r/EPA
United States
Environmental Protection
Agency
Office of Pollution Prevention
and Toxics
(7406)
EPA-744-R-01-001
June 2001
Alternative
Technologies for
Surface finishing
Cleaner Technologies for
Printed Wiring Board
Manufacturers
Office of Pollution
Prevention and Toxics
U.S. EPA
-------
vvEPA
AlternativeTechnologies for
Surface Finishing
Cleaner Technologies for Printed Wiring Board Manufacturers
U.S.EPA
Office of Pollution
Prevention and Toxics
This document and other DfE PWB Project documents are available online at www.epa.gov/dfe
orwww.epa.gov/opptintr/library/ppicdist.htm
For copies of this document and other DfE PWB Project documents,contact:
Pollution Prevention Information Clearinghouse (PPIC)
U.S. Environmental Protection Agency (Mailcode 7407)
1200 Pennsylvania Avenue,NW
Washington, DC 20460
Phone:202-260-1023
Fax:202-260-4659
E-mail: ppic@epa.gov
website: www.epa.gov/opptintr/library/ppicdist.htm
This summary document is based on information presented in the project report, Printed
Wiring Board Cleaner Technologies Substitutes Assessmen t (CTSA): Surface Finishes,
written by University of Tennessee under a grant from EPA. Some information in the CTSA
was provided by individual technology vendors and has not been independently corrobo-
rated by EPA. The identification of specific products or processes in this document are not
intended to represent an endorsement by EPA or the U.S.Government. This summary
document has not been through a formal external peer review process.
On the cover is a
photograph of the
test board used in
this project.
.
vin v
Recycled/Recyclable
Printed with vegetable oil based inks on paper that contains at least 50% post-consumer recycled fiber.
-------
Acknowledgments
This document was prepared for the U.S. Environmental Protection Agency's Design for the
Environment (DfE) Printed Wiring Board (PWB) Surface Finishes Project by Abt Associates under
contract #68-W6-0021. This document is based primarily on the full project report, Printed Wiring
Board Surface Finishes: Cleaner Technologies Substitutes Assessment (CTSA), prepa red by the
University of Tennessee Center for Clean Products and Clean Technologies, under a grant from
the U.S. Environmental Protection Agency's Design for the Environment Program.
The CTSA would not have been possible without the assistance of the technology suppliers and
their customers, who voluntarily participated in the project. The project Core Group provided
valuable guidance and feedback throughout the preparation of the report. Core Group Members
include: Kathy Hart and Dipti Singh of U.S. EPA; Fern Abrams of IPC Association Connecting
Electronics Industries; John Sharp of Teradyne Inc.; John Lottof DuPont Electronic Materials; Jack
Geibig, Lori Kincaid,and Mary Swanson of the University of Tennessee Center for Clean Products
and Clean Technologies; Greg Pitts of Ecolibrium; Gary Roper of Substrate Technologies, Inc.;Ted
Smith of the Silicon Valley Toxics Coalition;and Christopher Rhodes and Holly Evans, formerly of
IPC.
-------
Contents
Question 1
Why should I consider an alternative surface finish?.
Question 2
Which surface finishes were evaluated in the DfE Project? 8
Question 3
How do alternative finishes compare to hot air solder leveling (HASL) overall? 14
Question 4
How may surface finishes affect worker health and safety? 15
Question 5
How may surface finishes affect people and the environment outside the facility? 21
Question 6
What kind of performance can I expect from alternative surface finishes?.
Question?
23
ill alternative surface finishes reduce my costs?
Question 8
Do alternative surface finishes use less water, metal, and energy?
Question 9
How can I make alternative surface finishes work for my facility?..
Question ID
31
34
39
Where can I find more information about pollution prevention in the PWB industry? 41
-------
Introduction
The project researched
how alternative surface
finishes compare to the
performance, cost, and
environmental and
health characteristics of
HASL
The Design for the
Environment (WE) PWB
Project is a voluntary,
non-regulatory
partnership among a
diverse group of
contributors.
The printed wiring board (PWB) is the base that connects components in electronic devices. One
of the final steps in the PWB manufacturing process is to provide a surface finish on exposed parts
of the board. This surface finish is important for two reasons: it protects the underlying copper
from corrosion,and it provides a solderable surface on which to apply the components in subse-
quent assembly steps.
To date, the industry's standard surface finish has been hot air solder leveling (HASL). This process
deposits a layer of tin-lead solder onto exposed portions of the PWB. HASL provides a highly
solderable coating, a wide process window in assembly, and a long shelf life. However, many PWB
manufacturers and assemblers are re-evaluating their choice of surface finish for boards with fine
pitch (small) surface mount components, because the HASL process typically creates a slight crest
on pads, rather than the planar surface required for assembly. An additional concern is the worker
health and environmental issues associated with lead use. With impending regulations in Europe
requiring the use of lead-free materials, market pressures are another consideration for PWB
manufacturers.
Several alternative surface finish technologies are available that can provide a planar mounting
surface and do not use lead. They range from other metals such as nickel, tin, gold, and silver to
organic-based coatings. Although many facilities use these alternative surface finishes, a compre-
hensive analysis has not been undertaken before to compare the performance, cost,and health
and environmental risks associated with them. In response to industry interest for this informa-
tion, the Design for the Environment (DfE) PWB Project undertook a comparative evaluation of
health risk and competitiveness issues for HASL and five alternative surface finishes. The project
was a voluntary,cooperative partnership among EPA and industry experts including: PWB
industry manufacturers,assemblers,and suppliers; the University of Tennessee Center for Clean
Products and Clean Technologies; a public interest group; and other stakeholders. Goals of the
project are to:
Encourage businesses to incorporate environmental concerns into their decision-making
processes, along with traditional parameters of cost and performance, when choosing
technologies and products.
Standardize existing information about surface finish technologies.
Present information about surface finish technologies not yet in widespread use, so PWB
manufacturers and designers can evaluate the environmental and health risks,along with
the cost and performance characteristics, of different technologies.
Encourage PWB manufacturers and designers to follow the example of this project and
systematically evaluate other technologies, practices, and procedures in their operations
that may affect the environment.
The project team evaluated six different surface finish technologies:
HASL
Electroless Nickel/Immersion Gold (Nickel/Gold)
Electroless Nickel/Electroless Palladium/Immersion Gold (Nickel/Palladium/Gold)
-------
Immersion Silver
Immersion Tin
Organic Solderability Preservative (OSP)
The analysis was intended to represent the use of these surface finishes under'Yeal world"
production conditions. To accomplish this,data were collected from several sources. These
included performance demonstrations at volunteer PWB facilities, chemical exposure estimates
from a survey of workplace practices, waste generation estimates from a survey of pollution
prevention practices, and cost estimates from surface finish suppliers.
Performance data were generated by applying surface finishes to standardized test boards at 13
volunteer facilities. Though this arrangement does not yield the type of results that would result
from a tightly controlled experiment, it presents a "snapshot"of each technology as they might
perform relative to each other under typical facility conditions. The PWBs produced at these
facilities then were subjected to accelerated aging, thermal shock, and mechanical shock condi-
tions. An ion chromatography failure analysis was then conducted to determine if the causes of
failure for boards that did not pass these tests were related to specific surface finishes.
The human health and ecological risk characterization was based in part on a survey of workplace
practices conducted by IPC. From this survey, the typical rate at which workers in a PWB facility
are exposed to chemicals used in surface finishes was estimated. When combined with known
information about the toxicity of chemicals, EPA was able to estimate the risks to employees
working with each surface finish. The ecological risk assessment was based on an estimate of the
concentration of chemicals in wastewater, combined with information about the toxicity of the
chemicals in the environment.
The costs of each technology were collected from the workplace practices survey, surface finish
suppliers, and industry experts. These data then were modeled to represent the costs, energy and
water usage, maintenance schedule,and labor needs that might be encountered by a facility that
has a throughput rate of 260,000 surface square feet per year (ssf/yr).
This booklet summarizes the key findings of the study. Each question in this booklet highlights a
different aspect of the research. The full report, Printed Wiring Board Cleaner Technologies
Substitutes Assessment:Surface Finishes (EPA 744-R-01 Ť003A and B), contains information that is
useful for readers who would like to learn more about each surface finish technology.
Detailed results can be
found in the full report.
The report, Printed
Wiring Board Cleaner
Technologies Substitutes
Assessment: Surface
/7n;s/)es(EPA744-R-01-
003A and B), contains
information that is useful
for readers who would
like to learn more about
eachsurfacefinish
technology. To download
the report, visit:
www.epa.gov/dfe
-------
Many alternative surface
finishes appear to
demonstrate
improvements in worker
health and safety,cost,
and reduced
environmental impacts.
Question 1
Why should I consider an alternative surface finish?
