EPA-744-S-05-001 

August 2005 

Solders in Electronics: 

A Life-Cycle Assessment 

Summary 

This summary document is based on information presented in the project report, 

Solders in Electronics: A Life-Cycle Assessment, written by the University of 

Tennessee under a grant from EPA. Some information in the Life Cycle Assessment was provided by individual technology vendors and has not been independently corroborated by EPA. The identification of specific products or processes in 

this document is 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. 
Acknowledgments

This document was prepared for the U.S. Environmental Protection Agency’s Design for the 

Environment (DfE) Lead-Free Solder Project by Abt Associates under contract #68-W-01­

039. This document is based primarily on the full project report, Solders in Electronics: A 

Life-Cycle Assessment, prepared by Jack R. Geibig and Maria Leet Socolof of the University of 

Tennessee Center for Clean Products and Clean Technologies under joint funding from the 

U.S. Environmental Protection Agency’s Design for the Environment Program in the Economics, Exposure, and Technology Division (EETD) of the Office of Pollution Prevention 

and Toxics (OPPT), and through financial contributions from the following organizations: 

Agilent Technologies, Cookson-Fry, Delphi-Delco, Hewlett Packard, Intel, International 

Business Machines (IBM), Sematech, Pitney Bowes, Rockwell Collins, and Thomson Consumer Media. 

The Life-Cycle Assessment 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 the Core Group Co-Chairs Kathy Hart, Project 

Lead, U.S. EPA OPPT, DfE Branch; Holly Evans, formerly of Electronic Industries Alliance; 

Fern Abrams, IPC; and the Core Group Members Todd Brady, Intel Corp.; Maria Socolof 

and Jack Geibig, University of Tennessee Center for Clean Products and Clean Technologies; 

Anne Brinkley, IBM; Lee Vroom, Thomson Consumer Electronics; Mark Corbett, Pitney 

Bowes; Walter Worth, International Sematech; Pete Palmer, Cookson-Fry; Jerry Gleason, 

Hewlett Packard; and Brenda Baney, Delphi-Delco. 
Contents

Introduction....................................................................................1


Question 1: 

What is a life-cycle assessment? .................................................. 3


Question 2: 

Which solders were investigated during the project? ................5


Question 3: 

How were life-cycle environmental and health


impacts evaluated?.....................................................................6


Question 4: 

How do the environmental and health impacts compare


among paste solders? .................................................................9


Question 5:


How do the environmental and health impacts compare


among bar solders?.................................................................. 16


Question 6: 

What are the limitations of the study? ..................................... 23


Question 7: 

What can electronics manufacturers do to reduce


environmental and health impacts?........................................ 27


Question 8:


What are the challenges to implementing


lead-free soldering? ................................................................. 31


Question 9: 

What are the performance differences among the solders?.... 36


Question 10: 

What are the potential market impacts of a switch


to lead-free solders?................................................................. 42


Introduction

This report summarizes the results of an analysis conducted by the University of Tennessee’s 

(UT) Center for Clean Products and Clean Technologies for the U.S. Environmental Protection Agency’s Design for the Environment (DfE) Lead-Free Solder Partnership (LFSP). The 

DfE LFSP is a voluntary, cooperative partnership among the DfE Program, UT, the IPC– 

Association Connecting Electronics Industries (IPC), the Electronic Industries Alliance 

(EIA), several individual electronics companies, and other interested parties. The partnership 

assessed the environmental life-cycle impacts of selected lead-free solders as alternatives to 

tin-lead solder. The DfE LFSP analysis also provides an assessment of the recyclability and 

leachability of the solders. 

PURPOSE AND SCOPE OF THE STUDY 

The purpose of the lead-free solder study is threefold: 

1. 	to evaluate the life-cycle environmental impacts of selected lead-based and lead-free 

solder alternatives using life-cycle assessment (LCA) 

2.	 to evaluate the effects of lead-free solders on leachability, recycling, and reclamation at 

the end-of-life 

3.	 to identify data gaps or other potential areas of analysis for future investigation by EPA 

or industry 

This study used LCA to evaluate both lead-based and lead-free solder alternatives. LCAs, 

which are generally global and non-site specific in scope, look at the full life cycle of the 

product being evaluated, from materials acquisition to manufacturing, use, and end-of-life 

(i.e., final disposition). The LFSP LCA considers impacts related to material consumption, 

energy use, air resources, water resources, landfills, human toxicity, and ecological toxicity, as 

well as leachability and recycling. 

NEED FOR THE STUDY 

Eutectic tin-lead (SnPb) solder has long been the primary choice for assembling electronics 

due to its reflow properties, low melting point, and the relative ductility of the solder joints 

formed; however, concern over lead’s relatively high toxicity to human health and the environment and ensuing international market and legislative pressures have led the U.S. electronics industry to begin switching to lead-free solders. Although the performance of the 

metals and fluxes of many of the alternatives has been studied, their life-cycle environmental 

impacts have not yet been evaluated. The LFSP offers the opportunity to mitigate current 

and future risks by helping the electronics industry to identify lead-free solders that are less 

toxic and that pose the fewest risks over their life cycles. The LFSP study also allows the 

electronics industry to make environmentally informed choices when assessing and implementing improvements, such as changes in product, process, and activity design, raw material use, industrial processing, consumer use, and waste management. Additionally, many 

other organizations and individuals in the U.S. and abroad have expressed interest in obtaining objective, detailed information about the life-cycle impacts of selected lead-free solders. 

About EPA’s Design for the 

Environment Program 

EPA’s Office of Pollution 

Prevention and Toxics 

established the DfE Program in 

1992 to encourage businesses 

to incorporate environmental 

concerns into their business 

decisions. DfE industry projects 

are cooperative, joint partnerships with trade associations, 

businesses, public-interest 

groups, and academia to assist 

businesses in specific industries 

to identify and evaluate more 

environmentally sound 

products, processes, and 

technologies. The DfE LeadFree Solder Partnership 

consisted of members of 

electronics industry trade 

associations, circuit board 

assemblers, solder suppliers, 

academic institutions, and 

EPA. The direction and focus 

of this project was determined 

by the project partners. 

1
Approximately 176 million pounds of lead-based solder were used world-wide in 2002. 

Electronics in the U.S. is a $400 billion-per-year industry facing significant legislative and 

market pressures to phase out the use of lead-based solder and switch to lead-free alternatives. The European Restriction of Hazardous Substances in Electrical and Electronic 

Equipment (RoHS) Directive (2002/95/EC) stipulates that lead and other selected toxic 

chemicals in electrical and electronic equipment be replaced by July 2006. In Japan, subsequent to take back (recycling) legislation that took effect in that country in 2001, the 

Japanese Ministry of the Environment and the Ministry of Economy, Trade and Industry 

suggested a voluntary phase-out of lead, along with increased end-of-life (EOL) product 

recycling. Consumer demand for lead-free products may also increase as the general public 

becomes more aware of lead issues. All of these forces combine to drive the U.S. electronics 

market inexorably toward lead-free solders. Managing the environmental impacts posed by 

this change is crucial to the long-term environmental sustainability of both the U.S. and 

global electronics industries. Using this evaluation, the U.S. electronics industry will be 

better prepared to meet the growing demand for extended product responsibility, to help 

guide public policy towards informed, scientifically-based solutions that are environmentally 

preferable, and be better able to meet the competitive challenges of the world market. In 

addition, the LCA model and associated results provide a baseline upon which solder alternatives not included in the study can potentially be evaluated. This will allow for further 

expedited LCA studies. 

This booklet summarizes the key findings of the DfE Lead-Free Solder Partnership study. 

The information is presented in ten sections that summarize the following: 

$ the study’s life-cycle assessment methodology; 

$ the environmental and health impacts of the solders evaluated; 

$ the limitations of the study and alternative data analyses; 

$ steps circuit board manufacturers can take to reduce environmental and health 

impacts; 

$ challenges to implementing lead-free soldering; and 

$ information on cost and performance differences among the solder. 

For more detailed information on any of these topics, the reader is encouraged to reference 

the full project report, Lead-Free Solders: A Life-Cycle Assessment (Geibig and Socolof, 2005). 

The document may be viewed at www.epa.gov/dfe. 

2
Question 1: 

What is a life-cycle assessment?


The DfE Lead-Free Solder Partnership (LFSP) conducted this analysis of selected lead-based 

and lead-free solder alternatives using a life-cycle assessment (LCA) approach, which allowed 

for a comprehensive analysis of the environmental consequences of a product system over its 

entire life. LCA, which is increasingly being used by industry, contains four major steps as 

defined by the Society of Environmental Toxicology and Chemistry (SETAC) and more 

recently by the International Standards Organization (ISO): 

1. 	Goal Definition and Scoping lays out the rationalization for conducting the LCA and 

its general intent, as well as specifying the product systems and data categories to be 

studied. 

2. 	Life-Cycle Inventory (LCI) involves the quantification of raw material and fuel inputs, 

and solid, liquid, and gaseous emissions and effluents. 

3. 	Life-Cycle Impact Assessment (LCIA) characterizes the environmental burdens 

identified in the LCI and assesses their effects on human and ecological health, as well 

as other abiotic effects, such as smog formation and global warming. 

