Cleaner Cleaner Cleaner Technologies for echnologies for echnologies for

Printed W inted Wiring Board

Manufacturers

EPA-744-R-01-001 

June 2001 

United States 

Environmental 

Agency 

Office of Pollution Prevention 

and Toxics 

(7406) 

Alternative

Technologies echnologies echnologies for

Surface Finishing

Office of Pollution Office of Pollution

Prevention and Toxics

Protection 
AlternativeTechnologies for 

Surface Finishing 

Cleaner Technologies for Printed Wiring Board Manufacturers

Office of Pollution 

Prevention and Toxics 

This document and other DfE PWB Project documents are available online at www.epa.gov/dfe 

or www.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 Assessment (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 corroborated 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. 

Recycled/Recyclable


Printed with vegetable oil based inks on paper that contains at least 50% post-consumer recycled fiber.

Acknowledgments Acknowledgments 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), prepared 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 Lott of 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. 

2
Contents Contents Contents

Question 1

Why should I consider an alternative surface finish? .............................................................. 6

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? ........................... 23

Question 7

Will alternative surface finishes reduce my costs? .............................................................. 31

Question 8

Do alternative surface finishes use less water, metal, and energy? ..................................... 34

Question 9

How can I make alternative surface finishes work for my facility? ....................................... 39

Question 10

Where can I find more information about pollution prevention in the PWB industry? .............. 41

3
Introduction 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 (DfE) PWB 

Project is a voluntary, 

non-regulatory 

partnership among a 

diverse group of 

contributors. 

Introduction 

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 subsequent 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 comprehensive 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 information, 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) 

4
• Immersion Silver 

• Immersion Tin 

• Organic Solderability Preservative (OSP) 

The analysis was intended to represent the use of these surface finishes under “real 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 conditions. 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•003A 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 

Finishes (EPA 744-R-01-

003A and B), contains 

information that is useful 

for readers who would 

like to learn more about 

each surface finish 

technology. To download 

the report, visit: 

www.epa.gov/dfe 

5
Question 1 Question 1

Why should I consider an alternative surface finish? Why should I consider an alternative surface finish?

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, manufacturers 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 workplace 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 technologies 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 assembled 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 inputs are 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. 

7
Question 2 Question 2

Which surface finishes were evaluated in the DfE Project? Which surface finishes were evaluated in the DfE Project?

Question 2 

Which surface finishes were evaluated in the DfE Project? 

Most technologies can be All the alternative surface finish technologies were wet chemistry processes involving a series of 

operated in either a chemical process baths and water rinse steps. The processes were operated either in a horizontal, 

horizontal, conveyorized conveyorized process or vertical, non-conveyorized process. Table 2.1 indicates the operation 

or vertical, non- mode for each technology.


conveyorized


configuration.


Table 2.1 Surface Finishes Included in the Analysis 

Process Conveyorized Non-Conveyorized

HASL � �

Electroless Nickel/ Immersion Gold �

Electroless Nickel/ Electroless Palladium/ 

Immersion Gold 

�

Immersion Silver �

Immersion Tin � �

OSP � �

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) 

HASL is the project’s 

baseline technology. 

Cleaner Miocroetch Dry Water 

Rinse X 2 

Flux 

Solder 

HighPressure 

Rinse 

Air Knife Water 

Rinse 

Tin-lead HASL has been the standard surface finishing method used in the manufacture of doublesided 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 are first 

8
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, nonconveyorized 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 manufacturing 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 Miocroetch 

Water 

Rinse 

Acid Dip 

Water 

Rinse Catalyst 

Water 

Rinse 

Electroless 

Nickel 

Water 

Rinse X 2 

Water 

Rinse 

The Electroless Nickel/ 

Immersion Gold finish 

consists of a relatively 

thick layer of nickel 

followed by a thin 

protective layer of gold. 