The industry's standard process for applying a surface finish to printed wiring boards (PWBs) has
been tin-lead hot air solder leveling (HASL). For some time, this process has been the most
accepted and reliable method of preserving solderability. However, many PWB manufacturers are
finding that the process has performance and environmental limitations. The solder leveling
process typically creates a crest on pads,especially with fine pitch surface mount pads, which can
lead to assembly defects. While HASL is still the preferred finish for through-hole PWBs, manufac-
turers working with surface mount technology (SMT) are looking for surface finish alternatives that
can provide a planar surface. In addition, the use of lead in the HASL process can result in work-
place health and environmental concerns. Although the benefits may not apply to all of the
alternative technologies, there are several reasons why PWB manufacturers are considering
alternative surface finishes:
Improved Chemical Safety
None of the alternative technologies are free of risk to workers. However, some of the technolo-
gies do not contain as many chemicals that pose flammability,explosiveness,and instability
concerns as HASL does.
Improved Worker Health
All technologies using an enclosed conveyorized process have a low estimated risk to workers
from inhalation. Several of the technologies have fewer chemicals that pose potential risks
through skin contact as well.
Comparable or Improved General Public and Ecological Health
None of the technologies, including the baseline HASL process, appear to present an appreciable
risk to the general population outside of PWB facilities under normal conditions (the effects of
unexpected spills and fires were not considered in this analysis). With regard to ecological risk,all
of the alternative technologies use fewer chemicals that may harm aquatic ecosystems.
Comparable Performance
In the evaluation of the comparative performance of the six surface finishes analyzed, 164 as-
sembled PWBs were subjected to accelerated aging (85°C and 85% relative humidity for three
weeks), thermal shock,and mechanical shock conditions. After each exposure, 23 electrical test
6
-------
measurements were recorded for each board. Although some anomalies were identified, these
were rarely related to the surface finish applied. A failure analysis using ion chromatography
indicated that all five alternative (non-HASL) finishes performed as well as, if not better than, the
HASL finish following accelerated aging conditions.
Lower Material Costs
For all but two of the alternative technologies (those involving the precious metals gold and
palladium), the chemical inputsare less expensive than those for HASL. In particular, the lower cost
is often driven by the thinner surface layer that is required. Lower material demands also may
have benefits for society by reducing the impacts associated with the raw material (e.g., metal
mining).
Less Water Consumption
The high-pressure rinse used in the HASL process consumes up to 2.5 times more water than a
normal rinse. For the alternative technologies that require relatively few rinse steps (Immersion
Silver and OSP), water consumption is considerably lower. A decrease in water consumption
benefits individual companies by reducing costs associated with obtaining water and processing it
as wastewater. Reduced water demand also benefits the general public and the environment by
preserving a valuable natural resource.
-------
Most technologies can be
operated in either a
horizontal, conveyorized
or vertical, non-
conveyorized
configuration.
Question 2
Which surface finishes were evaluated in the DfE Project?
All the alternative surface finish technologies were wet chemistry processes involving a series of
chemical process baths and water rinse steps. The processes were operated either in a horizontal,
conveyorized process or vertical, non-conveyorized process. Table 2.1 indicates the operation
mode for each technology.
Table 2.1 Surface Finishes Included in the Analysis
Process
HASL
Electroless Nickel/ Immersion Gold
Electroless Nickel/ Electroless Palladium/
Immersion Gold
Immersion Silver
Immersion Tin
OSP
Conveyorized
J
S
S
J
Non-Conveyorized
V
V
V
V
V
HASL is the project's
baseline technology.
All surface finish suppliers were invited to submit a product as long as they provided all of the data
required for the analysis. Because the DfE project is voluntary and the products were not chosen
systematically, the results may not be representative of all variants of a technology. Typical steps
required for each technology are described below.
Hot Air Solder Leveling (HASL)
Cleaner
>
Miocroetch
>
Water
Rinse X 2
>,
'
Dry
^
Flux
Solder
>
Air Knife
>
High-
Pressure
Rinse
-*>
Water
Rinse
8
Tin-lead HASL has been the standard surface finishing method used in the manufacture of double-
sided and multi-layer boards due to its excellent solderability during assembly. It was considered
the baseline for the DfE analysis. During the HASL process, soldermask-coated boards a re first
-------
cleaned and etched to prepare the contact surfaces for the solder. Following the application of
flux to a board, a layer of solder is applied to the copper surfaces by submersing the panel in
molten solder. The excess solder is then blown from the board by an air knife, leaving a thin,
protective layer of solder on the exposed circuitry.
The process can be operated either in a horizontal, conveyorized mode or as a vertical, non-
conveyorized system. Flux selection is critical to the sound operation of the HASL process. The
flux is responsible for creating the surface conditions required to achieve a high quality solder
deposit on the PWB. Fluxes are available in a variety of formulations with differing characteristics
such as viscosity, foam level, acidity, volatile content, and type of activator. The type of HASL flux
ultimately selected will depend on the type of chemicals and processes used in previous manufac-
turing stages, type of solder mask, and the solder deposit characteristics required.
HASL finishes are compatible with surface mount technology (SMT) and typical through-hole
components; however, the lack of planarity,or flatness, of the finish makes assembly with fine pitch
surface mount components difficult to control. Extended shelf life is not a concern with HASL
finished boards, because of the durability of the finish.
Electroless Nickel/Immersion Gold
Cleaner
>
Water
Rinse
>
Miocroetch
-*>
Water
Rinse
^
Catalyst
$
Water
Rinse
>
Acid Dip
>
Water
Rinse
-+
Electroless
Nickel
^
Water
Rinse X 2
t
Immersion
Gold
>
Water
Rinse X 2
The Electroless Nickel/
Immersion Gold finish
consists of a relatively
thick layer of nickel
followed by a thin
protective layer of gold.
The Nickel/Gold process is applied through the deposition of an initial layer of nickel followed by a
thin, protective layer of gold onto the exposed copper surfaces of the PWB. Nickel characteristics
such as hardness, wear resistance, solderability, and uniformity of the deposit makethisa desirable
-------
surface finish. The thin layer of immersion gold preserves the solderability of the finish by prevent-
ing oxidation of the highly active nickel surface. Nickel/Gold finishes typically can withstand ermal
excursions (heating cycles) without losing solderability.
The process is operated in a vertical, non-conveyorized mode. An Electroless Nickel/Immersion
Gold finish is compatible with SMT,flip chip,and ball grid array (BGA) technologies,as well as
typical through-hole components. The finish is also aluminum wire-bondable. The high plating
temperatures and low pH of the Nickel/Gold plating process can be incompatible with
soldermasks with high acrylic content; however, soldermasks high in epoxy content are not
affected by the plating solutions. Nickel/Gold plated boards have a shelf life of two years or more.
Electroless Nickel/Electroless Palladium/Immersion Gold
The Electroless Nickel/
Electroless Palladium/
Immersion Gold finish is
similar to the Nickel/Gold
finish but has a
palladium layer between
to provide hardness.
Cleaner
>
Water
Rinse X 2
>
Miocroetch
-+
Water
Rinse X 2
^
Catalyst
f
Water
Rinse X 2
>
Acid Dip
>
Water
Rinse X 2
-ť
Electroless
Nickel
*
Water
Rinse X 2
*
Preinitiator
>
Electroless
Palladium
>
Water
Rinse X 2
Immersion
Gold
^
Water
Rinse X 2
The Electroless Nickel/Electroless Palladium/Immersion Gold process is similar to the Nickel/Gold
process, except that it uses a palladium metal layer that is deposited after the nickel layer, and prior
to the final gold layer. The palladium layer is much harder than gold, providing added strength to
the surface finish for wirebonding and connector attachment, while protecting the underlying
nickel from oxidation.
The process can be operated in either a horizontal, conveyorized or a vertical, non-conveyorized
mode. (Only the vertical process was evaluated in the DfE study.) Like a Nickel/Gold finish, a
Nickel/Palladium/Gold finish is compatible with SMT,flipchip,and BGA technologies,as well as
with typical through-hole components. The finish is also both gold and aluminum wire-bondable.
The Nickel/Palladium/Gold plated boards have a shelf life of two years or more.
10
-------
Immersion Silver
Cleaner
>
Water
Rinse
>
Miocroetch
>,
'
Water
Rinse
^
Predip
Immersion
Silver
>
Water
Rinse
>
Dry
The Immersion Silver finish is produced by the selective displacement of copper atoms with silver
atoms on the exposed metal surface of the PWB. To minimize silver tarnishing, an organic inhibitor
is co-deposited to form a hydrophobic layer on top of the silver. The typical thickness of an
Immersion Silver finish depends on the chemistry. It can range from 3 to 10 microinches (0.08 to
0.25 microns) thick. There are two chemistries in production; one is operated exclusively as a
horizontal, conveyorized process,and the other can be operated either horizontally or vertically.
(The DfE study only evaluated the horizontal configuration.) Immersion Silver finishes are compat-
ible with SMT,flipchip,and BGAtechnologies,as well as typical through-hole components. Silver
finishes appear to be compatible with all types of solder masks, can withstand five thermal excur-
sions during assembly, and are anticipated to have a shelf life of at least six months.