4. 	Improvement Assessment or Interpretation of Results uses findings from the analysis 

to identify and evaluate opportunities for reducing life-cycle environmental impacts of 

a product, process, or activity, or to reach conclusions and provide recommendations. 

SETAC’s definition includes the improvement assessment component, whereas ISO 

includes the life-cycle interpretation component. The LFSP LCA did not perform this 

step; it is left to the electronics industry and others to complete this step for their 

specific operation or interests using the results of this study. 

LCA evaluates the life-cycle environmental impacts from each of five major life-cycle stages: 

raw materials extraction/acquisition, materials processing, product manufacture, product use, 

and final disposition/end-of-life. Figure 1.1 briefly describes each of these stages for a solder 

product system. The resource flows (e.g., material and energy inputs) and the emissions, 

waste, and product flows (e.g., outputs) within each life-cycle stage, as well as the interaction 

between each stage (e.g., transportation) are evaluated to determine the environmental 

impacts. The LFSP LCA combines raw materials extraction and materials processing into one 

“upstream” life-cycle stage in the presentation of results. 

3
Figure 1.1. Life-Cycle Stages for Solder Alternatives 

4
Question 2: 

Which solders were investigated 

during the project? 

Both paste and bar solders were evaluated in this study. Paste solders are screened onto 

printed wiring boards (PWBs) to facilitate placement of components, then reflowed by 

passing the PWB assembly though a high-temperature oven. Reflow soldering is used to 

attach surface mount components and other micro-componentry to a circuit board during 

assembly. Bar solders are melted in a solder pot and then pumped through a nozzle that 

forms a defined wave over which the assembly is passed. Wave soldering is used to attach 

large surface devices and feed-through components. Wave soldering is used mostly in lowtech, low-cost applications, and reflow soldering is usually used for higher-tech applications. 

Table 2.1 lists the specific solders that were investigated in this study. 

Table 2.1. Solders Selected for Evaluation 

The project participants chose the individual solders based on a variety of factors, such as 

current market trends and solder performance studies; all of the solders are currently available for use in the electronics industry. Eutectic tin/lead (SnPb) solder, the only lead-based 

solder that was evaluated, was chosen as the baseline for both wave and reflow applications. 

Tin/copper (SnCu) was selected because it is currently being used by segments of the 

industry as a low-cost substitute for SnPb in wave solder applications. Tin/silver/copper 

(SAC) was selected because of its ability to function in both a wave solder and reflow environment and because it appears to be emerging, through testing, as a top choice for a 

substitute for SnPb (NEMI, 2002). The evaluation group also includes two bismuthcontaining solders—bismuth/tin/silver (BSA) and tin/silver/bismuth/copper (SABC)—in 

order to assess their environmental impacts, particularly at the end-of-life, because they are 

being considered by the industry partners as possible replacements for lead-based solder. 

FUNCTIONAL UNIT 

In an LCA, product systems are evaluated on a functionally equivalent basis. The “functional 

unit” normalizes data based on equivalent use to provide a reference for relating process 

inputs and outputs to the inventory and impact assessment across alternatives. 

For this project, the functional unit is a unit volume of solder required to form a viable 

surface mount or through-hole connection between the PWB and the component. The 

functional unit is based on the understanding that a similar volume of solder is required to 

fill the space in a solder joint regardless of the type of solder used. Thus, a volume of one 

thousand cubic centimeters of solder was selected for use as the functional unit in the LCA. 

5
QUESTION 3: 

How were life-cycle environmental 

and health impacts evaluated? 

Two of the phases of an LCA, life-cycle inventory and life-cycle impact assessment, are 

necessary to calculate environmental impacts. 

LIFE-CYCLE INVENTORY 

Life-cycle inventory (LCI) involves identifying and quantifying material and resource inputs, 

and emission and product outputs, from the product being evaluated. For the LFSP, LCI 

inputs include materials, energy, and other resources used throughout the life cycle of the 

solders. Outputs include products, air emissions, water effluents, and releases to land. 

Figure 3.1 shows the processes that are included in the scope of the LFSP for the SnPb paste 

solder life cycle. Although the process diagrams for solder alternatives may vary somewhat 

from solder to solder and from paste to bar, the scope for each alternative is similar to that 

shown for the SnPb paste solder, except for the following differences: 

1. 	The upstream production of lead is replaced with the appropriate alternate metals 

found in each alloy. 

2. 	In addition to the fuels used in paste manufacturing (i.e., natural gas, heavy fuel oil), 

liquefied petroleum gas (LPG) is also used as a fuel input in bar manufacturing. 

3. 	The cost of copper smelting for the BSA alloy is potentially prohibitive because of its 

high bismuth content. Therefore, flows from demanufacturing are assumed to be sent 

to a landfill or an incinerator rather than to a copper smelter. 

Figure 3.1. SnPb Paste Solder Life-Cycle Processes 

6
Given the enormous amount of data involved in inventorying all of these inputs and outputs, 

decision rules were used to determine what to include in the LCI. Decision rules are designed to make data collection manageable, but still representative of the product and its 

impacts. For example, upstream process inputs in major processes that meet one or more of 

the following criteria would be included in this study: 

$ constitutes greater than one percent of the total mass or energy required to manufacture the solder; 

$ materials falling into the one to five percent range were evaluated based on the other 

decision rule criteria, as well as the availability of data; 

$ is known or suspected to have environmental significance; 

$ is known or suspected to have significant energy requirements; 

$ is physically unique to a solder alternative over the baseline SnPb solder; or 

$ is functionally significant to the solder. 

The data collected for this study included primary data that were obtained for this project, 

data obtained through site visits, and testing or secondary data that were obtained from 

existing databases. LCI data were imported into GaBi, a publicly available life-cycle assessment tool in which customized life-cycle process profiles were developed for each of the 

solders. 

LIFE-CYCLE IMPACT ASSESSMENT 

Life-cycle impact assessment (LCIA) is the process by which the environmental burdens 

identified in the LCI are translated into environmental impacts. It is important to note that 

direct comparisons cannot be made across impact categories, because impacts in different 

impact categories are generally calculated based on different scales. The LFSP LCIA consisted of two steps: classification and characterization. 

CLASSIFICATION 

The LCIA methodology employed in this study places each impact and output from the LCI 

into one or more of sixteen impact categories, including global warming, stratospheric ozone 

depletion, photochemical smog, energy consumption, potential chronic human health, and 

aquatic ecotoxicity. 

CHARACTERIZATION 

The characterization step of LCIA converts and aggregates LCI results to common units 

within an impact category to produce an impact score. Three different approaches are used 

to quantify the magnitude of potential impacts, depending on the impact category: 

$ Loading: An impact score is based on the inventory amount (e.g., resource use). 

$ Equivalency: An impact score is based on the inventory amount weighed by a certain 

effect, equivalent to a reference chemical [e.g., global warming impacts relative to 

carbon dioxide (CO2

)]. 

7
$ Scoring of inherent properties: An impact score is based on the inventory amount 

weighted by a score representing a certain effect for a specific material (e.g., toxicity 

impacts are weighted using a toxicity scoring method). 

Table 3.1 presents the 16 impact categories and a description of how each is calculated. 

Table 3.1. Impact Categories 

a

Acronyms: Particulate matter with average aerodynamic diameter less than 10 micrometers (PM10); total 

suspended particulates (TSP); biological oxygen demand (BOD); total suspended solids (TSS). 

8
Question 4: 

How do the environmental and 

health impacts compare among 

paste solders? 

This section compares the results for each impact category described in Question 3 for the 

paste solders. Although some LCAs assign importance ranks or weights to impact categories, 

this LCA does not include this step because it requires subjective choices that might not be 

appropriate for all stakeholders. 

WHICH SOLDER SCORED HIGHEST AND LOWEST IN 

EACH IMPACT CATEGORY? 

Table 4.1 presents the life-cycle impact scores for each of the paste solders evaluated and a 

quality rating given to each impact category score. Highlights from the results are as follows: 

$ Among all of the solders, 

–	 SnPb has the highest impact category score (shown in bold) for six impact 

categories; 

–	 SAC has the highest impact category score in ten impact categories; 

–	 SnPb has the lowest impact category score (shaded values) in five impact categories; 

and 

–	 BSA has the lowest impact category score in seven impact categories. 

Table 4.1. Paste Solder Life-Cycle Impact Scores 

a

The functional unit is 1,000 cc of solder applied to a printed wiring board. 

b

Quality summarizes the overall relative data quality associated with each impact category: high (H), medium 

(M), or low (L). 

Note: Bold indicates the solder with the highest impact score within an impact category; shaded scores indicate 

the solder with the lowest impact score. 9
$ Among the lead-free solders, 

–	 BSA has the lowest impact score in all categories except non-renewable resource use; 

–	 SAC has the highest impact score in all categories except aquatic ecotoxicity and 

occupational cancer; and 

–	 SABC has the highest impact score in occupational cancer and aquatic ecotoxicity, 

and the lowest impact score in non-renewable resource use. 

Note that these impact scores only indicate the relative or incremental differences among the 

solders and do not necessarily indicate any particular level of concern. 

