surface. Silicon wafers are subsequently covered with a thin film of silicon
12
dioxide. The techniques by which an epitaxial layer of material is grown on
an existing surface fall into two classifications, direct and indirect.
Direct techniques involve deposition of the semiconductor on the existing
surface directly with no intervening chemical reactions. Direct processes
include sputtering, evaporation, and sublimation.
Indirect techniques, which involve chemical and physical interaction of
reactants to form the semiconductor in a multistep deposition technique, are
used far more often than direct techniques. The indirect technique is per-
formed in either a closed-tube or open- tube system. In a closed-tube sys-
tem, the substrate and reactants are sealed in a precleaned quartz tube that
is under vacuum or filled with an inert gas. The sealed tube is placed in a
two-zone oven and heated utilizing radio frequency (RF) induction. The re-
actants are in the high temperature zone and the wafer is in the lower tem-
perature zone. Germanium and silicon wafers are first treated at high tem-
peratures with a dilute gaseous etchant. Under heat, the semiconductor mate-
rial reacts with the etchant to produce a highly polished surface prior to
epitaxial growth. The reaction rate varies with etchant concentration.
Deposition of semiconductor onto the substrate proceeds after stopping the
etchant gas flow and starting the flow of the gaseous reactants which starts
a "disproportion" reaction. Doping of the film is achieved with predoped
reactants.
Open-tube systems are used for "disproportionation" reactions, as well as
"decomposition and reduction" reactions. Decomposition and reduction reactors
have only one temperature zone. A flat external heater or direct RF heating
Q
is used. After epitaxial growth is completed, silicon wafers are exposed to
a source of oxygen which causes an oxide film that acts as an insulator to
32
-------
12
grow on the top surface of the wafer. Process No. 5 presents further de-
tails of the open-tube system. Table 2-8 1s a summary of methods (open-tube
or closed-tube system) for silicon, germanium, and gallium arsenide wafer
g
substrates.
2. Input Materials - For silicon wafer polishing etch, the gaseous
mixture used contains hydrogen as the carrier gas with <1 percent of hydrogen
chloride, sulfur hexafluoride, hydrogen bromide, hydrogen Iodide, chlorine,
hydrogen sulfide, water vapor, or a hydrogen iodide-hydrogen fluoride mixture.
Germanium can be polish-etched with anhydrous hydrogen chloride, a mixture of
hydrogen iodide in hydrogen, hydrogen sulfide in hydrogen, or water vapor in
hydrogen. Epitaxial growth reactants and dopants are all used in gaseous
forms. Dopants consist of phosphorus, arsenic, or boron in either of two
different compounds. These may be pnosphine (PH.) or phosphorus trichloride
(PCI,), arsine (AsH.) or arsenious chloride (AsCl.), or boron hydride {B,He)
j J j c. o
or boron trichloride (BC1_). Dopants are always diluted with hydrogen (H_)
gas. Reactants for silicon growth are silicon tetrachloride (S1C1.) or silane
(SiH.), which are also diluted with hydrogen. Reactants for germanium growth
are germanium tetrachloride (GeCl.) or germanium tetraiodide (Gel.), and they
are also diluted with hydrogen. The reactants for semiconductor growth are
mixed with the dopants prior to feeding into the oven. Nitrogen or hydrogen
may be used as inert gas prior to or after the epitaxial reactions. After
epitaxial growth, oxygen or steam is used as the oxygen source to grow the
silicon dioxide film on the top surface of the wafer.
3. Operating Conditions - Etching temperatures are primarily 1050° to
1200°C for silicon and 650° to 910°C for germanium, with a gas flow rate of 9
liters/min. Temperatures in the two-zone oven reach up to 1300°C. The ovens
are maintained under a vacuum of 10~ torr. The wafers are heated for several
hours.
4. Utilities - Electric power is required for operating vacuum pumps,
induction heaters, and control equipment. Inert gas is required for relieving
vacuum and diluting dopant gases.
5. Waste Streams - Air emissions consist of excess dopant gases and out-
gassed dopant from substrate material. In addition to hydrogen chloride vapor
from the etchant, hydrogen chloride is also produced as a reaction by-product
from the chlorinated compounds that are used.
33
-------
TABLE 2-8. INDIRECT EPITAXIAL GROWTH TECHNIQUES5
Wafer
substrate
Method
Reaction
Normal growth
temperature, °C
Contents
Silicon
ui
Germanium
Gallium
arsenide
Open tube
Open tube
Open tube
Open tube
Open tube
Closed-tube disproportionate
Open-tube disproportionate
Open tube
Open tube
Closed-tube disproportionate
Open-tube disproportlonatlon
Combination
Closed-space disproportionate
H2 red. of S1C14
HZ red. of S1HC13
HZ red. of S1Br4
H2 red. of SI 14
Thermal decomposition of
S1H4
2S1Iz * SI + SI 14
SI + HC1 -•
S«C14 + HZ
S1C14 +
» SI %
H? red. of GeCl4
Thermal decamp, of GeH4
2GeI2 * Ge + GeI4
HC1 transport
HC1 transport of gallium,
reduction of AsCl3
Water vapor
1050-1250
1050-1250
1050-1200
450-650
1050-1250
600-800
500-800
350-450
Host widely used
Faster growth rates than for S1C14
system
Expensive, seldom used
Expensive, seldom used
Very high deposition rate at reduced
pressures, hydrogen only by-product
Has been used for very low temperature
growth, closed tubes Inconvenient to
use
Seldom used Intentionally, often occurs
on back of slices
Host widely used
Very connonly used
-------
Water emissions consist of excess etchant. Process waste characteristics
at an Isolated plant for quartz tube cleaning are presented In Table 2-9.
There are no solid wastes.
6. Control Technology - The epitaxial furnaces are vented to wet air
scrubbers to remove pollutants from the air prior to discharge.
The water from the wet air scrubbers 1s reclrculated. An average bleed-
off rate of 35 liter/min discharged to waste treatment has been reported.
The bleed-off 1s performed to reduce scrubber water acidity and pollutant
concentrations.
35
-------
TABLE 2-9. SEMICONDUCTOR PROCESS WASTE FOR AN ISOLATED PLANT3
Process
Flow (liter/h)
Duration (h)
Pollutant
Antimony
Arsenic
Beryl 1 i urn
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Al umi num
Barium
Boron
Calcium
Cobalt
Gold
Iron
Magnesium
Manganese
Molybdenum
Palladium
Platinum
Sodi uma
Tellurium
Tin
Titanium
Vanadium
Yttrium
Fluoride
Quartz tube
cleaning
29
24
Concentration,
mg/ liter
<0.005
0.074
<0.001
0.05
<0.001
<0.001
0.25
<0.001
0.90
<0. 003
<0. 005
<0.025
0.80
16.31
0.05
60.66
45.92
0.48
0.02
0.46
23.78
<0.001
0.57
<0.08
<0.05
161.57
0.02
1.01
0.03
0.16
<0.001
290
Crystal growth
scrubbers
2580
24
Concentration,
mg/liter
0.017
0.007
<0.001
<0.001
0.011
0.007
<0.001
<0.001
<0.001
<0.003
<0.005
<0.025
0.059
<0.001
0.026
0.164
35.830
0.003
<0.020
0.047
19.080
<0.001
0.004
<0.080
<0.050
49.711
<0.020
0.011
<0.001
0.130
<0.001
290
Carry through from incoming water.
Note: Analyses not conducted for organics.
36
-------
SEMICONDUCTORS PROCESS NO. 4
Circuit Fabrication
1. Function - Circuit fabrication 1s actually a series of steps designed
to produce Images of both devices and circuits on the surface of a wafer.
Specific methods used to create and transfer the circuit pattern vary depend-
ing on design specifications and overall precision required for the final
product. All methods Involve use of a photosensitive emulsion called photore-
sist, or simply resist, that hardens and clings to the wafer surface when
exposed to light. Additional Information on photoresist materials and processes
can be found In Section 6, Printed Circuit Boards.
Adherence of resist to the wafer depends on thorough cleaning of the
oxide surface and proper drying to ensure that pockets of solvent are not
trapped on the wafer surface. The oxide surface of the wafer 1s cleaned In
alternating baths of alcohol and boiling solvent, followed by a soak In hot
add. Final rinses In alcohol and solvent precede drying. A simple solvent
bath will suffice for wafers properly stored prior to the circuit fabrication
process. To reduce the probability of trapping solvent pockets, drying is
performed by spinning the wafer in the air; this is followed by heating.
After drying, a thick coat of photoresist is applied, often using a dropper to
distribute resist onto a wafer spinning at high speed. During the spinning,
excess photoresist is quickly thrown off by centrifugal force. Resist film
thicknesses range between 0.2 and 1.0 ym. The resist then goes through a
911
short drying step followed by baking. '
Next, a photographic reproduction of the circuit pattern ("photomask") is
aligned with the wafer. The resist is exposed for 5 seconds to ultraviolet
light through transparent areas of the photomask. Negative-image resist
materials polymerize and stabilize upon exposure to ultraviolet light, fol-
lowing which unexposed areas are dissolved away by developer solvent. This
leaves resist on the areas of the wafer which were under the transparent areas
of the photomask. Positive-image resist materials, on the other hand, are
made more soluble by exposure to ultraviolet light. Following resist ex-
posure, developer solvent is used to remove resist material which was under
37
-------
the transparent areas of the photomask. ' For either Image transfer
method, the remaining resist 1s spun or blown dry and given a post-development
bake. Some processes use another exposure to ultraviolet light Instead of
baking. Both procedures Improve polymerization, adherence, and resistance of
the photoresist to subsequent etching. After baking, the wafer 1s allowed to
cool.9*11
The wafer oxide surface not protected with resist Is then subjected to an
acid etch that Is completed when the wafer substrate material 1s exposed.
Etching produces depressions 1n the oxide layer called windows. The windows
are holes through which the diffusion of dopants later occurs (Process No. 5).
Etch time 1s determined by oxide thickness and etch rate. Etch rate-1s a
function of acid concentration. After the add etch, the wafer 1s rinsed.
This Is followed by Immersing the wafer In resist stripping solution to remove
all remaining resist and another rinse. The wafer 1s then spun or blown dry
g
with nitrogen.
2. Input Materials - The chemicals used to clean the wafer surface are
composed of methyl alcohol, methylene chloride, trichloroethylene, and nitric
acid. Photosensitive resist is a light sensitive polymer. These polymers are
available either as a liquid or dry solid. The nature of these resists is
proprietary but they typically contain vinyl cinnamate, quaternary salts, and
azide polymers. Developing solutions used to remove soluble resist are gen-
erally trichloroethylene, chlorinated hydrocarbons, mixtures of either 10
percent alcohol and 90 percent Stoddard solvent, proprietary commercial de-
veloping solutions, or xylene, acetone, ketones, esters, and alkali-based
solutions. Etching is carried out using hydrofluoric acid. Resist strippers
consist of sulfuric acid and proprietary commercial strippers which contain
sulfuric-dichromate, ammoniacal hydrogen peroxide, metachloroperbenzoic acid,
or other chemicals.
3. Operating Conditions - For wafer cleaning with trichloroethylene, the
cleaning solvent is kept at a gentle boil (~90°C). Nitric acid soaks are
performed at 80°C for approximately 20 minutes. No Information was found for
the operating temperatures of hydrofluoric acid, methyl alcohol, or methylene
chloride. Spin drying requires 30 seconds at 2000 to 4000 rpm. Wafer heating
to remove solvent uses hot plates at 150°C to 175°C for 1 minute. During
resist application, the wafer spins at 4000 to 10,000 rpm for about 1 minute.
38
-------
Predevelopment drying takes place in a nitrogen box for 15 to 30 minutes or In
a dessicator for 1 hour. Predevelopment baking requires approximately 10 to
20 minutes at 85° to 120°C. Developing temperatures range from ambient to
90°C, while developing times range from 30 seconds to 4 minutes. Postdevelop-
men t baking lasts for 10 to 30 minutes at 120°C to 200°C. Commercial resist
strippers require approximately 10 minutes, while sulfuric acid requires 20
minutes at 100°C.
4. Utilities - Circuit fabrication is typically automated, requiring
electricity to run conveyors and other mechanical equipment. Baking and other
heated operations also use electricity to maintain desired temperatures.
Deionized water is required for rinsing.
5. Waste Streams - Air emissions consist of organic solvent vapors from
wafer cleaning, drying, baking, and developing solvents, as well as fumes of
nitric acid, hydrofluoric acid, and possibly sulfuric acid.
Liquid wastes include rinse waters from developing, acid etching, and
resist stripping as described in Table 2-10. These wastes contain solvents,
acids, and photoresists.
There are no solid wastes from this process.
6. Control Technology - Organic solvent vapors that are produced from
cleaning, resist drying and baking, and developing may be collected with fume
hoods and conveyed through ducts to a carbon absorption bed. The carbon bed
is regenerated with steam and the organic solvents are collected in drums or
tanks and hauled off-site for recycling or disposal. Acid fumes may be col-
lected with separate chemical fume hoods and conveyed through ducts to a wet
scrubber where they are contacted with water or some other material which will
collect the fumes. The scrubbed air then passes on to the atmosphere, and the
scrubbing solution is treated along with the other acidic waste streams.
Rinse waters containing developing solvents and resist are routed to one
sump where these materials can be collected for recovery or disposal. Dis-
posal methods include incineration or contract hauling. Spent developing
solvents are collected and contract hauled. Acidic rinse waters receive pH
adjustment using sodium hydroxide or lime followed by sedimentation. The
collected solids are then dewatered and hauled away for disposal.
39
-------
TABLE 2-10. SEMICONDUCTOR PROCESS WASTES FOR THE
CIRCUIT FABRICATION PROCESS3
Process
pollutant
Antimony
Arsenic
Beryl 1 i urn
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Aluminum
Barium
Calcium
Cobalt
Iron
Magnesium
Manganese
Molybdenum
Sodium3
Tin
Titanium
Vanadium
Yttrium
Phenols
Oil and grease
Cyanide
Total suspended solids
Total organic carbon
Biochemical oxygen demand
Fluoride
Chloroform
Methylene chloride
Toluene
Developer
rinse
concentration,
mg/ liter
<0.005
<0.003
<0.001
0.003
0.004
0.015
0.019
<0.001
0.057
<0.003
<0.003
<0.025
0.022
0.046
0.004
1.718
<0.001
0.005
0.077
0.001
0.004
0.071
0.023
0.002
0.001
0.005
0.014
3.0
<0.005
<5.0
30
<4.0
0.15
0.026
0.042
0.017
Etch
rinse
concentration,
mg/ liter
0.005
0.003
0.001
0.003
0.003
0.046
0.161
<0.001
0.07
<0.003
<0.003
<0.025
0.048
5.781
0.011
2.371
<0.001
0.149
0.142
0.006
0.019
18.315
0.203
0.036
0.081
<0.001
0.016
<1.0
<0.005
31.0
<1.0
<4.0
875
<0.01
<0.01
Strip
resist rinse
concentration,
mg/ liter
<0.005
<0.003
<0.001
0.001
0.001
0.019
0.012
<0.001
0.005
O.003
<0.003
<0.025
0.032
0.031
0.006
0.258
<0.001
0.026
0.034
0.001
<0.001
0.143
0.006
0.001
0.001
0.001
0.007
1.0
<0.005
<5.0
<1.0
<4.0
0.24
0.021
<0.01
<0.01
Carry through from incoming water.
40
-------
SEMICONDUCTORS PROCESS NO. 5
Diffusion
1. Function - Dopants are Impurities such as boron, phosphorus, and
other specific metals introduced into the semiconductor to form both devices
and circuits through which electrical impulses are conducted. Diffusion is an
evaporative process in which the dopant is heated in a furnace which causes it
to reach a gaseous state. The atoms of the dopant bombard the wafer and enter
the semiconductor substrate through the "windows" (see Process No. 4) and
penetrate to controlled depths to form the lattice of devices within the
wafer.3
The most commonly used diffusion technique employs the open-tube system.
The semiconductor wafers are placed in a heated tube and a continuous flow of
inert gas is maintained across the wafer slices during diffusion. Liquid or
gaseous dopant sources require a single zone furnace around the tube. The
dopant source is either deposited on the surface of the wafer before it enters
the tube, or is carried in by the inert gas stream. In the first surface
deposition method, a "paint-on" dopant is used in which some evaporable liquid
containing the desired diffusing element is applied to the wafer by dipping or
spraying. In the second method, a gaseous dopant is added to the flow of
inert gas passing through the furnace. Solid dopants require a two-zone
furnace around the tube. Solid dopants are heated in the higher temperature
zone of the two-zone furnace to a temperature at which there is an appreciable
vapor pressure. An inert gas is then used to sweep the vapor into the other
zone of the furnace where the diffusion of the dopant into the semiconductor
takes place.11'14
2. Input Materials - The inert gas carriers are usually argon or nitro-
gen. Common flow rates for open-tube systems are 0.5 to 5.0 liter/min. When
liquid or gaseous dopants are used, oxygen is also introduced into the gas
11
11
stream at rates of up to several hundred cm /min. Table 2-11 shows the
dopants used and their physical states at room temperature.
3. Operating Conditions - The semiconductor wafer is heated to between
900° to 1300°C in the furnace. Diffusion times range from 25 minutes to
several hours. The temperature ranges of dopants during diffusion are not
41
-------
TABLE 2-11. COMMON DIFFUSION SOURCES FOR OPEN TUBE SYSTEMS
11
Dopant source
material
Commonly used for
silicon diffusion:
As2I3
2 5
H,BO,
3 3
B2°3
Sb90A
2 4
Commonly used for
germanium diffusion:
As
Sb
Others:
P3N5
In
P
POC13
PC13
PBr3
AsCl3
BCl,
BBr3
Ga
PH,
AsH3
B2H6
Physical
statea
S
S
S
S
S
S
S
S
S
S
L
L
L
L
L
L
L
G
G
G
Temperature
ranges, b
170-220
100-300
600-1200
50-400
300-600
500-1000
550-700
150-350
0-40
170
Room temperature
0-30
600-900
Room temperature
Room temperature
Room temperature
S-solid, L-liquid, G-gas (at room temperature).
Dopant source during diffusion, °C.
42
-------
necessarily the same as the wafer. Dopant temperatures are shown In Table
2-n.11
4. Utilities - Furnaces are heated directly or indirectly by electric-
ity. Inert gas is also required for diffusion.
5. Waste Streams - Inert gases (argon or nitrogen) contaminated with
dopant gases are vented from diffusion furnaces. The contaminant dopant gases
are listed in Table 2-11.n
There are no process liquid or solid wastes.
6. Control Technology - Diffusion furnaces may be vented to the same wet
scrubbers as the epitaxial growth furnaces (Process No.'s 3 and 4) to remove
pollutants from the gas stream prior to discharge. The water from the scrub-
bers is recirculated, with an average bleed-off rate reported to be 35 liter/
min discharged to the plant waste treatment system.
43
-------
SEMICONDUCTORS PROCESS NO. 6
Metal Interconnection
1. Function - A thin metal film is deposited onto the wafer surface to
provide contact points for final product assembly and to electrically connect
two or more doped semiconductor layers that make up a circuit. One of two
methods is commonly used to effect this metallization, sputtering or evapora-
tion. ' In sputtering, the metal charge and precleaned wafer are mounted in
a vacuum system. An electron beam bombards the metal charge directly without
heating anything else. A small puddle of metal is melted in the center of the
surface of the charge and emission takes place from its surface. The metal
then collects on the wafer surface. Evaporation is somewhat similar to sput-
tering, but the metal charge is heated by a hot filamet. When the process is
completed and the wafer has cooled, the vacuum is relieved and the wafer is
removed.3'9'11
The metal charge and the wafers to be coated are thoroughly cleaned prior
to metallization. The filament used in evaporation is degreased in hot sol-
vent. The metal charge and wafers are each cleaned in a dilute acid, rinsed
3911
in deionized water, and blown dry with nitrogen. '
For either method, the entire surface of the wafer is coated with resist
after it is covered with a thin layer of metal. This is followed by a pre-
exposure bake. The wafer is aligned with the proper photomask and exposed to
ultraviolet light. Resist is developed using a developer solvent, and unex-
posed resist is then washed away. Both positive and negative image transfer
methods may be used (see Process No. 4). This is followed by drying and
another baking. The metal film that is not protected with resist is etched
away in an acid bath, and the wafer is rinsed and dried. Resist remaining
after etching is removed by immersing the wafer in a resist stripping solu-
tion, which is followed by a water rinse, a hot alcohol soak, a cold alcohol
rinse, and a final drying. Finally, if the metal deposition step was not
carried out at high temperatures, the deposited metal undergoes an alloying
step to improve metal-semiconductor contact. This alloying involves heating
the wafer to a temperature just above the semiconductor-metal eutectic temper-
ature. The effect is a microalloying of the deposited film into the silicon
44
-------
surface with which it is in contact. This step promotes good electrical
q
contact.
The entire metal deposition procedure may be repeated for Instances where
more than one metal layer is to be deposited. Following metallization, an
insulator 1s deposited which prevents outside contact to the metal films. The
finished wafer is then diced and mounted.
2. Input Materials - Aluminum is the most common metallization used. A
thickness of 1 urn 1s deposited for most thin film circuits, while high powered
circuits require up to an 8 urn thick layer. Other metals used for intercon-
nection include chromium, platinum, and the alloys of chromium-gold, chromium-
copper, and tantalum-aluminum. The insulation is mainly silicon oxide.
g
Insulator thickness is regularly 50 urn for all crossovers. Prior to metal
film deposition by the evaporation method, tungsten filaments are degreased in
trichloroethylene. The metal charge 1s cleaned with dilute hydrofluoric and
phosphoric acid, while silicon wafers are also cleaned with dilute hydro-
910
fluoric acid. Photosensitive resists are described in Process No. 4. The
primary etchant used to remove metal films is a mixture which contains 85
percent phosphoric acid, 70 percent nitric acid, and deionized water in a
ratio of 10:1:2.5 (by volume). Some use is also made of potassium hydroxide
solutions for electrochemical etching. Commercial resist strippers may be
used alone or mixed with methylene chloride in a ratio of 1:3. Following the
stripper rinse, methyl alcohol is used to aid removal of stripper and to speed
q
drying without leaving a film of residue.
3. Operating Conditions - The vacuum system containing the metal charge
and wafer is evacuated to a pressure of 10" to 10" torr. When the charge is
2 1
heated, its vapor pressure reaches 10 to 10 torr. Deposition of the metal
film occurs at a rate of about 1 urn/sec. Deposit of the sputtered metal oc-
curs on the target (silicon substrate) or within the vacuum containment vessel.
No particulate or gaseous emissions are anticipated from a sputtering opera-
tion. The silicon wafer is heated to 540° to 575°C for the deposition of
aluminum on silicon. After coating the metal, the wafers are resist-coated
directly or stored. If stored for any length of time, the wafers are heated
for 10 minutes at 150°C before applying resist. During resist application,
the wafer spins at 4000 to 10,000 rpm for about 1 minute to disperse the
45
-------
resist evenly. Pre-exposure baking 1s performed at 85°C for 10 to 20 minutes.
Exposure to an ultraviolet source requires only 5 seconds. Developing In-
volves immersion in several solutions and requires 5 minutes. Post-exposure
bake requires approximately 30 minutes at 135°C. Add etching baths are
maintained at 45° to 55°C. Wafers are immersed in the add until etching is
complete as determined by visual observation.
4. Utilities - Electricity is required to heat the metal charge and the
wafer, to bake the resist, and to do other process heating. DeIonized water
is used for rinsing and making up etching solutions. Compressed nitrogen is
used to dry the wafer after rinsing.
5. Waste Streams - Air emissions consist of organic solvent vapors from
filament cleaning, resist drying, developing solutions, and resist strippers.
Acid fumes originate from acid cleaning the metal charge and wafer surface,
and from acid etches used to remove metal from unwanted areas of the wafer
surface.
Liquid organic wastes include spent baths of developer and resist strip-
per and rinsewater contaminated with stripper and photoresist. Liquid wastes
also Include spent acid baths and acidic rinsewater containing dissolved
metals, as described in Table 2-12.
Solid wastes from this process are minimal.
6. Control Technology - Organic vapors from cleaning, resist drying, and
baking may be collected with fume hoods and conveyed through ducts to a carbon
adsorption bed. The carbon bed is regenerated with steam and the solvent is
collected for off-site disposal or recycle. Acid fumes may be collected with
a separate .chemical fume hood and conveyed through ducts to a wet scrubber
where they are contacted with water or some other liquid which will remove the
fumes. The scrubbed air then passes on to the atmosphere while the scrubber
liquid is treated along with the other acidic waste streams.
Rinse water containing developing solvents and resists is routed to one
sump where these materials can be collected for recovery or disposal. Dis-
posal methods include incineration or contract hauling. Spent developing
solvents are collected and contractor hauled. Acidic rinse waters receive pH
adjustment using sodium hydroxide or lime, followed by sedimentation. The
collected solids are dewatered and hauled away for disposal.
46
-------
TABLE 2-12. METAL INTERCONNECTION ETCH RINSE FOR
AN ISOLATED PLANTS
Pollutant
Concentration,
mg/liter
Antimony
Arsenic
Cadmiurn
Chromium
Copper
Lead
Mercury
Nickel
Silver
Thallium
Zinc
Phenols
Cyanide
Chloroform
Methylene chloride
Bi s(2-ethylhexyl)phthalate
Butyl benzyl phthalate
Di-N-butyl phthalate
Di-N-octyl phthalate
Diethyl phthalate
Toluene
<0.002
<0.003
<0.003
<0.02
<0.003
<0.01
<0.001
<0.025
<0.002
<0.02
0.002
<0.01
<0.005
0.066
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
47
-------
REFERENCES FOR SECTION 2
1. Jones, Thomas H. Electronic Components Handbook. Reston Publishing Co.,
Inc., Reston, Virginia, 1978.
2. Colwell, Morris A. Electronic Components. Newnes Technical Books,
Butterworth, England, 1976.
3. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80-075-a, October
1980.
4. Briggs, T.M., and T.W. Owens. PEDCo Environmental, Inc. Industrial
Hygiene Characterization of the Photovoltaic Solar Cell Industry. Pre-
pared for the U.S. Department of Health, Education, and Welfare under
Contract No. 218-78-0059, 1980.
5. Owens, T., Ungers, L and T. Briggs. PEDCo Environmental, Inc. Estimates
of Occupational Safety and Health Impacts Resulting from Large-Scale
Production of Major Photovoltaic Technologies. Prepared for Brookhaven
National Laboratories, Biomedical and Environmental Assessment Division
under Contract No. 510191S, 1981.
6. U.S. Department of Commerce. 1977 Census of Manufactures: Electronic
Components and Accessories. June 1980.
7. Components: Unaggressive Growth in Store. Electronics. January 3,
1980.
8. Spotlight on Discrete Semiconductors. Electronic News Suppl, November
24, 1980.
9. Harper, C.A., ed. Handbook of Materials and Processes for Electronics.
McGraw-Hill, New York, 1970.
10. Kern, W. Chemical Etching of Silicon, Germanium, Gallium Arsenide, and
Gallium Phosphide. RCA Review, Vol. 39, June 1978, pp. 278-308.
11. Hunter, L.P., ed. Handbook of Semiconductor Electronics, 3rd Edition.
McGraw-Hill, New York, 1970.
12. Stern, L. Fundamentals of Integrated Circuits. Hayden Book Co., New
York, 1968.
48
-------
13. Coombs, C.F., Jr., ed. Printed Circuits Handbook, 2nd Edition. McGraw-
Hill, New York, 1979.
14. Runyan, W.R. Silicon Semiconductor Technology. McGraw-Hill, New York,
1965.
49
-------
SECTION 3
CAPACITORS
INDUSTRY DESCRIPTION
Capacitors are electronic devices that are basically used for the storage
of electrical energy, although depending on their characteristics, they may
serve in various other functions. Major applications include the following:
0 Energy storage elements - to accumulate electrical energy at one
rate and to discharge it at a faster rate; typical examples are
motor starting capacitors, fluorescent lamp ballasts, and automotive
ignition condensers.
0 Protective devices - in combination with resistors to reduce radio
interference caused by arcing.
0 Filtering devices - to distinguish among currents of different
frequencies.
0 Bypass devices - to prevent the flow of direct current without
impeding the flow of alternating current; bypass capacitors atten-
uate low frequency currents while permitting higher frequency cur-
rents to pass.
There are many examples of the latter three applications in electronic and
television components, audio equipment, and instrumentation.
A large variety of capacitors are manufactured. The particular applica-
tion will determine the type and size of capacitor used. Capacitance is a
measure of the quantity of electrical charge the capacitor will hold per unit
of potential between conductors; it is independent of the potential impressed
on the unit.