Immersion 

Gold 

Water 

Rinse X 2 

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 make this a desirable 

9
surface finish. The thin layer of immersion gold preserves the solderability of the finish by preventing 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 Miocroetch Water 

Rinse X 2 

Water 

Rinse X 2 Catalyst 

Water 

Rinse X 2 

Water 

Rinse X 2 

Water 

Rinse X 2 

Water 

Rinse X 2 

Water 

Rinse X 2 

Acid Dip Electroless 

Nickel 

Preinitiator 

Electroless 

Palladium 

Immersion 

Gold 

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, flip chip, 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 Miocroetch 

Water 

Rinse 

Water 

Rinse Predip 

Dry 

Water 

Rinse 

Immersion 

Silver 

The Immersion Silver 

finish consists of a silver 

layer and a protective 

organic coating. 

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 compatible with SMT, flip chip, and BGA technologies, as well as typical through-hole components. Silver 

finishes appear to be compatible with all types of solder masks, can withstand five thermal excursions during assembly, and are anticipated to have a shelf life of at least six months. 

11
Immersion Tin


The Immersion Tin finish 

displaces surface copper 

with a thin layer of tin. 

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 throughhole 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 Miocroetch Water 

Rinse X 2 

Water 

Rinse X 2 Catalyst 

Water 

Rinse 

Water 

Rinse X 2 Immersion 

Tin 

Dry 

Cleaner Miocroetch 

Water 

Rinse 

Water 

Rinse 

Dry 

Water 

Rinse 

OSP Air Knife 

Air Knife 

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 Question 3

How do alternative finishes compare to hot air How do alternative finishes compare to hot air

solder leveling (HASL) overall? solder leveling (HASL) overall?

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 

14
Question 4 Question 4

How may surface finishes af How may surface finishes affect worker health and fect worker health and

safety?

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 lack of toxicological data for some chemicals, the potential 

inaccuracy of the release and exposure models, and the lack of 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 fivestep 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 hazards from 

material safety data 

sheets (MSDSs) for 

surface finishing 

chemical products 

and discusses process 

safety issues. 

15
•	 Of the five non-conveyorized processes, only Immersion Tin contained no chemicals that 

A chemical is of concern presented a concern from inhalation.

when it is present at a • Most chemicals of concern are used either in cleaning or finish deposition steps. concentration that 

toxicological research 

indicates may cause Table 4.1 Chemicals of Concern for Inhalation Riska


adverse effects in humans


or aquatic organisms.


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 Immersion Tin presented a potential 

dermal risk to workers who do not wear gloves. 

• Both line operators and laboratory technicians may be exposed to chemicals of concern. 

16
17

• The potential dermal risks for conveyorized processes were lower than those for nonconveyorized processes. 

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 HASL are uncertain. 

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 oncern for Dermal Riska

(Conveyorized processes were expected to result in dermal exposure

Monitoring data indicated that the level

Chemicals of C
Cancer Risks 

A surface finish technology poses a potential cancer risk if chemicals in the formulations are carcinogenic (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 human carcinogenindicates 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 but inadequate or a lack of 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, Immersion 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 technologies 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 considerable 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
Table 4.3 Chemical Safety Information


20
Question 5 Question 5

How may surface finishes af How may surface finishes affect people and the fect people and the

environment outside the facility environment outside the facility?

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 risk characterization 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 2x10-11 (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 be at risk from surface finish processes through other pathways, including solid waste releases 

or contaminated 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 the federal 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
Ecological risks were estimated by calculating the concentration of each chemical in surface finish 

Most metals used are process wastewater, then dividing that by the concentration of concern (CC) – the concentration at 

regulated and must not which a chemical is expected to present risks to organisms in aquatic ecosystems. This ratio is called 

exceed regulated levels an aquatic risk indicator. A value greater than one indicates that the chemical is present in wastewater 

upon release. Although at a concentration that may harm aquatic organisms. The calculations assumed that the wastewater is 

metals are present in treated by a publicly owned treatment works (POTW), which reduces the concentration of many 

wastestreams in chemicals by approximately 90%. 