Figure 4.1 displays the relative differences of the 16 environmental and human health impact 

categories presented in Table 4.1. The values derived for the figure are the log of the ratio of 

the alternative solder impact score to that of the SnPb baseline solder score for each impact 

category. Log ratios reported as a positive number reflect a favorable comparison (lesser 

relative impacts) to the baseline SnPb solder for the alternative; a negative number represents 

an unfavorable result (greater relative impacts) as compared to the baseline solder. Note that 

comparisons should only be made within not across impact categories. 

Figure 4.1. Relative Comparison of Paste Solder Life-Cycle Impact Scores 

10

Note: Do not compare across impact categories. 
WHICH LIFE-CYCLE STAGES DRIVE THE IMPACT SCORES? 

A summary of the top contributing life-cycle stages for each solder by impact category is 

presented in Table 4.2. The life-cycle stage or stages that contribute 50 percent or more to 

impacts in each impact category are listed in the table. In cases where an individual lifecycle stage did not constitute a majority, the top stages that together exceed 50 percent are 

listed; the life-cycle stage with the greatest contribution is listed first. The use/application 

life-cycle stage dominates many of the solder impacts. 

$ For SnPb, the use/application stage contributes the majority of the impacts for thirteen 

out of sixteen impact categories. Nearly all of the impacts associated with the use/ 

application stage result from the generation of the energy consumed during the solder 

reflow process during PWB assembly. 

$ SAC has nine impact categories where the use/application stage is a major contributor 

and six categories in which the upstream stage provides the majority of impacts. The 

upstream impacts are primarily from silver production. EOL and manufacturing are 

top contributors to the occupational non-cancer impact category only. 

$ The BSA impacts are driven by the use/application stage in eleven categories, by the 

upstream stage in three categories, and by EOL in two categories. 

$ The impact categories for SABC are driven by the same life-cycle stages as BSA with 

the exception of the occupational non-cancer impact category, which is driven by the 

EOL and manufacturing stages, as is the case for SnPb and SAC. 

Table 4.2. Paste Solder Life-Cycle Stages Contributing a


Majority to Each Life-Cycle Impact


NATURAL RESOURCE IMPACTS 

Non-renewable resource use. Non-renewable natural resources are typically abiotic materials, such as mineral ore or fossil fuels. The use/application stage contributes 65 to 96 

percent of the non-renewable natural resource use impact category depending on the solder. 

Electricity generation in the reflow application process is the main driver for this impact 

11
category. SnPb consumes the most electricity per functional unit due to its higher relative 

density (see Table 2.1). BSA consumes less energy during reflow application relative to the 

other paste solders, because of its lower melting temperature (despite its high density). SAC 

and SABC have greater overall impacts for this category due to the significant contribution of 

upstream silver production. 

Renewable resource use. Renewable resources are typically biotic materials, such as forest or 

animal products, plants, and water. Impacts from the use/application stage contribute 93 to 

99 percent of the total renewable resource use category and are due primarily to the consumption of water for electricity generation in the reflow application process. SnPb has the 

highest impact score in this category, because it consumes the most electricity per functional 

unit due to its higher relative density (see Table 2.1). BSA has the lowest impact category 

score, because it consumes less electricity during reflow application relative to the other paste 

solders due to its lower melting temperature (despite its high density). 

Energy use. Energy use impact scores are the sum of electrical and fuel energy inputs. 

Electricity use in the reflow application process is the main driver for this impact category. 

SAC has the highest impact score due to the energy used during silver extraction and processing. The energy impacts from silver processing approach those of tin processing, even 

though the silver content (3.9%) of SAC is considerably less than the tin content (95.5%). 

BSA’s energy use score is lower relative to the other paste solders because of its lower melting 

temperature (see Table 2.1). 

Landfill space use. Landfill space use impacts are calculated based on the volume of landfill 

space consumed by solid, hazardous, and/or radioactive waste. SnPb has the lowest score for 

this impact category; SAC has the highest score. Silver production, specifically the generation of slag, is responsible for the upstream life-cycle stage dominating this impact category 

for the lead-free solders. For example, the upstream life-cycle stage accounts for 67 to 84 

percent of the total landfill space impact score for the lead-free solders. In contrast, the 

upstream stage accounts for less than 1.4 percent of the total SnPb landfill space impact 

score, which is driven by the use/application stage. 

ABIOTIC ECOSYSTEM IMPACTS 

Global warming. The impact scores for the effects of global warming and climate change are 

calculated using the mass of a global warming gas released to air modified by a global 

warming potential equivalency factor. Global warming impacts follow the trend observed for 

the energy use category (i.e., the use/application stage drives this impact category), which is 

expected given that electricity generation produces significant amounts of carbon dioxide, a 

global warming gas. BSA has a substantially lower score in this category because it has a 

lower melting temperature, which reduces its energy consumption during reflow application. 

SAC has the highest score in this category due to the higher global warming scores for 

upstream silver extraction and processing relative to the other metals. 

12
Stratospheric ozone depletion. Ozone depletion impact scores are based on the identity and 

amount of ozone depleting chemicals that are released to air. SAC has the highest score for 

this impact category, whereas BSA’s score is the lowest. The use/application phase dominates 

the impacts for all of the solders, although the upstream stage contributes a larger portion of 

the total impacts for the lead-free alternatives than for SnPb. Electricity consumption in the 

solder reflow process is entirely responsible for ozone depletion impacts in the use/application phase. Silver production is the top contributor to the upstream life-cycle stage for the 

non-lead alternatives. It should be noted that some of the materials in the ozone depletion 

inventory should have been phased out and might have been (the inventory is just dated). 

An alternate analysis that was performed with only the non-phased out ozone depleting 

chemicals in the inventory showed similar differences between the solders; however, the 

manufacturing stage now dominates for all of the solders. 

Photochemical smog. Photochemical smog refers to the release of chemicals that may react 

with sunlight in the atmosphere to produce photochemical oxidants, such as tropospheric 

ozone. Upstream and use/application stages both contribute significantly to the photochemical smog impact category for the lead-free solders, whereas the use/application stage 

contributes nearly 93 percent of the SnPb smog impacts. The solder reflow application 

process is the only contributor to the use/application stage, whereas silver production is the 

main contributor to the upstream stage. 

Acidification. Acidification impacts refer to the release of chemicals that may contribute to 

the formation of acid precipitation. SAC has the highest impact score for this category; SnPb 

has the lowest score. Approximately 93 percent of the SnPb life-cycle acidification impacts 

are driven by the use/application stage. The lead-free solder impacts are driven by both the 

upstream and use/application stages. Electricity generation is the largest contributor to the 

use/application phase, whereas silver production drives the upstream contribution. Sulfur 

dioxide and nitrogen oxides are the main contributors of the acidification impacts. 

Air particulates. Air particulate impacts are based on the amount of particulate matter with 

an average aerodynamic diameter less than 10 micrometers (PM10) that is released to the air. 

Total suspended particulates/dust was used if PM10 data were not available. SnPb has the 

lowest score for this impact category; SAC has the highest score. Approximately 79 percent 

of the life-cycle air particulate impact score for SnPb is driven by the use/application stage. 

Dusts generated during silver production and during electricity generation for reflow application drive the impact score for the lead-free alternatives. 

Water eutrophication. Eutrophication (nutrient enrichment) impacts to water are based on 

the identity and concentrations of eutrophication chemicals released to surface water after 

treatment. The use/application phase accounts for 95 to 99 percent of total water eutrophication impacts for all of the paste solders. Chemical oxygen demand from the electricity 

generation process is responsible for most of these impacts. SnPb has the highest score for 

this impact category, although its score may be indistinguishable from those of SAC or SABC 

given uncertainties in the data. BSA has less of a water eutrophication impact than the other 

solders because it consumes less energy during solder application. 

13
Water quality. Water quality impacts are characterized as surface water impacts due to the 

biological oxygen demand and total suspended solids in the wastewater streams released to 

surface water. SAC has the highest score for this impact category, and BSA has the lowest 

score. The use/application stage accounts for 95 percent of the water quality impacts for the 

SnPb solder and between 71 to 78 percent for the lead-free solders. Upstream production of 

the lead-free alternative solders contributes 18 to 26 percent of the water quality impacts, 

with silver production contributing a disproportionately large amount relative to the silver 

content in the solders. 

HUMAN HEALTH AND ECOTOXICITY 

Occupational health—non-cancer. Occupational impact scores are based on the potential 

toxicity of material inputs to each process. This characterization method does not necessarily 

indicate where actual exposure is occurring. Instead, it uses the inputs of potentially toxic 

materials as surrogates for exposure. Occupational non-cancer impacts for SnPb, SAC and 

SABC receive significant contributions from the solder manufacturing process. The toxicity 

of lead is very high relative to the other metals, which, when combined with lead’s relatively 

high input amount, results in the lead-based occupational non-cancer impacts being far 

greater than those from the lead-free alternatives. SnPb impacts range from 69 to 239 times 

greater than the other solders. Silver drives the occupational non-cancer impacts for the leadfree solders because it has the highest non-cancer toxicity among the constituent metals of 

the non-lead alternatives. BSA has the lowest impact score for this impact category because 

it is comprised of the least amount of silver of the non-lead solders. 