Two basic types of capacitors are manufactured, fixed and variable.
Fixed capacitors are layered structures of conductive and dielectric (i.e.,
nonconductive)' surfaces. The layering is either in the form of rigid plates
or thin sheets of rolled flexible material. Fixed capacitor types are dis-
tinguishable in terms of type of conducting, dielectric, and encapsulating
materials. The major types include:
50
-------
Paper dielectric Tantalum wet slug
Film dielectric Aluminum electrolytic
Metallized dielectric Mica dielectric
Dual dielectric Ceramic
Tantalum dry slug and Glass encapsulated
wire
Tantalum foil
Variable capacitors are larger versions of fixed capacitors with provisions
for adjustment of plates separating the dielectric. They serve two basic
functions, tuning and trimming. The two types of tuning capacitors are air
2
dielectric and semi-conductor voltage-variable (varactors). Trimming capaci-
tors are small-value adjustable capacitors usually used in parallel with the
larger-value tuning or fixed capacitors to make fine adjustments of total
capacitance in a circuit. These are classified by the dielectric used into
2
such categories as air, mica, ceramic, glass, and plastic.
Raw Materials
The raw materials for capacitors include conductors, dielectrics, elec-
1 2
trolytes, leads, and encapsulating materials: '
0 Conductors - High-purity aluminum foil is used extensively in sever-
al types of fixed capacitors, as aluminum is an excellent conductor
and is relatively inexpensive compared with other conductive materi-
als. Tantalum foil and tantalum sintered metals are also used.
This material is relatively expensive, but because of its durability
and electrical stability, is often used in miniature and subminiature
capacitor applications. Other foils used less often include tin-
lead, tin, brass, and copper. Numerous types of precious metal inks
or pastes serve as conductors in layered monolithic capacitors;
because of their expense, they constitute a significant portion of
miniature and subminiature costs. Conductors in variable capacitors
are usually aluminum plates, but brass and copper are also used.
Brass and copper plates may be plated with silver to increase sur-
face conductivity or with nickel or cadmium to prevent corrosion.
0 Dielectrics - Dielectrics may be solids, liquids, or gases, or
combinations chosen to take advantage of various electrical charac-
teristics. Ceramic capacitors use solid ceramic dielectrics which
display exceptional dielectric and thermal properties that increase
their durability and reliability. They are also relatively inexpen-
sive. Ceramic materials are usually mixtures of complex compounds
such as barium titanate, calcium titanate, strontium titanate, and
lead niobate. Mixtures of fine ceramic powders and resins are used
in monolithic ceramic capacitors.
51
-------
Kraft paper, glass cloth, and plastic film are used as dry dielec-
trics and are relatively Inexpensive but are not as useful 1n high-
voltage (above 1000 volts) applications as are mica, low-loss ceram-
ic, or oil-soaked paper dielectrics. Glass cloth materials also
exhibit good dielectric loss and Insulation resistance. Phenolic
resins are often used to Impregnate paper dielectrics, whereas
silicone, melamlne, and epoxy resins are used with glass cloth.
Plastic film dielectrics include polyester (polyethylene pterap-
thalate), polysulfone. Teflon, and polyimide. Both paper and
plastic dielectrics may be metallized with aluminum or zinc.
Glass and mica are excellent dielectric materials and, although
relatively Inexpensive, require special skills and equipment for
efficient handling. M1ca may also be coated with a silver oxide oil
paint by silk-screening or spraying methods. This paint is fired to
reduce the film to pure metallic silver. Electrochemically-formed
oxide coatings are used extensively as dielectrics in higher quality
aluminum electrolytic, tantalum foil, and tantalum slug capacitors.
These coatings provide exceptional dielectric properties.
Electrolytes - Electrolytic capacitors usually use a liquid elec-
trolyte and an oxide film as the dielectric. The tcraft paper also
serves as a spacer and an absorbing medium for the electrolyte. The
electrolyte is usually less than a one percent solution of strong
acids, glycols, and salts dissolved in deionized water. Acids used
in wet-slug tantalum capacitors include sulfuric add and lithium
chloride.
Leads - Copper and tantalum are the most common materials for
capacitor leads. Capacitors that are used on printed circuit boards
often do not have leads but are attached directly to the board.
Encapsulating materials - Steel and aluminum containers, phenolic
moldings, and epoxy moldings are the most conrnon encapsulating mate-
rials for fixed capacitors. Wax and various other plastics are used
to seal metal capacitor containers. Glass encapsulation is also
used. Ceramic and brass are used as enclosures for variable capaci-
tors.
Products
The Bureau of the Census classifies fixed and variable capacitors Into
SIC 3675. Varactors are classified with semiconductors (SIC 3674) and are not
discussed in this section.
Capacitor sales by U.S. companies exceeded $1 billion for the first time
in 1979, an increase of nearly 20 percent over the previous year. Due to the
recession, however, the overall growth rate is expected to decrease in 1980
and 1981.
52
-------
According to one report, aluminum electrolytic capacitors will be among
the hardest hit in the near future due to their heavy use in consumer items in
the automotive and entertainment markets. However, they are becoming in-
creasingly attractive for other applications, due to their reduced size,
improved performance characteristics, lower price, and wide availability. It
is predicted that in low impedance applications, where aluminum capacitors are
particularly suitable, tantalum capacitors may lose up to 60 percent of their
market share. A major factor is the rising cost of tantalum, which has
increased sixfold in the past five years to about $550 a kilogram. Tantalum
ore is in short supply, and the mineral is presently mined in only three
regions: Africa, South America, and Canada. It is reported that there is
little likelihood of new mines opening because costs are too high for the
expected return. Reworking slag heaps is also not .a promising prospect.
Although new film capacitors are not expected to increase in sales to any
great extent in the near future, new processing techniques already developed
and improvements in manufacturing and packaging techniques yet to come should
keep prices of these capacitors down. With the prices of aluminum, tantalum,
and ceramic caps rising, films are becoming more attractive. Film capacitors
are also more amenable to automation than aluminum electrolytics, thus allow-
ing price reductions when made in large quantities. They are expected to
penetrate several new markets, particularly in high-frequency and high-current
applications.
Monolithic ceramic chip capacitors are the fastest growing segment of the
industry. It is expected that their production will further increase upon
introduction of automatic chip insertion equipment. These capacitors find a
wide variety of applications, but are used particularly in computers and as-
sociated peripherals. Since these applications do not show significant signs
of weakness, the demand for these capacitors remains strong.
Mica capacitors are expected to suffer due to high metal costs. Silver,
which amounts to a significant part of total materials cost in mica capaci-
tors, increased in cost sharply in early 1979, though it has come down some-
what since.
53
-------
Table 3-1 provides details of the sales of major capacitor types over the
past 10 years. Figure 3-1 shows the changes over the past decade in sales
for each major type of capacitor. A summary of forecasted sales for 1980 and
1983 is given in Table 3-2.4
Companies
According to the 1977 Census of Manufactures, there are approximately 118
plants which produce capacitors, including oil-filled capacitors (which are
not included in SIC 3675). The number of companies involved in production of
the various types of capacitors is presented in Table 3-3. The size of these
establishments based on total employment is presented in Table 3-4.
There are four major producers of tantalum capacitors: Kernet of Greens-
ville, South Carolina, with a 40 percent share of the market; Sprague Electric
of North Adams, Massachusetts, 38 percent; and Mepco/Electra of Morristown,
New Jersey, and P. R. Mallory & Co., of Indianapolis, Indiana, 7 percent
each.
There are two major producers of mica capacitors: Cornel1-Dubilier
Electric of Newark, New Jersey, with a 50 percent share of the market; and
Sangamo Weston of Pi kens, South Carolina, with 40 percent.
Table 3-5 shows the market share of companies manufacturing monolithic
ceramic capacitors. By far the largest is AVX Ceramics, which has almost a
third of the market.3
There are three major manufacturers of aluminum capacitors. Sprague is
the largest, with a 45 percent share of the market, and Mallory and Mepco/
Electra each have 20 percent. The remaining 15 percent of the market is
reportedly filled by foreign suppliers.
Environmental Impacts
The capacitor manufacturing industry includes a number of capacitor
types, a variety of production methods, varying degrees of manufacturing
automation, and facilities ranging in size from those with only a few workers
to those with hundreds or even thousands of employees. There thus may be
considerable variation in the discharges that are produced at various facil-
ities, even those which manufacture the same type of capacitors.
54
-------
TABLE 3-1. CAPACITOR SALES OVER PAST 10 YEARS'
Millions of units
Paper and film
Tantalum
Aluminum
Mica
Ceramic
Other fixed
Variable
Total
Year
70
542
285
204
173
1,376
49
50
2,678
71
570
272
208
173
1,757
49
55
3,084
72
496
364
234
208
2,113
63
71
3,609
73
666
564
312
278
2,646
79
103
4,648
74
591
610
296
254
2,180
63
57
4,032
75
396
353
149
135
1,659
37
53
2,781
76
474
526
195
164
2,822
62
62
4,305
77
582
637
201
201
3,451
49
57
5,179
78
662
786
202
b
3,614
1983
61
5,523
79
621
899
205
b
1,371
7
53
5,156
Millions of dollars
Paper and film
Tantalum
Aluminum
Mica
Ceramic
Other fixed
Variable
Total
Year
70
185
101
82
20
75
9
12
483
71
153
81
77
22
82
7
12
435
72
104
91
88
22
106
9
19
438
73
138
135
118
31
154
11
27
612
74
139
162
137
34
173
13
19
676
75
94
108
83
22
139
11
14
470
76
129
132
111
24
185
12
16
608
77
160
156
128
24
241
13
16
744
78
205
188
151
30
289
43
20
897
79
214
262
185
b
352
12
26
1,050
Includes mica.
No data available.
55
-------
UNIT SALES
NULTIUUR
1969
3.1 BILLION UNITS
1979
6.2 BILLION UNITS
DOLLAR SALES
1969
$489.7 MILLION
1979
$1.05 BILLION
Figure 3-1. Capacitor sales: A comparison of
growth over the past decade.3
56
-------
TABLE 3-2. FORECAST FOR CAPACITOR SALES ,
$ MILLION*
Capacitor type
Al electrolytic capacitors
Tantalum capacitors
Paper capacitors
Film capacitors
Ceramic capacitors except chip
Ceramic chip capacitors
Mica capacitors
Variable dielectric capacitors
Glass and porcelain capacitors
Quantities
1980
200.0
177.8
90.4
115.0
364.4
50.3
35.5
29.0
5.2
1983
220
215
98
123
509
78
36
34
4
Annual
growth
%
5.7
5.6
2.4
0.8
13.1
15.1
1.4
5.3
-7.2
57
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TABLE 3-3. NUMBER OF COMPANIES MANUFACTURING VARIOUS CAPACITOR TYPES"
Capacitor type
Paper dielectric:
Metal case
Nonmetal case
Film dielectric, metal and nonmetal case
Metal i zed dielectric:
Metal case
Nonmetal case
Dual dielectric, metal and nonmetal case
Tantalum electrolytic:
Slug and wire solid dry electrolytic:
Metal case, hermetic
Metal case, nonhermetic
Nonmetal case
Foil and wet slug electrolytic
Aluminum electrolytic:
Metal case tubular:
Standard (6/8-inch diameter)
Standard (under 5/8-inch diameter)
All others
Mica dielectric, fixed
Ceramic dielectric:
Fixed tubular, disc, plate, stand-off
tubular and disc, and all two- thermal
ceramic devices
•Monolithic:
Chips
Leaded- radial
Leaded-axial
Other
All other fixed
Variable air dielectric, mica, ceramic,
and glass dielectric
No. of companies
20
8
30
11
11
23
6
7
11
8
9
8
9
9
9
19
22
14
5
8
16
58
-------
TABLE 3-4. SIZE BREAKDOWN OF CAPACITOR PRODUCERS
BASED ON TOTAL EMPLOYMENTS
Average employee range
Number of establishments
1-4
5-9
10-19
20-49
50-99
100-249
250-499
500-999
1000-2499
2500 or more
7
3
11
20
11
32
15
16
2
1
59
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TABLE 3-5. MAJOR MONOLITHIC CERAMIC MANUFACTURERS"
Company
AVX Ceramic, aff ill late
of AVX Corporation
Kemet, affilliate of
Union Carbide Corporation
Centralab Electronics Div.,
Globe Union Iric.
Sprague Electric, subsidiary
of General Cable
San Fernando Electric Mfg. Co.,
subsidiary of West-Cap Arizona
Corning Glass Works, Corning
Electronics
Vitramon, Inc.
All other companies
Location
Myrtle Beach, SC
Greensville, NC
Milwaukee, Wisconsin
North Adams, MA
San Fernando, CA
Corning, NY
Bridgeport, CT
Market share, %
32
17
9
8
8
7
7
11
60
-------
The only reported sources of air emissions from capacitor production are
metal fumes from soldering and possible organic vapors from paint drying and
use of molten epoxy and phenolic compounds. The use of specific controls 1s
not reported in the literature examined.
Liquid effluents generally consist of weak acidic solutions and rinse and
cooling waters. The production of glass encapsulated capacitors results In
discharge of fluorescent penetrating solutions. Stronger acidic solutions,
which may contain dissolved metals, are released from etching operations at
aluminum electrolytic capacitor plants. None of these effluents represent a
particular treatment problem, and most are discharged directly to municipal
treatment systems. Pretreatment of the effluents (e.g., sand filtration or
settling) Is employed at some facilities before being released Into municipal
systems.
There are no significant sources of solid waste from capacitor manu-
facturing.
INDUSTRY ANALYSIS
The following Industry analysis considers each Individual production
operation (or series of closely related operations), called here a process, to
examine In detail Its purpose and actual or potential effect on the environ-
ment. Each process Is examined 1n the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
Some information was found in the literature on the production methods used
for six distinct capacitor types: tantalum wet and dry slug, tantalum foil,
glass encapsulated, aluminum electrolytic, ceramic, and mica. Each is dis-
cussed separately in the following analysis. Figures 3-2 to 3-6 are flow-
sheets showing the processes used for the first four of these capacitor types,
as well as their interrelationships and major waste streams.
61
-------
TANTALUM
DRY SLUG
CAPACITOR
ANODE
FABRICATION 1
FORMATION
REACTIONS 2I
1 1
FORMING
I
ACID/CARBON
SLURRY DIPS
1
ASSEMBLY
(DRY SLUG)
1
3
«*
4
C
5
ASSEMBLY
(WET SLUG) 6
X^TANTALUM^S,
( WET SLUG
V CAPACITOR >
? ^'^'^ — *x<^
^ WATER
O AIR
O SOLID
Figure 3-2. Tantalum wet and dry slug
capacitor production flowsheet.
62
-------
ELECTROCHEMICAL
OXIDE
FORMATION 1
i
ASSEMBLY
2
TANTALUM
FOIL
CAPACITOR
a WATER
O AIR
O SOLID
Figure 3-3. Tantalum foil capacitor
production flowsheet.
63
-------
ASSEMBLY
TERMINAL
CLEANING 2I
GLASS
CUTTING 3
GLASS
ENCAPSULATED
CAPACITOR
a WATER
O AIR
O SOLID
Figure 3-4. Glass encapsulated capacitor production flowsheet.
64
-------
OXIDE
FORMATION
i
ASSEMBLY
ALUMINUM
ELECTROLYTIC
CAPACITOR
A WATER
OAIR
O SOLID
Figure 3-5. Aluminum electrolytic capacitor production flowsheet.
65
-------
c
BALL
MILLING i
<
p
CERAMIC
FORMATION 2
.
' 1
BAKING 3
.
r ^
ASSEMBLY 4
1
ZCERAMICN
CAPACITOR^
OAIR
A WATER
0 SOLID
Figure 3-6. Ceramic capacitor production flowsheet.
66
-------
The lack of information on the production of mica capacitors precludes a
complete assessment of this process sequence in the IPPEU format. The dielec-
tric fabrication operation is briefly described, but the sequence of subse-
quent steps in the process is unclear from the descriptions in the literature.
Similarities have been reported to the manufacture of both glass encapsulated
and layered ceramic capacitors. The IPPEU description of the dielectric
fabrication process of mica capacitor production is included in this draft;
however, subsequent steps are not characterized.
67
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TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 1
Anode Fabrication
1. Function - Tantalum powder is combined with an organic binder and
pressed into a pellet on a tantalum lead wire. The pellets are heated in a
vacuum furnace to produce a sintered tantalum slug.
2. Input materials - Tantalum powder and wire are the primary input
materials in the production of the sintered tantalum slug. An organic binder
(of unknown composition) is added to the tantalum powder to allow it to be
compressed into a pellet. Specific quantities for these inputs are not
available.
3. Operating Conditions - The temperature and pressure of the vacuum
furnace are not known. All other steps in this process (i.e., mixing, pel-
letizing) are performed at ambient conditions.
4. Utilities - The heating elements and vacuum pump of the furnace are
electrically controlled. There are no other utility requirements.
5. Waste Streams - There are no air, water, or solid wastes reported for
this process.
6. Control Technology - The use of controls for this process is not
discussed in the literature.
63
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TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 2
Formation Reactions
1. Function - An oxide film must be formed which will serve as the
dielectric for the capacitor. The sintered tantalum slugs are dipped into a
dilute acid solution to form a thin tantalum oxide film. This reaction pro-
ceeds rapidly and the sintered tantalum slug is then rinsed with deionized
water and air dried. The product of these formation reactions is tantalum
slug anodes that are further treated to form either wet or dry slug capaci-
tors.
2. Input Materials - The acids used in the dilute acid bath are nitric
and phosphoric. The concentration of the acid solution is not known. The
only other input material to this process is deionized water used to rinse the
sintered tantalum slug.
3. Operating Conditions - The acid oxidation and rinse steps are per-
formed under ambient conditions of temperature and pressure.
4. Utilities - Water is used to dilute the acid and rinse the tantalum
slugs of any acid residue. Electricity powers the automated equipment.
Specific quantities are not available.
5. Waste Streams - There are no air emissions reported for this process.
A small wastewater stream results from this process. It consists of
batch dumps of very weak acid solutions and deionized rinse water. The quan-
tity is reported as 38 liter/h at one plant.
There are no solid wastes from this process.
6. Control Technology - Special wastewater control procedures are not
employed. Effluent streams are discharged directly to the general municipal
sewer or the surface.
69
-------
TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 3
Formi ng
1. Function - An additional oxide coating is desirable in the production
of dry slug capacitors. Sintered tantalum oxide coated pellets are dipped
into a viscous solution of manganese nitrate and then placed in a heated
atmosphere with steam. A manganese oxide coating develops on the tantalum
oxide coating.
2. Input Materials - Manganese nitrate is the input material for this
reforming process. The solvent used in the manganese nitrate solution is not
known. Steam is used presumably to provide a humid atmosphere.
3. Operating Conditions - Operating conditions for the reforming process
are not available.
4. Utilities - The source of energy used to generate the steam for this
process is not reported.
5. Waste Streams - There are no air emissions associated with this
process other than steam.
The process has a very low discharge of manganese nitrate solutions,
estimated at 19 liter/h for one plant. No other effluents are associated
with this process, except water condensate.
There are no solid wastes from this process.
6. Control Technology - Observed wastewater control technologies include
settling and contract hauling of sludge.
70
-------
TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 4
Acid/Carbon Slurry Dips
1. Function - Coated pellets intended for dry slug capacitors are
dipped into a dilute acid solution to eliminate any defects in the oxide
coatings. They are then rinsed with deionized water, dipped into a carbon
slurry, and air dried.
2. Input Materials - Nitric and phosphoric acids are used in this
process. The acid is diluted with deionized water; the final concentration is
unavailable. The composition of the carbon slurry is unknown, as are the
quantities of input materials used.
3. Operating Conditions - These dipping operations are performed at
ambient conditions.
4. Utilities - Water is used to dilute the acid and rinse the manganese
oxide-coated slug of any residual acid.
5. Waste Streams - There are no air emissions.
There is a wastewater discharge which consists of batch dumps of the
dilute acids and deionized rinse water.
There are no solid wastes from this process.
6. Control Technology - No wet treatment systems are used for this
process. Wastewater is discharged directly to municipal sewers or the sur-
face.
71
-------
TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 5
Assembly (Dry Slug)
1. Function - The dry tantalum slug anodes are coated with a special
silver paint which becomes the cathode. Another tantalum lead wire is sol-
dered to the coating to electrically complete the capacitor. The capacitor is
dipped into a molten epoxy or phenolic compound and air dried. The capacitor
is then electrically evaluated and shipped.
2. Input Materials - The composition of the special silver paint that
comprises the cathode is unavailable and is probably proprietary. Other
inputs include tantalum wire, an epoxy or phenolic compound used to coat the
capacitor, and the solder used to attach the tantalum lead wire to the cathode
coating. Specific quantities for these inputs are not available.
3. Operating Conditions - All assembly processes are presumably per-
formed under ambient conditions.
4. Utilities - Electricity is used to operate the automated assembly and
testing equipment and generate the heat for soldering.
5. Waste Streams - Potential air emissions include metal fumes from
soldering operations and organic vapors from air drying paint or the molten
epoxy or phenolic compounds.
There are no liquid or solid waste streams generated by this process.
6. Control Technology - Controls used in this process, if any, are not
reported in the literature.
72
-------
TANTALUM WET AND DRY SLUG CAPACITORS PROCESS NO. 6
Assembly (Wet Slug)
1. Function - Tantalum slugs used in wet capacitors receive no further
treatment after the formation reactions. The sintered tantalum slug with an
oxide coating is inserted into a silvered metal can (the cathode), filled with
an electrolyte, and sealed. The unit is then electrically evaluated and
shipped.
2. Input Materials - The base composition of the silvered metal can and
the chemical composition of the liquid electrolyte are not available.
3. Operating Conditions - The assembly of tantalum wet slugs is con-
ducted at ambient conditions.
4. Utilities - Electricity is the only utility used (i.e., automated
equipment, quality control testing).
5. Haste Streams - There are no air, water, or solid waste streams
associated with this process, other than possible spills of electrolyte.
6. Control Technology - There are no controls applicable to this proc-
ess.
73
-------
TANTALUM FOIL CAPACITORS PROCESS NO. 1
Electrochemical Oxide Formation
1. Function - An oxide coating must be developed on the tantalum foil to
provide the dielectric of the capacitor. Tantalum foil (usually in strips) is
electrochemically reacted with mildly acidic glycol solutions to form this
oxide layer.
2. Input Materials - Tantalum foil is the base material, and is typi-
cally handled in individual strips or rolls. Other inputs include acidic
glycol solutions and water. The chemical compositions of these various solu-
tions are not described in the literature.
3. Operating Conditions - Formation reactions are typically batch dip-
ping operations, performed in open tanks under ambient conditions of tempera-
ture and pressure.
4. Utilities - Electricity is used to operate the electrochemical proc-
essing equipment.
5. Waste Streams - There are no air emissions from this process.
The oxide formation reaction is the primary water discharging process
from tantalum foil capacitor manufacturing facilities. The mass discharge
from this reaction is directly proportional to the surface area of foil proc-
essed. The wastewater discharge results from batch dumps of acid solutions
and subsequent water rinsing. An estimated discharge rate of 115 liter/h has
been reported.
No solid wastes are characteristic of this process.
6. Control Technology - Wastewater discharges receive no special treat-
ment and are routed directly to publicly-owned treatment works.
74
-------
TANTALUM FOIL CAPACITORS PROCESS NO. 2
Assembly
1. Function - The dried tantalum foil with oxide coating is layered with
kraft paper and sometimes plastic sheets and wound to form a capacitor core.
The core is then inserted into a metal container. The containers and cores
are placed under heavy vacuum, the vacuum is released, and the chamber is
flooded with electrolyte. The capacitors are then sealed, air dried, and
electrically aged. The electrical aging improves the integrity of the oxide
coating and establishes the equilibrium capacitance of the capacitors. The
finished capacitors are electrically evaluated and shipped.
2. Input Materials - Input materials include kraft paper or plastic film
which is used as a dry dielectric, a liquid electrolyte, and the metal con-
tainer which houses the core. Kraft paper serves as a spacer and an absorbing
medium for the electrolyte. The electrolyte is usually less than a one-
percent solution of strong acids, glycols, and salts dissolved in deionized
water. Specific chemical components and the amounts used in electrolyte
solutions are not available.
3. Operating Conditions - The capacitor core and housing is placed under
heavy vacuum prior to treatment with the electrolyte. All other process
operations are performed under ambient conditions.
4. Utilities - Electricity is used to operate the manufacturing and
testing equipment and to "age" the electronic components.
5. Waste Streams - There are no air, water, or solid wastes reported to
be generated during this process.
6. Control Technology - The use of controls for this process is not
discussed in the literature.
75
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GLASS ENCAPSULATED CAPACITORS PROCESS NO. 1
Assembly
1. Function - Ultra-thin glass ribbon serves as the dielectric material
in glass encapsulated capacitors. The ribbon is alternately stacked with
high-purity aluminum foil (unetched and unformed). Leads are attached and a
glass cover is placed into position. Annealing bonds the glass ribbons and
foil strips to form the body of the capacitor.
2. Input Materials - Glass ribbon and high-purity aluminum foil are the
base materials for these capacitors. Lead wires are made of copper. The
composition of the glass ribbon and covers is not known.
3. Operating Conditions - The assembly of glass encapsulated capacitors
is performed at ambient conditions. The annealing temperature is not re-
ported.
4. Utilities - Electricity is used to operate the assembly equipment.
The annealing furance is heated with electricity or gas.
5. Waste Streams - This is a dry operation, and there are no air, water,
or solid wastes known to be generated.
6. Control Technology - The use of controls for this process is not
discussed in the literature.
76
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GLASS ENCAPSULATED CAPACITORS PROCESS NO. 2
Terminal Cleaning
1. Function - Annealing at high temperatures results in a coating of
the copper leads with copper oxide. To remove the oxide, the leads are dipped
into a mild sulfuric acid solution and rinsed.
2. Input Materials - Sulfuric acid and water are the input materials.
3. Operating Conditions - Terminal cleaning is presumably conducted at
ambient conditions.
4. Utilities - There are no special utility requirements.
5. Haste Streams - There are no air emissions associated with this
process.
A wastewater discharge results from contact cooling acid bath dumps and
subsequent water rinsing. The total discharge is a function of the number of
leads cleaned, rather than surface area. However, it can be related to the
total number of capacitors produced because there is not a large difference in
surface area between the smallest and the largest glass encapsulated capaci-
tors. The process has been characterized by a flow of 76 to 114 liter/h
and fluctuating concentration levels.
There are no solid waste streams.
6. Control Technology - No special systems are used to treat the water
discharge from this process. Wastewater is discharged directly to municipal
treatment works.
77
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GLASS ENCAPSULATED CAPACITORS PROCESS NO. 3
Glass Cutting
1. Function - In a final step, special cutting disks are hydraulically
lowered through a bar of uncut capacitors which have been fabricated as a
group. Water sprayed over the bar and spinning disk cools the disk and
flushes away sawed glass particles (kerf). The capacitors are then penetrant
inspected, rinsed, electrically evaluated, and shipped.
2. Input Materials - Water is the only input material associated with
this operation.
3. Operating Conditions - Glass cutting operations are presumably per-
formed at ambient conditions.
4. Utilities - Electricity is used to operate the hydraulic cutting
equipment. Water is used to cool the glass capacitor bar during cutting and
to flush away glass particles.
5. Waste Streams - There are no air emissions associated with this
process.
A wastewater discharge results from the water spray used to cool the bar
while cutting. Total discharge is related to the cross-sectional surface area
and the number of cuts. One production facility had a flow rate of 679
liter/h and high solids content in this raw wastewater stream.
An additional wastewater discharge results from the wash and rinse steps
of the penetrant inspection process, during which parts are examined for
minute cracks and flaws. The chemical composition of the fluorescent penetrat-
ing solution is not available. This process, in which the component is dipped
into a solution, examined under UV light, then washed, rinsed, and dried is
not unique to the electronics industry.
There are no solid wastes.
6. Control Technology - There are not thought to be special wastewater
treatment systems for this process. The effluent is likely discharged to
municipal treatment works.
78
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ALUMINUM ELECTROLYTIC CAPACITORS PROCESS NO. 1
Oxide Formation
1. Function - An oxide film must be formed on the surface of the alumi-
num foil. High-purity aluminum foil is first etched to Increase its effective
surface area. This increases the capacitance. The foil 1s etched by passing
current through it while submerged in strong acids, a process similar to
anodizing. The forming reaction itself is an additional electrochemical
operation in which a direct current potential is applied between the aluminum
foil roll and the steel reaction tank, which is filled with a dilute ammonium
pentaborate solution. The aluminum foil is slowly unwound and passed through
the solution and then rewound. This causes an aluminum oxide film of a pre-
determined thickness to form on the foil.