-------
The Immersion Tin finish
displaces surface copper
with a thin layer of tin.
Immersion Tin
Cleaner
>
Water
Rinse X 2
>
Miocroetch
>.
Water
Rinse X 2
^
Catalyst
Water
Rinse
Immersion
Tin
Water
Rinse X 2
Dry
The Immersion Tin process utilizes a displacement reaction between the board's copper surface
and stannous ions in solution to reduce a layer of tin onto the copper surfaces of the PWB. The
process may be installed as a conveyorized system or in a vertical, non-conveyorized mode.
Immersion Tin surfaces are compatible with SMT,flip chip, BGA technologies,and typical through-
hole components, but it is not a wire-bondable finish.
There are a number of different Immersion Tin systems available, including those based on
methane sulfonic acid, sulfate, chloride, and fluoborate chemistries. Tin surfaces are compatible
with all solder masks, have a shelf life of at least one year, and can typically withstand a minimum
of five thermal excursions during assembly.
Organic Solderability Preservative (OSP)
The OSP finish is an
organic (non-metal) film
that bonds to exposed
copper.
Cleaner
>
Water
Rinse
>
Miocroetch
"w
Water
Rinse
^
Air Knife
OSP
Air Knife
Water
Rinse
Dry
12
-------
The OSP finish is an anti-oxidant film applied to exposed copper surfaces that reacts with copper
to form an organometallic layer. This coating is nearly invisible,and may be applied either as a
thick benzimidazole (4 to 20 microinches / 0.1 to 0.5 microns) or thin imidazole [mono-molecular
(30 to 100 angstroms)] layer. The thicker OSP coatings were considered in the DfE analysis. The
OSP process typically is operated in a horizontal, conveyorized mode but can be modified to run
in a vertical, non-conveyorized mode. OSP processes are compatible with SMT,flip chip, and BGA
technologies, and with typical through-hole components, but the OSP finish cannot be
wirebonded. OSP surfaces are compatible with all soldermasks and have a shelf life of up to one
year.
13
-------
Question 3
How do alternative finishes compare to hot air
solder leveling (HASL) overall?
HASL and the five alternative technologies were evaluated in several categories. Table 3.1 shows a
summary of how each performed relative to the baseline technology with respect to worker risk,
environmental risk, performance, cost,and resource use. More detailed information on each of
these evaluation criteria can be found in subsequent sections of this document.
Table 3.1 Summary of Surface Finish Technologies
Technology
(see
question 2)
HASL (NC)
BASELINE
HASL (C)
Ni/Au (NC)
Ni/Pd/Au (NC)
Imm. Silver (C)
Imm. Tin (C)
Imm. Tin (NC)
OSP (C)
OSP (NC)
Worker Risk
(see question 4)
^ "ID
if 8
§1
to o
Ť 0
.ES.
1
/
X
X
y
/
y
y
=
"ST
(fl '?:
if o
eg o
i°
aŁ
2
=
X
X
/
/
/
X
X
Environmental
Risk (see
question 5)
(0 A
So|
El3 8
6^
;: ,- **
O +3 U>
* scc
4
/
/
/
/
/
/
/
*
Performance
(see
question 6)
_(/>
1 3
o |> 2
"t^ o
woe <
=
=
=
=
=
=
=
=
=
Cost
(see
question 7)
(i
Sf
8
°-
S
^
$94,200
=
X
X
/
/
y
y
y
Resource Use
(see question 8)
t
J5 "S
§S
322,000
/
X
X
/
/
X
y
y
t
0) 8
uj o
3 o"
Q) D
c Si
11J&
56,700,000
/
X
X
X
X
X
-------
Question 4
How may surface finishes affect worker health and
safety?
Chemicals in surface finishes can affect workers in PWB manufacturing facilities either when
handled or when chemical vapors are inhaled. The DfE risk screening compared the potential risks
to workers from using the five alternative surface finishes to those from using HASL The following
types of effects were considered in the analysis:
Chronic (non-cancer) health risks from inhalation exposure
Chronic health risks from dermal (skin) exposure
Cancer risks
Chemical safety concerns
The risk screening was based on the exposures expected in a model facility. The characteristics of
this model facility were developed from several sources including PWB facilities, supplier data, and
input from PWB manufacturers at project meetings. The model was not entirely representative of
any one facility,and actual risk at a facility could vary substantially, depending on site-specific
operating conditions and other factors.
Several assumptions are associated with this approach. These include assumptions that workers do
not wear gloves, that all non-conveyorized lines are operated by manual hoist,and that the air
concentration of chemicals is constant over time. These assumptions are applied consistently for all
surface finishes evaluated. Significant uncertainties are associated with all risk assessments. In this
analysis, uncertainties arise from the lackof toxicological data for some chemicals, the potential
inaccuracy of the release and exposure models, and the lackof information about potential acute
effects resulting from exposure to chemicals at peak concentration levels.
Inhalation Risks
During the surface finishing process,chemicals can be released to the air either by evaporation of
the volatile chemicals or by the formation of aerosols as tank contents are stirred. The DfE study
assumed inhalation exposure only for non-conveyorized presses. Workers on conveyorized process
lines were expected to have a negligible rate of exposure by inhalation because the lines are
typically enclosed and vented to the outside.
Workers using non-conveyorized systems can inhale chemicals that pose
potential risks.
The Nickel/Gold and Nickel/Palladium/Gold processes had the highest number of
chemicals of concern.
The risk screening and
characterization in the
CTSA comprised a five-
step process:
The source release
assessment
identifies possible
sources of
environmental
releases from surface
finishing and, in some
cases, discusses the
nature and quantity
of those releases.
The exposure
assessment
quantitatively
estimates
occupational and
general population
exposures to surface
finishing chemicals.
The hazard data
assessment presents
human health hazard
and aquatic toxicity
data for surface
finishing chemicals.
The risk
characterization
combines the
previous two steps to
measure the
situation-specific risk
of the surface
finishing chemicals.
The process safety
assessment
summarizes chemical
safety hazardsfrom
material safety data
sheets (MSDSs) for
surface finishing
chemical products
and discusses process
safety issues.
15
-------
A chemical is of concern
when it is present at a
concentration that
toxicological research
indicates may cause
adverse effects in humans
or aquatic organisms.
Ofthefivenon-conveyorized processes,only Immersion Tin contained no chemicals that
presented a concern from inhalation.
Most chemicals of concern are used either in cleaning or finish deposition steps.
Table 4.1 Chemicals of Concern for Inhalation Risk3
Chemical
Alkyldiol b
Ethylene glycol
Hydrochloric
acid
Hydrogen
peroxide
Nickel sulfate
Phosphoric
acid
Propionic acid
Process Step
b
Cleaner,
microetch
Acid dip,
catalyst, cleaner
Microetch
Electroless
nickel
Cleaner
Electroless
palladium
HASL
y
Nickel/Gold
y
/
/
y
y
Nickel/
Palladium/Gold
y
/
/
y
y
y
OSP
y
a Immersion tin and immersion silver did not contain any chemicals that presented a concern from inhalation
exposure.
b Actual name is Confidential Business Information; the process step is withheld to protect the chemical's
identity.
For lead, the relationship
between exposure level
and health effects is
complex. As a result, the
health risks of lead were
assessed separately using
several data sources,
including facility-level
monitoring data, and
modeling results of the
relationship between
exposure rates and the
concentration of lead in
blood.
Dermal Risks
Dipping boards, adding bath replacement chemicals, or testing bath chemistry can expose workers to
chemicals though the skin. Risks were calculated for both line operators and laboratory technicians.
Although industry survey results indicate that most line operators wear gloves, this analysis measured
the risk to workers who do not wear gloves to account for the fraction that do not. It is important to
note that dermal risk is usually negligible when workers wear proper gloves and other protective
equipment.
Most technologies pose a potential risk from dermal exposure when gloves
are not worn.
All technologies except Immersion Silver and conveyorized ImmersionTin presented a potential
derma I risk to workers who do not wear gloves.
Both line operators and laboratory technicians may be exposed to chemicals of concern.
16
-------
The potential dermal risks for conveyorized processes were lower than those for non-
conveyorized processes. (Conveyorized processes were expected to result in dermal exposure
only for maintenance tasks; non-conveyorized processes result in dermal exposure for both
routine operation and maintenance.)
For laboratory technicians, fewer chemicals were of concern for most technologies because
laboratory technicians are expected to have lower exposure rates.
Most chemicals of concern are used in cleaning or microetch steps.
The risks associated with lead in HASLare uncertain. Monitoring data indicated that the level
of lead in workers' blood was one-sixth to one-half of the lowest federal target/action levels.
However, model results indicated that lead levels potentially could be considerably above
target/action levels if workers do not wash their hands after handling lead.