Occupational health—cancer. Natural gas used to generate electricity for reflow application 

is the greatest contributor to this impact category for all of the paste solders. SnPb has the 

greatest occupational cancer impact score, but it is not significantly higher than those for 

SABC and SAC. BSA has the lowest impact score, because less electricity is used to reflow 

BSA. The high impact score for natural gas is primarily due to the relatively large amount of 

natural gas inputs to the associated processes and not necessarily due to its carcinogenicity. 

When no cancer classification or measure of carcinogenicity has been given to a potentially 

toxic material, the LCA methodology assigns average default values to those materials. Thus, 

the occupational cancer results indicate that impacts are not driven by any classified (known 

or suspected) carcinogen. 

Public human health—non-cancer. Impact scores are calculated based on the identity, 

inherent chronic toxicity, and amount of toxic chemical outputs to air, soil, and water. The 

public non-cancer impacts for SnPb are far greater than the other solders due to lead’s high 

toxicity and its greater landfill leachability as determined by TCLP testing. SnPb impacts, 

which are driven by the end-of-life stage, range from eight to seventeen times greater than 

the lead-free solders. For the non-lead solders, the public non-cancer impacts are driven by 

sulfur dioxide emissions from upstream silver production. BSA has the lowest score for this 

impact category. 

14
Public human health—cancer. Nitrogen oxides from electricity generation needed for reflow 

application are the greatest contributors to public cancer impacts for all of the solders. SAC 

has the highest score in this impact category due to the significant contribution from the 

upstream production of silver. BSA has the lowest score in this category because it has a 

lower melting temperature, which reduces its energy consumption during reflow application. 

Similar to occupational cancer impacts, results are driven by materials that have not been 

classified or measured as carcinogens, indicating little concern over any known carcinogens. 

Aquatic ecotoxicity. Aquatic ecotoxicity impacts refer to the effects of chemical outputs on 

non-human living organisms. SnPb has the highest score for this impact category; BSA has 

the lowest score. The EOL stage accounts for 99.9 percent of the aquatic ecotoxicity impact 

category for SnPb, 70 percent for BSA, 65 percent for SABC, and 45 percent for SAC. The 

SnPb solder impacts are driven by lead emitted to water from landfills. The upstream lifecycle stage is the main contributor to aquatic toxicity for SAC, and it is a significant contributor for the other lead-free solders. Cadmium emitted to water from silver production is 

the driver. 

15
Question 5: 

How do the environmental and 

health impacts compare among 

bar solders? 

This section compares the results for each impact category described in Question 3 for the 

bar solders. Table 5.1 presents the life-cycle impact scores for each of the bar solders evaluated and a quality rating given to each impact category score. Highlights from the results are 

as follows: 

$ Among all of the solders, 

–	 SnPb has the greatest impact category score (shown in bold) in four impact categories, all of which are toxicity-related; 

–	 SAC has the highest impact category score in the remaining twelve impact categories; 

–	 SnPb has the lowest impact category score (shaded values) among the solders in five 

impact categories; and 

– SnCu has the lowest scores in the remaining eleven categories.


$ Among the lead-free solders,


–	 SAC has the highest impact score in all sixteen of the categories evaluated. 

Note that these impact scores only indicate the relative or incremental differences among the 

solders and do not necessarily indicate any level of concern. 

Table 5.1. Bar Solder Life-Cycle Impact Scores 

a

The functional unit is 1,000 cc of solder applied to a printed wiring board.


b

Quality summarizes the overall relative data quality associated with each impact category: high (H ), medium


(M), or low (L).


Notes: Bold impact scores indicate the solder with the highest score for an impact category.


Shaded impact scores indicate the solder with the lowest score for an impact category.


16
Figure 5.1 displays the relative differences of the 16 environmental and human health impact 

categories presented in Table 5.1. The values derived for the figure are the log of the ratio of 

the alternative solder impact score to that of the SnPb baseline solder score for each impact 

category. Log ratios reported as a positive number reflect a favorable comparison (lesser 

relative impacts) to the baseline SnPb solder for the alternative. A negative number represents an unfavorable result (greater relative impacts) as compared to the baseline solder. 

Note that comparisons should only be made within not across impact categories. 

Figure 5.1. Relative Comparison of Bar Solder Life-Cycle Impact Scores 

Note: Do not compare across impact categories. 

WHICH LIFE-CYCLE STAGES DRIVE THE IMPACT SCORES? 

A summary of the top contributing life-cycle stages for each solder by impact category is 

presented in Table 5.2. The life-cycle stage or stages that contribute 50 percent or more to 

impacts in each impact category are listed in the table. In cases where an individual lifecycle stage did not constitute a majority, the top stages that together exceed 50 percent are 

listed. The life-cycle stage with the greatest contribution is listed first. The use/application 

life-cycle stage dominates many of the impacts. 

$ For SnPb, eleven of the sixteen impact categories are driven by contributions from the 

use/application stage. 

17
$ SnCu has thirteen impact categories where the use/application stage is the major 

contributor. 

$ For SAC, the upstream life-cycle stage plays a more important role than it does for 

SnPb or SnCu. The upstream impacts are primarily from silver production. SAC has 

ten impact categories where the upstream stage is the main contributor. The use/ 

application stage dominates four categories. 

$ The end-of-life stage drives the aquatic ecotoxicity impact category for all three solders. 

$ For all categories that are dominated by the use/application stage, except for occupational and public health categories, impacts result from the generation of electricity 

used in the wave application process. 

$ For the public and occupational health categories, inputs to the wave application 

process itself dominate the use/application stage. 

Table 5.2. Bar Solder Life-Cycle Stages Contributing a Majority of


Life-Cycle Impacts


NATURAL RESOURCE IMPACTS 

Non-renewable resource use. Non-renewable natural resources are typically abiotic materials, such as mineral ore or fossil fuels. The use/application stage dominates the impacts for 

SnPb and SnCu, whereas the upstream stage contributes 66 percent of the non-renewable 

18
resource impacts for SAC. An interesting note is that the use/application stage scores are 

nearly the same for all three solders. However, silver production contributes significantly to 

the upstream impacts for SAC, despite the fact that silver comprises only 3.9 percent of the 

overall solder content of SAC. These upstream impacts cause SAC to have a greater impact 

score than SnPb or SnCu. 

Renewable resource use. Renewable resources are typically biotic materials, such as forest or 

animal products, plants, and water. Impacts from the generation of electricity in the use/ 

application stage dominate impacts for all three solders, contributing 63 to 94 percent of the 

total impacts. The upstream stage is an important contributor to the overall SAC impact 

score, resulting in a greater total impact score for SAC compared to SnPb and SnCu. 

Energy use. Energy use impact scores are the sum of electrical and fuel energy inputs. The 

materials extraction and processing (upstream) life-cycle stage drives the SAC results for this 

impact category and causes it to dominate the other two solders. SnPb and SnCu are driven 

by the use/application stage for this impact category, which is driven entirely by electricity 

consumption in the bar solder process. Energy impacts from silver processing are greater 

than impacts from tin processing, even though the silver content (3.9%) of the SAC solder is 

much less than that of tin (95.5%). This illustrates the relatively high energy intensity of 

silver extraction and processing compared to the other solder metals. 

Landfill space use. Landfill space use impacts are calculated based on the volume of landfill 

space consumed by solid, hazardous, and/or radioactive waste. Impacts for SAC are 16 times 

greater than those for SnPb and SnCu. Landfill space use for SAC is driven by the upstream 

life-cycle stage, which alone exceeds the total impacts from SnPb and SnCu. Upstream silver 

production, specifically the generation of slag, contributes 87 percent of the total life-cycle 

landfill space use for SAC. The end-of-life stage is the leading contributor to the total 

impacts for SnPb and SnCu. 

ABIOTIC ECOSYSTEM IMPACTS 

Global warming. The impact scores for the effects of global warming and climate change are 

calculated using the mass of a global warming gas released to air, modified by a global 

warming potential equivalency factor. Global warming impacts follow the trend observed for 

the energy use category (i.e., SAC is driven by the upstream stage, SnPb and SnCu are driven 

by the use/application stage) due to the large amounts of electrical energy used over the lifecycle of these solders. Electricity generation produces considerable amounts of carbon 

dioxide, a global warming gas. Unlike the paste solders where the global warming impacts 

are dominated by the use/application stage, both the upstream and use/application stages 

contribute significantly to the global warming impacts for each of the bar solders. This is 

because the reflow process uses more energy than the wave process and thus dominates the 

impacts for paste solder. 

Stratospheric ozone depletion. Ozone depletion impact scores are based on the identity 

and amount of ozone depleting chemicals that are released to air. SAC has more than twice 

the ozone depletion impact score of the other bar solders. The use/application stage dominates for SnPb (82%) and SnCu (87%); however, despite SAC’s nearly equivalent impact 

19
score for use/application, the upstream stage contributes 59 percent of the ozone depletion 

impact score for SAC. Electricity generation for the solder wave process is entirely responsible for the use/application stage impacts. Emissions from the extraction and processing of 

the metals, mainly silver, drives the upstream impacts. It should be noted that some of the 

materials in the ozone depletion inventory should have been phased out and maybe have 

been (the inventory is just dated). An alternate analysis that was performed with only the 

non-phased out ozone depleting chemicals in the inventory showed similar differences 

between the solders; however, the manufacturing stage now dominates for all of the solders. 