2. Input Materials - High-purity aluminum foil is the base material.
Sulfuric or nitric acids are used in the etching process. Ammonium penta-
borate and water are the only other known inputs.
3. Operating Conditions - Operating conditions for the oxide formation
process are presumably ambient pressure and temperature.
4. Utilities - Electricity 1s consumed 1n the electrochemical treatment
of the aluminum foil. Water is used in the etching and ammonium pentaborate
solutions.
5. Waste Streams - There are no air emissions from this process.
The number of water discharging operations varies from plant to plant
because not all processes are used an equal number of times at each facility.
Some facilities do not use the etching step. The process flow rate from the
acid etch is estimated to be 300 liter/h at one plant and is characterized by
batch dumps of high concentrations of acid containing dissolved metals. The
discharge rate from the ammonium pentaborate reaction is estimated to be 190
liter/h at one plant and is characterized by a mildly acidic solution with
variable solids contents and water from subsequent rinsing.
There are no solid wastes from this process.
6. Control Technology - Wastewater controls at a representative number
of production facilities have not been described. One facility discharges one
of its process lines directly to a municipal treatment system and the other to
a sand filter which discharges to a drainage ditch.
79
-------
ALUMINUM ELECTROLYTIC CAPACITORS PROCESS NO. 2
Assembly
]. Function - The etched and formed aluminum foil 1s cut and leads are
attached. The foil Is Interwoven with a kraft paper spacer, wound, and In-
serted Into a metal container. The capacitors are then placed under heavy
vacuum and heated. The vacuum 1s released and the chamber 1s filled with an
electrolyte which fills the capacitors. The chamber 1s drained, opened, and
the fill holes In the capacitors are soldered closed. The capacitors are
electrically aged by application of direct current. This heals voids In the
oxide coating and brings the capacitance to an equilibrium value. The fin-
ished capacitors are electrically evaluated and shipped.
2. Input Materials - Lead wires, kraft paper, and a metal container are
used in the assembly of these capacitors. Leads are usually made of copper,
while containers can be steel or aluminum. The electrolyte is composed of
water, trace amounts of ethylene glycol, phosphoric acid and/or ammonium
borate. Specific quantities are not available.
3. Operating Conditions - Capacitors are placed under heavy vacuum and
heated during this process. The pressure and temperature are not reported.
Other assembly operations are presumably conducted at ambient conditions.
4. Utilities - Electricity is used for soldering, vacuum pumps, fur-
naces, and aging and testing equipment.
5. Waste Streams - The only possible source of air emissions is solder-
ing, but emission data are not available.
There are no liquid or solid wastes reported.
6. Control Technology - The extent of engineering controls for these
processes is unknown.
80
-------
MICA CAPACITORS PROCESS NO. 1
Dielectric Fabrication
1. Function - M1ca is the dielectric material used 1n this type of
capacitor. Pure mica Is subjected to high-velocity water jets which shred It
Into thin, small flakes. The flakes are passed over a moving vacuum belt
which dries the mica flakes and forms them into a fragile mica sheet. The
mica sheet is treated with sllicone resins to add strength.
2. Input Materials - Mica, water, and sllicone resins are the inputs for
this process. Specific quantities for these materials are not available.
3. Operating Conditions - Except for the vacuum drying step, these
operations are presumably performed under ambient conditions of temperature
and pressure.
4. Utilities - Water is used to shred the mica into thin, small par-
ticles. Electricity is used to operate the fabrication equipment (water
pumps, conveyor belts, vacuum pumps).
5. Waste Streams - There are no air emissions associated with this
process.
The process has a wastewater discharge from the water used as a medium to
carry the mica flakes to the paper making process. The quantity of water
discharged from a typical dielectric fabrication process is not known. The
wastewater probably contains mica particles.
There are no solid wastes.
6. Control Technology - Mica particles in the wastewater are probably
removed by settling and/or sand filtration before discharging to a municipal
treatment works. Specific treatment systems used by industry are not de-
scribed.
81
-------
CERAMIC CAPACITORS PROCESS NO. 1
Ball Milling
1. Function - Ball milling is the initial step in the production of the
solid ceramic substrates which are used as dielectrics in ceramic capacitors.
Ceramic powders are carefully weighed and introduced into a ball mill which
breaks the powders down into smaller particles. Water and occasionally a
solvent are added to control the viscosity of the resulting slurry.
2. Input Materials - The ceramic substrate consists of barium titanate
with trace amounts of other compounds. These powders are either purchased
from vendors or manufactured at the capacitor facility. The only other inputs
are organic solvents. Neither the trace constituents of the ceramic substrate
nor the solvents used in the slurry are characterized in the literature,
probably because of proprietary considerations.
3. Operating Conditions - Ball milling is performed under ambient con-
ditions.
4. Utilities - Electricity is used to operate the ball mill and slurry
mixers. Incoming municipal water is used for ball milling, washdown of the
ball mill, and mixing.
5. Waste Streams - There are no air emissions reported for this process.
Ceramic capacitor manufacturing requires regular (usually daily) cleanout
of the ball mill. The procedure requires that an operator hose down the
interior of the ball mill and the surrounding area. The wastewater discharge
rate varies widely according to the size of the ball mill and operator vari-
ability in cleaning. However, this does not affect the pollutant discharge
mass associated with washdowns. One estimated flow rate for the ball mill
washdown is 1130 liter/h.1
There are no solid wastes from this process.
6. Control Technology - Wastewater from this process is treated in
settling tanks and/or sand filtration systems and discharged to a municipal
treatment plant.
82
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CERAMIC CAPACITORS PROCESS NO. 2
Ceramic Formation
1. Function - In this process the ceramic slurry from the ball mill is
mixed with organic binders similar to those used in latex paint. The result-
ing slurry is sheet cast onto a moving, heated paper belt. At the end of the
heated chamber, the ceramic substrate is separated from the paper belt and
rolled. The resulting solid material is used as the substrate in ceramic
capacitors.
2. Input Materials - Organic binders are added to the ceramic slurry to
provide adhesive properties that will facilitate casting into a sheet. The
specific composition of these organic binders is not available.
3. Operating Conditions - The slurry is sheet cast in a heated chamber;
the operating temperature is not reported. Conditions for other process steps
are assumed to be ambient.
4. Utilities - Electricity is used to operate the mixers, conveyors, and
process equipment. The method of heating the curing chamber is not reported.
5. Waste Streams - There are no air emissions reported for this process.
However, it is possible that organic vapors could be emitted while the mixture
cures in the heated chamber.
There are no liquid or solid waste streams reported for this process.
6. Control Technology - No controls are known to be applied to this
process.
83
-------
CERAMIC CAPACITORS PROCESS NO. 3
Baking/Printing
1. Function - Following the formation of the ceramic sheet, the process-
ing sequence depends on whether or not the capacitor to be manufactured is
single- or multiple-layered. If single-layered, the sheet is cut into squares,
cured by baking, and followed by a silver coating on both sides of each square.
If multiple-layered, the ceramic sheets are first printed with a precious
metal ink, then stacked in layers, followed by a heat treatment under vacuum.
This latter treatment removes air voids between the sheets and hardens the
ceramic so it can be cut. The layered sheets are next cut into individual
capacitors and baked at high temperatures to fully cure the ceramic. Both
sides of each capacitor are then coated with the conductive silver.
2. Input Materials - The major input to this process is the precious
metal ink used to coat both sides of the ceramic sheets. The ink is produced
by dissolving ingots of precious metal (usually silver) into solution.
Further specifics are not reported.
3. Operating Conditions - The specific temperatures and pressures de-
veloped during the baking process are not reported in the literature.
4. Utilities - Electrical service will be required to operate portions
of this process. The type and quantity of additional utility service is
unknown.
5. Waste Streams - No air emissions associated with this process could
be identified in the literature. Depending on the composition of the inks and
coatings used, however, organic vapor (VOC) emissions could result.
There is no wastewater discharge associated with baking processes that do
not provide their own ink. Some plants do manufacture this ink, however, and
the chemical characteristics of process wastewater from a facility performing
this operation are given in Table 3-6.
6. Control Technology - Process wastewater discharge from a facility
involved in ink manufacturing operations at a minimum is treated through a
process of pH adjustment and sedimentation. Additional treatment that can be
performed includes sludge dewatering and filtration of the sedimentation
process effluent.
84
-------
TABLE 3-6. ANALYSIS OF PROCESS WASTEWATER FROM A CERAMIC
CAPACITOR INK MANUFACTURING OPERATION!
Toxic organics
Benzene
Chloroform
1,2 Transdichloroethylene
Ethyl benzene
Fluoranthene
Methylene chloride
Napthalene
Phenol
Bis(2-ethylhexy1)phthalate
Di-B-Butyl phthalate
Chrysene
Pyrene
Toluene
Trichloroethylene
Total toxic organics
Toxic metals
Antimony
Arsenic
Beryl 1 i urn
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Total toxic metals
Non- toxic metals
Al umi num
Barium
Boron
mg/liter
< 0.010*
< 0.010
< 0.0103
< 0.01
< 0.010
< 0.010
a
< 0.010,
0.027
0.027
< 0.005
< 0.003
< 0.001
0.006
0.061
0.389
0.213
< 0.001
0.056
< 0.003
0.034
< 0.025
0.269
1.028
0.903
3.025
0.800
kg/day
0.0012
0.0012
0.00026
0.00263
0.01678
0.00919
0.00242
0.00147
0.0116
0.0444
0.0389
0.1305
0.0345
(continued)
85
-------
TABLE 3-6 (continued)
Non- toxic metals (continued)
Calciumb
Cobalt
Iron .
Magnesium0
Manganese
Molybdenum
Sodium3
Tin
Titanium
Vanadium
Yttrium
Total non- toxic metals
PH
Temperature, °C
Cyanide, total
Oil and grease
Total organic carbon
Biological oxygen demand
Total suspended solids
Phenols
Fluoride
mg/ liter
11.767
0.005
1.513
3.311
0.031
0.004
370.64
0.044
2.770
0.035
< 0.001
9.130
8.9
23
56.0
38.0
56.0
kg/day
0.5075
0.00022
0.06525
0.1428
0.00134
0.00017
15.985
0.0019
0.1195
0.00151
0.3938
2.415
1.639
2.415
Concentration found in blank sample.
Metals not included in totals.
86
-------
CERAMIC CAPACITORS PROCESS NO. 4
Assembly
1. Function - During final assembly, the leads are soldered to the
ceramic substrate, and the capacitor Is dipped In molten epoxy, or as Is the
case with multiple-layered capacitors, epoxy molded. The epoxy 1s air dried,
and the capacitor is electrically evaluated and shipped.
2. Input Materials - Copper is most commonly used for capacitor leads.
The epoxy materials used to encapsulate the ceramic components are not identi-
fied in the literature. The solution used to clean the leads 1s a mild de-
tergent dissolved in water.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the assembly process are not reported.
4. Utilities - The types and quantities of utility service required for
this process are not reported.
5. Waste streams - There are no air emissions reported for this process.
The capacitor lead cleaning operation will produce some discharge level
of wastewater; the specific composition and quantity of this waste are un-
known.
There are no solid wastes associated with final assembly.
6. Control Technology - The type of system used for wastewater treatment
is unknown. It is assumed that this stream is subjected to pH control and
settling before discharge to the environment.
87
-------
REFERENCES FOR SECTION 3
1. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80-075-a, October
1980.
2. Jones, Thomas H. Electronic Component Handbook. Reston Publishing Co.,
Inc., Reston, Virginia, 1978.
3. Spotlight on Capacitors. Electronic News Suppl., August 18, 1980.
4. Predicasts Forecasts - 1980 Annual Cumulative Edition Issue No. 80. 4th
Quarter. July 24, 1980. Predicasts, Inc.
5. U.S. Department of Commerce. 1977 Census of Manufacturers: Electronic
Components and Accessories. June 1980.
88
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SECTION 4
RESISTORS
INDUSTRY DESCRIPTION
Electronic resistors are devices that provide electrical resistance and
are used in circuits for protection or current control. Resistors, like
capacitors, can be divided into two broad categories, fixed and variable.
A fixed resistor has two terminals and provides relatively constant
electrical resistance. The three basic types are carbon composition, wire-
wound, and film. In carbon composition resistors, the element 1s composed of
finely ground carbon or graphite, an inert nonconducting filler (usually
silica), and a synthetic resin binder. The proportions of carbon and filler
are adjusted to produce different resistances. Wire-wound resistors generally
consist of a single layer of high resistance wire wrapped around an insulating
core of ceramic or fiberglass. The element in film resistors consists of a
thin layer of resistive material applied to the surface of a ceramic or glass
rod or tube. Application of the film may be by spraying, dipping, evapora-
tion, sputtering, or pyrolytic cracking of gas, depending on the material.
Both carbon and metal films are used, but specific materials and manufacturing
processes vary widely. Metal film resistors can provide very high resistance
paths, are very accurate, and have a low temperature coefficient. They are
often used when a high degree of reliability and stability is required.
Variable resistors include potentiometers and trimmers. Potentiometers
have three terminals: two fixed terminals attached to each end of the resis-
tive element, and a third attached to a tap or contact that can be moved along
the element to vary the resistance. Potentiometers are usually used to control
or vary voltage across a circuit branch. On trimmers or rheostats two termi-
nals are used: one stationary, and one moving. Rheostats are used primarily
to limit current flowing in circuit branches.1 Potentiometers are designed for
89
-------
frequent or continuous tap movement, whereas trlnners are Intended for only
occasional movement of the tap.
Variable resistors are manufactured with a variety of materials and
processes. Potentiometers or rheostats may be wire-wound or non-wire-wound.
Wire-wound potentiometers are fabricated by space-winding (I.e., winding with
a specified distance between each turn of the wire) a single layer of bare
resistance wire around an Insulating core. Element resistance 1s controlled
by varying the core cross section and wire diameters. Non-wire-wound poten-
tiometers Include carbon composition, conductive plastic, and cermet types.
Carbon composition resistive elements can be either coated films or molded
Into a cavity 1n a plastic base. Conductive plastic elements are produced by
a number of molding techniques. Cermet potentiometers are made with resistive
elements composed of a ceramic and metal. Although very resistant to humidity
and temperature, the abrasiveness of cermet materials may result In shorter
2
service. Trimmer elements may be carbon composition, wire-wound, or cermet.
Raw Materials
The raw materials for resistors are divided into resistive elements,
contacts, encapsulants, insulators and substrates, and leads: '^
0 Resistive elements - Wire-wound resistors are manufactured with
various wire alloys. The primary element material for carbon
composition resistors (both fixed and variable) 1s carbon or graph-
ite. A filler, usually silica, and a synthetic resin binder com-
plete the mixture. Metal film resistor elements may be composed of
various metals, metal alloys, or metal oxides. The most commonly
used are a nickel-chromium alloy composed of the alloy with traces
of other metals; tin-oxide doped with antimony; and cermet, a mix of
glass and metal alloys.
The specific composition of the carbon-resin mixture used in fabri-
cation of conductive plastic potentiometers is not known. In addi-
tion, no information was found on the composition of materials used
in cermet potentiometers and fixed resistors. Most are likely
proprietary.
0 Insulators/Substrates - A number of insulators or substrates are used
in variable and fixed resistors. The most common types are glass,
ceramic (alumina), fiberglass, flexible polyester, and various
plastics.
0 Contacts - Contacts, which are found only on variable resistors, may
be made of brass or phosphor bronze.
0 Leads - Leads are usually copper or aluminum.
90
-------
Encapsulants - A wide variety of encapsulants are used for mechan-
ical and environmental protection of resistors. Coatings Include
phenolic compounds, ceramic, vitreous enamel, slllcone ceramic,
sillcone, glass, varnish, and metal, as well as various other
proprietary materials.
Products
The Bureau of the Census classifies all types of electronic resistors
Into SIC 3676. In 1979, domestic manufacturers sold almost 10 billion units
of fixed resistors at a total market value of over $350 million. An Industry
breakdown of each of the major types consumed 1n 1977, 1978, and 1979 1s
presented 1n Figure 4-1. Table 4-1 presents data on sales of the various
types of resistors in the U.S. market by both domestic and foreign manufac-
turers In 1978 and 1979, and estimated sales for 1980 and 1983.5>6 The total
market for fixed resistors Increased by almost 20 percent In 1979. Resistor-
capacitor networks led with a 36 percent increase, followed by metal film
resistors (28 percent), carbon films (19 percent), wire-wounds (6 percent),
and carbon compositions (3 percent).4
It is the general consensus within the Industry that growth (in numbers of
units and in dollars of sales) Increases 1n 1980 will fall short of those in
1979, partly due to the economic recession. A softening of demand for video
and electronic games, as well as the automotive market, are partially responsi-
ble for the expected decline. The Industrial market, which Includes computers,
communications, and instrumentation, also showed a slowing trend in the second
quarter of 1980. However, companies heavily Involved in industrial and mili-
4
tary markets remain optimistic.
As to specific resistor types, a slowdown has been expected in the carbon
composition business for several years. However, it still retains a respect-
able share of the total resistor market, and should not disappear rapidly. On
the other hand, the resistor-capacitor network market is expected to rise
sharply in the next 2 to 3 years, possibly even doubling by 1982 and doubling
again by 1984.
The production of wire-wound resistors remained relatively unchanged in
numbers of units produced from 1978 to 1979. Rapid growth is not expected, with
rates of 5 to 6 percent predicted. These resistors primarily serve the power
and precision markets. The power segment is the faster growing of the two, which
is due in large part to the more widespread use of metal film resistors in the
91
-------
BILLIONS
OF UNITS
1977
1978
1979
1977
1978
1979
NETWORKS
HIREUOUNO
I METAL FILM [ (CARBON COMP.
I CARBON FILM
Figure 4-1. Sales of major resistor types, 1977-1979.4
92
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TABLE 4-1. INDUSTRY-WIDE CONSUMPTION OF RESISTORS SHIPPED BY U.S. AND
FOREIGN MANUFACTURERS FOR THE U.S. MARKET,b'5 $ million
Resistor type
Fixed (total)
Carbon composition
Deposited carbon
Metal -film
Wire-wound
Variable (total)
Potentiometers, wire-wound
Potentiometers, nonwi re-wound
Trimmers, wire-wound
Trimmers, nonwi re-wound
Resistive networks (total)
Thin-film
Thick-film
1978
218.5
60.0
21.5
75.0
62.0
239.5
38.5
98.5
22.5
80.0
149.0
69.0
80.0
1979
229.4
62.3
23.1
79.0
65.0
267.2
43.0
109.7
24.5
90.0
177.6
79.0
98.6
1980
229.1
62.6
22.0
81.0
63.5
272.0
43.0
109.0
25.5
94.5
198.2
88.0
110.2
1983
258
63
26
99
70
318
50
130
28
110
269
114
155
Annual
growth, %
3.0
0.3
3.0
5.8
1.9
4.4
3.8
4.3
3.4
5.1
10.9
9.6
12.0
93
-------
precision area. Reluctance to redesign military circuits and lack of suffi-
cient power ratings for metal film resistors in the power market has resulted
in wire-wound resistors maintaining these areas.
The market share for metal film resistors will continue to increase as
their characteristics are improved. Corning, the largest producer, increased
its metal film capacity by about 60 percent between the beginning of 1979 and
mid-1980. Another producer, TRW-IRC, finished construction of the last of
three plants in Barbados, increasing its low-cost metal film resistor output
A
by 400 percent.
Companies
The 1977 Census of Manufactures reports that a total of 102 companies are
involved in the production of electronic resistors. This figure excludes
companies with 20 employees or less. A breakdown of companies manufacturing
each type of resistor is presented in Table 4-2, and Table 4-3 categorizes
these firms by number of employees. Tables 4-4 and 4-5 show the product mix
of the major manufacturers of fixed and variable resistors, respectively.^
Relative market shares of the major suppliers of fixed resistors are shown in
Table 4-6. It can be seen that several companies manufacture more than one
type of resistor, but no single company really dominates the market for more
than one type.
Environmental Impacts
The manufacture of electronic resistors involves a variety of operations.
Emissions of participate matter can result from milling and trimming of metal
and plastic compounds, and aerosols of silicone- or epoxy-based coatings may
be released during their application. Other possible sources of atmospheric
emissions are degreasing and plating tanks, and fumes and organic vapors are
generated during brazing, soldering, and plastic melting processes. The
principal waterborne effluents are spent solvents and other degreasing, clean-
ing, and cooling solutions. Scrap metals and plastics are also generated
during some processes.
The types and extent of control technologies employed at resistor produc-
tion facilities are not well documented in the literature. Some materials are
likely recycled to the process or sold for recovery. Control of particulate
94
-------
TABLE 4-2. NUMBER OF COMPANIES PRODUCING EACH RESISTOR TYPE7
Resistor type
Number of
companies
Fixed, composition
Fixed, deposited carbon
Fixed, evaporated metal film and other metal oxide, metal/glass,
or metal/ceramic element
Variable nonwlre-wound:
Single turn, carbon and other file, nonpreclslon
Single turn, precision and nonpreclslon
Trimmers (Industrial and military grade):
Square and round
Rectangular
Fixed, wire-wound:
Nonprecision (fixed and adjustable) over 1%
Precision, unsealed
Precision, encapsulated and miniature, 3% or under
Variable, wire-wound:
Nonprecision, single turn (wiper or shaft traverses 360° or
less)
Precision single turn, linear (0.5% linearity or less) and
and nonlinear (1% linearity or less)
Trimmers (industrial and military grade)
Miscellaneous:
Varactors
Thermistors, bead type, disc, rod, etc.
Multiturn, all types, wire-wound and non-wirewound
Fixed resistor networks
12
17
32
9
17
10
7
14
6
18
11
17
9
7
12
12
15
95
-------
TABLE 4-3. RESISTOR MANUFACTURERS BY EMPLOYMENT
RANGE CLASSIFICATION7
Employment range
1-4
5-9
10-19
20-49
50-99
100-249
250-499
500-999
1000-2499
Number
of companies
9
6
6
17
16
18
15
11
2
96
-------
TABLE 4-4. MAJOR MANUFACTURERS OF FIXED RESISTORS
Carbon composition
Mi re-wound
Phenolic
Ceramic Shell
Flameproof
Vitreous enamel
Si li cone ceramic
Si li cone coated
Aluminum heat-s inked
High power
Carbon film
Metal film
Cermet
High-voltage/high-resistance
Metal oxide film
Metal film
Carbon film
Mire-wound
Mire-wound, aluminum heat-s inked
Mire-wound, Bobbin
0*
T3
ID
V.
oo
i
c
01
I—
a
I.
Q.
X
X
X
X
01
ft
u
U)
X
~y
^~
^^
Q2
1—
X
X
X
X
X
X
X
X
X
X
X
X
-------
TABLE 4-5. MAJOR MANUFACTURERS OF VARIABLE RESISTORS
General -purpose potentiometers
Carbon composition
Wi re-wound
Conductive plastic
Cermet
Precision single-turn potentiometers
Wire-wound
Conductive plastic
Cermet
Single-turn trimmers
Carbon composition
Wire-wound
Cermet
Rectangular multi-turn trimmers
Carbon composition
Wire-wound
Cermet
Square multi-turn trimmers
Wire-wound
Cermet
Rheostats, all types
Precision multi-turn potentiometers
Wire-wound
Conductive plastic
01
To
L.
CO
O)
p_
•*
X
X
X
X
X
X
X
X
in
c
3
o
ca
X
X
X
X
X
X
X
X
.a
^
^
o
p_
ro
z
X
X
X
01
'i
j=
o
X
X
X
X
p_
o
0
0)
Q.
l/l
X
X
X
X
X
X
X
X
X
X
X
O)
Q
Q.
u
as
4->
10
X
X
{J
ce.
•3.
C£.
r-
X
X
X
X
X
X
X
X
X
X
X
93
-------
TABLE 4-6. MARKET SHARES OF MAJOR RESISTOR SUPPLIERS"
Type resistor
Wi re-wound
Metal film
Networks
Carbon film
Carbon Compositions
Company
TRW/ IRC
Dale
RCL
Ohmite
Small cross
All others
Corning
Dale
TRW/ IRC
Mepco/Electra
All others
CTS
Beckman
Sprague
Centralab
Allen-Bradley
Dale
All others
R-Ohm
Mepco/Electra
KOA Speer
Al 1 others
Allen-Bradley
Stackpole
TRW- IRC
Market share (%)
28
25
12
9
5
21
33
20
20
17
10
30
20
10
10
9
9
10
35
28
25
12
57
23
20
99
-------
matter and organic vapors can be effected through use of readily available
control devices. Wastewater streams can be treated by precipitation, set-
tling, and subsequent filtration, as well as other methods.
INDUSTRY ANALYSIS
The following industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potential effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
Figure 4-2 is a flowsheet showing the processes used for resistors, as well as
their interrelationships and waste streams.
100
-------
RESISTIVE
ELEMENT
FORMATION 1
IMPREGNATION
AND COATING
APPLICATION 2
ASSEMBLY
AND LEAD
ATTACHMENT 3
PROTECTIVE
COVER
FORMATION 4
a WATER
OAIR
OSOLID
Figure 4-2. Resistor production flowsheet.
101
-------
RESISTORS PROCESS NO. 1
Resistive Element Formation
1. Function - The resistive element 1s the heart of the resistor. Ele-
ments can be carbon composition, conductive plastic, cermet, metal film, and
wire-wound. Differing manufacturing techniques are used for each type.
The material for carbon composition resistors 1s carbon or graphite
milled to a powder. A binder and filler 1s mixed with the powder and molded
or extruded using either heat, pressure, or both.2*8 Heat 1s applied 1n a
baking process to remove gaseous Impurities and to catalyze the binding agent;
this results in adhesion of the particles into a solid mass. The cores are
then formed by molding Into a cylindrical shape. It is reported that in
variable resistors the resistive element is molded Into a plastic base to
produce one integral unit. The carbon resistive element usually requires
trimming, which can be performed by a mechanical etch. Methods of trimming in
thick film applications include air abrasion, pulse trimming, scribe trimming,
and laser trimming.9
Carbon film resistor elements are manufactured by application of a
layer of carbon to glass, ceramic, or other Insulating materials. The ap-
plication methods are by screen-on through a mask, brush-on spraying, and
dipping.9 Adhesion of the film to the substrate is enhanced by baking or
heating. A pyrolytic process to decompose gaseous hydrocarbons and cure
the film is also reported.8 A variation of carbon film, known as cracked-
carbon film, is provided with a helical groove cut around the cylinder to allow
adjustment of final resistance. This spiralling can be made with a high-veloc-
ity air stream propelling an abrasive powder, a thin high-speed grinding wheel,
or a laser.2 As the resistor is turned, the cutting tool traverses its length.
Conductive plastic resistor elements are made of a carbon-resin mix.
This composition is either molded into a plastic substrate or molded simul-
taneously with the substrate. In the latter case, the carbon-resin mix is
sprayed onto a plastic preform prior to application of heat and pressure.
Conductive plastic mixes may also be applied to flexible polyester, molded
plastic, or ceramic substrates by silk-screening methods.2
102
-------
Cermet resistor films are usually mixtures of precious metals or metal
oxides and glass frit. Inks made by adding an organic vehicle of suitable
viscosity to the cermet powder are applied to an Insulating substrate, usually
by silk-screening or brushing to form the cermet film. The element Is
then fired to cure the cermet. A casting method 1n which the cermet powder Is
made Into a slurry and cast Into a continuous flexible sheet for later appli-
cation has also been devised. The advantage of this method Is less waste of
material. Films are usually 6 to 50 pm thick.9
Metal film resistors are made by coating a glass or ceramic substrate
with a thin film of metal by vacuum evaporation, sputtering, or chemical vapor
deposition by pyrolytic decomposition of gases.2*9 The substrate 1s glazed
prior to metal deposition and then overglazed after deposition to protect the
metal film.9 The overglaze must be alkali-free to prevent Ionic conduction
and degradation. The resistor is fired after deposition.
Mire-wound resistor elements are produced by space-winding (I.e., winding
the wire so that there is a specific distance between each turn) a single
layer of conductive wire around an Insulating core.
2. Input Materials - Primary materials used 1n resistive element fabri-
O Q
cation include carbon, graphite, metals, and metal oxides. ' Ceramics,
plastics, resins, binders, and fillers are also employed. Carbon and graphite
are the major components of carbon composition resistive elements. Fillers
used in these devices include silica sand and titanium oxide.8 One binding
a
reported in the literature 1s zinc stearate. Another material added is
boron, which improves performance by preventing oxidation of the carbon.9
Carbon and resin are used for conductive plastic resistor elements.