Table 4.2 Chemicals of Concern for Dermal Risk3
Chemical
Ammonia compound Ab
Ammonium chloride
Ammonium hydroxide
Copper ion
Copper salt Cb
Copper sulfate
pentahydrate
Hydrogen peroxide
Inorganic metallic salt Bb
Lead
Nickel sulfate
Urea compound C
Process
Step
b
Immersion
gold
Immersion
gold
OSP
b
Microetch
Microetch
b
Solder
Electroless
nickel
b
HASL
NC
yv
X
c
/v
X
Nickel/
Gold
NC
/
y
yv
/
yv
yv
Nickel/
Palladium/Gold
NC
/
^
yv
/
yy
ss
Immersion
Tin
NC
/
OSP
C
/V
JJ
NC
//
J
yv
a Immersion Silver and conveyorized Immersion Tin did not contain any chemicals that presented a concern from
dermal exposure.
b Actual name is Confidential Business Information; the process step is withheld to protect the chemical's identity.
/ Line operator risk results above concern levels
JJ Line operator and laboratory technician risk results above concern levels
X Risk indicators were not calculated for lead as with the other chemicals. Other information, however, indicates that
incidental ingestion of lead from contact with hands could result in lead exposure at levels of concern.
NC: Non-conveyorized (vertical) process configuration.
C: Conveyorized (horizontal) process configuration.
17
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Cancer Risks
A surface finish technology poses a potential cancer risk if chemicals in theformulations are carcino-
genic (cancer-causing). However, the carcinogenic properties are not known for all chemicals.
Therefore, chemicals are classified into carcinogen categories based on the strength of evidence that
a chemical does cause cancer,as follows:
The classification of ftumancaranogen indicates that there is sufficient evidence that a chemical
causes cancer in humans.
A probable human carcinogen has some evidence that it causes cancer in humans, but not
sufficient evidence to classify it as a human carcinogen.
A possible human carcinogen has sufficient evidence that the substance causes cancer in
animals butinadequateora lackof evidence in humans.
Other possible classifications are that the chemical is not classifiable as to its carcinogenicity to
humans, or that the chemical is probably not carcinogenic to humans.
The cancer risks of the surface finishes are either low or not quantifiable.
For known carcinogenic chemicals, it is assumed that any level of exposure can put a person at risk
for cancer. The probability of developing cancer from that chemical can be determined from the
use of slope factors. These quantitative measures were only available for the one carcinogenic
chemical used in the study: inorganic metallic salt A in the Nickel/Gold process. For workers,
this chemical has a maximum individual cancer risk over a lifetime of one iin five million at the
typical concentrations in a PWB facility. Because this risk is less than one in a million, the cancer
risk is considered to be of low concern.
Other chemicals may be carcinogenic:
Lead is a possible human carcinogen used in the HASL process.
Thiourea is a possible human carcinogen used in the Immersion Tin process.
Urea compound B is a possible human carcinogen used in the Nickel/Gold and Nickel/
Palladium Gold processes.
Strong sulfuric acid mist is known to be a human carcinogen. Sulfuric acid is used in all of
the evaluated surface finishes, but in a diluted form; it is not expected to be released to
the air as a strong acid mist.
The cancer risks associated with these chemicals could not be determined because the slope
factors of the chemicals have not been developed.
18
-------
Summary of Worker Health Risks
Several of the alternative surface finishes evaluated may offer an improvement in potential worker
health risks over non-conveyorized HASL Each conveyorized process (Immersion Silver, Immer-
sion Tin, OSP, and HASL),as well as non-conveyorized Immersion Tin, was operated without
exposing workers to chemicals of concern through inhalation. Furthermore, Immersion Silver,
Immersion Tin, and OSP had fewer chemicals of concern for dermal exposure. However, the results
highlight the importance of good workplace ventilation and of wearing gloves; all of the technolo-
gies except Immersion Silver and conveyorized Immersion Tin contain at least some chemicals
that are of concern when workers regularly handle them with bare hands.
Several uncertainties remain about the relative risks of these technologies. The cancer risks of
three possible carcinogens lead, thiourea, and urea compound B are not known. With regard
to chronic health effects, several chemicals have only limited or no toxicological information. The
uncertainty associated with lead levels in the blood of workers indicates that despite the consid-
erable attention given to reducing lead in the workplace, little is known about the quantitative
risks that workers operating the HASL process face.
Chemical Safety
All of the surface finish technologies in this study use formulations that
may harm workers when mishandled.
In addition to chronic health and carcinogenic risks, surface finish formulations may pose an
immediate safety hazard to workers. For each technology, the chemicals were evaluated to
determine if any were flammable, explosive, a fire hazard, corrosive, an oxidizer, capable of a
sudden release of pressure upon opening, unstable, combustible, or reactive.
Table 4.3 presents the safety hazards associated with each system as indicated by the Material
Safety Data Sheets (MSDSs). A check mark indicates that at least one chemical used for that
technology presents a particular type of hazard. There is a range in the types and number of
hazards associated with the different technologies. Immersion Tin presented concern only for
explosiveness and corrosiveness, but HASL presented a concern for seven of the nine listed hazard
categories. For each of the technologies, it is important to follow the handling instructions
provided by the supplier.
19
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Table 4.3 Chemical Safety Information
Hazard
Flammable
Explosive
Fire Hazard
Corrosive
Oxidizer
Sudden
Release of
Pressure
Unstable
Combustible
Reactive
HASL
y
J
S
/
S
/
s
Nickel/
Gold
J
S
J
Nickel/
Palladium/Gold
J
S
/
Immersion
Silver
^
^
y
S
S
Immersion
Tin
y
-------
Question 5
How may surface finishes affect people and the
environment outside the facility?
The PWB surface finish application process produces air and water wastes that could impact a
facility's surroundings. Air emissions result from vapors that are generated from chemicals used in
manufacturing, such as baths and drying ovens. Water releases occur when rinse water is sent to the
sewer system or into the environment, after meeting treatment requirements.
There are two areas of potential concern for these releases. The general public may be at risk to the
vapors emitted to the air that are carcinogenic or cause other long-term health problems. Aquatic
organisms may be adversely affected if their water bodies are contaminated with toxic chemicals.
The riskcharacterization for the surface finish technologies modeled the potential risks to these two
groups.
Public Health Risks
Risks to nearby residents are minimal for all technologies.
Public health risk was estimated for inhalation exposure from each type of surface finish for people
living near a facility (defined as within 100 meters of a facility). For both cancer and non-cancer
effects, the impacts on public health are expected to be small. One chemical, inorganic metallic salt
A in the Nickel/Gold process, is a known human carcinogen. However, the estimated lifetime risk of
getting cancer from this chemical at the expected exposure rate for a resident is 2x10"" (one in 50
billion). The cancer risks associated with those chemicals classified as"probable"or"possible"
carcinogens, including lead, thiourea, and strong sulfuric acid mists, were not known.
Non-cancer inhalation effects were expected to be low as well. Based on available information, it
appears that the chemicals used in the surface finishes would be found in the air outside the facility
in concentrations too low to cause significant concern for health effects. It should be noted that
toxicity information was inadequate or absent for some chemicals, and that the public potentially
could beat riskfrom surface finish processes through other pathways, including solid waste releases
orcontaminated drinking water.
Ecological Risks
Wastewater from most surface finish processes is capable of harming aquatic organisms.The
discharge of wastewater from industrial facilities is regulated under thefederal Clean Water Act,
which limits the concentrations of the chemicals that may be discharged. Facilities discharging to
the local sewer or to surface water must meet the permitting regulations of their federal, state, or
local authority. State and local permits may require even stricter limits than are required by the
federal government.
The public may be
exposed to the vapors of
PWB chemicals, which
are released through
vents or escape through
doors and windows.
An ecological indicator
value greater than one
indicates that the
chemical is present in
wastewater at a
concentration that may
harm aquatic organisms.
21
-------
Most metals used are
regulated and must not
exceed regulated levels
upon release. Although
metals are present in
wastestreamsin
concentrations above
levels of concern for
somesurfacefinishes,
most are removed before
discharge, in accordance
with regulations.
Ecological risks were estimated by calculating the concentration of each chemical in surface finish
process wastewater, then dividing that by the concentration of concern (CC) - the concentration at
which a chemical is expected to present risks to organisms in aquatic ecosystems. This ratio is called
an aquatic risk indicator. A value greater than one indicates that the chemical is present in wastewater
at a concentration that may harm aquatic organisms. The calculations assumed that the wastewater is
treated by a publicly owned treatment works (POTW), which reduces the concentration of many
chemicals by approximately 90%.