Photochemical smog. Photochemical smog refers to the release of chemicals that may react 

with sunlight in the atmosphere to produce photochemical oxidants, such as tropospheric 

ozone. SAC has the highest score for this impact category; SnPb has the lowest score. 

Nearly 91 percent of the SAC photochemical smog impacts are driven by the upstream stage, 

whereas SnPb and SnCu are driven by the use/application stage. Air emissions from silver 

production account for 87 percent of the total smog impact for SAC. Air emissions from 

electricity generation for the solder wave process are the only contributors to the use/application stage impacts. 

Acidification. Acidification impacts refer to the release of chemicals that may contribute to 

the formation of acid precipitation. SAC has the highest acidification impact score, with the 

upstream stage accounting for nearly 91 percent of the score. The use/application stage 

scores are approximately equal for each solder. However, this stage contributes a majority of 

the total SnPb and SnCu impacts due to the much lower impacts from the upstream stage. 

Electricity generation is the largest contributor to the use/application phase, whereas silver 

production drives the upstream contribution. Sulfur dioxide and nitrogen oxides are the 

main contributors of the acidification impacts for all of the solders. 

Air particulates. Air particulate impacts are based on the amount of particulate matter with 

an average aerodynamic diameter less than 10 micrometers (PM10) that is released to the air. 

Total suspended particulates/dust was used if PM10 data were not available. The upstream 

stage drives the air particulate impact category for all of the solders due to dusts generated 

during upstream metals production. The total impact category score is significantly higher 

for SAC due to dusts generated during silver production, which accounts for 84 percent of 

the total impact category score. Dusts from electricity generation for wave application 

contribute 38 percent and 29 percent of the impacts for SnPb and SnCu, respectively. 

Water eutrophication. Eutrophication (nutrient enrichment) impacts to water are based on 

the identity and concentrations of eutrophication chemicals released to surface water after 

treatment. SAC has the highest score in this impact category, and SnCu has the lowest. The 

use/application phase accounts for at least 75 percent of the total water eutrophication 

impacts for each of the bar solders. Upstream process impacts, primarily silver production, 

account for 23 percent of the overall impacts for SAC, but the upstream stage contributes 

less than 1 percent of the total impact scores for SnCu and SnPb. Flows of chemical oxygen 

demand from the electricity generation process for all of the solders and from silver production for SAC are responsible for most of these water eutrophication impacts. 

20
Water quality. Water quality impacts are characterized as surface water impacts due to the 

biological oxygen demand and total suspended solids in the wastewater streams released to 

surface water. SnCu has the lowest score for this impact category; SAC has the highest 

impact score. The upstream stage contributes a significant portion of the total water quality 

impacts for SAC. SnCu and SnPb water quality impacts are driven by the use/application 

phase. Silver production is again the primary contributor to the upstream impacts, whereas 

electricity generation for bar solder application drives the use/application stage impacts. 

HUMAN HEALTH AND ECOTOXICITY 

Occupational health—non-cancer. Occupational impact scores are based on the potential 

toxicity of material inputs to each process. This characterization method does not necessarily 

indicate where actual exposure is occurring. Instead, it uses the inputs of potentially toxic 

materials as surrogates for exposure. The occupational non-cancer score for SnPb is far 

greater than the score for the other solders because of SnPb’s higher inherent toxicity 

compared to the other solders. The manufacturing, use/application, and EOL life-cycle 

stages largely contribute to the total impacts, regardless of the solder type. Bar solder inputs 

to the wave application process are the top contributors to the use/application stage for all of 

the solders. 

Occupational health—cancer. SnPb has the greatest occupational cancer impact score, but 

its score is not significantly higher than those for SnCu and SAC. All four life-cycle stages 

contribute to the occupational cancer scores. The use/application stage is the greatest 

contributor to the total. The top three contributors to the SnPb impacts are bar solder from 

wave application, solder on a PWB going to a landfill, and dross inputs to post-industrial 

recycling. For SAC and SnCu, the top three contributors are natural gas from tin production, bar solder from wave application, and tin from bar manufacturing. The high impact 

score for natural gas is primarily due to the relatively large amount of natural gas inputs to 

the associated processes and not necessarily due to its carcinogenicity. When no cancer 

classification or measure of carcinogenicity has been given to a potentially toxic material, the 

LCA methodology assigns average default values to those materials. Thus, the occupational 

cancer results indicate that impacts are not driven by any classified (known or suspected) 

carcinogen. 

Public human health—non-cancer. Impact scores are calculated based on the identity and 

amount of toxic chemical outputs with dispositions to air, soil, and water. Inventory items 

do not truly represent long-term exposure. Instead, impacts are relative toxicity weightings 

of the inventory. The public non-cancer impacts for SnPb are far greater than the other 

solders due to lead’s high hazard value and its greater landfill leachability as determined by 

TCLP testing. The EOL stage contributes 99.5 percent of the total SnPb public non-cancer 

impacts. SAC is driven largely by sulfur dioxide emissions (50%) and lead emissions to soil 

(37%) from silver production in the upstream stage. SnCu is driven by sulfur dioxide 

emissions from the generation of electricity in the use/application stage (62%). 

21
Public human health—cancer. SAC has the highest public cancer impact score of the three 

solders. Wave soldering during the use/application life-cycle stage dominates the impacts for 

all three solders, whereas the upstream stage is a significant contributor to the total impact 

for SAC. Flux material released during wave soldering is the top contributor to the use/ 

application impact score. Potential upstream impacts arise from outputs of potentially 

carcinogenic materials in the extraction and processing of the various metals present in the 

solders. Potential cancer impacts from silver extraction and processing are disproportionately 

high compared to the percentage of metals in the solders. 

Aquatic ecotoxicity. Aquatic ecotoxicity impacts refer to the effects of chemical outputs on 

non-human living organisms. The EOL stage accounts for 99.96 percent of the aquatic 

ecotoxicity impact category for SnPb, 96.4 percent for SnCu, and 86 percent for SAC, 

although the absolute aquatic ecotoxicity impact score is far greater for SnPb than for the 

other bar solders. For SAC, the upstream life-cycle stage contributes 14 percent to the total 

impacts; cadmium emitted to water from silver production is the driver. Landfilling is the 

largest contributor to the EOL impact for SnPb. Unregulated recycling and disposal is the 

greatest process group contributor to EOL impacts for the lead-free solders. 

22
Question 6: 

What are the limitations of the study?


This section summarizes the main limitations and data uncertainties in the study’s methodology. It also presents the results of additional analyses that were performed for the reflow 

energy consumption, silver mining and processing data set, and leachate data. These analyses were performed because they evaluated data with the largest uncertainty or because the 

data were major contributors to the inventory results. 

LCA LIMITATIONS AND DATA UNCERTAINTIES 

Uncertainties exist in the life-cycle inventory (LCI) and life-cycle impact assessment (LCIA). 

Uncertainty in the inventory data for the LFSP life-cycle assessment (LCA) includes, but is 

not limited to, the following: 

$ missing individual inventory items; 

$ missing processes or sets of data; 

$ measurement uncertainty; 

$ estimation uncertainty; 

$ allocation uncertainty/working with aggregated data; and 

$ unspeciated chemical data. 

Uncertainties related to the impact assessment include, but are not limited to, the following: 

$ missing chemical equivalency or toxicity data; and 

$ model uncertainty/screening level analysis. 

ADDITIONAL REFLOW ENERGY DATA ANALYSIS 

Energy consumed during the use/application life-cycle stage constituted a majority of the 

impacts for many of the impact categories evaluated. Electricity consumption data for the 

paste solder application process are based on primary data (considered to be of good quality) 

collected from two facilities where test runs were conducted. The two ovens in which these 

tests were performed represent a large range in energy consumption due to the difference in 

the efficiencies of the ovens. In the baseline analysis, an average energy consumption value 

from these two test runs was used to determine the life-cycle impacts. The additional 

analysis determined the sensitivity of these results to the energy consumption rate using both 

the high and low data points from the testing. The energy use impact category was selected 

as an example of the potential sensitivity to the electricity consumption data, because a large 

percentage (between about 82 and 91 percent) of the baseline impacts in this category for all 

four solders resulted from the energy consumed during reflow. 

Figure 6.1 shows the results of the reflow application energy additional analysis for all three 

scenarios (low energy, baseline, and high energy). Although the magnitude of the scores 

changed, the relative comparison among the solders did not: SAC still has the highest 

23
impacts, followed by SABC, then SnPb, and finally BSA. As illustrated in Table 6.1, the use/ 

application phase still drives the energy use impact category. This suggests that the results 

are not too sensitive to the uncertainties in the reflow application energy estimates (assuming 

the range used in this sensitivity analysis represents a true or realistic range of the energy 

estimates for a reflow application process). 