Plastics used as substrates may be thermosetting plastics (e.g., phenolics,
alkyds, epoxies, diallyl phthalates, silicones) or thermoplastics (e.g.,
polyesters, polyimides, cellulose, polystyrene).9 Flexible insulating sub-
strates that might be used include cotton or glass cloth impregnated with
oleoresins, phenolic resins, alkyds, epoxies, or silicones; inorganic paper
insulations composed of asbestos, wood pulp, starch, or rubber binder (pos-
sibly containing glass flakes, resin binder, polyvinyl acetate, epoxy, or
silicones); and 2- or 3-ply combinations of polyester, acetate, or polyimide
bonded with rubber adhesive and mat film composites of polyester between 2
layers of acrylic- or polyester-based mat.9
103
-------
Various metals and metal oxides are used as the resistive element. For
wire-wound resistors, nickel-chrome wire in various combinations Is most often
2
employed. Table 4-7 lists some of these wire alloys.
TABLE 4-7. CHARACTERISTICS OF ALLOYS USED IN WIRE-WOUND
POTENTIOMETERS AND RESISTORS?
Alloy
Evanohmab
N1 chrome
Advance*3
Cupronf
M1dohmb
No. 90 Alloy3
Lohmb
No. 30 Alloy3
Copper
Approximate composition
N1 75%, Cr 20%, Al 2.5%, Cu
N1 60%, Cr 16%, Fe 24%
Ni 43%, Cu 57%
Cu 55%, NI 45%
Ni 23%, Cu 77%
Ni 12%, Cu 88%
Ni 6%, Cu 94%
Ni 2%, Cu 98%
Cu 100%
2.5%
a Trademark, Wilbur B. Driver.
Trademark, Driver-Harris.
Cermet films are composed of various mixtures of metal, metal oxides, and
glass or ceramic. Metals usually used include silver, platinum, ruthenium
Q
oxide, irridium oxide, gold, palladium, and palladium oxide. One cermet
reported is a mixture of palladium, silver, and lead-borosilicate glass.9
These are mixed in an organic vehicle for application. Specific organics were
not identified in the literature.
Ceramics used as insulating elements or substrate are usually composed of
alumina (Al-O-).
3. Operating Conditions - Heat and pressure are used to fuse and form
resistive elements, or to cure and fire them after deposition on a substrate.
Specific temperatures used in baking or firing are not generally reported.
For drying films printed on a substrate, temperatures from 100° to 150°C for
15 minutes are required. This is accomplished in a hot air or infrared
moving-belt furnace. Temperatures of 450° to 1000°C are required to burn off
g
organic binders. These temperatures are also required to develop proper film
parameters and to sinter the colloidal glass used in certain resistor coat-
ings. Pressures used in forming carbon-graphite resistive cores are not re-
ported.
104
-------
4. Utilities - Electricity is required for operating various machinery
used for molding, extruding, wire winding, spraying, mixing, vacuum deposi-
tion, and heating. Dryers and ovens for firing operations may be gas-fired.
Water may be used in conjunction with the trimming operation to flush away the
particles.
5. Waste Streams - Trimming operations could result in generation of
airborne participates. This could also be true of milling of carbon and
graphite prior to molding. Airborne materials would be primarily carbon
and/or graphite, as well as some silica, titanium oxide, boron, and metal
oxides. Volatile organics and other impurities are emitted during drying and
firing operations. Some volatile constituents of the various plastics and
resins used in manufacturing of conductive plastic resistors may also be
released. Other areas of potential airborne waste streams include aerosols
and vapors emitted during spraying operations.
There are no sources of process wastewater described in the literature.
The only source of solid wastes would be scrap materials from trimming of
carbon composition resistive elements, off-spec materials, and mask disposal
from screen-on operations.
6. Control Technology - Specific control technologies used in resistor
manufacture are not cited in the literature. However, removal of participate
and organic vapors would be required in some cases. Participate removal can
be accomplished using cyclone separators, baghouses, and electrostatic pre-
cipitators. Organic vapors can be removed by passing the contaminated air
through an activated carbon filter.
105
-------
RESISTORS PROCESS NO. 2
Impregnation and Coating Application
1. Function - Impregnation is performed to waterproof the porous carbon
resistor elements. Barrier coatings are applied to wire-wound resistors. Their
functions are to provide some degree of moisture, gas, and dust prevention,
thus preventing corrosion and electrical malfunctions; to provide an insula-
tion barrier; to provide stress relief during molding and thermal cycling; and
Q
to hold components together, thus increasing their ruggedness.
Impregnation consists of immersing the element in the liquid material to
thoroughly soak and wet any interstices present. This is usually accomplished
Q
with vacuum or pressure equipment. The material is then cured with heat.
Application of barrier coatings is accomplished by a number of methods; these
Q
include dipping, spraying, fluidized-bed, and eye dropping. These coatings
are also cured with heat following application.
2. Input Materials - Impregnants are usually various types of lacquers,
varnishes, or waxes. Specific types used are generally not reported in the
literature. In one plant surveyed, polychlorinated bipheynyls (PCB's) were
Q
used to impregnate resistor cores. At the time of the survey, however, these
operations were being phased out.
A variety of materials, usually high-molecular-weight polymers, are used
8 9
for coatings. Most widely used are silicone- or epoxy-based substances.
Other coating materials may be polyester, polyvinyl formal, and polyvinyl
butyral.9
3. Operating Conditions - Impregnation is accomplished in pressure or
vacuum cycling apparatus. Specific pressures or vacuum settings are not cited
in the available literature. Curing temperatures required will vary with the
impregnate or coating. For various silicone coatings, cure temperatures range
from 60°C for 4 hours to 250°C for 4 hours.9
4. Utilities - Electricity is required for operation of various types of
machinery performing operations such as molding, injection, extrusion, spray-
ing, eye dropping, and fluidized-bed. Compressed air may be required for
pressure application machines, and some ovens are gas-fired. Water is likely
required in some applications.
106
-------
5. Waste Streams - Airborne waste streams would be primarily from loss
of materials during application processes. Aerosols and high vapor pressure
constituents would be emitted, especially during such application processes as
spraying and fluidized-bed.
Cleaning of equipment will most likely require solvents which will re-
quire disposal. Other process liquid wastes are not reported.
There are no solid wastes from this process.
6. Control Technology - Control of organic vapors could*be accomplished
by collecting vapors via hoods and passing them through an activated carbon
bed.
Any waste solvents generated by cleaning could be reclaimed by the
manufacturer or sent for reclamation or disposal. Information on specific
treatment methodologies presently in use at manufacturing plants is not avail-
able.
107
-------
RESISTORS PROCESS NO. 3
Assembly and Lead Attachment
1. Function - Final assembly and lead attachment varies with resistor
type. In molded carbon composition resistors, leads may be embedded in the
resistive core at the time it is formed. They may also be welded, brazed, or
soldered to an end cap that is mechanically force-fit onto the ends of the
carbon composition core. In carbon film-type resistors, the leads may be
inserted into the glass or ceramic rod on which the resistive coating was
applied. At the ends of the tube, a connection is made between the coated
glass and leads with conductive cement. In wire-wound resistors, the lead
wire may be mechanically crimped to the resistance wire element. Alterna-
tively, the resistance wire may be welded to a nickel-chrome wire which is
then brazed to the inside of an end cap with an attached lead. The lead may
be brazed directly to the resistance wire.
Variable resistors require assembly of a larger number of component parts
than do fixed resistors. The resistance track, sliding contact, spindle,
bearing assembly (in some instances), and the three terminals may all require
assembly. Details of assembly methods were not found in the literature.
2. Input Materials - Input materials are primarily various metal parts.
Leads may be copper, silver, aluminum, gold, or wire plated with tin, silver,
or gold. A variety of alloys may be made with these metals using nickel,
chromium, palladium, iron, molybdenum, tungsten, and magnesium. Sliding
? Q
contacts on variable resistors may be brass, bronze, or phosphoric bronze. '
A copper-graphite contact has also been reported. One conductive cement
Q
reported to be used in electronic component assembly is a silver-based epoxy.
The most commonly used solder in the resistor industry is 60/40 tin/lead
Q
alloy. Various acid fluxes containing zinc chloride, ammonium chloride,
hydrochloric acid, or stannous chloride may be used in soldering operations.
Brazing filler metals may include copper, copper-phosphorus, aluminum-silicon,
and silver-, gold-, and nickel-based alloys. Fluxes or resin co-solders may
also be used in brazing operations.
108
-------
3. Operating Conditions - Mechanical lead attachment and various assem-
bly operations are performed at ambient temperature and pressure. Soldering
operations involve melting temperatures below 500°C, whereas brazing involves
higher temperatures. Other wire assembly methods may include thermal com-
pression and ultrasonic bonding. Temperatures and pressures used in thermal
compression bonding would depend on the metal or alloy.
4. Utilities - Electricity would be required for operation of machinery
for assembly, soldering, welding, or brazing operations. Process water may be
required for cooling and cleaning purposes.
5. Waste Streams - The only air emissions are fumes from brazing and
soldering operations.
Removal of solder flux could possibly result in small amounts of contami-
nated water containing metals.
Solder dross and scrap metal from brazing, soldering, wire forming, and
cutoff operations represent potential solid wastes from lead attachment and
a
assembly operations.
6. Control Technology - Fumes from soldering and/or brazing operations
will require collection and treatment. Satisfactory treatment could be ac-
complished using a packed tower scrubber.
Wastewater containing acid flux and metal wastes can be treated by pH ad-
justment to neutralize the waste and precipitate the metals. Subsequent fil-
tration may or may not be required. Sludge can be disposed of in a secured
landfill or, if feasible, sold for recovery.
Most metals in the form of scrap will likely be recovered and sold for
reprocessing, especially precious metal scrap.
109
-------
RESISTORS PROCESS NO. 4
Protective Cover Formation
1. Function - The purposes of a final cover for resistors (as well as
other electronic components) are to provide a well-defined structure to permit
standardization and inter-changeability of parts; to provide a degree of impact
and mechanical shock resistance; and to provide some degree of environmental
q
protection from moisture, sunlight, and various corrosive agents. Final
covers for resistors are either metal, a combination of a thermosetting or
thermoplastics and metal, or thermosetting or thermoplastics alone.
The processes used for embedding, which is employed primarily for plastic
materials, can be categorized generally into four types: casting, potting,
encapsulation, and transfer molding. Casting consists of pouring a catalyzed
thermosetting plastic or a thermoplastic liquid into a reusable mold. Potting
is basically the same as casting, with the major exception that the mold
(metal or plastic) becomes an integral part of the component. Encapsulation
coating is usually by dipping into a curable or hardenable plastic. These
coatings are relatively thick compared to barrier coatings. Encapsulation can
also be accomplished using spray techniques. Transfer molding involves the
transfer of a catalyzed or hardenable material under pressure from a container
q
into a mold which contains the part to be covered.
Some resistors may be hermetically sealed in small metal cannisters or,
as is the case many times with variable resistors, sealed in molded plastic or
plastic/metal cases. Metal cases usually require cleaning and subsequent
plating.
2. Input Materials - A variety of materials can be used for protective
coverings. Metals are usually steel, aluminum, and brass, which are often
tin- or nickel-plated.
Thermosetting plastics (which cure chemically) used for embedding include
alkyds, aminos, diallyl pthalates, epoxies, phenolics, polyesters, and sili-
cones. Embedding thermoplastics (which liquify under heat and pressure and
harden when cool) include ABS (acrylonitrile, butadiene, and styrene), acetals,
acrylics, ethylene vinyl acetates (EVA), fluorocarbons, nylons, phenoxies,
polyimides, polycarbonates, polyesters, and polystyrenes.
110
-------
Degreasing of metal used for covers may involve use of various halo-
genated and non-halogenated solvents. Most commonly used halogenated solvents
are perchloroethylene and 1,1,1 trlchloroethane. Non-halogenated solvents
include methanol, acetone, Stoddard solvent, methyl ethyl ketone (MEK), and
isopropyl alcohol.8
Plating of metal cans involves use of nickel and tin plating solutions.
The composition of typical solutions can be found in the discussion of printed
circuit board manufacture in Section 6.
3. Operating Conditions - Operating conditions of temperature and pres-
sure vary widely depending on specific materials and processes used.
4. Utilities - Electricity would be required to run various machines
used for molding and dispensing liquid materials, and to supply heat for melt-
ing thermoplastics. Water is probably required for cooling and cleaning
purposes.
5. Waste Streams - Some airborne emissions would result from encapsula-
tion by the spray method, from degreasing tanks, plating tanks, and (depending
on the material) from melting of plastics.
The only liquid wastes would be used chlorinated or petroleum-based
hydrocarbon degreasing solutions from metal cleaning, wasted nickel or tin
plating solutions, and other contaminated cleaning and cooling water.
Solid wastes include scrap from trimming the molded components, unused
portions of mixed thermosetting plastics which cannot be reused, off-spec
plastics, and metal scrap.
6. Control Technology - Emissions from degreasing tanks can be reduced
by increasing freeboard in the degreaser tank and using refrigerated chillers
to create a cold air blanket above the solvent. Emissions can be controlled
by the use of chillers or condensers and carbon adsorption. ' Spraying emis-
12
sions can be reduced by use of water curtains or dry baffles.
Rinse water and dumped plating solutions will contain tin and nickel and
can be treated by pH adjustment using lime, precipitation, settling, and
subsequent filtration of supernatant using diatomaceous earth. Other tech-
niques used for recovery of plating solutions include reverse osmosis, distil-
lation, and ion exchange. Sludges from treatment of plating solutions can be
dewatered by centrifuge, vacuum filter, or pressure filter apparatus, and dis-
posed of by landfilling. 3> 4 Non-halogenated hydrocarbons used for cleaning,
111
-------
such as methanol, acetone, MEK, and Ispropyl alcohol, are usually reclaimed
Q
on-site or sent away for recycle. Halogenated solvents such as perchloro-
ethylene and 1,1,1 trichloroethane are again either reclaimed on-site or given
Q
to a contractor for reclamation.
Waste thermoplastic materials may be recycled through the molding proc-
ess, since they can usually be melted and remelted.8 They may also be hauled
to a landfill along with thermosetting plastic wastes.8 Metal scrap can be
recovered and recycled where feasible. Bottoms from degreasing tanks may
warrant reclamation if metals content 1s high, but are usually drummed and
landfilled.
112
-------
REFERENCES FOR SECTION 4
1. Wolf, Stanley. Guide to Electronic Measurements and Laboratory Practice.
Prentice-Hall, Inc., Englewood Cliffs, New Jersey. 1973.
2. Jones, Thomas H. Electronic Components Handbook. Reston Publishing Co.,
Inc., Reston, Virginia, 1978.
3. Colwell, Morris A. Electronic Components. Newnes Technical Books,
Butterworth, England, 1976.
4. Spotlight on Resistors. Electronic News Suppl., July 21, 1980.
5. Predicasts Forecasts - 1980 Annual Cumulative Edition Issue No. 80. 4th
Quarter. July 24, 1980. Predicasts, Inc.
6. Components: Unaggressive Growth in Store. Electronics. January 3,
1980.
7. U.S. Department of Commerce. 1977 Census of Manufacturers: Electronic
Components and Accessories. June 1980.
8. U.S. Environmental Protection Agency. Assessment of Industrial Hazardous
Waste Practices - Electronics Components Manufacturing Industry. EPA
Contract No. 68-01-3193. January 1977.
9. Harper, C.A., ed. Handbook of Materials and Processes for Electronics.
McGraw-Hill, New York, 1970.
10. Dummer, G.W.A. Electronic Components, Tubes, and Transistors. Pergamon
Press, Oxford, 1965.
11. U.S. Environmental Protection Agency. Controlling Pollution from the
Manufacturing and Coating of Metal Products: Solvent Metal Cleaning Air
Pollution Control-II. EPA 625/3-77-009, May 1977.
12. U.S. Environmental Protection Agency. Controlling Pollution from the
Manufacturing and Coating of Metal Products: Water Pollution Control-I.
EPA 625/3-77-009, May 1977.
13. U.S. Environmental Protection Agency. Development Document for Proposed
Existing Source Pretreatment Standards for the Electroplating Point
Source Category. EPA 440/1-78-085, February 1978.
14. U.S. Environmental Protection Agency. Controlling Pollution from the
Manufacturing and Coating of Metal Products: Water Pollution Control-
II I. EPA 625/3-77-009, May 1977.
113
-------
SECTION 5
TRANSFORMERS AND INDUCTORS
INDUSTRY DESCRIPTION
An electronic transformer 1s used to convert variations of AC current In a
primary circuit Into variations of voltage and current 1n a secondary circuit
through mutual induction. A transformer is basically two coils of wire in
close proximity on a common core; if one coil is energized, a magnetic field
is created which, depending on its strength or polarity, induces the flow of a
secondary current in the other coil. If an AC voltage is applied to one coil,
an AC voltage of the same frequency is induced in the other coil. The magni-
tude of this induced voltage is approximately equal to the applied voltage
times the ratio of the number of turns on each coil. The degree of Induction
is dependent to a large extent on the nature and construction of the core.
Transformers are made in great variety, many times to meet a specific
application requirement. Four basic types of transformers are power, audio,
pulse, and radio frequency (rf). Power transformers change an AC power supply
voltage and current to that required for operation of electronic equipment.
Audio and communications transformers transmit information of varying frequen-
cy, amplitude, and wave shape between electronic equipment or between circuits
in a single piece of equipment. They are used to couple signals whose fre-
quencies fall in the 20 to 20,000 Hz range. Pulse transformers operate over a
wide band of frequencies and are designed to transmit pulses with good wave-
shape fidelity, rather than the continuous sinusoidal wave resulting with audio
transformers. Radio-frequency transformers are used to couple high-frequency
signals and thus the cores are composed of powdered iron or ferrite to minimize
energy losses. These type cores are used up to about 50 MHz. Above this fre-
quency air cores are often used.
Closely related to a transformer is an induction coil, or inductor, which
is basically a single wire wound around an air or magnetic core with a terminal
114
-------
at each end of the winding. The Inductance of this wire coll 1s a measure of
its ability to Induce a current to flow when subjected to a magnetic field or,
conversely, the ability to produce a magnetic field when current 1s passed
through the coll. The magnetic field produced stores energy, the amount
depending on the magnitude of the current. When the current flowing 1n an
Inductor reaches a steady value, the magnetic field also stabilizes and stores
a steady value of energy. The energy stored Increases as the square of the
magnitude of the current. The magnitude of the Inductance of a coll 1s deter-
mined by the number of coll turns, the type and shape of the core material,
and the diameter and spacing of the turns. Inductors may be used as power
supply filters, oscillators, frequency discriminating filters, and for tuning
circuits.1
Inductor design 1s essentially dependent upon operating frequency.
Magnetic cores are used at audio and low carrier frequencies to combine large
Inductance and low DC resistance. In low frequency applications a high In-
ductance value 1s required, the core material must have a high permeability,
and the number of coil turns must be large. The laminated cores used for
these applications are made of thin sheets of steel or other Iron alloys
separated by insulating glue. These laminated cores can be used since at low
frequencies, energy losses due to eddy currents and hysteresis are small. In
applications where core losses need to be minimized such as In high-frequency
inductors, ferrites, powdered iron, or other high permeability magnetic
alloys can be used.1'^
Raw Materials
Raw materials can be broken down into core materials, windings, and
1 2
encapsulants: '
0 Core materials - Core materials are usually composed of iron, an
iron alloy, or a ferrite. A current flowing through a primary
winding may induce current flow through the magnetic core as well as
the secondary winding. The usefulness of a solid Iron block as the
core is therefore limited, as the current flow in the magnetic core
or eddy current creates its own magnetic field which opposes the
115
-------
field Induced by the primary winding and results 1n power losses.
To alleviate this problem, cores are made by stacking thin sheets of
metal with an insulating glue between each. This serves to break up
the electrical continuity of the cores. Some cores are made by com-
pressing grains of ferrous metal together with an Insulating binder.
Perrites or artificial magnets, composed chiefly of Iron oxide and
other metallic ions, are preferred for high-frequency and audio ap-
plications because of their high permeability and Inherent electri-
cal resistance. Soft ferrites are also used in some transformer
cores. These are usually made from combinations of nickel, zinc,
and iron oxides; manganese, zinc, and iron oxides; and nickel, copper,
zinc, and iron oxides. Inductor cores are also made of iron, iron
alloys, and ferrites. Phenolic compounds, air, and air and phenolic
combinations are also used. Table 5-1 lists some high permeability
magnetic materials and alloys, many of which are used in coils and
transformers.3
Coil materials - Very little information is available in the litera-
ture concerning specific winding materials. Copper and aluminum
wire are probably the most widely used windings. Lesser amounts of
other conductive metals such as silver, gold, nickel, and chromium
may also be used to increase conductivity. In some applications,
metal pastes with a conductive metal covering are employed.
Encapsulants - In the manufacture of laminated cores, varnish,
lacquer, or wax generally serve as an impregnant to prevent any
vibration of the laminations. These materials may also be used in
transformers with other core types to prevent vibration of the
winding. In some cases, the assembly itself may be encapsulated
with an epoxy molding, resin, or metal case.
Products
The Bureau of the Census classifies the manufacture of electronic trans-
formers, coils, and inductors into SIC 3677. This SIC classification does not
include the following related products:
0 Transformers and inductors for telephone and telegraph apparatus
(SIC 3661)
Electric lamps (SIC 3641)
Coils for electrical end uses in industry (SIC 3629)
Electrical transformers (SIC 3612)
Semiconductor (solid state) and related devices (SIC 3674)
a breakdown of the various components produced under this SIC in 1977 is
4
presented in Table 5-2.
It is reported that the total value of shipments increased 43 percent
from 1972 to 1977. As can be seen in Table 5-3, this growth rate is expected
to decrease significantly. ' An annual growth rate of only 4.2 percent is
estimated from 1978 to 1983.
116
-------
TABLE 5-1. HIGH PERMEABILITY MATERIALS AND ALLOYS3
Material
Cold rolled steel
Iron
Purified iron
4% sili con- iron
Grain oriented
45 Permalloy
Hipernik
Monimax
Sinimax
78 Permalloy
4-79 Permalloy
MuMetal
Supernal loy
Permendur
2V Permendur
Hi perco
Form
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Sheet
Fe
98.5
99.91
99.95
96
97
54.7
50
50
54
21.2
16.7
18
15.7
49.7
49
64
Approximate
percent composition
Ni
45
50
47
43
78.5
79
75
79
Co
50
49
34
Mo
3
Other
4 Si
3 Si
0.3 Mn
3 Si
0.3 Mn
0.3 Mn
2 Cr
5 Cu
0.3 Mn
0.3 Mn
2 V
Cr
Use
Low core losses
Audio transformers, coils
and relays
High frequency coils
High frequency coils
Audio coils, transformers,
magnetic shields
Audio colls, magnetic
shields, transformers
Pulse transformers, magnetic
amplifiers, colls
D-C electromagnets, pole tips
-------
TABLE 5-2. SHIPMENTS OF ELECTRONIC TRANSFORMERS, INDUCTORS,
AND COILS, 19774
Component description
Coils, transformers, reactors, and chokes for
electronic applications:
As reported in the Census of Manufactures
As reported in Current Industrial Reports
MA-36N, selected electronic and associated
products, including telephone and tele-
graph apparatus
Audio transformers
Low frequency chokes
Plate and filament transformers, including
autotransformers, except toroidal
Pulse transformers, computer, and other
types
Radio frequency (RF) chokes
RF coils
Intermediate frequency (IF) transformers
Television deflection, focus coils,
deflection yokes, etc.
Toroidal windings (transformers and
reactors), except complete magnetic
amplifiers
Other (balum coils, permeability tuning
devices, etc.)
Coil, transformers, reactors, and chokes for
electronic applicaton, not specified by kind,
typically for establishments with less than
20 employees
Product shioments
Quantity,
million
NA
NA
26.8
11.0
33.9
21.3
94.1
NA
16.0
18.5
33.9
NA
NA
Value,
$ million
588.4
560.5
63.5
19.6
152.3
40.7
19.7
37.6
12.7
81.4
52.3
80.7
17.4
NA - Not available.
118
-------
TABLE 5-3. MARKET
ESTIMATES FOR,.COILS, TRANSFORMERS,
AND CHOKES,5*6
Product
Total - transformers, coils
and chokes
Transformers and chokes,
except T.V.
Transformers and chokes,
laminated
Transformers and chokes,
torroidal
Pulse transformers
Rf coils
TV magnetic components
Sales, $ million
1978
795.2
269.0
1720
57.0
40.0
15.8
171.4
1979
852.1
299.0
193.0
62.0
44.0
14.7
176.4
1980
872.0
316.0
205.0
65.0
46.0
13.0
177.0
1983
984
382
237
80
65
10
200
Annual
growth, %
4.2
7.0
7.1
6.3
7.7
-10.2
2.3
119
-------
Companies
According to data presented in the 1977 Census of Manufactures, 294
companies were engaged in the manufacture of coils and transformers for elec-
4 4
tronic applications. A breakdown of these companies is given in Table 5-4.
Table 5-5 shows their size by total employment. A list of some major trans-
former and inductor manufacturers 1s given in Table 5-6. There are three
principal companies that produce a full line of Iron and ferrlte core trans-
formers and inductors: Stancor, Thordarson Meissner, and TRW/UTC. Each of
these companies also manufactures miniature and smaller units and, with the
exception of Stancor, pulse transformers. Radio frequency inductors are
produced only by other companies.
Environmental Impacts
Very few data are available in the literature concerning emissions
during the manufacture of transformers and Inductors. Dusts and particulate
matter may result from grinding operations associated with core fabrication,
and organics may be released during impregnation and curing of coatings.
There is also scrap in the form of metals from core fabrication and contami-
nated impregnant and coating materials (plastics, resins). The use of spe-
cific control technologies or disposition of scrap materials are not reported.
INDUSTRY ANALYSIS
The following industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potential effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
Figure 5-1 is a flowsheet of the processes used for transformers, as well as
their interrelationships and waste streams.
120
-------
TABLE 5-4. COMPANIES MANUFACTURING VARIOUS PRODUCTS
UNDER SIC 36774
Transformer type
Number of
companies
Audio transformers 87
Low frequency chokes 84
Plate and filament transformers, Including autotransformers,
except torroidal 101
Pulse transformers, computer, and other types 59
Radio frequency (RF) chokes 37
RF coils 33
Intermediate frequency (IF) transformers 24
Television transformers and reactors (horizontal output, vertical
deflection, focus coils, deflection yokes, etc.) 21
Other (balun coils, permeability tuning devices, etc.) 51
121.
-------
TABLE 5-5. DISTRIBUTION OF COMPANY SIZE IN SIC
3677 BY TOTAL EMPLOYMENT*
Employment range
1 to 4 employees
5 to 9 employees
10 to 19 employees
20 to 49 employees
50 to 99 employees
100 to 249 employees
250 to 499 employees
500 to 999 employees
1,000 to 2,499 employees
Total
Number of
companies
33
23
44
69
67
44
10
3
1
294
122
-------
TABLE 5-6. TRANSFORMER AND INDUCTOR MANUFACTURERS
Iron core transformers and
inductors (full line)
Miniature, subminiature, and
ultraminiature transformers
and inductors
Pulse transformers
Radio frequency inductors
e
^™
^^^
^—
i/i
|
•3
X
s.
at
*"*
t
if
36
-3
X
c
to
£
£
u
s
X
(/I
•j
,j-
|
^
X
o
u
°-
X
X
ai
o>
ID
a.
X
s.
o
u
-------
CORE
FABRICATION
COIL
WINDING 2
IMPREGNATION
AND COATING 3
ENCAPSULATION
(^TRANSFORMER^)
Figure 5-1. Transformer production flowsheet.
124
-------
TRANSFORMERS AND INDUCTORS PROCESS NO. 1
Core Fabrication
1. Function - A transformer core must be fabricated with characteristics
suitable for Its Intended application. Laminated cores are often used in low
frequency (20 to 20,000 Hz) applications such as 1n audio-frequency transform-
ers. High-permeability magnetic alloys or ferrites are used in high-frequen-
cy applications where accurate Inductance 1s required.
High-permeability magnetic alloys or soft magnetic alloys have low mag-
netic hysteresis loss resulting from variations in the magnetic flux produced
within the alloy and a low residual magnetism even after being highly magnet-
ized. Alloys of nickel-Iron, cobalt-iron, and silicon-Iron may be used.
Heat treatment must be performed to increase the high-permeability character-
istics of commercially available nickel-iron alloys. These steps should be
conducted in a nonoxidizing, noncarburizing, noncontaminating atmosphere.