concentrations above 

levels of concern for As indicated in Table 5.1, each technology except Nickel/Gold and Nickel/Palladium/Gold had chemisome surface finishes, cals with an aquatic risk indicator greater than one. Therefore, if the wastewater from the other 

most are removed before technologies were released to a body of water after being processed at a treatment facility, it could 

discharge, in accordance adversely affect organisms in the water. HASL contained the most chemicals with an indicator greater 

with regulations. than one. There were four chemicals in the HASL non-conveyorized process and five in the conveyorized 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 HASL Nickel/ 

Gold 

Nickel/ 

Palladium/ 

Gold 

Immersion 

Silver 

Immersion 

Tin 

OSP 

Number of 

Non-Metal 

Chemicals 

with Indicator 

>1a 

3-4 0 0 1 0-1 1 

Chemical with 

Largest Aquatic 

Risk Indicator 

Potassium 

peroxymonosulfate 

None > 1 None > 1 Hydrogen 

peroxide 

Potassium 

peroxymonosulfate 

Alkylaryl 

imidazole 

Aquatic Risk 

Indicator 

8.2 (NC) 

6.1 (C) 

— 1.3 3.6 (NC) 6.6-33 (NC) 

3.6-18 (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 Question 6

What kind of performance can I expect from alternative What kind of performance can I expect from alternative

surface finishes? surface finishes?

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“snapshot”of the way the technology 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 the facilities 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 performance of the assembled boards (164 boards in total) then was tested before and after exposure to 

accelerated aging, thermal shock, and mechanical shock conditions. 

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 Materials Task 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) 

• Stranded wire (SW) 

This study was intended 

to provide a “snapshot” of 

the performance of 

different surface finishes. 

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, and HF 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 measurements: 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. 

Table 6.1 Electrical Responses for the Test PWA and Acceptance Criteria 

Response Circuitry Acceptance Criteria 

High Current Low Voltage 

1 HCLV PTH ∆ Voltage from Pre-test < 0.50V 

2 HCLV SMT ∆ Voltage from Pre-test < 0.50V 

High Voltage Low Current 

3 HVLC PTH 4μA < X < 6μA 

4 HVLC SMT 4μA < X < 6μA 

High Speed Digital 

5 HSD PTH Propagation Delay < 20% increase from Pre-test 

6 HSD SMT Propagation Delay < 20% increase from Pre-test 

High Frequency Low Pass Filter 

7 HF PTH 50 MHz ±5dB of Pre-test 

8 HF PTH f(–3dB) ±50MHz of Pre-test 

9 HF PTH f(–40dB) ±50MHz of Pre-test 

10 HF SMT 50 MHz ±5dB of Pre-test 

11 HF SMT f(–3dB) ±50MHz of Pre-test 

12 HF SMT f(–40dB) ±50MHz of Pre-test 

High Frequency Transmission Line Coupler 

13 HF TLC 50MHz Forward Response ±5dB of Pre-test 

14 HF TLC 500MHz Forward Response ±5dB of Pre-test 

15 HF TLC 1GHz Forward Response ±5dB of Pre-test 

16 HF TLC Reverse Null Frequency ±50MHz of Pre-test 

17 HF TLC Reverse Null Response < 10dB increase over Pre-test 

Other Networks—Leakage 

18 10 mil Pads Resistance > 7.7 log10 ohms 

19 PGA A Resistance > 7.7 log10 ohms 

20 PGA B Resistance > 7.7 log10 ohms 

21 Gull Wing Resistance > 7.7 log10 ohms 

Stranded Wire 

22 Stranded Wire 1 ∆ Voltage from Pre-test < 0.356V 

23 Stranded Wire 2 ∆ 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, 164×23 = 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,by Circuit Type and Test Time 

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.” 