Figure 6.1. Reflow Application Energy Additional Analysis 

Table 6.1. Percent Contribution of Use/Application Stage to Energy Impacts 

An additional energy analysis was not performed for the wave application process, because: 

(1) the energy data that were used are expected to be representative of general wave applications, even though they are only from one data set; and (2) the relative magnitude of the 

energy from use/application compared to the other life-cycle stages was lower for wave 

applications than for reflow applications. 

ADDITIONAL SILVER INVENTORY ANALYSIS 

Due to the large influence that silver production had on many of the impact categories of the 

lead-free solder pastes, an additional analysis was performed by substituting a publicly 

available silver data set for the one used in the LFSP (i.e., GaBi). Although the quality of 

24
this alternate data set could not be verified, and thus it was not used for the LFSP baseline 

analysis, it is used here to demonstrate the impacts of using another data set on the overall 

results. Table 6.2 compares the results of the additional analysis to the baseline results for 

paste solder. For the paste solders, the alternate silver data set resulted in a significant shift 

in the relative scores of the solders, increasing the number of categories in which SnPb has 

the highest impact score from six to fourteen impact categories. SAC on the other hand, 

despite having many scores very close to SnPb, has the highest score in only one category. 

BSA remains the solder with the lowest relative impacts compared to the other solders. The 

overall shift in results is due to various flows in the alternate silver inventory that have lower 

values than the associated flows in GaBi. Due to a lack of available documentation for the 

alternate data, it is unclear what is causing the differences in the data sets. Some potential 

reasons could be different scoping boundaries of the inventories, different processes included, 

or different mines or processing plants represented. 

Table 6.2. Comparison of Paste Solder Baseline and Additional LCA Analyses 

a

Numbers indicate the number of impact categories where solder has the highest or lowest score. 

b

GaBi: Software system for Life Cycle Engineering, PE & IKP, 2000; DEAM: Database for Environmental Analysis 

and Management, Ecobilan, 1999. 

As shown in Table 6.3, the additional analysis for bar solders also results in an overall decrease in importance of the silver mining process. The number of categories for which SnPb 

has the highest relative impact score rises from four to nine, whereas SAC decreases from 

twelve to only seven. This is not as dramatic a change as was seen with the paste results; 

however, several impact-specific conclusions were altered. Unlike the paste solders results, 

the solder with the lowest relative impact score for any category is split among the solders. 

Table 6.3. Comparison of Bar Solder Baseline and Additional LCA Analyses 

*

Numbers indicate the number of impact categories where solder has the highest or lowest score. 

These results indicate the high sensitivity of the overall life-cycle results for paste solders to 

the silver data set. The baseline GaBi data set is believed to be of good quality and attempts 

to verify the alternate data set were inconclusive; therefore, the GaBi data set was chosen for 

the LFSP baseline analysis. However, these results show the possible variability and sensitivity of the results to the silver inventory data and suggest that additional effort to increase the 

quality of the silver mining and extraction data would be well spent. 

25
ADDITIONAL LEACHATE DATA ANALYSIS 

The leachability study conducted for the LFSP project was used to estimate the outputs of 

metals from landfilling printed wiring board (PWB) waste or residual metals in incinerator 

ash. Lead was found to leach to a much greater extent than the other metals in the solders 

being analyzed in this study. This leachability contributed to the large public non-cancer 

and aquatic ecotoxicity impacts for the SnPb solder as compared to the other solders for both 

the paste and the bar solder results. The Toxicity Characteristic Leaching Procedure (TCLP) 

used for the LFSP study is based on a standard EPA TCLP test protocol using acetic acid, a 

substance known to readily leach lead. However, it is unknown to what extent these test 

conditions represent actual landfill conditions, which can vary dramatically over the lifetime 

of a landfill. The additional analysis, therefore, was conducted using the detection limit of 

lead during the leachability testing as a lower bound of lead leachability to determine the 

sensitivity of the results to the lead leachability. 

Results of the analysis indicated that even with the assumption that the lead essentially does 

not leach (i.e., assuming the amount leached is equivalent to the study detection limit for 

the leachability of lead), the SnPb solder impact scores are still at least 2.5 times higher than 

the score of the next closest solder for public non-cancer impacts, and a full order of magnitude higher for aquatic toxicity. However, the relative differences between SnPb and the 

lead-free solders are far less than in the baseline analysis. This analysis suggests that any 

elevation of the leachability data for SnPb due to the aggressive nature of acetic acid towards 

the lead-based solder was unlikely to have changed the overall impacts for SnPb relative to 

the other solders. The SnPb solder would still have higher potential impacts for both public 

non-cancer and aquatic toxicity than the other solders, based primarily on its relative toxicity. 

26
Question 7: 

What can electronics manufacturers 

do to reduce environmental and 

health impacts? 

This section identifies selected opportunities for reducing the overall environmental and 

human health impacts of solder used in electronics manufacturing based on the results of the 

LCA. Improvements in the upstream and use/application stages are presented and analyzed 

due to the significant impacts resulting from these stages and their associated potential for 

improvement. Though not specifically detailed here, additional opportunities for improvement may exist in other areas of the solder life cycle. 

AREAS OF OPPORTUNITY FOR HUMAN HEALTH AND 

ENVIRONMENTAL IMPACT REDUCTIONS 

Upstream and Solder Manufacturing. Upstream processes result in significant contributions to the environmental and human health impacts for solder, particularly the lead-free 

alternatives containing silver. Table 7.1 presents impact categories in which at least 30 

percent of the overall impact score resulted from upstream processes. The overall percentage 

contribution in each category is presented for each solder type. As shown in the table, flows 

from upstream materials extraction and processing made significant contributions in a total 

of seven different categories for paste solders and in as many as eleven impact categories for 

bar solders, depending on the solder. 

Table 7.1. Percentage Contribution of Upstream Processes to


Overall Impacts by Category


1

As an indication of significance, table includes only categories for which the contribution from upstream processes


to the overall impact score exceeds 30 percent for at least one solder.


‘—‘ indicates the contribution made by upstream processes does not exceed 30 percent of the overall impacts in


the category.


27
Virgin materials extracted and refined during upstream processes are often combined with 

recycled metal during the manufacture of solder. The percentage of the solder comprised of 

virgin material can vary widely by solder type and solder manufacturer. Table 7.2 lists the 

average virgin material content of each of the solders evaluated, along with the range of data 

as reported by the manufacturers for this study. 

Table 7.2. Average Virgin Content of Base Metals Used in Solder Manufacturing 

1

Range of virgin content used across solder types as reported by solder manufacturers. 

Composition of the solders ranged from no recycled content to 80 percent of the composition of some solder alloys for Sn and Pb, and as high as 100 percent recycled content for 

silver, depending on the solder manufacturer and the alloy. Because the recovery process is 

prohibitively expensive, bismuth is not currently being reclaimed by the electronics industry. 

Therefore, Bi is composed of nearly entirely virgin material. Manufacturers producing both 

paste and bar solders of a particular alloy reported no difference in virgin material content 

between the solder types for the alloy. 

Post-consumer recycling reclaims scrap metal from electronic products that enter the waste 

stream at their end-of-life, refining the metallic content to its base metals. By contrast, postindustrial recycling processes are operated by solder manufacturers to accept and reclaim inprocess manufacturing wastes from the manufacture or use/application of solder during the 

PWB assembly process. Because the process wastes are mostly waste solder compounds, the 

metals need only to be refined to common alloys rather than to base metals. Use of secondary metals reclaimed through post-industrial recycling, therefore, are preferable to those 

derived from post-consumer scrap due to the energy efficiency of the reclamation process. 

Given the importance of the upstream processes in many of the life-cycle impact categories, 

and the high percentage of virgin material used to manufacture the solders, an opportunity 

exists to reduce these impacts through the use of recycled metal. Reclaimed metal derived 

from either post-industrial or post-consumer recycling produces less environmental impact 

per volume than does the mining and extraction of virgin metal. Substituting recycled 

metals for virgin content will reduce the overall environmental footprint of the solder life 

cycle in several categories. For example, implementing a 25 percent reduction of virgin 

materials used in SAC solder paste results in a corresponding decrease of the overall impacts 

to air particulates, landfill space use, photochemical smog, and acidification of at least 22 

percent. Similar, though less dramatic, reductions in the overall environmental footprint 

would occur in other categories listed in Table 7.1. 

28
Use/Application of Solder Paste. The generation of energy required for the application of 

paste and bar solders results in the largest contribution to the overall impact score for many 

of the impact categories, regardless of the solder type. Table 7.3 displays the percentage of 

the impacts attributable to use/application processes for each impact category for which the 

use/application stage made the largest contribution. As shown in the table, the use/application stage was the top contributor to as many as fourteen separate impact categories for paste 

solders. Impacts from the use/application stage were equally dominant for bar solder. 

Table 7.3. Percentage Contribution of Use/Application Processes 

by Impact Category 

‘—‘ indicates an impact category where the largest contributions resulted from a life-cycle stage other than use/ 

application. 

After being applied to the PWB, solder paste must be heated to a temperature high enough 

to melt, or reflow, the solder. The majority of impacts shown in the above table directly 

result from the production of the large amounts of energy required to heat the solder during 

the reflow process. Energy consumption can vary widely depending on the solder type and 

the equipment specifications and process operating parameters employed by the facility (see 

Question 8 for more details). Table 7.4 presents the energy consumption data collected 

during reflow solder testing conducted at two separate facilities in support of this project. To 

facilitate comparison of the results, testing was conducted using an identical protocol and 

under controlled conditions. 