As indicated inTable 5.1,each technology except Nickel/Gold and Nickel/Palladium/Gold had chemi-
cals with an aquatic risk indicator greater than one. Therefore, if the wastewater from the other
technologies were released to a body of water after being processed at a treatment facility, it could
adversely affect organisms in the water. HASL contained the most chemicals with an indicator greater
than one. There were four chemicals in the HASL non-conveyorized process and five in the convey-
orized process. The most significant chemical, however, is alkylaryl imidazole used in OSP. The
concentration of this chemical can be 3.6 to 33 times greater than the threshold at which effects
appear. This indicates that facilities should make sure the alkylaryl imidazole in the wastewater from
the OSP process is treated prior to disposal.
Table 5.1 Aquatic Risks of Surface Finish Chemicals
Process
Number of
Non-Metal
Chemicals
with Indicator
Chemical with
Largest Aquatic
Risk Indicator
Aquatic Risk
Indicator
HASL
3-4
Potassium
peroxy-
monosulfate
8.2 (NC)
6.1 (C)
Nickel/
Gold
0
None > 1
Nickel/
Palladium/
Gold
0
None > 1
Immersion
Silver
1
Hydrogen
peroxide
1.3
Immersion
Tin
0-1
Potassium
peroxy-
monosulfate
3.6 (NC)
OSP
1
Alkylaryl
imidazole
6.6-33 (NC)
3.6-1 8 (C)
a This table only contains non-metal pollutants. It is assumed that metals are removed from wastewater at the
facility during pretreatment in order to comply with discharge permit requirements.
NC: Non-conveyorized (vertical) process configuration.
C: Conveyorized (horizontal) process configuration.
22
-------
Question 6
What kind of performance can I expect from alternative
surface finishes?
Surface finishes were applied to test boards at volunteer facilities.
The performance of the surface finishes was evaluated by processing standardized test panels at 13
volunteer PWB facilities, where the finishes were already in use. Each volunteer facility ran the
boards through their surface finish line during their normal production operation. The information
collected through the demonstrations was intended to provide a "snapshof'of the way the technol-
ogy was performing at a particular facility at that particular time.
Each supplier was asked to submit the names of up to two facilities at which they would like the
demonstrations of their technology to be conducted. This selection process encouraged the
suppliers to nominate thefacilities where their technology was performing at its best. This,in turn,
provided for more consistent comparisons across technologies.
After each PWB facility completed the surface finish application, the boards were assembled using
either a halide-free low-residue flux or a halide-containing water soluble flux. The electrical perfor-
mance of the assembled boards (164 boards in total) then was tested before and after exposure to
accelerated aging, thermal shock, and mechanical shockconditions.
The test board was designed to represent a variety of circuits.
The test board used was based on a design for the Circuit Card Assembly and MaterialsTask Force
(CCAMTF),a joint industry and military initiative. The test board is 1994 technology and does not
incorporate today's state-of-the-art circuitry,as it would not be possible to have a test vehicle keep
pace with today's rapid changes in circuit technology. The test printed wiring assembly (PWA) was
divided into six sections, each containing one of the following types of electronic circuits:
High current low voltage (HCLV)
High voltage low current (HVLC)
High speed digital (HSD)
High frequency (HF)
Other networks (ON)
Strandedwire(SW)
This study was intended
to provide a "snapshot" of
the performance of
differentsurfacefinishes.
It was not a substitute for
thorough facility-specific
testing to determine
what works best for your
operation.
The functional test
boards included a variety
of extreme circuits to
maximize the
applicability of the test
results.
23
-------
The components in the HCLV,HVLC,HSD,andHF circuits represented both plated through-hole (PTH)
components, which were wave soldered,and surface mount technology (SMT) components, which
were soldered through a reflow oven. The other networks were used for current leakage measure-
ments: 10-mil pads, a socket for a PGA, and a gull wing. The two stranded wires were hand soldered.
The test board provides 23 separate electrical responses as shown in Table 6.1.
Table6.1 Electrical Responses for the Test PWA and Acceptance Criteria
Response
Circuitry
Acceptance Criteria
High Current Low Voltage
1
2
HCLV PTH
HCLV SMT
A Voltage from Pre-test < 0.50V
A Voltage from Pre-test < 0.50V
High Voltage Low Current
3
4
HVLC PTH
HVLC SMT
4|iA < X < 6|iA
4|iA < X < 6|iA
High Speed Digital
5
6
HSD PTH Propagation Delay
HSD SMT Propagation Delay
< 20% increase from Pre-test
< 20% increase from Pre-test
High Frequency Low Pass Filter
7
8
9
10
11
12
HF PTH 50 MHz
HF PTH f(-3dB)
HF PTH f(-40dB)
HF SMT 50 MHz
HF SMT f(-3dB)
HF SMT f(-40dB)
+5dB of Pre-test
+50MHz of Pre-test
+50MHz of Pre-test
+5dB of Pre-test
+50MHz of Pre-test
+50MHz of Pre-test
High Frequency Transmission Line Coupler
13
14
15
16
17
HF TLC 50MHz Forward Response
HF TLC 500MHz Forward Response
HF TLC 1GHz Forward Response
HF TLC Reverse Null Frequency
HF TLC Reverse Null Response
+5dB of Pre-test
+5dB of Pre-test
+5dB of Pre-test
+50MHz of Pre-test
< 10dB increase over Pre-test
Other Networks Leakage
18
19
20
21
10 mil Pads
PGA A
PGAB
Gull Wing
Resistance > 7.7 Iog10 ohms
Resistance > 7.7 logio ohms
Resistance > 7.7 Iog10 ohms
Resistance > 7.7 logio ohms
Stranded Wire
22
23
Stranded Wire 1
Stranded Wire 2
A Voltage from Pre-test < 0.356V
A Voltage from Pre-test < 0.356V
24
-------
Boards were exposed to stress conditions.
Each of the 164 PWAs was exposed to the following environmental, thermal,and mechanical shock
test sequence:
1. Exposure to three weeks of 85°C and 85% relative humidity
2. 200 cycles of thermal shock with the PWAs rotated between chambers at -50°C and 125°C,
with 30 minute dwells at each temperature
3. Mechanical shock, where the PWA was mounted in a rectangular fixture and dropped 25
times on a concrete surface from a height of 1 meter
Over 15,000 test measurements were recorded.
The PWAs were functionally tested at four test times: Pre-test, Post 85/85, Post Thermal Shock,and
Post Mechanical Shock. At each of the four test times, 164x23 = 3772 electrical test measurements
were recorded. An overall summary of success rates is shown for each major circuit group in Table
6.2. (These values are based on 3,608 measurements at each test time. Because the 164 HF TLC RNF
measurements gave a constant response of 50 MHz throughout, there was no variability to analyze.)
Table 6.2 Overall Success Rates,byCircuitTypeandTestTime
Circuitry
HCLV
HVLC
HSD
HFLPF
HFTLC
Other Networks
Stranded Wire
Total % Success Rate
Total anomalies per test time
85/85
100.0%
99.7%
99.7%
98.7%
99.8%
99.8%
100.0%
99.5%
17
Thermal Shock
100.0%
99.7%
98.8%
89.4%
99.5%
100.0%
99.7%
96.9%
113
Mechanical Shock
48.2%(7.1%SMT)
50.0% (0.0% SMT)
99.1% (99.3% SMT)
82.6% (74.8% SMT)
99.4%
100.0%
98.5%
85.4%
527
It should be noted that
the acceptance criteria
are not absolutes, but
rather guidelines. This
distinction is notable
when values fall just
outside the acceptance
criterion and may be
considered "not of
practical significance."
25
-------
Table 6.3 summarizes how problem areas developed during exposure to the three test conditions.
Table 6.3 Frequency of Anomalies by Individual Circuit overTestTimes
Circuitry
Post
85/85
Post
TS
Post
MS
Comments
HCLV
1
2
HCLV PTH
HCLVSMT
0
0
0
0
12
158
Some need further Failure Analysis
SMT components came off board during MS
HVLC
3
4
HVLC PTH
HVLC SMT
0
1
0
1
0
164
Excellent performance throughout
SMT components came off board during MS
HSD
5
6
HSD PTH
HSD SMT
0
1
2
2
2
1
Component problem
Component problem
HFLPF
7
8
9
10
11
12
HF PTH 50 MHz
HF PTH f(-3dB)
HF PTH f(-40dB)
HF SMT 50 MHz
HFSMTf(-SdB)
HFSMTf(-40dB)
4
4
4
0
0
1
15
15
13
18
16
27
15
18
14
30
29
65
Failure Analysis of open PTH needed
Failure Analysis of open PTH needed
Failure Analysis of open PTH needed
Failure Analysis of open PTH needed
Failure Analysis of open PTH needed
Failure Analysis of open PTH needed
HFTLC
13
14
15
16
17
HF TLC 50MHz
HFTLC 500MHz
HFTLCIGHz
HFTLCRNF
HFTLCRNR
0
0
0
0
1
0
0
1
0
2
7
1
1
0
5
Minor anomalies
Minor anomalies
Minor anomalies
Constant response of 50MHz throughout
Minor anomalies
Leakage
18
19
20
21
10-MilPads
PGA A
PGAB
Gull Wing
0
0
0
1
0
0
0
0
0
0
0
0
Excellent performance throughout
Excellent performance throughout
Excellent performance throughout
Excellent performance throughout
Stranded Wire
22
23
SW1
SW2
0
0
0
1
1
4
Excellent performance throughout
Minor anomalies
26
-------
Statistical analyses of results were conducted.