Dry hydrogen is recommended as the best atmosphere, although dissociated
ammonia, argon, dry nitrogen, and vacuum are also used. One recommended heat
treatment process to obtain highest permeability involves heating in a sealed
retort filled with a protective atmosphere for 2 to 4 hours at 1130° to
1170°C. After cooling to 200°C, an inert atmosphere 1s introduced until the
temperature is below 100°C. Various types of nickel-iron alloys may also be
produced in laminations that can be stacked with Insulating glue.
Silicon-iron alloys are low in cost, and though their response to mag-
netic fields is inferior to nickel-iron alloys, their magnetic characteristics
are superior under certain conditions. Alloys 1n thick strip and bar forms
are fabricated into many shapes of magnetic cores by machining, forging, and
precision casting operations. Heat treatment is required to obtain uniform
magnetic properties from part to part, and magnetic properties improve with
increasing heat-treating temperature. Cobalt-iron alloys are used for their
high magnetic saturation and relatively low coercive force in AC and DC appli-
cations. Commercial irons and commercially pure irons are also used for
cores; they have good magnetic properties and are relatively low in cost
125
-------
compared to many alloys. Magnetic properties vary depending on the manu-
facturer and degree of heat treatment. These products are usually manufac-
tured by consumable electrode melting or vacuum induction melting to assure
low carbon content, low gas content, and a minimum of residual elements.
2. Input Materials - Raw materials for transformer and Inductor cores
are usually high-permeability alloys. High-permeability alloys can be subdi-
vided into nickel-iron alloys, cobalt-iron alloys, silicon-iron alloys, and
commercial and commercially pure irons. Table 5-7 gives approximate composi-
tions of some nickel-iron alloys. Silicon-iron alloys contain usually 1.0 to
2.5 percent silicon with the remainder iron, though silicon content may be as
high as 4 percent. Some commercial silicon-iron alloys Include Hipersil (4
percent Si, 96 percent Fe), and silicon core iron 1, 2.5, or 4 percent Si;
balance He). Table 5-8 gives compositions of some cobalt-iron alloys. Some
commercial and commercially pure irons Include ingot iron (Armco, Consumet),
Vacumet core irons (Carpenter Technology), and Ferrovac E (Crucible Steel).
Cores may also be fabricated using phenolic compounds, and some transformers
and inductors have air cores.
3. Operating Conditions - Heat treatment is crucial in obtaining the
desired characteristics for high-permeability alloys. The following condi-
tions are recommended:
Alloy Temperature. °C Time
Nickel-iron 1120-1170 2-4 hours
Silicon-iron 1350-1950 2 hours
Cobalt-iron 815-925 2 hours
Irons 850-1000 2 hours
4. Utilities - Electric or natural gas is required to heat furnaces for
heat treatment of the varous alloys. Electricity is also required for fan
motors.
5. Waste Streams - Airborne dusts could be released during grinding
operations. There are no other atmospheric emissions reported.
There are no wastev/ater effluents from this process.
Scrap metals are generated as a result of various machining operations.
126
-------
TABLE 5-7. HIGH-PERMEABILITY NICKEL-IRON ALLOYS'
Approximate composition
Commercial name
80% Ni, 4% Mo, balance Fe
77% Ni, 1.5% Cr, 5% Cu,
balance Fe
49% Ni, balance Fe
45% Ni, balance Fe
49% Ni, 0.15% Se, balance Fe
47% Ni, 3%3 Mo, balance Fe
80% Ni, 5% Mo, balance Fe
4-7,9 Permalloy
HyMu 80
Hipernon
MuMetal
Deltamax
HyRa 49
High Permeability 49
Hipernik and Hipernik V
Universal-Cyclops
Simmonds Saw and Steel Co.
Armco Steel Corp.
127
-------
TABLE 5-8. COBALT-IRON ALLOYS'
Alloy composition
50% Co, 50% Fe
49% Co, 49% Fe, 2% V
49% Co, 49% Fe, 2% V
35% Co, 1% Cr, balance Fe
Commercial name
Permendur, Hy-Sat 50
Hlperco 50, Hy-Sat 48,
Hy-Sat 48 FM
Hiperco 27, Hy-Sat 27
2- Vanadium Permendur
128
-------
6. Control Technology - Dust from grinding operations would probably be
captured by exhaust hooding and routed to a cyclone separator. Dusts would be
drummed and landfilled or if economical, recycled.
Most scrap metal waste would likely be recovered and sold for reclama-
tion.
129
-------
TRANSFORMERS AND INDUCTORS PROCESS NO. 2
Con Winding
1. Function - Wire must be wound around a core to form a transformer.
This 1s followed by a layer of Insulation. The coll may be wound directly
around the core, or 1t may be wound separately and Inserted on the core.
Various methods are used, but they are not described 1n the literature.
2. Input Materials - Raw materials for coll winding Include conductors,
conductor Insulation, and layer and Interlayer Insulation. Wire 1s usually
copper, nickel-clad or plated copper, silver-plated copper, anodized aluminum,
or silver. Conductor insulation materials vary widely. It should be rela-
tively thin to permit good coil space factors; have uniform high insulation
strength along its length; be compatible with the impregnant; and permit
«
winding by conventional methods with a reasonable amount of care. Conductor
insulations may be bakelite varnish, epoxy varnish, ceramic-coated Teflon,
Teflon, silicone-treated glass fiber, Formex, Kel-F, polyurethanes, poly-
imides, nylon, polyvinyl chloride, polyester polyvlnyl formyl, and oleores-
1ng. Insulation should be compatible with the winding and be capable of
being impregnated, have sufficient mechanical strength to permit winding on a
multiple winding machine, retain insulation resistance after creasing, be thin
enough to permit a good working space factor, and have a nonslippery surface.
Some materials used in this capacity Include kraft paper, Mylar, Teflon, mica
Q
paper, split mica, fiberglass cloth, and glass paper.
3. Operating Conditions - Coil and insulation winding is conducted at
ambient temperature and atmospheric pressure.
4. Utilities - Electricity would be required for operation of winding
machines.
5. Waste Streams - There are no air or water emissions associated with
this process.
It is likely that scrap materials (e.g., insulation, metal from con-
ductors) are generated during these operations.
130
-------
6. Control Technology - Wire scrap is likely collected and sold for
recycle. Insulator plastics could be recycled through the process or stored
and landfilled.
131
-------
TRANSFORMERS AND INDUCTORS PROCESS NO. 3
Impregnation and Coating
1. Function - The Impregnant or coating in coils serves to provide high
electrical insulation between conductors; provide a mechanical bonding agent;
assist in dissipating generated heat; and assist in environmental protection
against dirt, moisture, oxygen, radiation, chemicals, etc. It should provide
the necessary dielectric strength, be essentially void free, retain insulating
properties and mechanical strength for the expected usage, impregnate thor-
oughly, and be compatible with other materials. A variety of materials and
7 8
processes are used. Three examples are cited below which illustrate these
differences.
One typical cycle cited for a silicone rubber impregnant used in coils
Q
for operation in the 100° to 150°C range is as follows:
0 Air-dry coil at 135°C for minimum of 8 hours.
0 Cool for 1 hour in a tank at pressure of 5 mm mercury.
0 Cover the coil with impregnant and, after 5 minutes, break the
vacuum and allow the coil to remain in solution for 5 to 10 minutes.
0 Air-dry at room temperature for 1 to 2 hours.
Prebake at 75°C for 8 to 10 hours.
0 Cure for 3 to 4 hours at 200°C.
For high-temperature applications (over 150°C), degassed silicone resins are
often used. This must be applied in an oxygen-free atmosphere. Impregnation
is followed by a pre-bake at 180° to 200°C for about 2 hours, then vacuum
degassing at temperatures ranging from 200° to 600°C.
Another material used to form a rigid coil structure that can be employed
at very high temperatures is aluminum phosphate (A1P04). In this impregnation
cycle, all organic material is removed from the assembled core and coil by
degassing under a vacuum in an oven linearly programmed to reach 500°C within
a 2-hour period. A pressure vessel is then filled with the required amount of
A1P04 solution, and the coil and core is immersed. A 50 pro vacuum is drawn,
132
-------
held for 15 minutes, and followed by a 2-minute 6.9 x 10 Pa (100 psig)
pressure. There are four additional cycles. The assembly is then removed,
air-dried at room temperature for 12 hours, and cured for 2 hours at 125°C, 2
hours at 150°C, and 15 minutes at 500°C.8
A third cycle described in the literature is for DC-997, a silicone
Q
varnish offered by Dow Corning. This procedure is as follows:
0 Prebake coils at 200°C for 4 hours.
0 Cool coils to 65°C for approximately 1 hour.
0 Evacuate the coils for 15 minutes at a pressure of no more than 20
mm of mercury.
0 Soak coils in impregnant for 1 hour.
0 Drain and dry coils for 30 minutes.
0 Bake at 200°C for 2 hours.
0 Cool to room temperature.
0 Dip, drain, and air-dry for 30 minutes.
0 Bake 6 hours at 200°C.
2. Input Materials - Various types of materials may be used for impreg-
nants; these include silicone resins, silicone rubber, refractory ceramics,
phenolic varnishes, epoxies, nylons, mineral waxes, polyesters, polyvinyl
7 8
formyl, and polyvinyl butyral. '
3. Operating Conditions - This process can cover a wide range of operat-
ing temperatures and pressures. Specific examples are presented in the
discussion of the process function.
4. Utilities - Electricity is required for vacuum pumps, fan and blower
motors, and pumps for moving impregnant materials. Natural gas would be
required to heat ovens.
5. Waste Streams - Organic solvents or various other organic consti-
tuents of the impregnant material could be volatilized during curing and
baking operations.
There are no wastewater effluents or solid wastes associated with this
process other than unused and contaminated impregnant materials.
133
-------
6. Control Technology - The use of controls for this process is not
discussed in the literature.
134
-------
TRANSFORMERS AND INDUCTORS PROCESS NO. 4
Encapsulation
1. Function - The encapsulant provides additional protection against
moisture, dirt, and chemicals, as well as resistance to thermal cycling and
added mechanical strength. It should have sufficient dielectric strength to
withstand voltage stresses and exhibit good adherence to coil and metal
7 8
parts. Casting and dipping are the usual application methods.
2. Input Materials - The most often used encapsulant materials are
mineral- (mica, silica) or fiberglass-filled silicons rubber, polyester
resins, and epoxies. Epoxies are used for temperature applications up to
200°C, whereas silicone rubbers are used for temperature applications from
200° to 300°C. Curing agents for epoxies are usually amine-based or an acid
catalyst.
3. Operating Conditions - Silicone resins require baking at 400°C for
one hour. Conditions for epoxy and polyester resin applications are not
cited in the literature. These probably vary according to type.
4. Utilities - Electricity is required for operation of conveyor motors
for dipping, for process controls, for operating molding machinery, heaters,
and drying. Natural gas may also be used to heat ovens.
5. Waste Streams - Curing of silicone resins may generate some organic
fumes, especially if a solvent is used to formulate the material. Details are
not available.
There are no known liquid or solid wastes other than unused or off-
spec or contaminated resins.
6. Control Technology - The use of air pollution control technologies
for this process is not described in the literature.
Epoxies, polyester resins, and silicones are thermosetting plastics which
cannot be reused. One survey of electronic component manufacturing plants
indicated that wasted plastics were stored and hauled to landfills for dis-
g
posal.
135
-------
REFERENCES FOR SECTION 5
1. Jones, Thomas H. Electronic Components Handbook. Reston Publishing Co.,
Inc., Reston, Virginia, 1978.
2. Colwell, Morris A. Electronic Components. Newnes Technical Books,
Butterworth, England, 1976.
3. CRC Handbook of Chemistry and Physics. 56th Edition. 1975. Chemical
Rubber Company Press, Cleveland.
4. U.S. Department of Commerce. 1977 Census of Manufactures: Electronic
Components and Accessories. June, 1980.
5. Components: Unaggressive Growth In Store. Electronics. January 3,
1980.
6. Predicasts Forecasts - 1980 Annual Cumulative Edition. Issue No. 80.
4th Quarter. July 24, 1980. Predicasts, Inc.
7. Harper, C.A., ed. Handbook for Materials and Processes for Electronics.
McGraw-Hill, New York, 1970.
8. Nordenberg, H.M. Electronic Transformers. Reinhold Publishing, New
York, 1964.
9. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80-075a, October
1980.
10. Wolf, Stanley. Guide to Electronic Measurements and Laboratory Practice.
Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1973.
136
-------
SECTION 6
PRINTED CIRCUIT BOARDS
INDUSTRY DESCRIPTION
Printed circuit (PC) boards consist of nonconductive board material onto
which a circuit pattern of conductive metal has been formed. The board pro-
vides a surface for the application of a conductive wiring path and supplies
support and protection for electrical components to be connected by the board
circuitry.
Printed circuit boards can be classified into three basic types: single-
sided, double-sided, and multilayer. The type of board used for specific
applications depends on such factors as spatial and density demands and intri-
cacy of the circuits.
Single-sided boards are used for relatively simple applications, where
circuit types and speeds do not place unusual demands on the electrical char-
acteristics of the wiring. When density demands require more than one layer
of wiring, circuits are printed on both sides of the board. The interconnec-
tion between the layers is accomplished through the board rather than around
it, and what are termed plated-through holes have come to be the conventional
way of making such a connection. The holes thus serve a dual purpose, provid-
ing an electrical connection from one side of the board to the other and
accommodating a component lead. These are, of course, more difficult to make
than the single-sided boards because of the extra steps involved (drilling and
through-hole plating).
The necessity for increased wiring density in many electronic packaging
applications can be met by the use of more than two layers of wiring in the
form of a multilayer printed board. A multilayer board is a series of indi-
vidual .circuit board layers bonded together by an epoxy glass material. It is
a monolithic assembly in which the internal and external connections to each
level of the circuitry are determined by the system wiring program.
137
-------
Three main printed circuit board production methods have evolved over the
years: the additive, subtractive, and semi additive techniques. The additive
technique involves electroless plating on unclad board materials to produce
printed circuits, and is used to produce 5 to 10 percent of the annual indus-
try production total. The subtractive technique involves the removal of a
large amount of metal from metal-foil-clad board material to form the desired
•circuit pattern, and is the major processing method used in the industry. The
semi-additive technique is a combination of the additive and subtractive
techniques. Production begins with unclad boards which are metallized with
electroless copper. This is followed by image transfer, pattern electroplat-
1 2
ing, and etching to remove unwanted copper as in the subtractive process. '
Raw Materials
Printed circuit boards are constructed of materials such as glass,
ceramics, and plastics. Copper is the primary metal used for conductive
circuitry, with nickel, gold, and rhodium in some applications. Solder (tin-
lead) and tin are used to protect copper or other metals during the etching
1 2
process.
Other major processing materials include cleaners, resists (etchant
resistive materials), adhesion promoters, catalysts, and etch solutions.
These cover a broad range of formulations (many proprietary) of abrasives,
acids, alkalis, chelating agents, organic solvents, etc., as described in the
123
detailed process descriptions. ' '
Products
The Bureau of the Census classifies printed circuit boards into SIC
3679052. Electronic assemblies using circuit boards were initially developed
for the demanding quality control requirements of the aerospace and computer
industries, primarily on the West Coast. Currently, printed circuit boards
are used in a broad range of products including business machines, computers,
communication equipment, and home entertainment equipment. The most typically
produced boards are two-sided or multilayered with plated-through holes. They
are fabricated from glass-epoxy, flame-retardant rigid laminates and designed
to accept all types of electrical components.
138
-------
Table 6-1 shows estimated sales from 1978 through 1983 for various
categories of printed circuit boards. These estimates represent industrywide
consumption of boards shipped by domestic and foreign manufacturers for the
U.S. market. Total annual board production is estimated to be about 14
million m2.1
Companies
There are 327 plants involved in the manufacture of printed circuit
boards. Total employment of these plants is approximately 20,600, while total
production employment is estimated to be 11,900. The domestic industry
consists of large facilities totally involved with printed board manufacture,
both large and small captive facilities, small job shops doing contract work,
and specialty shops which do low volume and high-volume precision work. A few
major companies involved in printed circuit board manufacture include TRW
Cinch Graphik, Texas Instruments, Motorola Semiconductor, Microtran, GTE
Sylvania, Western Electric, Rockwell International, Synthane-Taylor, Cincinnati
Millacron, and Chicago Etching.
Environmental Impacts
Air emissions from printed circuit board manufacturing include particu-
lates, acid and alkali fumes, and chlorinated organic solvent vapors. Par-
ticulates are generally released during board preparation operations. Acid
fumes originate from solutions used in most wet processes. Chlorinated
organic solvent vapors are primarily the result of board surface cleaning and
preparation processes. Control of air emissions involves collection of con-
taminated air streams using hoods above processing baths. Contaminant removal
is based on segregation and treatment of similar air streams.
Total process water flow from printed circuit board manufacturing dis-
charged to POTW's on a national basis is estimated to be 23 million liters per
day. An average plant process water flow is estimated to be 70,800 liters per
4
day. The principal constituents of the liquid waste streams from printed
circuit board manufacturing are suspended solids, copper, lead, fluorides,
phosphorus, tin, palladium, and chelating agents. A range of constituent
139
-------
TABLE 6-1. PRINTED CIRCUIT BOARD SALES, $ MILLION5
Product
Printed circuits (total)
Rigid boards (total)
Single-sided
Double-sided
Multilayer
Flexible circuits
Year
1978
532.5
474.0
70.0
253.0
151.0
58.5
1979
611.0
548.5
76.0
277.5
195.0
62.5
1980
669.0
602.0
76.0
302.0
225.0
67.0
1983
834.0
743.0
86.0
359.0
298.0
91.0
Annual
growth, %
13.8
13.8
6.5
10.9
20.1
13.2
140
-------
concentrations found in end-of-pipe raw liquid waste streams from printed
circuit board manufacturing is shown in Table 6-2.
Low pH values are characteristic of the wastes because of the acid clean-
ing and necessary surface pretreatment. The suspended solids are primarily
metals from plating and etching operations and dirt that is removed during the
cleaning processes prior to plating. The large amount of copper present in
the waste stream comes from both electro!ess copper plating and copper elec-
troplating and etching operations. Fluorides are primarily the result of
cleaning and surface treatment processes utilizing hydrofluoric and fluoro-
boric acids. Phosphorus results from the large amount of cleaning that is
performed on the boards. Tin is released during catalyst application and
solder electroplating; palladium is also a waste constituent from catalyst
application. The chelating agents present are primarily from the electroless
plating operations, although others may have been added by cleaning, immersion
plating, and gold plating.
The liquid wastes from printed circuit board manufacture may be con-
trolled using end-of-pipe treatment systems. Alternatively, some plants
segregate wastes into separate streams and treat each individually. Also,
there are many commonly used in-line technologies for reducing pollutant
concentrations, for reducing wastewater quantities discharged, for reclaiming
potential pollutants for reuse, and for reusing water itself. Generally, in-
line treatment and separate treatment of segregated waste streams provide the
most effective treatment of printed circuit board manufacturing wastes.
Solid wastes produced during printed circuit board manufacturing include
sludges generated during treatment of liquid process wastes and participates
removed from dust collectors. Collected particulates typically contain fine
printed circuit board materials, copper, and small amounts of inorganic metals
from wear of board machining equipment. Sludges contain primarily metal
hydroxides and other precipitates of spent processing chemicals; they may be
dewatered and disposed on-site or contract hauled off-site. Metals and other
chemicals recovery from sludges may also be practiced on or off-site.
141
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TABLE 6-2. CHARACTERISTICS OF RAW WASTE STREAMS FROM
PRINTED CIRCUIT BOARD MANUFACTURING1
Constituent
Total suspended solids
Cyanide, total
Cyanide, amenable to chlorination
Copper
Nickel
Lead
Chromium, hexavalent
Fluorides
Phosphorus
Silver
Palladium
Gold
EDTA
Citrate
Tartrate
NTA
Range
0.998
0.002
0.005
1.582
0.027
0.044
0.004
0.648
0.075
0.036
0.008
0.007
15.8
0.9
1.3
47.6
, mg/ liter
- 408.7
5.333
4.645
- 535.7
8.440
9.701
3.543
- 680.0
- 33.80
0.202
0.097
0.190
- 35.8
- 1342
- 1108
- 810
142
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INDUSTRY ANALYSIS
The following Industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potentail effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
There are three principal production methods for printed circuit boards:
additive, subtractive, and semi-additive. These methods have many processes
in common, and many combinations of processes are employed. The principal
emphasis in the remainder of this section is on the subtractive processing
sequence, which is the most commonly employed. Figures 6-1, 6-2, and 6-3 are
flowsheets showing the processes used for each method, as well as their inter-
relationships and major waste streams.
143
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A WATER
OAIR
O SOL ID
tfo
BOARD
PREPARATION 1
BOARD
CLEANING 2
IMAGE
TRANSFER
tf
SURFACE
PREPARATION 3
CATALYST
APPLICATION
4
ELECTROLESS
PLATING (FLASH) 5
ELECTROPLATING
(TABS)
MULTILAYER
BOARD
FABRICATION,
C FINISHED ^\
MULTILAYER )
BOARDS '
Figure 6-1. Additive printed circuit board production flowsheet.
144
-------
COPPER-CLAD"
BOARD
BOARD
PREPARATION
BOARD
CLEANING 2
SURFACE
PREPARATION 3
CATALYST
APPLICATION 4
ELECTROLESS
PLATING (FLASH),
IMAGE
TRANSFER 6
ELECTROPLATING
(SOLDEP) 7
ETCHING
ELECTROPLATING
(TABS)
C FIN I SHED
BOARDS
MULTILAYER
BOARD
FABRICATION
O FINISHEDx
IULTILAYER )
BOARDS_^^
A WATER
OAIR
O SOL ID
Figure 6-2. Subtractive printed circuit board production flowsheet.
145
-------
ELECTROLESS
PLATING (FLASH) 5
IMAGE
TRANSFER
6
ELECTROPLATING
(COPPER) 7
ELECTROPLATING
(SOLDER)4 7
0_
MULTILAYER
BOARD
FABRICATION g
CFINISHED x
MULTILAYER )
BOARDS^^
A HAT;:?
OAIR
O SOL ID
Not required with negative Image transfer method.
Figure 6-3. Semi-additive printed circuit board production flowsheet.
146
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PRINTED CIRCUIT BOARDS PROCESS NO. 1
Board Preparation
1. Function - Individual or multilayer boards or laminates are sawed Into
blanks slightly larger than Is desired for the finished product. Generally, a
one-Inch border 1s left on each edge to allow excess material for "tabs" and
for board finishing.1 Circular saws with carbide teeth are generally used for
paper-base laminated boards. Diamond-steel-bonded saws are widely used for
high volume glass-base laminates. Alternatively, entire boards or selected
board areas may be die cut (blanked) or sheared to obtain the desired board
2
size and shape.
Board cutting is followed by hole drilling or punching in a predetermined
pattern for mounting various electronic components. At some plants, holes
are drilled by computer controlled machines at rates of approximately 300
holes per minute, with hole location accuracies of +_ 0.025 mm. Next, the
board is deburred on top and bottom surfaces by sanding and beveling, removing
loose chips remaining from previous steps. Hand sanders equipped with fine
sandpaper or machines with composition abrasive brushes (operated either wet
o
or dry) are used. Other operations used to prepare boards for subsequent
processes include routing and slotting. Board routing 1s performed to produce
boards with superior edge finishes and closer tolerances than can be provided
1 2
with shearing or sawing. '
2. Input Materials - Printed circuit boards are generally composed of
nonconductive materials such as glass, ceramics, or plastics. The most common
board materials are glass epoxy and phenolic paper. For the subtractive
technique, raw printed circuit boards are copper-foil clad on one or both
sides. Boards vary in thickness from 0.8 mm to 3.2 mm. Board sizes range
from less than 1.3 cm square to 45 cm square. Typically, copper cladding is
305 g/m2, with a range of 153 g/m2 to 610 g/m2.1'2'3
The National Electrical Manufacturers Association (NEMA) and the Federal
government have standardized the characteristics of several commonly used
copper-clad laminates:
147
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NEMA Military
Standard Standard Description
G-10 MIL-P-13949D, Type GE General purpose glass fiber, epoxy
laminate. Moisture resistant, ex-
cellent electrical and physical
properties
G-ll MIL-P-13949D, Type GB Similar to G-10 but better tempera-
ture stability
FR-4 MIL-P-13949D, Type GF Similar to G-10 but flame-retardant
FR-5 MIL-P-13949D, Type GH Similar to G-ll but flame-retardant
3. Operating Conditions - Generally, board preparation operations are
performed at ambient temperatures. Operations on paper-base laminated boards
are frequently performed at 32° to 38°C.
4. Utilities - Machining requires electricity for operation of small
equipment motors.
5. Haste Streams - Cutting, sanding, routing, drilling, beveling and
slotting operations all generate airborne particulates. The particulates are
composed of fine printed circuit board materials (i.e., paper, phenol, epoxy,
polyester, and polyimide), copper, and small amounts of inorganic metals
resulting from wear of saws, drills, and other equipment.
A liquid waste stream is generated when sanding operations are accom-
panied by a water flush. Varying amounts of printed circuit board and sanding
materials are generally present in the flush water effluent.
The only solid wastes are scrap board materials from cutting, sanding, and
machining operations.
6. Control Technology - Dust collection is required to protect employees
and equipment from particulates. Cyclone separators and baghouses may be used
2
to separate collected particulates from the exhaust air.
Solid particles in the liquid waste stream are removed in solids traps or
collected along with precipitates during subsequent treatment.
148
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PRINTED CIRCUIT BOARDS PROCESS NO. 2
Board Cleaning
1. Function - As a result of such operations as board drilling and sand-
ing during board preparation, there are numerous particulates, imperfections,
and epoxy smears which must be removed to provide good plating adhesion.
Printed circuit boards must therefore be cleaned to facilitate board plating
without flaws. Improper board cleaning is probably the greatest source of
problems in subsequent processes and is responsible for a wide variety of
2
image and plating defects.
Circuit boards are cleaned both mechanically and chemically. Mechanical
cleaning consists of brushing holes, power rinsing, and air blasting. Power
rinsing entails high-pressure jets of abrasive slurry oscillated across the
board surface to remove particulates. This is followed by a water rinse and
an air knife drying cycle. The boards are then chemically cleaned to remove
2
soil, fingerprints, smears, or other substances which cause plating flaws.
This includes an acid hole cleaning operation to remove particulates and any
bonding epoxy which obstruct the holes. ' Chemical cleaning may also include
vapor degreasing, ultrasonic cleaning, and repeated dipping in chemical baths
to obtain the desired results.
2. Input Materials - Mechanical cleaning is generally accomplished with
2 3
an abrasive slurry of water and pumice, followed by water rinses. Various
acid and alkaline compounds, as well as organic solvents, are used in chemical
cleaning. Concentrated sulfuric acid (>90 percent), fluoroacetic acid, hydro-
fluoric acid, and other acids may be used to dissolve epoxy material. Organic
solvents such as trichloroethylene, 1,1,1-trichloroethane, perchloroethylene,
trichlorotrifluoroethane, and methylene chloride are widely used as surface
degreasers. Alkaline cleaners contain sodium hydroxide and potassium hy-
droxide compounds.1>2>3'6
3. Operating Conditions - Organic solvents are used at temperatures
ranging from 40° to 120°C. The two extremes are for special situations while
the middle of the range is the most common. Available data indicate that acid
solutions are used at ambient temperatures, while alkaline cleaning solutions
27
are used at temperatures up to 65°C. *
149
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4. Utilities - Electricity is required for direct immersion coil heating
of baths, mechanical cleaning equipment motors, pumps, and blowers for bath
agitation. Steam is required for vapor degreasing equipment and bath heating
in large plants. Water is required for rinses.
5. Waste Streams - Air emissions consist of acid fumes and organic
vapors from vapor degreasing. The fumes and vapors are usually not contami-
nated with other materials. Since different control technology is required,
the two air emissions are kept separate.
Spent acid and alkaline solutions and rinses contain dissolved copper
fluoride and/or resin. Spent organic degreasers and rinses contain organic
contaminants (primarily from the solvents used).
There are no solid wastes from this process other than minor residues
from mechanical cleaning.
6. Control Technology - Wet scrubbing is required to remove acid fumes
from the air. The contaminated airstream is collected via chemical fume hoods
and sent through ducts to a scrubber where it is contacted with either water
or some other material which will absorb the fumes. The scrubbed air then
passes on to the atmosphere and the absorbing solution is treated along with
the other acidic waste streams. Chlorinated solvent fumes are collected via
chemical fume hoods and then passed through a bed of activated carbon. The
o
carbon bed is regenerated with steam to recover the solvent for reuse.