29
Table 7.4. Power Consumption During Reflow Testing 

As shown in the table, power consumption for the reflow solder process varied significantly 

across facilities, despite the use of similar test protocols. Energy consumption at the Intel 

facility was at a minimum 2.3 times greater than the energy consumed at Vitronics-Soltec for 

each solder evaluated. Reflow equipment designed for the high temperatures associated with 

lead-free, such as the oven at Vitronics-Soltec, are developed using the latest technologies and 

are optimized to achieve greater temperature stability through increased thermal efficiency. 

Given the importance of the use/application stage and the relative thermal inefficiency of 

assembly equipment optimized for SnPb, an opportunity exists to reduce the amount of 

energy consumed during lead-free assembly through equipment changes and process optimization. As shown in Table 7.4, power consumption can be reduced significantly by replacing 

older, less efficient reflow assembly equipment, or by optimizing current equipment to 

perform at the elevated temperatures required for lead-free soldering. For example, using the 

data in Table 7.4 for SnPb, a facility realizing a 65 percent reduction in power consumption 

through the replacement of equipment or by other means would result in reductions in 

potential environmental impacts ranging from 40-60 percent in most categories, as well as a 

20 percent or greater reduction in occupational and public human health impacts. Though 

not presented in detail here, similar though less dramatic improvements would result from a 

reduction in energy consumption associated with the wave soldering process. 

30
Question 8: 

What are the challenges to 

implementing lead-free soldering? 

There is no drop-in replacement for SnPb solder. The switch to lead-free solders affects 

many aspects of the manufacturing and assembly process, all of which must be considered by 

manufacturers seeking to effectively implement lead-free solder. The electronics industry and 

its suppliers have been working to develop the materials and techniques required for the 

successful implementation of lead-free solders during the manufacture of electronic devices. 

This section presents information developed or recorded during the performance of the LCA 

that can aid in the implementation of lead-free solder by industry. Even though there are 

many barriers and subtleties to implementation of an entirely new metallurgy, this section 

summarizes the current industry wisdom regarding key challenges to adopting lead-free 

solders. 

Components. Identifying and securing lead-free components can be the most timeconsuming and important aspect of lead-free soldering. Components used for SnPb are not 

capable of withstanding the elevated temperatures of lead-free assembly. Components 

manufactured with Sn or with NiPdAu finishes have successfully been developed for use with 

lead-free solders. Components that are certified for lead-free use conform to the RoHS 

standard of less than 0.1% Pb content. Components, however, must also be able to withstand 260o

C peak temperatures associated with lead-free assembly. Particularly susceptible 

are plastic components such as connectors, LEDs, and capacitors. Many types of components rated for use in 255-260o

C are currently being offered and certified for lead-free solder 

assembly (Lange et al., 2004). 

Laminates. The higher temperatures needed for lead-free soldering place additional stress on 

the circuit board laminate, especially when performing multiple soldering operations. Some 

commonly used laminates, such as FR-4, may not be able to withstand the 260o

C peak 

temperatures possible during lead-free assembly without charring or significant warping. 

Testing has indicated that key parameters to consider when choosing a laminate include the 

glass transition temperature (Tg), the decomposition temperature (Td), and the material 

coefficient of thermal expansion (CTE) (McGrath, 2005). 

New high reliability laminates are being introduced for lead-free soldering. These laminates 

can be processed in a similar manner to “standard” laminate, but are able to withstand 

higher process temperatures and are better suited for use in situations where the end product 

may operate at higher temperatures or may be subject to thermal cycling. The higher 

temperature laminates can be more expensive than typical FR-4, but may be required 

depending on the assembly requirements. 

31
Cleaning. Cleaning of flux residues from surfaces of process work takes on additional importance to remove more aggressive flux residues from circuitry. Lead-free flux formulations 

require higher flux capacity, higher oxygen barrier capability, and increased thermal stability 

to withstand the elevated process temperatures. Cleaning lead-free flux residues remaining 

on the surface becomes more challenging due to increased residue activity from flux-induced 

metallurgical reactions and more insoluble tin-salt formation. Cleaning takes on additional 

importance when pure tin components or tin surface finishes are used, as these lead to tin 

whisker formation that may create electrical shorting if not removed during cleaning. 

Some combination of increased cleaning time, higher temperature cleaning, increased 

mechanical energy, or inclusion of a cleaning additive will likely be required to meet the 

increased cleaning requirements of lead-free soldering. The correct combination of factors 

depends greatly on process characteristics such as flux type, wave or reflow temperature, and 

the amount of non-soluble surface materials (e.g., solder balls) present. Although more 

difficult, cleaning of residues from lead-free assembly surfaces should be possible using 

existing SnPb process cleaning equipment. 

WAVE SOLDERING 

Wave soldering will require solder pot temperatures in the range of 260-275oC depending on 

the solder. Under these conditions, a longer preheat will be needed to keep thermal shock to 

the board below 100o

C, and to prevent damage to components. Other considerations 

specific to implementation of lead-free wave soldering are discussed below. 

Equipment maintenance. Tin in high concentrations and at elevated temperatures has 

proven to be corrosive to many metals, including stainless steel. Leading lead-free solders 

(e.g., SAC) are comprised of a higher percentage of Sn than is SnPb. These high Sn solders 

have melting points at least 30o

C higher than SnPb on average. At these elevated temperatures, the lead-free solders have been observed to be corrosive to process equipment used to 

both manufacture and apply the lead-free solders to PWBs (Sweatman et al., 2004; Morris 

and O’Keefe, 2003). 

During the smelting and refining of the metals, solder manufacturers and post-industrial 

recyclers have observed more rapid corrosion of pumps, nozzles, and refining pots resulting 

in shortened equipment life (Cookson, 2002). In some cases, equipment that typically 

lasted seven years needed replacing in as little as two years. Erosion of stainless steel parts of 

wave soldering equipment including solder pot and pot fittings has been observed in wave 

soldering processes using high tin, lead-free solders. Corrosion of solder pots constructed of 

stainless steel can lead to failure in as little as 6 months (Morris, 2003). This phenomenon 

can pose a serious worker safety concern and increase substantially the industry costs of 

converting to lead-free solder. 

Several potential solutions are being assessed and implemented by equipment manufacturers. 

The use of a small addition of nickel to stabilize wave soldering baths has been shown to 

inhibit corrosion in industry testing (Sweatman, 2004). Coatings, such as Melonite, have 

also been shown to slow the rate of corrosion, extending the life of the equipment. However, 

the coatings typically break down after time, leading eventually to the corrosion of the solder 

32
pot. Cast iron pots have been used by some equipment manufacturers to good effect, but 

can lead to the eventual leaching of iron that will contaminate the solder requiring more 

frequent bath dumps. 

Solder bath maintenance. The higher temperatures of lead-free solder can lead to shortened 

bath life through the increased corrosivity of the high Sn-content solders. Increased erosion 

of copper from PWB circuitry has been observed during wave soldering leading to faster 

copper build-up in SAC and SnCu. The dissolution of copper in lead-free solders is nearly 

3x as that in SnPb requiring frequent dilution or replacement with fresh solder (Aim, 2001). 

Iron leached into the bath as a result of Sn corrosivity must also be monitored (Barbini, 

2005). Bath maintenance must be performed more frequently to prevent the buildup of 

harmful contaminants that adversely affect product reliability. 

Solder dross. Higher dross rates from the formation of oxides at higher temperatures place 

an emphasis on solder pot control and maintenance. Dross consists of oxides formed at the 

surface of the molten solder through interaction with air. Due in part to higher pot temperature, dross formation rates for SnCu and SAC are roughly 2.5 times the rate for SnPb 

(Hwang et al., 2004). To minimize the formation of dross, the solder wave should be kept in 

standby mode or shut off when not actively passing work over the wave to reduce turbulence. 

Addition of solder dross inhibitors, such as phosphorus, can be effective inhibitors of dross 

formation, though phosphorus has been known to increase Sn corrosivity of copper 

[Sprovieri, 2004]. Higher dross rates may make the use of solder skimming or purifying 

equipment desirable, but care should be taken to not use the equipment on both SnPb and 

Pb-free solders to prevent lead contamination of the dross, which would preclude recycling. 

Rework/Repair. Rework and repair conducted with lead-free solders differs from typical 

SnPb procedures because the alloys do not wet to the surface or wick into the holes as easily 

as does SnPb. Despite these differences, successful rework methods have been developed 

with lead-free solders for most types of components using a variety of tools and methods, 

both semi-automatic and by hand. Rework equipment used for SnPb can be used for rework 

of the lead-free solder with some minor modifications. The greatest problems arise from the 

different CTEs of the laminate, solder, and the underlying circuitry. The 30o

C higher 

temperatures required to rework lead-free connections place thermal stress on the materials 

that expand at different rates, potentially causing failure of the solder joint. Undergoing an 

additional thermal cycle may also damage components already stressed from the higher 

temperatures. Rework should also be performed using a solder that is metallurgically 

compatible with the original solder to prevent future solder joint reliability issues. 