General linear models (GLMs) were used to analyze the test data for each of the 23 electrical circuits
in Table 6.1 at each test time. The GLM analyses are extremely useful in identifying which experi-
mental factors or combinations of factors explain a statistically significant portion of the observed
variation in the test results and in quantifying their contribution. Another statistical approach, with an
analysis of variance (ANOVA), was used to determine which groups of site/flux meanswere signifi-
cantly different from one another for a given electrical response from the test PWA.
In the CTSA document,
boxplots are used for
convenient displays of
multiple comparison
results.
Overall, the alternative surface finishes performed as well as, if not
better than, HASL.
The analysis of the tested boards showed no failures that could be definatively related to any
particular surface finish. There were failures, however, which are described below for each type of
circuitry.
HVLC PTH, HSD, HF TLC, Leakage Circuits, and Stranded Wire
For most circuits, results of the GLM analyses showed no practical significance relative to the accep-
tance criteria, which indicates that surface finish, flux, and site did not influence the test measure-
ments. Thesecircuits include High voltage lowcurrent (HVLC) plated through holes (PTH);High
speed digital (HSD); High frequency (HF) transmission line coupler (TLC); Leakage circuits (10-mil
Pads, PGA-A, PGA-B, Gull Wing); and Stranded Wire.
While no surface finish-related effects were seen, there were some anomalies, as summarized in
Table 6.3. The sources of three types of anomalies of note are explained below; none of these are
surface finish-specific.
Some anomalies were seen at various test times for the HSD circuits. However, the testing
technician indicated that these anomalies occurred because the HSD device itself failed (and
that they were unrelated to the surface finish).
In the HF TLC and Stranded Wire circuits, there were several minor anomalies. They were
very close to the acceptance criteria guidelines and are not considered of practical concern.
The leakage circuits showed excellent performance across tests and across surface finishes.
However, for all leakage circuits, the GLM analyses showed an effect due to flux. These
differences from the base case essentially disappeared after exposure to the 85/85 test
environment. This result was not unusual and may be due to a cleansing effect from the 85/85
test environment that removes residues resulting from board fabrication,assembly,and handling.
This phenomenon was observed for all leakage circuits.
27
-------
HCLV SMT and HVLC SMT
Over 300 anomalies were introduced on HCLV SMT and HVLC SMT circuits during mechanical shock
testing. These anomalies were attributed to separation of SMT components due to the severity of the
mechanical shock testing (i.e., 25 drops on concrete from a height of 1 meter). This affected every
board, and failures were equally distributed across all surface finishes, including the HASL baseline.
When assessing the HCLV SMT and HVLC SMT results, product and process designers should consider
the severity of the mechanical shocktest.
HFLPF
The GLM analyses indicated that surface finish, flux, and site did not influence the HF LPF measure-
ments at any of the test times. However, the test measurements contained many extreme outlying
observations at post thermal shockand post mechanical shock, which greatly increases the sample
variance and in turn hinders the interpretation of the GLM results. The HF LPF anomalies are summa-
rized by surface finish inTable6.4foreachofthesixHF LPF circuits.
Table 6.4 Observed Number of HFLPF Anomalies (Compared to the Expected Number)
Process
No. of
PWAs
HASL
32
Ni/Au
28
Ni/PD/Au
12
Imm
Silver
20
Imm Tin
36
OSP
36
TOTALS
164
HF LPF PTH
50MHz
f(-3dB)
f(-40dB)
1 (2.9)
2(4.1)
1 (2.9)
2 (2.6)
3 (3.6)
2 (2.6)
0(1.1)
0(1.5)
0(1.1)
6(1.8)
6 (2.6)
7(1.8)
4 (3.3)
5 (4.6)
3 (3.3)
2 (3.3)
2 (4.6)
1 (3.3)
15
18
14
HF LPF SMT
50MHz
f(-3dB)
f(-40dB)
6 (5.9)
7 (5.9)
15
(13.1)
0(5.1)
0(5.1)
1 (11.4)
0 (2.2)
0 (2.2)
1 (4.9)
7 (3.7)
6 (3.7)
1 1 (8.2)
11 (6.6)
11 (6.6)
17(14.7)
6 (6.6)
5 (6.6)
20(14.7)
30
29
65
The test technician indicated that most of the HF LPF anomalies were due to an open PTH, which
affects both PTH and SMT. Although an open PTH is a fabrication issue, there does appear to be a
relationship with surface finish. Under the assumption that the anomalies occur independently of
surface finish, the expected number ofanomalies can be calculated for each cell. Achi-square
statistic was calculated on the differences of the observed and expected number in each cell.
28
-------
While there were no significant differences in the number of anomalies among the surface finishes
for the HF LPF PTH 50 MHz and HF LPF PTH f(-3dB) circuits, such was not the case for the other HF LPF
circuits. For these circuits, the statistical analysis indicated that the anomalies were not independent
of surface finish. The expected values for anomalies appear in parenthesis in each cell in Table 6.4.
These comparisons showed:
HASL anomalies were close to the expected values throughout.
Nickel/Gold and Nickel/Palladium/Gold had far fewer anomalies than expected.
Immersion Silver had many more anomalies than expected for all circuits.
ImmersionTin anomalies wereclose to expectedfor PTH circuits,but were higher than expected
for SMT circuits.
OSP anomalies were close to expected, except for the f(-40dB) circuit, where they had more
anomalies than expected.
The number of open PTH anomalies may be related to the inherent strength of the metals. Tin and
silver are relatively weak; OSP has no metal,and nickel makes the PTH stronger. To determine the
relevancy of metal strength to the open PTH anomalies, the HF LPF circuits would need to be
subjected to failure analysis to checkfor copper plating thickness and PTH voids in the vias, as both of
these may be problems in small vias. In addition, the chemical removal of copper from the via may
be much greater in Immersion Tin and Immersion Silver,depending on how they were processed.
In general, problems related to open PTHs result from a combination of board fabrication materials
and processes and board design (e.g., the small diameter vias in the HF LPF circuit). Product design-
ers should be aware of these phenomena when considering a change to a new surface finishes.
HCLV PTH
Although none of the HCLV PTH voltage measurements exceeded the acceptance criterion of AV <
0.50V after exposure to 85/85 or Thermal Shock, there were 12 HCLV PTH anomalies following
Mechanical Shock. Several of the differences were well above the acceptance criteria. A significant
difference in means was found for this circuit at Post Mechanical Shock, and is attributed mostly to
Immersion Silver at one site processed with water soluble flux. It should be noted, however,that the
other two Immersion Silver sites showed no anomalies. This may indicate a site-specific problemand
not a surface finish problem. While additional failure analysis would be needed to drawfurther
conclusions, in this level of testing, Immersion Silver had more anomalies than expected (5 of 12),
and Nickel/Gold and Nickel/Palladium/Gold had fewer anomalies than expected (0 of 12).
Nickel/Gold and Nickel/
Palladium/Gold had
fewer HF LPF anomalies
than expected, and
Immersion Silver had
more than expected.
29
-------
The Failure Analysis showed no link between 85/85 failures and any
of the surface finishes.
Following the analysis of the test boards, ion chromatography was used as a tool to analyze boards
thatfailed 85°C/85%RH exposure. Contamination Studies Laboratories, Inc. (CSL) in Kokomo, Indiana,
conducted this failure analysis. The purpose of the analysis was to determine if any links exist
between board contamination from fabrication and assembly process residues and the electrical
anomalies.
The testing analyzed the residue species per square inch of extracted surface (u,g/in2); specifically,
bromide, weak organic acids (WOAs),and chloride were analyzed. Tests were conducted on a set of
boards thatfailed after 85/85 testing, and a control group of boards that were not subjected to the
85/85 environment.
Based on CSL's guidelines,the observed bromide and WOA levels on all assemblies and the chloride
levels on the group of test boards were typical, and as such do not pose a threat for electrochemical
failures. The two untested (control) boards with the HASLfinish exhibited levels significantly above
CSL's recommended limits,and are therefore at riskfor electrochemical failures. Ineffective cleaning
is the likely culprit. The one tested HASL board with the reported anomaly exhibited a level only
slightly above CSL's recommended limit.
30
-------
Question 7
Will alternative surface finishes reduce my costs?