Circuitry 85/85 Thermal Shock Mechanical Shock 

HCLV 100.0% 100.0% 48.2% (7.1% SMT) 

HVLC 99.7% 99.7% 50.0% (0.0% SMT) 

HSD 99.7% 98.8% 99.1% (99.3% SMT) 

HF LPF 98.7% 89.4% 82.6% (74.8% SMT) 

HF TLC 99.8% 99.5% 99.4% 

Other Networks 99.8% 100.0% 100.0% 

Stranded Wire 100.0% 99.7% 98.5% 

Total % Success Rate 99.5% 96.9% 85.4% 

Total anomalies per test time 17 113 527 

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 over Test Times 

Circuitry 

Post 

85/85 

Post 

TS 

Post 

MS 

Comments 

HCLV 

1 HCLV PTH 0 0 12 Some need further Failure Analysis 

2 HCLV SMT 0 0 158 SMT components came off board during MS 

HVLC 

3 HVLC PTH 0 0 0 Excellent performance throughout 

4 HVLC SMT 1 1 164 SMT components came off board during MS 

HSD 

5 HSD PTH 0 2 2 Component problem 

6 HSD SMT 1 2 1 Component problem 

HF LPF 

7 HF PTH 50 MHz 4 15 15 Failure Analysis of open PTH needed 

8 HF PTH f(-3dB) 4 15 18 Failure Analysis of open PTH needed 

9 HF PTH f(-40dB) 4 13 14 Failure Analysis of open PTH needed 

10 HF SMT 50 MHz 0 18 30 Failure Analysis of open PTH needed 

11 HF SMT f(-3dB) 0 16 29 Failure Analysis of open PTH needed 

12 HF SMT f(-40dB) 1 27 65 Failure Analysis of open PTH needed 

HF TLC 

13 HF TLC 50MHz 0 0 7 Minor anomalies 

14 HF TLC 500MHz 0 0 1 Minor anomalies 

15 HF TLC 1GHz 0 1 1 Minor anomalies 

16 HF TLC RNF 0 0 0 Constant response of 50MHz throughout 

17 HF TLC RNR 1 2 5 Minor anomalies 

Leakage 

18 10-Mil Pads 0 0 0 Excellent performance throughout 

19 PGA A 0 0 0 Excellent performance throughout 

20 PGA B 0 0 0 Excellent performance throughout 

21 Gull Wing 1 0 0 Excellent performance throughout 

Stranded Wire 

22 SW 1 0 0 1 Excellent performance throughout 

23 SW 2 0 1 4 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 experimental 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 means were significantly different from one another for a given electrical response from the test PWA. 

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 acceptance criteria, which indicates that surface finish, flux, and site did not influence the test measurements. These circuits include High voltage low current (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 effectfrom the 85/85 

test environment that removes residues resulting from board fabrication,assembly,and handling. 

This phenomenon was observed for all leakage circuits. 

In the CTSA document, 

boxplots are used for 

convenient displays of 

multiple comparison 

results. 

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 shock test. 

HF LPF 

The GLM analyses indicated that surface finish, flux, and site did not influence the HF LPF measurements at any of the test times. However, the test measurements contained many extreme outlying 

observations at post thermal shock and post mechanical shock, which greatly increases the sample 

variance and in turn hinders the interpretation of the GLM results. The HF LPF anomalies are summarized by surface finish in Table 6.4 for each of the six HF LPF circuits. 

Table 6.4 Observed Number of HF LPF Anomalies (Compared to the Expected Number) 

Process HASL Ni/Au Ni/PD/Au Imm 

Silver 

Imm Tin OSP TOTALS 

No. of 

PWAs 32 28 12 20 36 36 164 

HF LPF PTH 

50 MHz 1 (2.9) 2 (2.6) 0 (1.1) 6 (1.8) 4 (3.3) 2 (3.3) 15 

f(-3dB) 2 (4.1) 3 (3.6) 0 (1.5) 6 (2.6) 5 (4.6) 2 (4.6) 18 

f(-40dB) 1 (2.9) 2 (2.6) 0 (1.1) 7 (1.8) 3 (3.3) 1 (3.3) 14 

HF LPF SMT 

50 MHz 6 (5.9) 0 (5.1) 0 (2.2) 7 (3.7) 11 (6.6) 6 (6.6) 30 

f(-3dB) 7 (5.9) 0 (5.1) 0 (2.2) 6 (3.7) 11 (6.6) 5 (6.6) 29 

f(-40dB) 15 

(13.1) 1 (11.4) 1 (4.9) 11 (8.2) 17 (14.7) 20 (14.7) 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 of anomalies can be calculated for each cell. A chi-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. 