Either batch or continuous treatment is used for pH control of acid and
alkaline rinse waters and dumps of spent cleaning solutions. Alternatively,
spent acid and alkaline baths are contract hauled for off-site disposal. pH
adjustment of copper bearing rinse waters is frequently practiced to precipi-
tate copper as an hydroxide. The precipitate is concentrated into a sludge
and hauled away for disposal or recovery. Waste stream segregation and lime
treatment are used to precipitate fluorides at pH 10 from cleaning bath rinse
waters. Due to their high costs, recovery of spent chlorinated organic
solvents from wastewater collection sumps is often economically attractive.
Collected solvents separated by gravity are then recovered in-house or hauled
away for reclaiming.
150
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PRINTED CIRCUIT BOARDS PROCESS NO. 3
Surface Preparation
1. Function - In the additive and semi-additive production processes,
unclad boards must undergo surface preparation to promote adhesion of a cata-
lyst and electro!ess plating in subsequent process steps. To accomplish this,
the boards are subjected to a mild chemical "etch" (not to be confused with
Process No. 8) to make the surface of the boards microporous. This allows
deep penetration of the catalyst and subsequent strong bonding of the electro-
less copper plate. It is followed by a water rinse. An acid dip follows to
solubilize etched copper salts, then another water rinse, a final acid dip,
and a final water rinse.1>2»6
Surface preparation for some unclad boards is initiated with the use of a
"swell-and-etch" procedure. In this procedure, the top layer of board epoxy
is swelled by use of a solvent system and then etched by a strong oxidizing
medium. The same rinsing and acid dipping routine used with other boards is
then followed. This procedure requires an extra thick epoxy surface; conven-
tional unclad boards are unacceptable because etching would penetrate the
fiberglass and degrade the board.
There are also specially fabricated laminate boards that have precondi-
tioned surfaces. The surfaces of these boards have, in essence, previously
been micro-etched. As a result, the handling and disposal of solvents, strong
oxidizers, and other special wastes are minimized.
Copper-clad boards used in the subtractive technique generally have an oxi-
dation inhibitor on their surfaces. If the inhibitor is not completely removed,
peeling will occur between the copper clad surface and the electroless deposit.
2 3
To accomplish this, a light etch is usually given as a preventive measure. '
2. Input Materials - For the "swell-and-etch" procedure, strong organic
solvents are used for swelling surfaces; these include trichloroethylene,
1,1,1-trichloroethane, and methylene chloride. Strong oxidizers are used as
etchants for this procedure (mainly a mixture of sulfuric and chromic acids).
For copper-clad boards, ammonium persulfate is the primary etchant used to
remove the oxidation inhibitor. Hydrogen peroxide, sulfuric acid, and cupric
2 3
chloride can also be used. '
151
-------
3. Operating Conditions - No information was found regarding the temper-
ature of solvent used in the "swell-and-etch" procedure. Strong oxidizers are
used at 50°C, followed by rinse water at ambient conditions. Ammonium persul-
fate solutions are maintained at 20° to 45°C. Immersion times are approxi-
mately 2 minutes.
4. Utilities - Electricity is required for direct immersion coil heating
of baths and blowers for bath agitation. Steam may be used for bath heating
in large plants.
5. Waste Streams - Depending on the specific chemicals used in the
process, air emissions will consist of acid fumes and organic solvent vapors.
The fumes and vapors are usually not contaminated with other materials. Since
different control technologies are required, the two air emissions are segre-
gated.
Spent solvents, acid solutions, and rinsewater are generated during board
preparation. The rinsewater will contain small amounts of solvents and acid.
All liquid waste streams will also contain some dissolved board materials,
including epoxy, phenolics, fiberglass, and dissolved copper from copper-clad
boards.
There are no solid wastes reported from this process.
6. Control Technology - Wet scrubbing is used to remove acid fumes from
the air. The contaminated airstream is collected via chemical fume hoods and
sent through ducts to a scrubber where it is contacted with either water or
some other material which will absorb the fumes. The scrubbed air then passes
on to the atmosphere and the absorbing solution is treated along with the
other acidic waste streams. Chlorinated solvent fumes are collected via
chemical fume hoods and then passed through a bed of activated carbon. The
2
carbon bed is regenerated with steam to allow solvent recovery.
Either batch or continuous treatment is used for controlling pH from acid
rinsewaters and dumps. Spent solvents and acids can be contract hauled to
disposal sites, or sent to recycling plants for regeneration and recovery.
Systems incorporating activated carbon adsorption are also available to re-
cover solvents "in-house." The high cost of chlorinated solvents makes re-
covery an economically attractive alternative. Ammonium persulfate control is
discussed in Process No. 8.
152
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PRINTED CIRCUIT BOARDS PROCESS NO. 4
Catalyst Application
1. Function - Catalyst application is the deposition of a thin layer of
palladium on board surfaces to be electro!ess plated. Catalyst deposition is
necessary for electroless copper to plate onto the exposed plastic of a bare
board in the next process for the additive and semiadditive techniques, and
for through-hole plating in the subtractive technique. Printed circuit
boards are immersed in a solution of stannous chloride (30 g/liter) and
hydrochloric acid (30 g/liter) followed by immersion 1n a solution of pal-
ladium chloride (0.25 g/liter) and hydrochloric acid (1.0 g/liter).2 A
reaction takes place with the adsorbed stannous chloride leaving a layer of
palladium metal on the surface as the catalyst. Catalyst application is not
necessary for copper-clad boards used in the subtractive process.
2. Input Materials - Stannous chloride, hydrochloric acid, and palladium
chloride are required for this process. Water is used for rinses between
immersion in the different solutions. '
3. Operating Conditions - Immersion time in the palladium chloride
solution is usually 2 to 10 minutes. Stannous chloride solution immersion
time is approximately 1 minute. Palladium chloride and stannous chloride
baths are maintained at room temperature.
4. Utilities - Electricity is used to power miscellaneous pumps and
motors and compressors or blowers that provide air to agitate baths.
5. Waste Streams - There are no air emissions reported from this proc-
ess.
Spent stannous chloride baths and rinsewater will contain dilute hydro-
chloric acid generated as a by-product of adsorbing tin on the board surface.
Stannic oxide is contained in spent palladium chloride baths and rinsewater as
a result of the substitution reaction between tin and palladium.
There are no solid wastes from this process.
6. Control Technology - pH adjustment and clarification are used to
control tin and palladium discharges from catalyst application waste streams
A
to less than 1.0 and 0.5 mg/liter, respectively.
153
-------
PRINTED CIRCUIT BOARDS PROCESS NO. 5
Electroless Plating (Flash)
1. Function - Electroless plating metallizes nonconductlve surfaces
without the use of the outside power source that 1s required for electroplat-
ing (electroless baths contain their own source of electrons for current
flow). Catalyzed printed circuit boards are Immersed In electroless copper
solution for the additive and semi-additive techniques and for through-hole
plating In the subtract!ve technique. Thicknesses of electroless copper
deposits range from 0.25 ym to 2.5 pm. Deposition rates are commonly 0.03 to
0.04 pm/min, but recent formulations have been able to give 0.1 pm/min. The
2 3
Ideal deposit will be dense, fine-graded, and oxide free. Following the
electroless bath, the boards are spray or counterflow rinsed with water and
acid rinsed to neutralize the residual alkaline film from the electroless
bath. This Is followed by another water rinse. Next, the boards are dried by
air, heat, or chemical displacement of water. Mechanical scrubbing Is also
used to condition the surface of the plated metal for further processing. '
There are several optional steps which a printed circuit board may under-
go as part of the electroless plating operation. After the above operations,
the printed circuit board must be thoroughly dried to prevent the electroless
deposit from oxidizing. An oxidized deposit results in voids or microfine
pits in the electroless coating which have a detrimental effect on image
transfer quality. Drying can be accomplished in hot air ovens, or by immer-
sion in a water displacing liquid, followed by immersion in a vapor degreaser
2 3
and evaportion of solvent. ' The printed circuit board may also undergo
mechanical scrubbing in order to precondition the surface of the board for
image transfer and electroplating. The procedure is the same as mechanical
scrubbing (Process No. 1) although not as aggressive. After scrubbing, the
board must be rinsed and dried, as above.
Immediately following the electroless copper plating operation, printed
circuit board manufacturers commonly flash panel-plate boards before the final
rinsing and drying. The flash is used to maintain the integrity of the elec-
troless deposit from either oxidation or subsequent etching. This is accom-
plished by either panel or pattern electroplating solder over the electroless
154
-------
plate. Panel plating consists of copper plating the entire board area (in-
cluding holes). In pattern plating, only holes and circuitry are copper
2
plated. The flash applies a minimum of 0.025 mm of copper.
2. Input Materials - Typically, electro!ess copper baths contain copper
sulfate with a mixture of sodium carbonate or sodium gluconate, Roche!le
salts, Versene-T, sodium hydroxide, and formaldehyde (37 percent), as de-
scribed in Table 6-3. Copper, formaldehyde, and sodium hydroxide are con-
sumed in the electroless plating process and must be replenished periodi-
cally. Other metals which can be electroless plated include gold, silver,
lead, iron, cobalt, nickel, chromium, arsenic, antimony, and alloys of nickel
with either tungsten, phosphorous, or boron. Only a few of these are com-
monly used in printed circuit board manufacture. The acid rinse usually
contains sulfuric acid (2 to 20 percent by volume), although other acids can
be used. The panel-plate flash consists of a copper pyrophosphate plating
solution.
3. Operating Conditions - Most electroless baths operate in the range of
21° to 27°C. Too low a temperature can result in a bath that plates slowly or
not at all. Too high a temperature can cause the chemicals to decompose or
cause a runaway reaction. Electroless baths commonly operate in the pH range
2
of 11 to 12. Rinses and baths are maintained at ambient temperatures.
4. Utilities - Electricity is required for direct immersion coil heating
of baths, blowers or compressors for bath agitation, and miscellaneous pumps
or motors.
5. Waste Streams - There are no air emissions reported for this process.
Liquid waste streams generated include spent electroless copper solu-
tions, rinsewater contaminated by dragout, and spent acid rinsewater. These
streams will contain acids and complexed copper.
There are no solid wastes reported for this process.
6. Control Technology - Complexed copper cannot be removed by pH eleva-
tion and precipitation. Heating or the addition of a catalyst is required to
initiate copper precipitation and collection as a sludge. An alternative
removal method is to add acid to the electroless copper solution to lower the
pH to 5 to 8, causing the copper to precipitate. Yet another method involves
heating and lowering the pH, followed by addition of caustic and sodium
hydrosulfite to form a copper oxide precipitate. It is estimated that effluent
155
-------
TABLE 6-3. TYPICAL ELECTROLESS COPPER PLATING BATHS'
Copper sulfate
Sodium gluconate
Sodium carbonate
Rochelle salts
Versene-T
Sodium hydroxide
Formaldehyde (37 percent)
PH
Temperature
Bath 1
29 g/ liter
25 g/llter
140 g/llter
17 g/liter
40 g/liter
150 g/llter
11.5
21 °C
Bath 2
25 g/liter
60 g/liter
20 g/liter
25 g/liter
11.5
24°C
156
-------
copper concentrations can be reduced to 1.4 mg/liter copper or less, with
2
typical removals of approximately 88 percent.
Distillation may also be used to recover electroless copper for reuse,
while the extracted water can be used as rinse make-up water. Using this
process, recovered copper concentrations of 21,800 mg/liter have been reported
for a wastestream initially containing 416 mg/liter. Extracted make-up water
copper concentration was approximately 3 mg/liter.
157
-------
PRINTED CIRCUIT BOARDS PROCESS NO. 6
Image Transfer
1. Function - Image transfer 1s a series of steps designed to produce a
circuit pattern on a printed circuit board. Specific methods used to create
and transfer the circuit pattern Image vary depending on circuit density,
product volume to be produced, and manufacturing techniques. In the simplest
method (subtract!ve), a copper-clad board 1s coated with the exact circuit
pattern using a protective resist material to create a positive Image on the
board. In a subsequent step (Process No. 8), the unprotected copper areas
(not covered by the protective resist) are chemically etched away to remove
unwanted copper from the board. A second method (additive) Involves creating
the reverse or negative pattern on a board by using a resist that leaves the
desired circuit pattern uncovered. The uncovered areas are later cleaned and
plated.
There are three principal methods in which the Image or circuit pattern
Is actually transferred to the board: screening, photosensitive resist
methods, and offset printing. There are two principal types of resist: those
which are cured by exposure to ultraviolet light (photo-sensitive resist) and
those which are cured by drying (thermal resist). Screening consists of se-
lectively applying resist material through the open areas of a stencil or
screen. The screen Is stretched tightly over a metal frame, which Is then
placed over the board. Ink or resist material 1s then squeezed through the
screen to produce either a positive or negative pattern. Another type of
resist that Is screened onto the board, which 1s applied "dry," is a thermo-
plastic material made fluid by passing through an electrically heated screen.
The resist then solidifies on contact with the board Into a nearly dry print.
The screening method 1s useful for simple low density circuits because Its
comparatively low cost allows for high volume production.
Photosensitive resist (photoresist) is applied by dipping or rolling a
pattern onto the board. The photosensitive resist is a light sensitive
polymer which, after curing, has a significant chemical resistance. Copper-
clad boards usually go through a prebake cycle before exposure. The resist is
then exposed to ultraviolet light through the pattern. The light sensitive
158
-------
material hardens and the unexposed resist material is removed. This is
followed by baking or curing the resist to allow it to withstand plating
solutions. This type of masking has made possible the production of high
density and intricate circuits because of the precision obtainable.
Offset printing, similar to a printing press, is applicable to high
volume production. An etched plate (the printing plate) serves as the master
pattern. After the plate is inked, the ink image is deposited on the copper-
clad board. By making several passes, enough ink can be built up on the board
to form a plating or etching resist. The same types of resists mentioned
earlier can be used for offset printing.
For all image transfer methods, excess or unexposed resist is washed away
with solvent, rinsed, and allowed to dry. The boards are then soaked in an
alkaline cleaner to remove any lingering resist and rinsed again. Copper-clad
boards, as a final step, are immersed in a tank of copper adhesion promoter,
rinsed, immersed in an acid solution, and rinsed one last time before being
electroplated.
2. Input Materials - For the screening image transfer method, screens
are either silk, polyester, or stainless steel. Screening inks are composed
of oil, cellulose, asphalt, vinyl, or other resins.
Photosensitive resists are light-sensitive solids, available as either
liquids or dry solids. They can be divided into two broad categories, posi-
tive and negative, with the latter used most often in circuit boards because
of their high chemical resistance, good image reproduction qualities, and low
cost. The basic components of resists are resins, sensitizers, additives, and
solvents. Although they do not necessarily have to be photosensitive, resins
must be capable of being rendered insoluble upon reaction with the sensitizer.
The major resins used for negative photoresists include polyvinyl cinnamate,
allyl ester resins, and isoprenoid resins. Sensitizers are added to provide
or increase photosensitivity. Commonly used sensitizers include thiazoline
compounds, azido compounds, nitro compounds, nitroaniline derivatives, an-
thrones, quinones, diphenyls, azides, xanthone, and benzil. Additives may be
added to photoresists, especially those which are polyvinyl cinnamate-based,
for a number of reasons: to increase adhesion; to reduce swelling during
development; to prevent formation of a scum layer; and to prevent darkening.
159
-------
Q
Table 6-4 lists some additives used In production of photoresists. Solvents
are added to resist formulas for dissolution purposes during storage and
application. Common resist solvents Include orthoxylene, metaxylene, para-
xylene, toluene, benzene, chlorobenzene, cellosolve and cellosolve acetate,
normal butyl acetate, 1,1,1-trichloroethane, acetone, methyl ethyl ketone, and
methyl isobutyl ketone.
Offset printing resists include many of those used in screening or photo-
sensitive application. Solutions to remove excess resist are generally tri-
chloroethylene, stabilized chlorinated hydrocarbons, mixtures of alcohol and
Stoddard solvent, xylene, commercial developing solutions, acetone, ketones,
esters, and alkali-based solutions.
3. Operating Conditions - Conditions vary with the particular resist
that is applied. Procuring temperatures vary from 45° to 120°C. Procuring
requires approximately 15 minutes. Developing temperatures range from ambient
to 90°C, while developing times range from 30 seconds to 4 minutes or longer
if thick resist coats are used. To complete the curing, some resists require
baking at 120°C for 15 minutes.2
4. Utilities - Electricity is required to provide heat for oven pre-
curing, developing, and curing.
5. Waste Streams - Depending on the processing method and the specific
chemicals used, air emissions will consist of various organic compounds.
Liquid waste streams are made up of water rinses containing chlorinated
hydrocarbon and batch dumps of spent chlorinated solvents. No other informa-
tion on copper or resist streams is available in the literature.
There are no solid wastes reported for this process.
6. Control Technology - Organic compounds fumes are collected and passed
2
through activated carbon beds.
The organic solvents and resists are immiscible with and heavier than
water. By routing all organic contaminated streams to one sump, the solvent
2
can be separated by gravity and collected for recovery or disposal. In some
instances solvent recovery using distillation may be feasible.
160
-------
TABLE 6-4. ADDITIVES USED IN PHOTOSENSITIVE RESISTS
To prevent scumming
A. Stabilizers
Phenol
Hydroquinone
Ca tec hoi
Resorcinol
o-tert-Butyl-p-methoxy phenol
Phenyl-B-naphthylamine
p-Hydroxyphenylmorphol1ne
p-Phenylenedlamine
B. Acids
Cinnamic acid
Benzole acid
Phenylacetic acid
Hydrocinnamic acid
Chloroacetic acid
Salicylic acid
Crotonic acid
To prevent darkening
A. Citric acid
B. Tartaric acid
C. Oxalic acid
To prevent polymerization
A. Hydroquinone
Pyridine
Copper resinate
Cuprous chloride
Nitrobenzene
6-napthol
B.
C.
D.
E.
F.
161
-------
PRINTED CIRCUIT BOARDS PROCESS NO. 7
Electroplating
1. Function - Electroplating is the process of depositing a metallic
coating on a board by immersing it in a conductive bath that utilizes an
external electrical power source to provide the driving force. The conductive
bath is usually water containing metal ions in solution. Printed circuit
boards may be electroplated with several different metals, one upon the other.
Between each electro-coat, the boards are rinsed, and after the last coat,
236
thoroughly rinsed and dried. *J* Electroplating is performed at several
junctures in the production of printed boards. It is employed in the actual
build-up of the circuit (in the additive and semi-additive processes); it
applies the anti-corrosive layer to the circuit; and it is used to cover the
tabs of all boards.
To build up the circuit in the additive and semi-additive processes,
copper electroplating is used, followed by either solder or tin electroplat-
ing. The solder plate or tin plate acts as a mask during the etching process
which follows electroplating, and secondly, protects the copper circuit from
corrosion. Printed circuit boards frequently receive an immersion tin coat-
ing, which is applied over both copper and solder plating. The coating is
temporary over copper plate, as it will oxidize. Over solder plate, the
coating prevents oxidation of lead in the solder during processing with
strong etchants.
For the additive and semi-additive processes, the tabs go through a
solder strip operation before tab plating to promote adhesion. This step is
not required in the additive process. Those tabs that require nickel or gold
plating, or both, are processed after the board is etched (Process No. 8).
The tab electroplating process is the same as described above.
2. Input Materials - Table 6-5 presents the plating bath constituents
237
that are used for plating specific metals. '
3. Operating Conditions - Table 6-6 presents common operating conditions
237
for the plating baths mentioned above. * ' Many other plating baths are used
but not described in the literature. These include hexavalent chromium-
based solutions.
162
-------
TABLE 6-5. PLATING BATH CONSTITUENTS2>3>7
Metal
A. Copper
B.
Solder
(tin-lead)
(continued)
1. Specifications for a Copper Pyrophosphate Bath
3.
-4
Component
Copper metal, Cu+2
Pyrophosphate, P207"
Oxalate
Nitrate, NOa
Ammonia, NH3 „
Orthophosphate, HP04
Concentration,
g/liter
22-38
150-250
15-30
5-10
1.5-3
No more than 1.3 to 1.7
Specifications for Acid-Copper Sulfate Baths
Component
Copper sulfate,
Standard
concentration,
g/1 1 ter
High throwing
power concentration,
g/11ter
160-300
40-75
52.5-135
As required
20-80 ppm
60-90
15-22.5
187.5-225
Copper, Cu+2
Sulfuric acid, H9SO.
Addition agents
Chloride ion
Specifications for a Acid-Copper Fluoroborate Bath
Component
Concentration,
g/liter
Copper fluoroborate, Cu(BF3)2
Copper metal, Cu+2
Fluoroboric acid, HBF. (free)
Boric acid, H3B03 *
Addition agents
224-448
60-120
10.5-30
15-30
As required
Specification of Standard Solder (60 percent tin,
40 percent lead) plating bath
Component
Stannous tin
Lead
Free fluoroboric acid
Free boric acid
Peptone
163
Concentration,
g/11ter
56.2
26.2
100.0
26.2
5.2
-------
TABLE 6-5 (continued)
C. Nickel
Specification of High-Throwing-Power Solder
(60 percent tin, 40 percent lead) Plating Bath
Component
Stannous tin
Lead
Free fluoroboric acid
Free boric acid
Peptone
Concentration,
g/liter
15.0
10.0
400.0
21.6
5.2
1. Typical Nickel Sulfamate Plating Bath
Component
Nickel sulfamate,
Ni(S03NH2)?a
Nickel metal, Ni
Boric acid, H3B03
Nickel bromide, NiBrg3
Concentration,
g/liter
300-525
60-120
30-45
11-19
Modified Watts Nickel Plating Bath
Component
Nickel sulfate,
NiS046H20
Nickel metal, Ni
Boric acid, taBO^
Nickel bromide, NiBr2
Stress reducer
Concentration,
g/liter
225-375
50-84
30-45
11-19
As needed
D. Tin-Nickel 1. Specifications for a Tin-Nickel Plating Bath
Component
Stannous chloride, SnCl2
Tin (stannous tin), Sn
Nickel chloride, NiCl2
Nickel, Ni
Ammonium bifluoride, NH4HF2
Total fluorine3
Concentration,
g/liter
48.8
26-38
300
68-83
41.0
34-45
(continued)
164
-------
TABLE 6-5 (continued)
E. Tin
F. Gold
G. Rhodium
1. Specifications for a Bright Acid Tin Plating Bath
2.
Component
Stannous sulfate, SnS04
Tin metal, Sn
C.P. sulfuric acid, H2S04
Brighteners
Concentration,
g/liter
30
13.5-15.6
184
Per vendor instructions
1. Specifications for a Typical Acid Gold Bath
Component
Gold metal as potassium
gold cyanide
Conductivity salts
pH-adjusting salts
Concentration,
g/liter
4-16
As necessary
As necessary
Specifications for a Typical Alkaline Noncyanide
Gold
Component
Metallic gold content
Conductivity salts
Reagent grade sodium
hydroxide
Reagent grade sulfuric
acid
g/liter
6-16
As necessary
To raise pH
To lower pH
Specifications of a Rhodium Sulfate Bath
Component Concentration
Rhodium sulfate
Sulfuric acid
1.3-2.1 g/liter
25-35 ml/liter
Specifications of a Rhodium Phosphate Bath
Component Concentration
Rhodium phosphate
Phosphoric acid
2.1 g/liter
40-80 ml/liter
Vs. Patent 3,554,878.
165
-------
TABLE 6-6. COMMON OPERATING CONDITIONS FOR PLATING BATHS
2,3,7
Bath type
Copper pyrophosphate
Acid-copper sulfate
Acid-copper fluoroborate
Standard solder
High- thrown ng-power solder
Nickel sulfamate
Modified watts nickel
Tin-nickel
Bright acid tin
Acid gold
Alkaline noncyanide gold
Rhodium sulfate
Rhodium phosphate
PH
8.1-8.8
strongly acid
0.2-1.7
<0.5
<0.5
2.5-4.2
2.5-4.2
1.5-2.5
proprietary
12
3.5-4.5
proprietary
proprietary
Temperature, °C
43-60
18-50
18-50
18-38
18-38
24-60
24-60
38-70
13-24
24-38
20-50
40-54
40-54
165
-------
4. Utilities - Electricity is required for direct immersion coil heating
of baths, blowers or compressors for bath agitation, direct current for plat-
ing, and miscellaneous pumps and motors. Steam may be used for bath heating
at large plants.
5. Waste Streams - There are no air emissions reported for this process.
Waste streams consist mainly of rinses and contaminated or spent dumps of
plating solutions. These streams will contain copper, nickel, lead, fluoride,
and possibly other metals, as well as inorganic chemicals found in plating
solutions (e.g., cyanides for processes using gold or copper cyanide plating
solutions).
There are no solid wastes reported for this process.
6. Control Technology - Rinse waters containing heavy metals such as
copper, nickel, and lead (if not complexed) can be precipitated as hydroxides
by proper pH adjustment and settling. Chromium wastes must first be reduced
from the hexavalent to the trivalent state. Cyanide-containing wastes must
first be oxidized using chlorine or other strong oxidants. Fluorides can be
partially removed by treating with lime to precipitate calcium fluoride at pH
10. Since calcium fluoride is somewhat soluble, it is generally advantageous
to segregate fluoride wastes in a separate solids removal system. It is
estimated that effluent copper concentrations can be reduced to 0.2 mg/liter
or less. Nickel and chromium removals of approximately 85 percent or greater
have been regularly reported, with final chromium concentrations of 0.05
mg/liter or less. Cyanide destructions using chlorine oxidation of greater
than 99.5 percent with remaining cyanide concentrations of less than 0.1
mg/liter are also reported. Typical concentrations following sedimentation
for copper, chromium (trivalent) and nickel are 0.49, 0.54 and 1.10 mg/liter,
respectively.
Removal data shown in Table 6-7 have been developed with pH adjustment
and precipitation, followed by diatomaceous earth filtration. The resulting
sludges are typically contract hauled for metals recovery or disposal.
Additional metals recovery techniques include reverse osmosis, ion ex-
change distillation, and electrolytic methods. Reverse osmosis may be used
for treatment and/or recovery of nickel or copper from acid plating solutions.
Ion exchange may be used for nickel or gold recovery or for rinsewater treat-
ment (as shown in Table 6-8). Distillation technology has been used to
167
-------
TABLE 6-7. DIATOMACEOUS EARTH FILTRATION PERFORMANCE DATA
1
Parameter
TSS
Cr(+3)
Fe
Cu
Ni
Removal, %
98
95
96
94
95
Raw
wastestream,
mg/ liter
524
12.2
5.81
7.53
2.57
Effluent
wastestream,
mg/ liter
10
0.611
0.248
0.444
0.044
TABLE 6-8. ION EXCHANGE PERFORMANCE DATA
1
Parameter
Cr
Cu
Fe
Ni
Ag
Sn
CN
S04
poj
Raw
rinsewater,
mg/ liter
7.60
4.45
3.70
6.20
1.50
0.50
0.80
21.0
3.75
Treated
effluent,
mg/ liter
0.06
0.09
0.10
0.00
0.00
0.00
0.20
2.0
0.80
163
-------
recover copper at 21,800 mg/liter and chromium at 27,500 mg/liter from feeds
initially containing 416 and 5060 mg/liter, respectively. Process condensates
generally contained less than 3 mg/liter of the metal being removed.
The fate of other inorganic chemicals in the plating solutions was not
found in the literature. Generally, spent electroplating baths, if they
cannot be regenerated, are contract hauled for disposal or incineration.
169
-------
PRINTED CIRCUIT BOARDS PROCESS NO. 8
Etching
1. Function - Etching 1s the process by which all unwanted copper (that
other than in the circuit) 1s removed from the board. Most manufacturers
employ mechanical etchers which spray etch solutions, solder brighteners or
activators, and rinsewaters onto horizontally traveling boards. Etching 1s
always used in the subtractlve technique, while an abbreviated etch is em-
ployed in the semi-additive technique.
An etch solution 1s then sprayed onto the boards; this 1s followed by a
rinse, mechanical scrub, another rinse, and thorough drying. Selection of
etchants and resist strippers Is based on board design, cost, pollution prob-
lems, and type of resist.
2. Input Materials - Resist stripping solutions which oxidize and de-
compose resist consist of sulfur1c-d1chromate, ammonlacal hydrogen perloxide,
metachloroperbenzoic acid, and others. Resist removal 1s also accomplished by
the use of commercial strippers which swell the resist, making it soft enough
to be scrubbed or washed off. Commercial strippers are composed of methylene
chloride, methyl alcohol (10 percent by volume), furfural, and phenol (1
percent by volume). Other strippers use various ketones, chlorinated hydro-
carbons, non-chlorinated organic solvents, and 2 to 10 percent sodium hy-
droxide. Resists may also be removed by high-temperature firing or boiling in
sulfuric or benzene sulfonic acids, but neither of these procedures is prac-
2 3
tical for conventional boards. '
Commonly used etchants are ferric chloride, ammonium persulfate, chromic
e
2
acid, cupric chloride, and alkaline etches. Tables 6-9 to 6-13 show the
compositions and variations of these etch solutions.