The cost of each surface finish technology was modelled to determine the relative expenses required
for each,and to identify the most costly components within each technology. The cost analysis
included capital, material, utility, licensing/permit, production,and maintenance costs. Table 7.1
presents a breakdown of the costs considered in the analysis, and Figure 7.1 displays the costs for
each technology, with non-conveyorized HASL (the baseline) highlighted for comparison. The costs
for each technology were calculated for processing 260,000 surface square feet (ssf) of board the
averageyearly production at facilities using the HASL process. Some potentially significant costs
were not included in the analysis, such as costs associated with on-site wastewater treatment and
sludge disposal, and costs of any changes elsewhere in the process required prior to implementing
the surface finish.
The cost analysis
estimated the costs
associated with each
surface finish technology
over 260,000 surface
square feet (ssf)-the
typical throughput at
facilities using the
baseline HASL process.
Table 7.1 Costs Considered in Analysis
Cost Category
Material cost
Production
Maintenance cost
Capital
Utility cost
Licensing/permit cost
Component
Process chemical(s)
Transportation of material
Labor for normal production
Tank cleanup
Bath setup
Sampling and testing
Filter replacement
Primary equipment and Installation
Facility (floor space)
Water
Electricity
Natural gas
Wastewater discharge
Many alternative surface finishes cost less to use than HASL.
Most processes were less expensive than HASL, because the material costs were lower.
ConveyorizedOSPwas
the least expensive
surface finish per
260,000 surface square
feet (ssf),and Nickel/
Palladium/Gold was the
most expensive.
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The Nickel/Gold and Nickel/Palladium/Gold processes were more expensive, because of their
precious metal content.
Conveyorized processes generally cost less per board than non-conveyorized processes of
the same technology, because of higher throughput rates.
Figure 7.1 Surface Finish Costs
$100,000
$200,000 $300,000
Cost per 260,000 ssf
$400,000
$500,000
Material costs are the most expensive component of each
technology.
Ta ble 7.2 shows the different cost components for each technology.
Material (chemical) costs are the main cost drivers.
Throughput rate is an important factor for labor and capital costs, because these costs are
lower per board if more boards are processed in a given time.
Because capita I costs area relatively mi nor cost compared to material costs (which are recurring),
the replacement costs associated with switching to an alternative technology may be easy to
overcome.
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Table 7.2 Cost Categories for Surface Finishes per 260,000 ssf
Process
Material
Production
Maintenance
Capital
Utility
Wastewater
Total
HASL
C
$75,200
$1 ,920
$1 ,880
$1 1 ,500
$1 ,062
$851
$92,400
NC
$74,800
$4,110
$2,950
$9,790
$1 ,460
$1,100
$94,200
Ni/Au
NC
$109,000
$19,800
$1 1 ,000
$10,200
$3,540
$2,050
$156,000
Ni/Pd/Au
NC
$321,000
$26,200
$20,900
$21,500
$6,110
$3,530
$399,000
OSP
C
$18,800
$1 ,440
$1 ,960
$3,140
$541
$463
$26,300
NC
$18,500
$3,330
$3,340
$1 ,950
$821
$704
$28,700
Immersion
Silver
C
$52,700
$5,430
$2,500
$11,400
$1,180
$529
$73,800
Immersion Tin
C
$28,900
$8,940
$4,280
$19,100
$2,170
$1,220
$64,700
NC
$29,000
$6,980
$3,770
$3,840
$1 ,686
$1 ,620
$46,900
NC: Non-conveyorized (vertical) process configuration.
C: Conveyorized (horizontal) process configuration.
33
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Resource consumption
for each surface finish
technology was
determined by
calculating the water,
metal, and energy use per
260,000 ssf.
Question 8
Do alternative surface finishes use less water, metal, and
energy?
Water Consumption
Water is consumed during rinse stages in each surface finish technology. The rinses remove contami-
nants from previous steps in the process and provide a clean surface on which to begin a subsequent
step. In PWB manufacturing, water use can be a significant concern - incoming water may require
purification, thereby necessitating purification equipment with a capacity large enough to match the
needs of thefacility. In addition, process wastewater usually requires pretreatment before being
released.
Facilities using water
conservation techniques
can reduce water
consumption. Examples
include counter-current
or cascade rinse systems,
ion exchange or reverse
osmosis devices, or reuse
of water elsewhere in the
plant.
Several alternative surface finishes consumed less water than HASL.
Table 8.1 presents the water consumption rates for each of the surface finish technologies. The
consumption rates were based on estimated flow rates of 0.258 gal/ssf for non-conveyorized
processes, 0.176 gal/ssf for conveyorized processes, and 0.465 gal/ssf for high-pressure water rinses
on both automation types. These flow rates were derived from industry surveys. The number of
rinses indicated in the table was based on supplier recommendations; facility practices may vary and
may have more rinse steps or higher water flow rates.
The Immersion Silver, OSP, and Conveyorized Immersion Tin processes consumed less
water than the baseline. The primary driver was the lower number of rinses required. Those
that consumed more water non-conveyorized Immersion Tin, Nickel/Gold, and Nickel/
Palladium/Gold, are more complex processes and require more rinse steps than HASL.
Conveyorized processes consumed less water than the corresponding non-conveyorized
processes. With the higher throughput of conveyorized processes, less water is used per
surface square foot of PWB at each rinse station.
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Table 8.1 Water Consumption by Surface Finish Technologies
Process
Number of
Rinses
Rinse Water
Consumed
(gal/260,000
ssf)
HASL
C
3(1)
258,000
NC
3(1)
322,000
Ni/Au
NC
8
537,000
Ni/Pd/Au
NC
14
939,000
Immersion
Silver
C
3
137,000
Immersion Tin
C
5
229,000
NC
7
469,000
OSP
C
3
137,000
NC
3
201 ,000
a Number in parentheses indicates the number of rinse stages that are high-pressure washes.
NC: Non-conveyorized (vertical) process configuration.
C: Conveyorized (horizontal) process configuration.
Metal Consumption
Each surface finish technology,aside from OSP, uses metal. These metals are crucial to the electrical
and protective properties that are needed in a surface finish. However, metals also are costly and can
complicate waste management processes. By minimizing the use of metal, regardless of the toxicity
and cost, the economic and environmental impacts of surface finish application can be reduced.
Several alternative surface finishes consume less metal per surface
square foot than the baseline.
The amount of metal consumed varied considerably among the technologies. As shown in Figure
8.1, Nickel/Palladium/Gold consumed a combined 617 pounds of metal per 260,000 ssf,and HASL
consumed 600 pounds. In contrast, Immersion Silver and Immersion Tin consumed only 21 and 63
pounds of metal, respectively, per 260,000 ssf. Because both conveyorized and non-conveyorized
versions of a technology produce the same finish, there is no difference in metal consumption
between the two.
It should be noted that these amounts do not include metal lost from dragout, nor do they account
for the environmental impacts associated with mining these metals in thefirst place. For example,
the impacts associated with mining a precious metal like gold are several times larger than those
resulting from tin or lead mining.
The metal consumption
calculations only include
metal actually applied to
the PWB. They do not
include metal lost during
the process due to
dragout, and do not
consider the fact that
impacts associated with
mining different metals
vary.
35
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Figure 8.1 Metal Consumption
Figure 8.1 Metal Consumption
HASL
Ni/Au
Ni/Pd/Au
Imm. Silver
Imm. Tin
100 200 300 400 500
Ibs. metal per 260,000 ssf
600
700
Energy Consumption
Energy consumption per
hour differs from energy
consumption per unit
area because the
processes operate at
different speeds.
Energy is used in the surface finish process to heat baths, operate pumps, and propel automated
conveyorized or immersion equipment. For heating applications, natural gas is often used; for other
applications, electricity is required. In each case, the demand for energy can be an expensive burden
on a PWB facility.
Most processes consume more energy per ssf than the baseline.
The difference in energy consumption among the different technologies was driven by several
factors. These include inherent differences in the processes as well as differences in the throughput
rate and number of steps (and requisite heaters).
With the exception of the two OSP technologies and conveyorized HASL, each alternative consumed
more energy than non-conveyorized HASL. In particular,the Nickel/Gold,conveyorized Immersion Tin,
and Nickel/Palladium/Gold used more than twice the energy of the baseline. It should be noted that
theconsumption rate per squarefootisdifferentfrom the hourly consumption rate. HASL had the
highest per-hour consumption rate because the process uses a drying oven and solder pot, yet had
36
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one of the lowest per square foot rates because of the high throughput rate. In contrast, Nickel/Gold
had the lowest per hour energy consumption rate, but the low throughput rate resulted in a high
energy rate per square foot. Figure 8.2 shows the results for each technology.