•	 Immersion Tin anomalies were close to expected for 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 check for 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 designers 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 ∆V < 

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 problem and 

not a surface finish problem. While additional failure analysis would be needed to draw further 

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 

that failed 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 (μg/in2); specifically, 

bromide,weak organic acids (WOAs), and chloride were analyzed. Tests were conducted on a set of 

boards that failed 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 HASL finish exhibited levels significantly above 

CSL’s recommended limits, and are therefore at risk for 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 Question 7

Will alternative surface finishes reduce my costs? Will alternative surface finishes reduce my costs?

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 

average yearly 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. 

Table 7.1 Costs Considered in Analysis 

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. 

Cost Category Component 

Material cost Process chemical(s) 

Production Transportation of material 

Labor for normal production 

Maintenance cost Tank cleanup 

Bath setup 

Sampling and testing 

Filter replacement 

Capital Primary equipment and Installation 

Facility (floor space) 

Utility cost Water 

Electricity 

Natural gas 

Licensing/permit cost Wastewater discharge 

Conveyorized OSP was 

the least expensive 

surface finish per Many alternative surface finishes cost less to use than HASL.	 260,000 surface square 

feet (ssf ), and Nickel/ 

•	 Most processes were less expensive than HASL, because the material costs were lower. Palladium/ Gold was the 

most expensive. 

31
• 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 

Material costs are the most expensive component of each 

technology. 

Table 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 capital costs are a relatively minor cost compared to material costs (which are recurring), 

the replacement costs associated with switching to an alternative technology may be easy to 

overcome. 

32
Table 7.2 Cost Categories for Surface Finishes per 260,000 ssf


Process HASL Ni/Au Ni/Pd/Au OSP Immersion 

Silver 

Immersion Tin 

C NC NC NC C NC C C NC 

Material $75,200 $74,800 $109,000 $321,000 $18,800 $18,500 $52,700 $28,900 $29,000 

Production $1,920 $4,110 $19,800 $26,200 $1,440 $3,330 $5,430 $8,940 $6,980 

Maintenance $1,880 $2,950 $11,000 $20,900 $1,960 $3,340 $2,500 $4,280 $3,770 

Capital $11,500 $9,790 $10,200 $21,500 $3,140 $1,950 $11,400 $19,100 $3,840 

Utility $1,062 $1,460 $3,540 $6,110 $541 $821 $1,180 $2,170 $1,686 

Wastewater $851 $1,100 $2,050 $3,530 $463 $704 $529 $1,220 $1,620 

Total $92,400 $94,200 $156,000 $399,000 $26,300 $28,700 $73,800 $64,700 $46,900 

NC: Non-conveyorized (vertical) process configuration. 

C: Conveyorized (horizontal) process configuration. 

33
Question 8 Question 8

Do alternative surface finishes use less water Do alternative surface finishes use less water, metal, and , metal, and

energy?

Resource consumption 

for each surface finish 

technology was 

determined by 

calculating the water, 

metal, and energy use per 

260,000 ssf. 

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. 

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 contaminants 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 the facility. In addition, process wastewater usually requires pretreatment before being 

released. 

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. 

34
Table 8.1 Water Consumption by Surface Finish Technologies


Process HASL Ni/Au Ni/Pd/Au Immersion 

Silver 

Immersion Tin OSP 

C NC NC NC C C NC C NC 

Number of 

Rinses 

3 (1) 3 (1) 8 14 3 5 7 3 3 

Rinse Water 

Consumed 

(gal/260,000 

ssf) 

258,000 322,000 537,000 939,000 137,000 229,000 469,000 137,000 201,000 

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 the first 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
Energy consumption per 

hour differs from energy 

consumption per unit 

area because the 

processes operate at 

different speeds. 