3. Operating Conditions - Etching solutions are maintained between 35
and 55°C depending on the particular etchant, and pH varies between 7.8 to
9.2. Temperatures used for resist stripping range from ambient to 60°C.
2
High-temperature firing to remove resist is carried out at 400° to 500°C.
170
-------
TABLE 6-9. CHARACTERISTICS OF FeCl3 SOLUTIONS3
Percent by weight
Specific gravity
Baume
g/liter
Molarity
Low
strength
28
1.275
31.5
365
2.25
Optimum
34-38
1.353-1.402
38-42
452-530
2.79-3.27
High
strength
42
1.450
45
608
3.75
Data taken at 20° to 25°C. Photoengraving Fed3 42° Baume has 0.2 to 0.4
percent free HC1; proprietary etchants contain up to 5 percent HC1.
TABLE 6-10. COMPOSITION OF TYPICAL PERSULFATE ETCH SOLUTIONS*
Solution
Component
(NH4)2S208
Na2S208
HgCl2
X-1343 (optional)
H3P04
1
240 g/liter
5 ppm
120 g/liter
2
240 g/liter
5 ppm
120 g/liter
15 ml/liter
3
360 g/liter
5 ppm
120 g/liter
15 ml/liter
FMC Chemical Corp.
171
-------
TABLE 6-11. COMPOSITION OF TYPICAL CHROMIC-SULFURIC
ACID ETCH SOLUTIONS32
Component
Cr03
Na2S04
H2S04 (96 percent)
Copper
Solution
1
240 g/liter
40.5 g/liter
180 g/liter
2
480 g/liter
31 ml /liter
4.9 g/liter
Proprietary agents contain wetting, antiforming, and chelating agents, and
catalysts.
TABLE 6-12. COMPOSITION OF TYPICAL CUPRIC CHLORIDE ETCH SOLUTIONS*
Solution
Component
CuCl2-2H20
HC1 (20° Baume)
NH4C1
1
2.2 M
8 ml/liter
2
2.2 M
0.5 N
3
0.5-2.5 M
0.2-0.6 M
2.4-0.5 M
172
-------
TABLE 6-13. COMPOSITION OF TYPICAL ALKALINE
ETCH SOLUTIONS, mol/liter2
Component
NH4OH
NH4C1
Cu (as metal)
NaC102
NH4HC03
(NH4)2HP04
NH4N03
Solution
1
3.0
0-1.5
10.375
0-1.5
0-1.5
2
6.0
5.0
2.0
0.01
3
2-6
1.0-4.0
0.1-6.0
0.05-0.5
173
-------
4. Utilities - Electricity is required for direct immersion coil heating
of baths, blowers or compressors for bath agitation, high-temperature firing
ovens, and miscellaneous pumps and motors. Steam may be used for bath heating
in large plants.
5. Waste Streams - There are no air emissions reported for this process.
Spent etchant and rinsewaters contain copper with either ammonia, chro-
mium, or iron also present. Rinsewaters from resist removal will contain
chlorinated hydrocarbons. The fate of the other resist stripping solutions
and etchants is not described in the literature.
There are no solid wastes reported for this process.
6. Control Technology - Heavy metals such as copper, chromium, and iron
(if not complexed) can be precipitated as hydroxides by adjusting the pH with
caustic or lime addition. Chromium treatment is accomplished in two steps.
First, hexavalent chromium is reduced to trivalent chromium using sulfur
dioxide, sodium bisulfite, or hydrazine at pH 3 or less. Following this step,
trivalent chromium can be precipitated as a metal hydroxide as described
above. Several copper removal and recovery techniques and effluent levels
achievable are described in Process No.'s 5 and 7.
Several methods are available for treating ammonium persulfate and cop-
per: removal by copper electrodeposition, precipitation of copper by reaction
with scrap aluminum and sodium chloride, and precipitation of copper hydroxide
after removal of ammonia with alkali and heat. Other ammonia removal methods
include phosphoric acid addition followed by lime addition to precipitate
heavy metal ammonium-phosphates, hydroxides, and other insoluble compounds.
2
The strippers and resists are heavier than and immiscible in water.
2
These materials can be collected in a sump for recovery and disposal. Etch-
ants may be recovered using distillation, reverse osmosis, ion exchange, or
electrolytic methods.
174
-------
PRINTED CIRCUIT BOARDS PROCESS NO. 9
Multilayer Board Lamination
1. Function - Multilayer boards consist of individual printed circuit
boards that have been bonded together and interconnected. Individual boards
that are to be laminated together have circuits imprinted in the same manner
as single- and double-sided boards.
The first step in the lamination process 1s the baking of laminates to
remove water, solvents, and chemicals used in earlier cleaning steps. This
assures that del amination will not occur. Next, semicured sheets of glass-
epoxy (called B-stage) are sheared and punched to match the size and shape of
the circuit panels being laminated. The sheets of B-stage are used as the
adhesive to bond circuit layers together. The circuit boards are stacked
together, with sheets of B-stage laid in between the boards in a press con-
taining registration pins to maintain circuit panel alignment. Application of
heat and pressure to the laminate press follows; this converts the semicured
B-stage material between circuits to fully cured C-stage epoxy. During the
process, the B-stage resin becomes a liquid adhesive which fills all circuit
pattern voids and bonds the layers together. Registration pins are then
pushed out and the top press plate is removed. Excess epoxy is removed from
the perimeter of the lamination and plugged racking holes are drilled out.
2
The laminate is then baked to assure final cure for the laminate bond resin.
2. Input Materials - Sheets of B-stage are available in standard G-10
and FR-4 material (described in Process No. 1). These sheets are semicured
glass-cloth-reinforced epoxy resin. The epoxy resin, however, has not fully
polymerized. Multilayer boards are fabricated almost exclusively from G-10
and FR-4 glass-filled epoxy boards. Other boards contain resins of polyimide,
2 "?
polyphenylene oxide (PRO) and glass-base Teflon. *
3. Operating Conditions - Lamination heating rate and final temperature
are specified by the B-stage supplier. Temperatures vary from 150° to 230°C,
2
and molding pressure averages 35 kg/cm . Molding times are approximately one
hour. The board must be allowed to cool, under pressure, to at least 50°C
2 3
before it can be removed from the press. ' The operating conditions of the
final curing oven are not described in the literature.
175
-------
4. Utilities - Lamination presses are either electrically or steam
heated.
5. Waste Streams - Resin volatiles are evolved during oven during and
laminate pressing from final curing of B-stage resin.
There are no liquid waste streams from this process.
Glass-epoxy solid matter is produced when trimming excess epoxy from the
boards.
6. Control Technology - Resin volatiles are handled the same as other
organic vapors. They are collected by hoods and passed through activated
carbon beds to adsorb the organic contaminants.
Control techniques for solid glass-epoxy matter were not found in the
literature.
176
-------
REFERENCES FOR SECTION 6
1. U.S. Environmental Protection Agency. Development Document for Proposed
Existing Source Pretreatment Standards for the Electroplating Point
Source Category. EPA 440/1-78-085, February 1978.
2. Coombs, C.F., Jr., ed. Printed Circuits Handbook, 2nd ed. McGraw-Hill,
New York, 1979.
3. Harper, C.A., ed. Handbook of Materials and Processes for Electronics.
McGraw-Hill, New York, 1970.
4. Federal Register. Vol. 44, No. 175. September 7, 1979, pp. 52590-52629.
5. Predicasts Forecases - 1980 Annual Cumulative Edition Issue No. 80. 4th
Quarter. Predicasts, Inc. July 24, 1980.
6. Hamm, Roger. Manufacturing Prototype Plated-Thru-Hole Printed Circuit
Boards. Plating. Vol. 64, No. 10, pp. 912-918.
7. Metal Finishing - Guidebook and Directory Issue 1980. Vol. 78 (1A).
Metals and Plastics Publications, Inc. Mid-January 1980.
8. DeForest, William S. Photoresist Materials and Processes. McGraw-Hill,
New York, 1975.
177
-------
SECTION 7
ELECTRON TUBES
INDUSTRY DESCRIPTION
Electron tubes are devices 1n which electrons or Ions are conducted
between electrodes through a vacuum or Ionized gas within a gas-tight en-
velope. The envelope may be made of glass, quartz, ceramic, or metal. This
category includes receiving-type tubes for radio and television use, and
transmitting, Industrial, and other special-purpose tubes.
Electron tubes depend upon two basic phenomena for their operation:
emission of electrons by certain elements and compounds when the energy of the
surface atoms (or gaseous atoms in the case of gas discharge tubes) 1s raised
by the addition of heat, light photons, kinetic energy of bombarding particles,
or potential energy; the control of the movement of these electrons or ions in
gas discharge tubes by the force exerted upon them by electric and magnetic
fields. The use of electron tubes 1s based upon the controlled flow of elec-
trons they produce. Receiving-type electron tubes are used primarily for low-
voltage and low-power applications. These include radio and television re-
ceivers and electronic control and measuring equipment. Transmitting and
special-purpose tubes Include a variety of devices:
0 High-vacuum tubes - diodes, triodes, multi-grid anodes.
0 Gas and vapor tubes - e.g., thyratrons (used for "triggering" a
current).
0 Klystrons (ultrahigh-frequency current).
0 Magnetrons (microwave frequencies).
0 Traveling wave tubes.
0 Light sensing tubes - camera tubes, image intensifies and con-
verters, photomultipliers.
0 Light emitting devices - storage tubes, special display devices.
178
-------
Electrodes are usually made of nickel mounted on a base glass or metal
envelope. The tube Is evacuated to 10 mm of mercury and the electrodes
and/or the envelope are heated to remove unwanted gases. The passage between
the tube and pumping system 1s sealed off and a getter material (usually
magnesium, calcium, sodium, or phosphorus) previously Introduced Into the
evacuated envelope Is flashed by applying an electric current to the elec-
trodes for several seconds. The getter material condenses on the Inside
surface and adsorbs any gas molecules. The vacuum within the tube Increases
progressively until an equilibrium value of 10 mm 1s reached.
Due to the Increasing use of semiconductors for applications that were
previously filled by electron tubes, the manufacture of some types of tubes
has dropped off sharply In recent years. Total shipments for receiving tubes
have decreased from 162.2 million units 1n 1972 to 60.9 million units In 1977,
and the total value of shipments over that same period has fallen from $182
million to $104.6 million.2
Raw Materials
Raw materials required for electron tube manufacture Include glass en-
velopes, Kovar and other specialty metals, tungsten wire, and copper wire.
They can be classified Into five major categories: *
0 Conductors - Copper and steel base materials with various plated
surfaces such as copper, nickel, gold, aluminum, silver, and chro-
mium are used extensively. These materials are good conductors
and/or supporting mediums, are easily shaped and formed, and are
cost-effective.
0 Leads - Copper and nickel are the most common material for electron
tube leads. Often the leads are a simple extension of one of the
conducting electrodes.
0 Encapsulating materials - Glass, ceramics, and various metals such
as steel are used for electron tube encapsulating materials. They
provide overall structural strength and assure integrity of the
applied vacuum or gas filling.
0 Inert gases - Electron tubes may either be filled with special inert
gases such as neon, argon, and krypton, or they may be completely
evacuated. Either method provides a dielectric medium of a prede-
termined resistance to the flow of electrons.
179
-------
Getters - Metals or mixtures of metals used In bulk getters include
thorium, titanium, cesium, zirconium, magnesium, calcium, sodium,
phosphorous, uranium, tantalum, hafnium, niobium, lanthanum, and
other rare earth elements. These metals, which are deposited by
evaporation on the walls of the glass or metal, adsorb gas molecules
that come in contact and thus maintain a high vacuum throughout the
life of the device.
Products
The analysis in this section includes the manufacture of receiving-type
electron tubes for radio, television, and other electronic applications (SIC
36711), and transmitting and special-purpose tubes (SIC 36713). It excludes
cathode ray picture tubes (SIC 36712) and cathode-ray tubes for industrial and
military use (SIC 3671385), which are covered in Section 3.
Applications for receiving-type electron tubes are rapidly being replaced
by solid state semiconductor devices. This is evidenced by the 57 percent
decrease in shipments of receiving tubes over the period from 1972 to 1977.
Table 7-1 presents Census Bureau data which shows the decline in this indus-
2
try. An industry source reported total value of shipments by domestic and
foreign manufacturers for the U.S. market at $111.6 million in 1978. Esti-
mates of the value of consumption of receiving-type electron tubes for 1979,
1980, and 1983 were reported to be $104, $96, and $34 million, respectively.
The annual decline from 1979 through 1983 is estimated to be 24.4 percent.
Table 7-2 presents information on sales of transmitting and special-
purpose electron tubes'for 1972 and 1977. Although incomplete, these data
indicate that many of these devices also face declining or at best relatively
stable markets.
Companies
The 1977 Census of Manufactures reports that 11 companies were involved
in the manufacture of receiving-type electron tubes and 43 in the manufacture
of transmitting and special-purpose tubes. Because all types of electron
tubes were categorized together, it is not possible to obtain information on
the size of the establishments by total employment from Census Bureau data.
Major manufacturers include General Electric, Westinghouse, GTE Sylvania, RCA,
Amperex, and International Components Corporation. »'
180
-------
TABLE 7-1. RECEIVING-TYPE ELECTRON TUBE MANUFACTURERS AND PRODUCT SHIPMENTS2
Product
Receiving tubes, except cathode ray:
As reported in the Census of Manu-
factures
As reported in Current Industrial
Reports MA-36N, selected electronic
and associated products, including
telephone and telegraph apparatus
Number of
companies
11
6
1972
Product shipments
Quantity,
million
a
162.2
Value,
$ million
189.6
182.0
1977
Product shipments
Quantity,
million
a
60.9
Value.
$ million
104.0
104.6
00
Not applicable.
-------
TABLE 7-2. TRANSMITTING AND SPECIAL-PURPOSE ELECTRON TUBE PRODUCT SHIPMENTS"
Product
Power and special tubes:
High-vacuum tubes
Gas and vapor tubes
Klystrons
Magnetrons
Traveling-wave tubes
Light-sensing tubes:
Camera tubes
Image intensifies and converters
Photomulti pliers and others
Light-emitting devices:
Storage tubes
Special display tubes
Miscellaneous other
1972
Product shipments
Quantity,
thousands
4855.0
3973.2
122.3
168.3
22.9
a
a
a
a
a
a
Value,
$ million
75.5
32.3
44.3
35.5
68.6
a
a
a
a
a
11.0
1977
Product shipments
Quantity,
thousands
2112.3
8471.0
192.3
22.8
a
49.8
310.7
16.0
a
Value,
$ million
73.7
33.7
48.1
52.9
90.3
36.0
30.0
21.2
19.0
74.5
Not available.
Does not include CRT's for industrial and military purposes.
-------
Environmental Impacts
There are few details In the literature concerning emissions from the
manufacture of electron tubes. No significant air or solid waste streams are
identified. The majority of water usage is for electroplating and part clean-
ing. Water effluents may therefore contain suspended solids, metals, and
acids. These wastes may be adequately controlled using end-of-pipe treatment
systems; there are many technologies that would be applicable. Recovery of
metals or other chemicals from wastewater treatment sludges could be practiced
on- or off-site.
INDUSTRY ANALYSIS
The following industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potential effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
Only limited data are available in the literature on electron tube manufac-
ture. This industry analysis covers two segments, receiving-tube and trans-
mitting tubes. Figures 7-1 and 7-2 are flowsheets showing the processes used
for manufacture of these devices, as well as their interrelationships and
waste streams.
Insufficient data were found in the literature to allow preparation of
individual process descriptions for the transmitting tube segment. The metal
components destined to be used in construction of the tube are first cleaned
in an unspecified solution and then electroplated with various metals (e.g.,
copper, gold, silver). Some of the finished metal components may be brazed to
glass components to form a metal-glass envelope. The envelope is washed in an
alkali or alcohol bath before proceeding to the tube assembly process, where
additional finished metal parts and the tube envelope are assembled into the
183
-------
TUBE MOUNT
ASSEMBLY1
I
GLASS MOUNT
ASSEMBLY 2
*
GETTERING/
FINAL ASSEMBLY
3
1
r
ELECTRC
RECEIVING
JBE
a WATER
OAIR
OSOLID
Figure 7-1. Receiving-type electron tube
production flowsheet.
184
-------
METAL COMPONENT
CLEANING 1
*
ELECTROPLATING 2
TUBE
ASSEMBLYg
GLASS COMPONENTS
CLEANING 3
*
ENVELOPE
ASSEMBLY 4
*
ENVELOPE
CLEANING 5
r
TRANSMITTING
ELECTRON TUBE
Figure 7-2. Transmitting electron tube production flowsheet.
185
-------
finished product. The final assembly stage may Include various combinations
of welding, soldering, annealing, and curing operations. The finished tube Is
then tested and packaged for shipment. Depending upon the exact type of tube
being produced, the production sequence may or may not Include the envelope
assembly and cleaning steps (Process No.'s 4 and 5 on Figure 7-2).
186
-------
RECEIVING-TYPE ELECTRON TUBES PROCESS NO. 1
Tube Mount Assembly
1. Function - Metal components used in the construction of tube grids
and anodes are cut and machined to specified dimensions. The cutting process
is most commonly performed using electron beam techniques. The machining in-
volves physical (abrasive), chemical (electrolytic depleting), or electron
beam evaporation methods. The metal parts are first cleaned in solvents, hot
alkaline, or acid baths depending upon the type of metal being cleaned and the
contaminant being removed. Next, the clean metal parts are "fired" in hydro-
gen or in vacuum bell jars to reduce further oxidation. The finished metal
parts are then assembled into what is described as the tube mount assembly.
2. Input Materials - The major inputs to the tube mount assembly consist
of specialty metals electroplated with copper, nickel, chromium, gold, or
silver. Dielectric material (mica) is used for spacers and to insulate the
tube components. Additional materials used during the plating and cleaning
operations include acids such as hydrofluoric, hydrochloric, sulfuric, and
nitric; electroplating solutions containing conductive metals like gold,
silver, copper, nickel, and chromium; and organic solvents such as methylene
chloride and trichloroethylene.
3. Operating Conditions - The exact temperatures and pressures developed
during the various operations of the tube mount assembly process are not
reported. A majority of the operations are probably performed under ambient
conditions, with the known exceptions being the metal cleaning and hydrogen
"firing" steps.
4. Utilities - The cutting, machining, and assembling steps of this
process require various forms of utility service, but the exact types and
quantities are unknown.
5. Waste Streams - The extent of air emissions, if any, are not reported
in the literature.
The majority of the water used in this process is for electroplating and
cleaning of tube parts. The composition of waterborne waste streams is un-
known .
187
-------
The only solid wastes from this process would be minor amounts of scrap
materials from cutting and machining operations.
6. Control Technology - The type of controls used in this process are
not documented in the literature.
138
-------
RECEIVING-TYPE ELECTRON TUBES PROCESS NO. 2
Glass Mount Assembly
1. Function - To form a glass mount assembly, the cathode, grid, anode,
and cathode lead wires are sealed in an annealed glass base. The sealing
operation is performed by a "glass mounting" machine. The entire component is
then heat treated by baking in an oven.
2. Input Materials - The cathode element of a receiving tube can be
constructed from various thermionic materials including tungsten or tungsten
alloys, and platinum with metal oxide coatings of barium, nickel, or iron. The
encapsulation materials are most commonly glass, but can also consist of
ceramic or metal, depending upon the structural strength required and the
vacuum to be maintained.
3. Operating Conditions - The exact temperatures and pressures developed
during the operations of the glass mount assembly process are unknown. A
majority of the operations are probably performed under ambient pressures.
4. Utilities - The metal to glass sealing operation and the glass tube
heat treatment require utility service, but the exact type and quantity are
unknown.
5. Waste Streams - There are no documented air, water, or solid waste
streams generated during this process.
6. Control Technology - The controls used in this proces's are-unknown.
139
-------
RECEIVING-TYPE ELECTRON TUBES PROCESS NO. 3
Getterlng/Flnal Assembly
1. Function - Getterlng describes the process by which the non-reactive
nature of electron tube gases 1s maintained. Getterlng 1s a process by which
chemically active metals are evaporated on the surface of the vacuum tube
enclosure, the grid work, the anode, or the cathode.
The finished electron tube Is physically evacuated before the Interior of
the tube Is coated with getter. Following the getterlng operation, the final
tube assembly Is completed by addition of the tube base. The reactive getter
metals added during the assembly preserve the non-reactive Integrity of the
tube vacuum or Inert atmospere by removing oxygen or oxidizing species from
the tube Interior. Upon completion of the electron tube, the glass exterior
1s rinsed and the finished tube 1s aged, tested, and packaged.
2. Input Materials - Barium 1s the most common metal used 1n gettering.
Calcium, strontium, magnesium, aluminum, thorium, titanium, cesium, zirconium,
and various other metals are also used. Glass, ceramics, and metals are used
for tube encapsulating materials.
3. Operating Conditions - The exact temperatures and pressures developed
during the sealing and evacuation procedures are unknown. The rinsing opera-
tion Is probably conducted under ambient conditions.
4. Utilities - The rinshing operations will require some level of water
service. This and the remaining operations will also require some additional
quantity of electrical service.
5. Waste Streams - There are no known air emissions associated with this
process.
The glass tube and bulb rinsing do not require a chemical cleaning proc-
ess and as a result will produce an effluent discharge with little if any
chemical pollutants.
There are no solid wastes from this process.
6. Control Technology - The controls used in this process, if any, are
not reported in the literature.
190
-------
REFERENCES FOR SECTION 7
1. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80/075-a, October
1980.
2. U.S. Department of Commerce. 1977 Census of Manufactures: Electrical
Components and Accessories. June 1980.
3. Kirk-Othmer Encyclopedia of Chemical Technology. 2d ed. Vol. 17. 1970.
John Wiley & Sons, New York.
4. Components: Unaggressive Growth In Store. Electronics. January 3,
1980.
5. Predicasts Forecasts - 1980. Annual Cumulative Edition Issue No. 80.
4th Quarter. July 24, 1980. Predicasts, Inc.
6. Electronic Designs Gold Book, 1978/1980. Vol. 1 and 2. Hayden Publish-
ing Co., Rochelle Park, New Jersey. 1979.
7. Electronic Industry Association Trade Directory and Membership List,
1979.
191
-------
SECTION 8
CATHODE RAY TUBES
INDUSTRY DESCRIPTION
Cathode r.ay tubes (CRT's) are special purpose vacuum tubes 1n which a
stream of electrons is focused onto a small area of a fluorescent screen,
producing a luminous spot. The focused beam of high-velocity electrons can be
deflected to allow any area of the screen to be scanned. The number of elec-
trons in the stream at any instant of time is varied by electrical impulses
corresponding to the transmitted signal. Most CRT's manufactured are used in
televisions.
CRT's consist of four major components: glass envelope, glass face panel,
steel aperture mask, and electron gun assembly. The face panel is made of a
special composition of glass which minimizes optical defects and provides
electrical insulation for high voltages. The glass bulb is designed to with-
stand 3 to 6 times the force of atmospheric pressure. The glass face panel is
a phosphorus-coated light-emitting screen at the front of the tube. The phos-
phor coating is applied to form small elemental areas, and in color picture
tubes each is capable of emitting light in one of the three primary colors
(red, green, blue), based upon the phosphor applied to that area. The
image is viewed'through this panel. An electron gun produces a stream of high
velocity eletrons which is aimed and focused on the panel by static and dynamic
convergence mechanisms and an electro-magnetic deflection yoke. An aperture
mask behind the face of the screen blocks portions of the beam, allowing the
unblocked portions to be focused on the panel. This allows phosphor excitation
in specific areas of the panel. Some color picture tubes use three electron
guns, one for each primary color. Commercially available aperture mask tubes
are manufactured in a number of sizes.
192
-------
Raw Materials
The raw materials for CRT production Include conductors, leads, encapsu-
lating materials, masks, phosphors, protective coating materials, graphite
coatings, and solders: * *3
rialsCused iC°*r "^ StCel an5 the maJ°r b8Se Conduct1ve
Leads - Copper and nickel are most often used. The leads are often
simply extensions of the conducting electrodes.
Encapsulating materials - Glass, ceramics, and various metals such
as steel are used as encapsulating materials. They provide overall
structural strength and assure integrity of the applied vacuum.
Special glass is used for television picture tubes to enhance
optical and electrical characteristics.
Mask - The aperture mask which allows electron beams to strike the
phosphor selectively in a color television picture tube is almost
always made from steel.
Photosensitive materials - A photosensitive solution is used to
prepare the glass surface for phosphor application. It commonly
contains di chroma te, alcohol, and other proprietary substances.
Developer solutions often are composed of hydrogen peroxide and/or
deionized water.
Phosphors - Common phosphor materials used in color picture tubes
Include cadmium sulfide, zinc sulfide, yttrium oxide, and europium
oxide. The red phosphor is a rare earth phosphor in which yttrium
oxide 1s activated with europium (1/203: Eu(lll)). The blue phos-
phor compounds are zinc and sulfide phosphors activated with silver
(ZnS:Ag). The green phosphors are composed of zinc-cadmium sulfide
activated with copper (Zn,(Cd)S:Cu). Many proprietary processes are
used in applying these materials as red, green, and blue phosphors
to the glass panel.
Protective coatings - Toluene-based lacquer and silicate coatings
are commonly applied to seal the phosphor coatings in place and
protect them from damage.
Graphite coatings - Slurries of carbon and a suitable binder are
applied to the surfaces of the panel and envelope to prevent re-
flection and secondary emission of electrons, and to provide a
conductive coating on the vacuum side of the glass envelope.
Solders - The four basic parts of a CRT are held together with
various solders; lead solders are the most commonly used.
193
-------
Products
The Bureau of the Census classifies CRT's Into two SIC codes: 36712 -
color and black-and-white television picture tubes; and 3671385 • CRT's
produced for military and Industrial applications. The 1977 Census of Manu-
factures reports that 7.7 million new CRT's for color televisions and 733,000
CRT's for Industrial and military applications were shipped In 1977.4 No
figures were given for new black-and-white television tubes.
Companies
There are 23 companies which manufacture CRT's for television and 13
involved in producing CRT's for military and industrial applications. A
breakdown of the manufacturers of television tubes 1s presented in Table
n
8-1. Major producers include RCA, GTE Sylvania. General Electric, Motorola,
Westinghouse, Amperex, Clinton, Raytheon, and ITT. '
Environmental Impacts
As 1s the case with electron tubes, there are few data available in the
literature concerning emissions during the manufacture of cathode ray tubes.
There are no air emissions reported other than possible release of vapors from
solvent degreasing tanks. Many steps in the manufacturing sequence do gen-
erate wastewater, however. These operations Include degreasing and a variety
of chemical cleaning, rinsing, and washing steps. The major wastewater pol-
lutants can include metals, toxic organics, cyanide, oils and grease, phenols,
fluorides, acids, and various proprietary photoresists and other solutions.
These streams may be pH adjusted with lime, settled, and discharged to the
environment or to municipal systems for futher treatment. Photoresist and
developer solutions require special treatment to reduce their chromium con-
tent; this may be achieved by reduction from the hexavalent to trivalent state
with sulfuric acid and sodium bisulfate, followed by further treatment with
sodium carbonate, calcium chloride, and sodium bisulfate. Waste streams from
phosphor application processes may be treated in separate settling and filtra-
tion systems prior to discharge.
194
-------
TABLE 8-1. COMPANIES PRODUCING CRT'S FOR TELEVISIONS
Product
No. of companies
New black and white TV's
Rebuilt black and white TV's
New color TV's:
17 inch and under
18 and 19 inch
20 inch and over
Rebuilt color
2
18
4
5
5
25
195
-------
The only sources of solid waste from-cathode ray tube manufacture are
scrap materials from various operations, including picture tube reclaim, and
wastewater treatment sludges. Recovery of metals and other chemicals from the
sludge can be practiced on- or off-site.
INDUSTRY ANALYSIS
The following industry analysis considers each individual production
operation (or series of closely related operations), called here a process, to
examine in detail its purpose and actual or potential effect on the environ-
ment. Each process is examined in the following aspects:
1. Function
2. Input materials
3. Operating conditions
4. Utilities
5. Waste streams
6. Control technology
The manufacture of cathode ray tubes is illustrated in this section by a
discussion of color television picture tubes. Figure 8-1 is a flowsheet of
these processes, as well as their interrelationships and waste streams.