Figure 8.2 Energy Consumption
Btu per 260,000 ssf
DBtu per hour
Btu per 260,000 ssf
50,000,000 100,000,000 150,000,000 200,000,000 250,000,000
HASL (C)
HASL (NC)
Ni/Au (NC)
Ni/Pd/Au (NC)
Imm. Silver (C)
Imm. Tin (C)
Imm. Tin (NC)
OSP (C)
OSP (NC)
^_34,6C
^^^^m
^^JSjfflOOOO
0,000
H 56,700,000
I RR ?nn
116,700
12198
180,200
1191 100
I 156.7C
^^g 32,600,000
1165
3
1203100
500
I 260 400
10
200,000,000
50,000 100,000 150,000 200,000 250,000 300,000
Btu per hour
Table 8.2 presents the energy consumption rate for each type of equipment used for the surface
finish technologies. The largest individual energy consuming device is the gas drying oven, which
consumes 90 cu.ft.of natural gas per hour (27 kW). Every technology except Nickel/Gold and Nickel/
Palladium/Gold used this device. In those two technologies, the majority of the energy consumption
resulted from the use of immersion bath heaters in every tank.
37
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Table 8.2 Energy Consumption by Surface Finish Equipment
Function of
Equipment
Panel Drying
Solder Heater
Conveyorized
Panel
Automation
Bath Heater
Air Knife/
Sparging
Panel Agitation
Fluid Circulation
Type of Equipment
Gas Drying Oven
Solder Pot
Conveyor System
Immersion Heater
Air Pump
Panel Agitation Motor
Fluid Pump
Process
HASL
Immersion Silver
Immersion Tin
OSP
HASL
Conveyorized:
HASL
Immersion Silver
Immersion Tin
OSP
All
HASL
Nickel/Gold
Nickel/Palladium/Gold
OSP
Non-conveyorized:
HASL
Nickel/Gold
Nickel/Palladium/Gold
Immersion Tin
OSP
All
Energy Consumption
(cu.ft./hr of Natural
Gas or kW of
Electricity)
90 cu.ft./hra
20 kW
14.1 kW
4.1 kW
3.8 kW
3.1 kW
0.9 kW
' Equivalent to 27 kW
38
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Question 9
How can I make alternative surface finishes work for my
facility?
Nearly all of the alternative surface technologies studied in the DfE analysis are used in commercial
production. Therefore,other PWB manufacturers have been through the process of implementing
these technologies and have learned how to make them work. As with any process change, facilities
need to decide upon a specific technology,debug the process,implement any necessary changes to
upstream or downstream processes,and train workers. The more a PWB manufacturer can learn
about these considerations from others in advance of the installation, the smoother the implementa-
tion will be.
Another document produced by the DfE PWB Project, Implementing Cleaner Printed Wiring Board
Technologies: Surf ace Finishes (EPA document 744-R-00-002),describes the experiences of PWB
manufacturers, assemblers, and suppliers who have worked with these alternative surface finishes in
production. The booklet provides information on these users'reasons for selecting each technology,
difficulties encountered during installation and debugging, observed comparison to HASL, as well as
general advice for others considering a new technology.
Although experiences differed among facilities, several recommendations emerged consistently for
PWB manufacturers are summarized below.
Evaluate your facility's needs.
PWB manufacturers have added alternative surface finish lines for a number of reasons:
To satisfy the request of a largecustomer
To expand into the manufacture of other types of boards,or to finish boards that previously
were finished atotherfacilities
Toproduceaflatterfinish
To move toward an overall lead-free facility
To reduce maintenance and equipment costs.
Each of these reasons comes with individual sets of conditions and motivations; focus on the specific
motivations at your facility to ensure that the alternative surface finish you select is a good match for
your needs.
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Understand the surface finish technologies.
Every surface finish has limitations. Some are not wire bondable, and others may have a short shelf
life, or an incompatibility with certain soldermasks. Also, the choice of surface finish can affect other
steps in the PWB manufacturing process and in board assembly. Learn thedetails of the different
finishes so that the oneyou select is a good match for your facility's technical needs. An important
step in your evaluation is to arrange with a supplier or another PWB manufacturer to have sample
boards finished with one or more of the candidate finishes.
Communicate with your customers.
Tell customers about your plans to add a new technology, so they understand the differences in the
boards you will deliver,and so you can discuss which of their products might benefit from the new
finish.
Work closely with the supplier.
Suppliers of the surface finish technology know the details of their product and the conditions under
which it works best. When evaluating different candidate finishes, ask plenty of questions about each
finish with respect to the type of boards it can run, process requirements, worker health issues, and
waste disposal and permitting considerations.
After a specific finish has been selected, the supplier can provideyou with guidance on the equip-
ment you will need, any changes that you will have to make in upstream or down stream processes,
and corrections to make during debugging.
Use quality equipment.
Several facilities and suppliers that have implemented an alternative technology have found that a
considerable number of problems could be traced back to poor equipment. In one case an old film
developer retrofitted as a bath caused contamination of the chemicals. Poor equipment also can lead
to excessive drag-out, resulting in considerable raw material and waste disposal costs. Most of the
alternative technologies have a tighter process window than HASL, so it is important to have equip-
ment that is calibrated and that functions smoothly.
Achieve a total commitment from the company for the new process.
Everyone, especially management and line operators, must help in ensuring that the implementation
process is successful. Line operators must learn how the process differs from the previous technology
and how to address potential problems. Management must provide adequate resources for the
installation, start-up, and debugging steps.
-------
Question 10
Where can I find more information about pollution
prevention in the PWB industry?
The DfE Printed Wiring Board Project has developed several materials specifically for the PWB
industry. Ranging from technical reports to case studies,these sources provide information on
several topics affecting the PWB manufacturing process including emerging technologies, pollution
prevention opportunities, regulations,and Environmental Management Systems (EMSs). The Printed
Wiring Board Project also has performed a detailed analysis on Making Holes Conductive (MHC)
technologies. Several other documents provide industry-wide information and case studies of
pollution prevention opportunities.
All of these documents, along with additional copies of this booklet, are availablefree of charge
from:
Pollution Prevention Information Clearinghouse (PPIC)
U.S. EPA
1200 Pennsylvania Ave., N.W (7407)
Washington, DC 20460
Phone:202-260-1023
Fax:202-260-4659
E-mail: PPIC@epa.gov
www.epa.gov/opptintr/library/ppicdist.htm
Information Products from DfE
Surface Finishes
PWB Surface Finishes: CleanerTechnologies Substitutes AssessmentEPA 744-R-01-003A and B
Implementing Cleaner Printed Wiring BoardTechnologies: Surface Finishes, EPA 744-R-00-002
Making Holes Conductive
Alterna five Technologies for MHC: Cleaner Technologies for PWB Manufacturers^^ 744-R-98-002
CleanerTechnologies Substitutes Assessment: Making Holes Conducf/Ve,EPA744-R-98-004AandB
Implementing CleanerTechnologies in the PWB Industry: Making Holes Conductive, EPA 744-R-97-001
General PWB Information
PWB Pollution Prevention and Control Technology:Analysis of Updated Survey Results,
EPA 744-R-98-003
PWB Industry and Use Cluster Profile,EP/\744-R-95-QQ5
Integrated Environmental Management Systems Implementation Gu/de,EPA 744-R-00-011
Federal Environmental Regulations Affecting the Electronics Industry^P^W-R^B-QQ]
Pollution Prevention Work Practices, PWB Case Study 1, EPA 744-R-95-004
On-Site Etchant Generation, PWB Case Study 2, EPA 744-R-95-005
Opportunities for Acid Recovery and Management, PWB Case Study 3, EPA 744-R-95-009
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Plasma Desmear, PWB Case Study 4, EPA 744-R-96-003
A Continuous-Flow System for Reusing Microetchant,PWB Case Study 5, EPA 744-R-96-024
Pollution Prevention Beyond Regulated Materials, PWB Case Study 6, EPA 744-R-97-006
Building an Environmental Management System, PWB Case Study 7, EPA 744-R-97-009
Identifying Objectives for Your EMS, PWB Case Study 8, EPA 744-R-97-010
Flexible Simulation Modeling of PWB Costs, PWB Case Study 9, EPA 744-F-99-004
Internet Sites
DfE Printed Wiring Board Project
www.epa.gov/opptintr/dfe/pwb/pwb.html
Contains projectdocumentsand information.
Printed Wiring Board Resource Center
www.pwbrc.org/
Developed by the National Centerfor Manufacturing Sciences (NCMS) in partnership with IPC, with
funding from EPA. Provides PWB industry-specific regulatory compliance and pollution prevention
information.
IPC Lead-Free Web Site
www.leadfree.org/
Developed by IPC; describes industry research and initiatives, as well as marketing and legislative news, in
areas relating to lead-free electronics.
University of Tennessee Center for Clean Products and Clean Technologies
eerc.ra.utk.edu/clean/
Provides information on theCenterforClean Products and CleanTechnologies at the University of
Tennessee in Knoxville.
Trade Associations and Research Institutions
IPC Association Connecting Electronics Industries
2215 Sanders Road
Northbrook,IL 60062-6135
phone: 847-509-9700
fax:847-509-9798
www.ipc.org
University of Tennessee Center for Clean Products and Clean Technologies
600 Henley Street, Suite 311
KnoxvilleJN 37996-4134
phone: 423-974-8979
fax:423-974-1838
eerc.ra.utk.edu/clean/
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