Figure 8.1 Metal Consumption 

Energy Consumption 

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 

the consumption rate per square foot is different from 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
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 

Btu per hour 

Btu per 260,000 ssf 

0 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) 

116,000,000 

200,000,000 

136,000,000 

56,700,000 

32,600,000 

18,900,000 

75,200,000 

74,600,000 

34,600,000 

260,400 

219,800 

180,200 

191,100 

156,700 

203,100 

165,500 

116,700 

88,700 

0 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
Table 8.2 Energy Consumption by Surface Finish Equipment


Function of 

Equipment 

Type of Equipment Process Energy Consumption 

(cu.ft./hr of Natural 

Gas or kW of 

Electricity) 

Panel Drying Gas Drying Oven HASL 

Immersion Silver 

Immersion Tin 

OSP 

90 cu.ft./hra 

Solder Heater Solder Pot HASL 20 kW 

Conveyorized 

Panel 

Automation 

Conveyor System Conveyorized: 

HASL 

Immersion Silver 

Immersion Tin 

OSP 

14.1 kW 

Bath Heater Immersion Heater All 4.1 kW 

Air Knife/ 

Sparging 

Air Pump HASL 

Nickel/Gold 

Nickel/Palladium/Gold 

OSP 

3.8 kW 

Panel Agitation Panel Agitation Motor Non-conveyorized: 

HASL 

Nickel/Gold 

Nickel/Palladium/Gold 

Immersion Tin 

OSP 

3.1 kW 

Fluid Circulation Fluid Pump All 0.9 kW 

a Equivalent to 27 kW 

38
Question 9 Question 9

How can I make alternative surface finishes work for my How can I make alternative surface finishes work for my

facility facility?

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 implementation will be. 

Another document produced by the DfE PWB Project, Implementing Cleaner Printed Wiring Board 

Technologies:Surface 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 large customer 

•	 To expand into the manufacture of other types of boards, or to finish boards that previously 

were finished at other facilities 

• To produce a flatter finish 

• 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. 

39
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 the details of the different 

finishes so that the one you 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 provide you with guidance on the equipment you will need, any changes that you will have to make in upstream or downstream 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 equipment 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 

40 installation, start-up, and debugging steps. 
Question 10 Question 10

Where can I find more information about pollution Where can I find more information about pollution

prevention in the PWB industry prevention in the PWB industry?

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 available free 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 Assessment,EPA 744-R-01-003A and B 

ImplementingCleanerPrinted WiringBoardTechnologies: SurfaceFinishes,EPA 744-R-00-002 

Making Holes Conductive 

AlternativeTechnologies for MHC: CleanerTechnologies for PWB Manufacturers,EPA 744-R-98-002 

CleanerTechnologies Substitutes Assessment: Making Holes Conductive,EPA 744-R-98-004A and B 

Implementing CleanerTechnologies in the PWB Industry: Making Holes Conductive,EPA 744-R-97-001 

General PWB Information 

PWB Pollution Prevention and ControlTechnology:Analysis of Updated Survey Results, 

EPA 744-R-98-003 

PWB Industry and Use Cluster Profile,EPA 744-R-95-005 

Integrated Environmental Management Systems Implementation Guide,EPA 744-R-00-011 

Federal Environmental Regulations Affecting the Electronics Industry,EPA 744-R-95-001 

Pollution PreventionWorkPractices,PWB Case Study 1, EPA 744-R-95-004 

On-SiteEtchantGeneration,PWB Case Study 2,EPA 744-R-95-005 

Opportunities for Acid Recovery and Management,PWB Case Study 3,EPA 744-R-95-009 

41
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 forYour 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 project documents and information. 

Printed Wiring Board Resource Center 

www.pwbrc.org/ 

Developed by the National Center for 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 the Center for Clean Products and Clean Technologies 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 

Knoxville,TN 37996-4134 

phone: 423-974-8979 

fax: 423-974-1838 

eerc.ra.utk.edu/clean/ 

42