196
-------
to
PA
Fil
1
^"""^
NEL ^
FfT /
APERTURE MASK
MANUFACTURE ]
1 <<
APERTURE MASK
DECREASING 2
t Cl
Rl flCC PANFI
UACU
1&
^*j
PHOTORESIST
APPLICATION
4
1 ^
PHOSPHOR
APPLICATION 5
*
j>
(^MASK*^^
V ^ ^
^ ^ PICTURE TUBE
- fPANFfv* RFPI ATM *
1
I
^^^^^^^^^^^^^
(^FUNNEL )
^^^ ^^S
\ ' \
SHIELD GLASS FUNNEL
DECREASING- PREPARATION,
j
i r
FINAL TUBE
ASSEMBLY g
/TELEVISION^
VpICTURE TUBE/
^ -N.
PTTTIIRF 1
\ TIIRTC /
ELECTRON GUN
ASSEMBLYg
1
A WATER
OAIR
O SOLID
Figure 8-1. Color television picture tube production flowsheet.
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 1
Aperture Mask Manufacturing
1. Function - Aperture masks used in conjunction with glass panels to
produce the visual image are manufactured by fabricating the metal form,
chemical cleaning, coating with a photosensitive material, etching, and rins-
ing. The holes produced in the aperture mask are the result of this etching,
which is generally performed with ferric chloride. Aperture masks are gen-
erally manufactured at facilities separate from those involved in the actual
construction of the CRT's.
2. Input Materials - The major structural material used for the manu-
facturing of aperture masks is steel. Additional substances involved in this
process are chromium, zinc, ferric chloride, and proprietary photochemicals.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the manufacturing of the steel aperture mask have not been
documented.
4. Utilities - The type and quantity of utility service required for
this process is unknown. Electricity is required to operate various machin-
ery.
5. Waste Streams - There are no air emissions reported to be associated
with this process.
The major waterborne pollutants include iron, chromium, zinc, ferric
chloride, and particulate in the form of total suspended solids. In addition
to these major pollutants, trace amounts of toxic contaminants have been
identified in raw waste from an aperture mask manufacturing process. A sum-
mary of these substances is presented in Table 8-2.
There are no solid wastes reported other than metal scrap.
6. Control Technology - The etching wastewater used during aperture mask
manufacturing is pH adjusted with lime before being sent to a settling pond.
The runoff from the settling pond is discharged directly into the environment.
198
-------
TABLE 8-2. SUMMARY OF RAW WASTE DATA FROM AN APERTURE MASK
MANUFACTURING OPERATION!
Substance
Concentration,
mg/liter3
Toxic organics
Methylene chloride
Toxic metals
Cadmiurn
Chromium
Copper
Lead
Zinc
Other pollutants
Cyanide
Oil and grease
Total organic carbon
Biochemical oxygen demand (BOD)
Total suspended solids
0.060
0.0002
3.480
0.570
0.009
0.193
2.1
8.4
4.0
18
52
Note: Data taken from a single operation.
a Single stream sample value.
199
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 2
Aperture Mask Degreasing
1. Function - Steel aperture masks are formed to the required size,
solvent degreased, and oxidized.
2. Input Materials - Various industrial solvents are used to clean and
degrease the steel apertures. Common solvents employed are methylene chlo-
ride, trichloroethylene, methanol, isopropanol, acetone, and polyvinyl al-
cohol.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the aperture mask degreasing process have not been documented.
It is assumed that this work is performed under ambient conditions.
4. Utilities - The types and quantities of utility service required for
this operation are not reported.
5. Waste Streams - Degreasing operations may result in release of
solvent vapors to the atmosphere.
Wastewater is produced during the operation of solvent recovery systems
associated with the degreasing operation. A characterization of wastewater
from two television picture tube manufacturing plants is summarized in Table
8-3. Wastewaters are not segregated, so these pollutants could be introduced
at any of several processes.
The generation of solid wastes during these operations is not reported.
6. Control Technology - Emissions from degreasing tanks can be reduced
by increasing freeboard in the degreaser tank and using refrigerated chillers
to create a cold air blanket above the solvent. Emissions can be controlled
by the use of chillers or condensers and carbon adsorption.
Wastewaters from the aperture mask degreasing are pH adjusted and set-
tled. The literature describes a system in which this stream flows through
three settling tanks prior to final discharge. All treated process waste-
water, untreated process wastewater, and non-contact cooling water flow to-
gether to the municipal treatment system.
200
-------
TABLE 8-3. SUMMARY OF RAW WASTE FOR TELEVISION PICTURE TUBE MANUFACTURE
1
Toxic organic!
1.1.1 trlchlorotthane
Methylene chloride
Tolutni
Trlchloroethylene
Total toxic organic!
Toxic mttali
Antimony
Arsenic
Cadmium
Chromium
Copptr
Lead
Nickel
Silver
Zinc
Non- toxic octal s
Aluminum
Manganese
Vanadium
Boron
BaHun
Molybdenum
Tin
Yttrlun
Cobalt
Iron
Titanium
Other pollutants
Cyanide, total
Oil and grease
Total organic carbon
Total suspended solids
Phenols
Fluoride
Plant Aa
Minima
concentration.
og/ liter
NA
NA
NA
NA
NA
0.126
0.100
0.135
2.476
0.052
10.600
0.070
0.001
5.120
3.276
0.040
0.003
7.080
0 586
<0.03S
<0.025
1.290
<0.050
7 720
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 3
Glass Panel Wash
1. Function - The steel aperture masks are Inserted within a glass
panel, with the result referred to as a panel-mask "mate". The mate is heat
annealed and the components are separated. The glass panels are then washed
in an acid bath and rinsed repeatedly with water. No additional operations
are performed on the mask.
2. Input Materials - Hydrofluoric and sulfuric acids are used in this
process.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during these process operations are not reported.
4. Utilities - Water is required for rinsing the glass panels. Specific
quantities of water or other utility service required are not reported.
5. Waste Streams - There are no air emissions from this process.
Wastewater 1s produced during the glass panel wash, and there may be high
concentrations of acids and fluorides. During the picture tube manufacturing
process the panels are inspected at various points along the production
sequence. A percentage of these panels are rejected and returned to the
initial panel wash. Because of this quality control procedure, pollutants
generated at the panel wash will include pollutants associated with the
wastewater from process steps further down line on the production scheme,
i.e., the photoresist and phosphor application steps. A characterization of
wastewater from"two television picture tube manufacturing plants is summarized
in Table 8-3.}
There are no solid wastes from this process.
6. Control Technology - Wastewater from the panel wash at some plants is
pH adjusted using sodium bicarbonate. The resulting neutral solution is
allowed to settle. The wastewater discharged from this initial settling
process flows through three additional settling tanks before it is discharged
into the municipal treatment system.
202
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 4
Photoresist Application *
1. Function - A chromium bearing photoresist solution Is applied to the
glass panel to prepare the surface for selective phosphor application. The
photoresist solution Is applied, the mask 1s placed over the panel, and the
panel 1s exposed to light, developed, graphite coated, re-developed, and
cleaned in several acid solutions. The photoresist application process re-
sults In a graphite-coated panel surface with a multitude of uncoated dots.3
These dots will be the future sites of phosphor application.
2. Input Materials - The major input materials to this process include
the photoresist solution containing chromium, the graphite coatings, developer
solutions composed of hydrogen peroxide and deionized water, and hydrofluoric-
sulfuric acid solutions.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the photoresist process have not been documented.
4. Utilities - The types and quantities of utility service required for
this process are not reported.
5. Waste Streams - There are no air emissions from this process.
Wastewater includes spent acid, photoresist, developer solutions, and
rinses. It contains high concentrations of hexavalent chromium, strong acids,
fluorides, graphite, and proprietary chemicals included in the photoresist
solutions. A characterization of wastewater streams from several processes at
two television picture tube manufacturing plants is summarized in Table 8-3.
The type or extent of solid waste generated during this process are
unknown.
6. Control Technology - The photoresist and developer solutions require
treatment to reduce the chromium before discharge to the environment. The
chromium-bearing wastewater is reduced from the hexavalent to the trivalent
state using sulfuric acid and sodium bisulfate. These partially treated
wastes are subjected to further chemical treatment with sodium carbonate,
calcium chloride, and sodium bisulfate. The chemically treated wastewater is
then clarified and filtered before discharge to the environment. Figure 8-2
summarizes the waste treatment facility at one picture tube manufacturing
process which handles hexavalent chromium wastes.
203
-------
su
CONCENTRATED
CHROMIUM
WASTE *
LFURIC SODIUM
ACID BISULFATE
i 1
REDUCTION -»• HOLI
TAI*
OTHER
PROCESS
WASTES
LIME
CALCIUM CHLORIDE
SODIUM BISULFATE
)ING RAPID
IK """" MIX
1
POLYELECTROLYTE
Tl flRTFIFR
t
VACUUM
FILTRATION
SLUDGE
DUAL-MEDIA HOLDING
*" FILTRATION ""LAGOON
ro
2
Figure 8-2. In-place waste treatment for hexavalent chromium wastes
from a picture tube manufacturing process.
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 5
Phosphor Application
1. Function - The panels leaving the photoresist application process
undergo another application of resists before deposition of phosphors. The
phosphors are deposited onto the panel as three separate colors (red, blue,
and green). The colors are applied to the glass panel as numerous triads of
dots. The panel and mask are again mated, and the entire assembly is exposed
to light. Next, the mask is removed and the panel is developed. A protective
lacquer coating is applied to the panel in order to seal in the phosphors.
Aluminum is vacuum-deposited onto the lacquered panel in order to enhance
reflection. The mask is reunited with the panel and the mask-panel mate is
cleaned first in an alkali, then in acid.
2. Input Materials - The main input materials to the phosphor applica-
tion process include photoresist, phosphors, a protective lacquer coating, and
aluminum. Photoresist or photosensitive solutions used in the picture tube
industry commonly contain dichromates. The developer solutions used in con-
nection with the photosensitive materials are composed of hydrogen peroxide
and deionized water. The phosphors are the source of the color associated
with modern television picture tubes. The red phosphors contain phosphor
activated by the rare earth metals yttrium and europium. The blue phosphors
contain zinc sulfide phosphors activated with silver. The green phosphors are
zinc-cadmium sulfide phosphors activated with copper. The protective coatings
used to cover the phosphor triads consist of either toluene-based lacquers or
silicates.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the phosphor application process are not documented in the
literature.
4. Utilities - The types and quantities of utility service required for
this process are not reported.
5. Waste Streams - There are no air emissions associated with this
process.
205
-------
Wastewater from the phosphor coating solutions, developer solutions, the
aluminizing process, panel cleaning solutions, and associated rinses all
contain high levels of phosphor. These contaminants include cadmium sulfide,
zinc sulfide, yttrium, europium, and moderate levels of proprietary photo-
resists. A summary of the raw waste for two television picture tube manu-
facturing operations is given in Table 8-3.
There are no solid wastes generated during this process.
6. Control Technology - Two categories of liquid waste streams are
generated during the phosphor application process, phosphor waste and "other"
pollutant wastes. These two categories are treated by different systems. The
red, blue, and green phosphors are treated by individual systems, as shown in
Figure 8-3. The composite waste stream containing non-phosphor-type sub-
stances is combined with other wastewaters and handled by the types of waste
treatment schemes described in previous processes.
206
-------
RED
PHOSPHOR
WASTE
BLUE
PHOSPHOR
WASTE
GREEN
PHOSPHOR
WASTE
MUNICIPAL
h*-TREATMENT
SYSTEM
Figure 8-3. In-place waste treatment for phosphor wastes
from a picture tube manufacturing process.
207
-------
COLOR TELEVISION PICTURE TUBES PROCESS NO. 6
Glass Funnel Preparation
1. Function - Glass funnels which are purchased from a supplier or
produced offsite must be prepared before entering the picture assembly proc-
ess. The glass funnels are first washed in an alkaline solution and then
rinsed in water. The inner surface of the clean glass funnel is coated with
graphite to prevent reflection within the picture tube. A lead glass frit is
then applied to the glass funnel along the surface which will eventually be
fused to the picture tube panel.
2. Input Materials - The glass funnel is made of specialty glass with
enhanced structural and electrical characteristics. The graphite coating is
free of additives or contaminants. The constituents of the lead frit and
alkaline wash are not known.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the glass funnel preparation process are not documented in the
literature.
4. Utilities - The types and quantities of utility service required for
this process are not reported.
5. Waste Streams - There are no air emissions from this process.
The wastewater discharge from this process contains a variety of heavy
metals, including lead from the frit that was applied to the edge of the glass
funnel. The wastewater also contains low levels of silicates. A summary of
the raw waste from two television picture tube manufacturing operations is
given in Table 8-3.
There are no process solid wastes.
6. Control Technology - The treatment of wastewater discharge from this
process was not specifically addressed in the literature. Lead-bearing wastes
are concentrated and treated separately at one manufacturing operation;
however, it is not clear whether the source of the lead waste was the glass
funnel preparation process, another process, or the combination of all lead
emitting processes. Treatment consists of chemical precipitation with sodium
carbonate, with the effluent then transferred to holding tanks. The resulting
lead carbonate material is land-filled.
208
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COLOR TELEVISION PICTURE TUBES PROCESS NO. 7
Shield Deqreasinq
The electric shields are degreased before entering the final tube as-
sembly. The nature of this degreasing operation, the input materials used,
the operating conditions required for proper processing, and the existence of
pollutant waste streams are not reported. Little information was available
concerning this portion of the cathode ray television picture tube operation.
209
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COLOR TELEVISION PICTURE TUBES PROCESS NO. 8
Electron Gun Assembly
The electron gun mount contains the cathode and grid which provide elec-
trons that bombard the light-emitting phosphor screen. The electron gun mount
assembly process includes a cleaning operation prior to the final picture tube
construction. The nature of this assembly process, the Input material used,
the operating conditions required for proper processing, and the existence of
pollutant waste streams are not documented in the available literature.
210
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COLOR TELEVISION PICTURE TUBES PROCESS NO. 9
Final Tube Assembly1
1. Function - The panel-mask mate with the finished phosphor coating
receives a degreased electron shield. Following attachment of the shield, the
assembly is heat-fused to the lead glass frit of the finished glass funnel. Next,
the electron gun mount is heat-sealed to the base of the panel-funnel assem-
bly. At this stage of construction, the assembly is described as a "bulb".
The bulb is exhausted, sealed, and the cathode is aged by applying a current
to the appropriate leads. The finished tube is tested, an external graphite
coating is applied, and an implosion band is secured to the tube. The fin-
ished tube receives a final test before shipment.
2. Input Materials - Graphite is used in the exterior coating.
3. Operating Conditions - The exact temperatures and pressures encoun-
tered during the assembly of the picture tube are not reported.
4. Utilities - The types and quantities of utility service required for
this process are unknown.
5. Waste Streams - The type and extent of air, water, and solid waste
streams generated from this assembly process are not reported in the litera-
ture.
6. Control Technology - The type and extent of control technologies
associated with this process are not known.
211
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COLOR TELEVISION PICTURE TUBES PROCESS NO. 10
Picture Tube Reclaim^
1. Function - Some picture tube production facilities may have picture
tube salvage and reclaim operations. The reclaim process includes the dis-
assembly of spent picture tubes into panel, mask, and funnel components. The
individual components are then reintroduced into the appropriate process
operations within the production scheme.
2. Input Materials - The only item introduced into this process is the
spent picture tube.
3. Operating Conditions - The exact conditions of operation developed
for this process are not documented in the literature. It is assumed that the
reclaim process is conducted at ambient temperatures and pressures.
4. Utilities - The types and quantities of utility service required for
this process are not reported.
5. Waste Streams - There are no known air or liquid wastes from this
process.
A variety of solid scrap materials (metal, glass, etc.) result from this
process.
6. Control Technology - There is no documentation on the use of control
equipment for this process.
212
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REFERENCES FOR SECTION 8
1. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80/075-a, October
1980.
2. Jacobs Engineering Group, Inc. April 1980. Draft Development Document
for Effluent Limitations Guidelines, New Source Performance Standards for
the Piezoelectric Crystals, Semiconducting Crystals, Phosphorescent
Coatings and Magnetic Coatings Segments of the Electrical and Electronic
Products Point Source Category.
3. Kirk-Othmer Encyclopedia of Chemical Technology. 2d Vol. 17. 1970.
John Wiley & Sons, New York.
4. U.S. Department of Commerce. 1977 Census of Manufactures: Electrical
Components and Accessories. June 1980.
5. Electronic Designs Gold Book, 1978/1980. Vol. 1 and 2. Hayden Publish-
ing Co., Rochelle Park, New Jersey. 1979.
6. Electronic Industry Association Trade Directory and Membership List,
1979.
7. U.S. Environmental Protection Agency. Controlling Pollution from the
Manufacturing and Coating of Metal Products: Water Pollution Control-II.
EPA 625/3-77-009, May 1977.
213
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APPENDIX
WASTEWATER TREATMENT AND CONTROL
The two best documented segments of the electronic component manufactur-
ing industry are semiconductors and printed circuit boards. Wastewater efflu-
ents are the most significant environmental control problems associated with
either of these production sequences. This appendix presents additional
information on wastewater control strategies and technologies for these indus-
tries beyond that presented in the IPPEU format.
SEMICONDUCTORS
Control technologies employed for semiconductor device manufacture con-
sist of both end-of-pipe and in-line systems.
End-of-pipe treatment systems employ segregation of waste streams into
acidic wastes, fluoride wastes, and spent solvents. A typical treatment
scheme is illustrated in Figure A-l; these technologies function as follows:
0 Chemical precipitation (pH adjustment) - Dissolved heavy metal ions
are often chemically precipitated as hydroxides using pH adjustment.
This allows removal by physical means such as sedimentation, filtra-
tion, or centrifugation. Reagents commonly used to effect this
precipitation include alkaline compounds such as lime and sodium
hydroxide. Calcium hydroxide is used to precipitate phosphates as
insoluble calcium phosphate. Solids formed in this step may be
pumped to a sedimentation tank or allowed to settle in the precipi-
tation tank. Hydroxide precipitation has proven to be an effective
technique for removing many pollutants from industrial wastewater.
It operates at ambient conditions and is well suited to automatic
control.
0 Sedimentation - Sedimentation is a process which removes solid
particles from a liquid waste stream by gravitational force. Waste-
water is fed into a high volume tank or lagoon where the suspended
solids are allowed to settle. Because metal hydroxides tend to be
colloidal in nature, coagulating agents or polyelectrolyte floccu-
lants may be added to facilitate settling. Inorganic coagulants
214
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COAGULANT OR
POLYELECTROLYTE
ADDITION
ACID
WASTE
ro
in
FLUORIDE
WASTE
SPENT
SOLVENTS
CHEMICAL
PRECIPITATION
(pH ADJUSTMENT)
SEDIMENTATION
CHEMICAL
PRECIPITATION
(pH ADJUSTMENT)
AND
SEDIMENTATION
EFFLUENT
DISCHARGE
SLUDGE
DEWATERING
RETURN FOR
pH ADJUSTMENT
SPENT
SOLVENT
COLLECTION
CONTRACTOR
• REMOVAL
OF SLUDGE
CONTRACTOR
- REMOVAL
OF SOLVENTS
Figure A-l. Wastewater treatment system - semiconductor manufacture.
-------
include sodium sulfate, sodium aluminate, ferrous or ferric sulfate,
and ferric chloride. Organic polyelectrolytes usually form larger
floccules than coagulants used alone. Actual plant performance of
chemical precipitation followed by sedimentation in the semicon-
ductor industry in shown in Table A-l.1 In general, sludges formed
in this step are pumped to a sludge dewatering unit such as a vacuum
filter, centrifuge, or filter press. The dewatered sludge is then
contractor removed for off-site disposal.
0 Fluoride treatment - Fluoride wastes are adjusted with Hme to a pH
of 11. This causes free fluoride ions to bond with calcium and
settle out of solution. Sulfuric acid is then used to readjust the
pH to 7.5, and polyelectrolytic flocculant is used to settle the
solids more rapidly. The decanted water is discharged to the waste
treatment system for further treatment prior to discharge, and the
sludge is dewatered -in a vacuum filtration unit and collected for
contractor removal. Actual plant performance of fluoride treatment
systems in the semiconductor industry is presented in Table A-2.'
0 Solvent collection - Due to their high costs, segregation of spent
organic solvents from wastewater is often economically attractive.
Spent solvents can be contractor hauled to disposal sites, sent to
recycling plants for regeneration and recovery, or recovered "in-
house." In-house systems may incorporate activated carbon adsorp-
tion followed by distillation to purify the recovered solvent.
In-line treatment technologies rely upon reducing wastewater volume using
water conservation techniques. This includes countercurrent rinsing, auto-
matic shut-off equipment for rinse tanks, and rinse water recycle:
0 Countercurrent rinsing - Semiconductor plants utilize two- to four-
stage countercurrent rinses following process baths. Countercurrent
rinses require much less water than a single overflowing rinse, yet
provide equivalent removal of process chenpcal dragout from the
wafer.
0 Automatic shut-off equipment - The ultrapure water required by the
semiconductor industry for process use must be in the range of 12 to
18 megohms of resistance. This measure of resistance reflects the
presence of ions in the water. As the conductance of the water
increases, the controller allows ultrapure water into the rinse
until the desired resistivity level of the water is reached. At
this point, the water flow stops until the conductivity controller
senses another increase in the conductance. These conductivity
controllers minimize the amount of make-up water added and provide
high purity water for semiconductor wafer rinsing.
216
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TABLE A-l. PERFORMANCE OF CHEMICAL PRECIPITATION AND
SEDIMENTATION - SEMICONDUCTOR MANUFACTURE1
Parameter
Arsenic
Chromium
Copper
Lead
Nickel
Zinc
Oil and grease
Total suspended solids
Fluoride
1 ,2,4-Trichlorobenzene
1 ,1 ,1-Trichloroethane
Chloroform
2-Chlorophenol
1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
Methyl ene chloride
Naphthalene
4-Nitrophenol
Phenol
Di-n-octyl phthalate
Tetrachloroethylene
Toluene
Trichloroethylene
Minimum
concentration,
ing/liter
<0.003
0.019
0.03
0.082
0.520
0.022
2.4
<1.0
5.42
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
Maximum
concentration,
mg/ liter
0.005
0.059
0.134
0.102
0.844
0.040
17.4
60.0
17.50
<0.01
0.013
0.02
<0.01
<0.01
<0.01
<0.01
0.049
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
<0.052
Mean
concentration,
mg/ liter
0.004
0.04
0.061
0.077
0.541
0.027
6.46
23.8
16.1
<0.01
0.005
0.013
<0.01
<0.01
<0.01
<0.01
0.03
<0.01
<0.01
<0.01
<0.01
<0.01
<0.01
0.024
217
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TABLE A-2. PERFORMANCE OF FLUORIDE TREATMENT
SYSTEMS - SEMICONDUCTOR MANUFACTURE"
Parameter
Flow, I/hour
Arsenic
Cadmium
Chromi urn
Copper
Lead
Mercury
Nickel
Selenium
Silver
Thallium
Zinc
Total suspended solids
Fluoride
Plant 1 mean
concentration,
mg/ liter3
In
1049C
0.087
< 0.003
217.16
2.14
0.075
0.0025
0.145
0.007
0.02
<0.03
0.11
4150
38750
Out
1049°
0.042
<0.003
0.39
0.11
0.065
0.007
0.2
<0.005
0.018
<0.03
0.218
747.3
24.3
Plant 2 mean
concentration,
mg/literb
In
22,583
<0.01
0.004
22.8
2.2
5.35
<0.001
0.69
< 0.005
0.024
0.005
<0.01
5.6
760.0
Out
22,583
<0.01
<0.001
0.055
0.145
0.005
<0.001
0.065
0.005
<0.01
0.012
<0.01
71.0
37.0
These values are means because these streams were sampled over three dif-
ferent sampling periods.
These are single stream values.
c This is total flow in liter/h for three streams sampled.
Note: The "in" streams are not total raw waste streams and thus cannot be
compared with values in summary of raw waste data, Table A-l.
218
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0 Rinse water recycle - Pollutants in the recycled process water are
removed in the deionized water production area. As much as 50 to 80
percent of the total process water used may be recycled. When the
components of deionized water production are backwashed and regen-
erated, the pollutants from reused rinse water and from supply water
are sent to the waste treatment area for treatment prior to dis-
charge. This reuse conserves water, concentrates the pollutants,
and decreases wastewater discharge. All of these factors contribute
to the cost effectiveness of end-of-pipe treatment processes.
PRINTED CIRCUIT BOARDS
Control technologies for printed circuit board manufacture also consist
of both end-of-pipe and in-line systems.
End-of-pipe treatment systems for non-segregated wastes generally involve
flocculation, clarification, and contract hauling of sludge. Chlorine is
added to the flocculation tank for the oxidation of cyanides (if present).
Lime is also added to the flocculation tank both to raise the pH for cyanide
oxidation and to precipitate metals as hydroxides in the clarifier. End-of-
pipe treatment systems employing segregation of waste streams generally sepa-
rate wastes requiring treatment. Typical treatment methods are described
below and shown in Figure A-2:
0 Cyanide-bearing wastes - This stream is composed of rinses following
any operation where cyanides are employed: cyanide copper plating,
cyanide gold plating, and cyanide gold stripping. Treatment of
these wastes involves oxidation of cyanides to cyanates and, in a
second step, to nitrogen and carbon dioxide. Chlorine addition (in
the form of sodium hypochlorite) is typically used to effect the
oxidation while the pH is maintained (by sodium hydroxide or other
base addition) at approximately 11. After oxidation, treated cya-
nide wastes may be combined with waste streams containing acid and
alkali cleaners and other non-chelated metals.
0 Acid-alkali and non-chelated metals streams - This stream consists
of rinse waters following several operations: acid and alkali
cleaners in all process lines, non-chromium and non-ammoniated
etches, catalyst application, acceleration, and non-cyanide and non-
chelated plating baths. This stream generally contains metals such
as tin, palladium, lead, and copper. Treatment of these wastes
involves flocculation using lime to precipitate metals followed by
settling. This flocculation and settling can remove 95 to 98 per-
cent of the metals, depending on the type of metals in the waste
streams. Alternatively, membrane or diatomaceous earth filtration
may be used to separate flocculated solids.
219
-------
ro
CM
o
SODIUM
HYPOCHLORITE NaOH
1 1
CYANIDE
WASTES
CYANIDE
OXIDATION
LIME
ACID/ALKALI
WASTES
SO,
CHROMIUM
WASTES
CHELATED
WASTES
SO, 11,50.
I I
HEXAVALENT
CHROHIUH
REDUCTION
/WON IA
WASTES
AMMONIUM
PHOSPHATE
PRECIPITATION
FLOCCULATOR
LIME
FLOCCULATOR
SETTLING
TANK
SLUDGE
SETTLING
TANK
SLUDGE
DRYING
BEDS
RECYCLE
. EFftUENT
DISCHARGE
SLUDGE
Figure A-2. Wastewater treatment system - printed circuit
board manufacture (segregated waste streams).
-------
0 Chelated waste streams - This stream consists of rinses following
operations where chelating agents are present. Included in this
group are electroless plating rinses. These wastes must be kept
separate from other metal-bearing wastes. Treatment generally
involves lime flocculation and settling or membrane filtration in a
method similar to that described for acid-alkali and non-chelated
waste streams.
0 Chromium-bearing wastes - This stream contains hexavalent chromium
from chromic acid etch rinses if such etching is used. This is
usually not found in the printed board industry. However, if such a
stream exists, the hexavalent chromium must first be reduced to the
trivalent form by lowering the pH and adding sulfur dioxide or
similar chemicals before introduction to the flocculation tank.
0 Ammonia waste streams - These streams consist of ammonia-base etch-
ants and rinses. Treatment involves pH adjustment (frequently using
caustic) and live steam injection. The effect of these two steps is
the precipitation of some metals and the dispersal of ammonia as a
gas. Alternatively, phosphoric acid may be added to precipitate
heavy metal ammonium phosphates. The treated ammonia wastes are
then combined with the cyanide waste stream (following oxidation)
and the acid-alkali and non-chelated waste streams.
In general, sludges formed in the flocculating and settling tanks are pumped
to a sludge dewatering unit such as a vacuum filter, centrifuge, or filter
press. The dewatered sludge is then disposed of at an on-site landfill or
off-site by contract hauling.
In-line treatment technologies rely on wastewater volume reduction using
water conservation techniques such as countercurrent rinsing, fog rinsing, and
automatic shut-off equipment for rinse tanks. In addition, recovery of plat-
ing and etching solutions is practiced using techniques such as reverse osmo-
sis, distillation, ion exchange, and electrochemical methods. Specific appli-
cations of in-line treatment techniques are discussed in Section 6.
221
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REFERENCES
1. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and Standards for the Electrical and Electronic
Components Point Source Category: Draft. EPA 440/1-80-075a, October
1980.
222
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