REFLOW SOLDERING 

The greatest challenges to implementation of lead-free solder technology during reflow arise 

from the tightened process control window and the ability of the equipment and materials to 

meet that window. The process window, which is defined at the lower end by the melting 

temperature of the alloy, and at the upper end by the maximum component temperature, 

drops from roughly 30o

C for SnPb solders to less than 20oC for SAC. Complicated assem33
blies with high component densities exacerbate the problems related to a narrow process 

window. Considerations specific to the implementation of lead-free reflow soldering are 

presented below. 

Paste Application. Solder paste is typically applied by a screen printing process. A paste is 

first applied to the stencil, filling the stencil apertures, and then applied to the PWB using a 

squeegee or enclosed print head. The release characteristics of SnPb solder paste are well 

known. Lead-free solder paste, however, has a higher viscosity than SnPb solder, due to its 

higher metal content, and has a tendency to stick to the aperture walls (Ashmore, 2005). 

Lead-free solder paste also exhibits lower wetting ability than SnPb solder, placing an emphasis on printing accuracy not needed with SnPb solder, which tends to self-correct during 

reflow. 

Research has indicated that stencil material, manufacturing, and screen printing techniques 

all have to be examined when implementing lead-free solder. Nickel-based stencils have 

displayed good release and accuracy characteristics under testing (Ashmore, 2005). Manufacture of stencils from the same material using different techniques displayed varying results, 

indicating that lead-free solder may be sensitive to the techniques used. Finally, adjustment 

in the rate and pressure of squeegee application of the solder may have to be adjusted to 

account for the differing characteristics of lead-free solder pastes. 

Reflow Profiles. Reflow profiles define the time/temperature relationship required to 

promote the formation of reliable solder joints on a PWB assembly. Key profile parameters 

include time above preheat, time above liquidous (TAL), peak temperature, preheat and 

cooling zone ramp rates, and overall cycle-time. Optimization of the profile involves the use 

of thermocouples to measure surface and component temperatures at key locations to determine if the temperatures fall within the process control window. A successful profile will 

minimize the temperature differentials (DT) for the assembly. A large DT indicates that areas 

of the assembly may have been heated excessively while other areas may be insufficiently 

heated, resulting in a variety of solder defects such as non-wetting, voiding, or damaged 

devices. 

Profiles are product-specific, solder/flux-specific, and are largely dependent upon the capabilities of the reflow equipment making it difficult to develop a standard profile for lead-free 

soldering. Lead-free solder profiles, however, are typically characterized by longer soak times 

during preheat and by higher peak temperatures than the profiles for SnPb assembly. The 

longer soak times are required to bring both the board and the components to equilibrium 

prior to reaching the reflow temperature to limit thermal shock and improper joint 

formation. 

Profiles exhibiting the best performance for lead-free soldering are either the ramp-soak-spike 

(RSS) or the ramp-to-spike (RTS) form. Solder pastes utilizing water-based fluxes should 

not be used with RSS profiles because the longer soak times may break down the flux prior 

to reflow. RTS profiles have a shorter cycle-time and have been demonstrated to perform 

well with lead-free solders. If, however, a large DT exists or if you have older reflow equipment, a RSS profile may be a more appropriate choice. 

34
Reflow Ovens. Although existing reflow equipment is able to provide the 250-260o

C 

heating environments required to process lead-free assemblies, the ability of the oven to 

maintain the process within the tighter process window should be investigated. Thermal 

efficiency in older equipment was often sacrificed in favor of shorter response times to the 

varying demands of multiple reflow profiles in the production environment. Many olderstyle ovens were prone to heating different parts of an assembly at varying rates, often 

depending upon the color and texture of the parts and substrates being reflowed. As a result, 

older equipment may lack the ability to maintain the proper amount of control over the oven 

environment needed to minimize DT on the product, and may have to be modified or 

replaced. 

Ovens developed to meet the challenges of lead-free soldering typically use forced convection 

heating. By circulating warm air around the assemblies, heat is provided in a uniform and 

controlled manner that minimizes DT. Testing confirmed that these ovens are more thermally efficient, consuming nearly a third of the power consumed by older ovens (see Table 

7.4). In addition, the maximum temperature and rate of heating for a given profile can be 

controlled strictly. These forced convection ovens offer greater zone-to-zone stability, providing a level of control necessary to operate within the shrinking operating window made 

necessary by the implementation of lead-free solders. 

REFERENCES 

AIM, “A Study of Lead-Free Wave Soldering,” Fact Sheet. 2001. <www.aimsolder.com/ 

techarticles/A%20Study%20of%20Lead-Free%20Wave%20Soldering.pdf> 

Ashmore, C. “Will Your Printing Process be Affected by Pb-Free?” Circuits Assembly, p.22, 

March, 2005. <http://circuitsassembly.com/cms/images/stories/pdf/0503/ 

0503screenprinting.pdf> 

Barbini, D. Personal communication between J. Geibig and D. Barbini of Vitronics-Soltec 

on February 25, 2005. 

Hwang, J., K. Chew, V. Kho. “Lead-Free Implementation: Drop-In Manufacturing,” Apex 

2004 Technical Conference Proceedings, Anaheim, CA, 2004. 

Lange, B., J. Huckabee, D. Romm. “Component Supplier’s Qualification of Lead-Free Green 

Package Solutions.” Electronics Goes Green 2004+, Berlin, Germany. 

McGrath, B. “The Effects of Lead-Free on PCB Fabrication,” Printed Circuit Design and 

Fabrication, p. 44-47. February 2005. <http://pcdandm.com/pcdmag/mag/0502/ 

0502mcgrath.pdf> 

Morris, J., M. O’Keefe. “Equipment Impacts of Lead-Free Wave Soldering,” Apex 2003 

Technical Conference Proceedings, Anaheim, CA, 2003. 

Sprovieri, J. “Stirring the Pot,” Assembly Magazine, October, 2004. <http:// 

www.assemblymag.com/CDA/ArticleInformation/features/BNP__Features__Item/ 

0,6493,135209,00.html> 

Sweatman, K., S. Suenaga, M. Yoshimura, T. Nishimura. “Erosion of Copper and Stainless 

Steel by Lead-Free Wave Solder,” Proceedings of IPC Printed Circuits Expo, 2004. 

35
Question 9: 

What are the performance 

differences among the solders? 

To supplement the LCA information on tin-lead and lead-free solders, a literature review was 

conducted to gather information on the performance characteristics of the lead-free solders. 

Although research on the health and environmental impacts of lead-free solders is very 

limited outside this study, research of alternative solders’ performance was found to be taking 

place on a large scale by multi-stakeholder partnerships and industry sectors, as well as 

academia. These studies, however, are difficult to compare. The studies differed in their 

focus and often considered different alloy combinations, as well as performance tests. Additionally, resulting data were presented in varying metrics. Such disparities in the available 

data hindered the comparability of performance results across sources. Most studies compared the performance of the alternative solders with existing SnPb alloy standards. The 

table below includes a list of the considered literature sources and a summary of the information presented in each source. Finally, the charts exhibited below present select comparative 

data. 

Table 9.1. Summary of Alloy Properties by Source 

36
37
*

Several literature sources cited select characteristics for alloys that differed in composition from that mentioned. 

Such compositions have been included in parentheses following the appropriate comment. 

REFERENCES 

AIM(a), “AIM Lead-Free Soldering Guide: Alloys, Chemistries, Data, Experience, Consultation,” <www.aimsolder.com/techarticles/AIM%20leadfree%20guide.pdf?section=assembly> (accessed November 2002). 

AIM(b), “Technical Data Sheet: Technical Articles: Lead-free Product Data Sheets,” 

<www.aimsolder.com/leadfree_tdss.cfm?section=assembly> (accessed November 2002). 

Bath, J., C. Handwerker, E. Bradley. “Research Update: Lead-Free Solder Alternatives,” 

Circuits Assembly, May 2000. p. 31-40, <www.circuitassembly.com> 

Grusd, A., C. Jorgensen. “Lead-FREE Alloys: Fitting the Square Peg in the Square Hole,” 

Circuitree, September 1999. p. 98-102. 

Kariya, Y., W. J. Plumbridge. “Mechanical Properties of Sn-3.0mass%Ag-0.5%mass%Cu 

Alloy,” Materials Engineering Department, The Open University, U.K. 

Lau, J. H., C.P. Wong, N.-C. Lee, S. W. R. Lee. “Electronics Manufacturing With Lead-Free, 

Halogen-Free & Conductive-Adhesive Materials,” McGraw-Hill, Ch. 13: Prevailing 

Lead-Free Alloys, September 2000. p. 13.1-13.62. 

National Institute of Standards & Technology (NIST) and Colorado School of Mines (CSM), 

“Database for Solder Properties with Emphasis on New Lead-free Solders Release 4.0,” 

Properties of Lead-Free Solders, February 11, 2002 (last updated). <www.boulder.nist.gov/ 

div853/lead%20free/props01.html> (accessed November 2002). 

Ochiai, M., T. Akamatsu, H. Ueda. “Reliability of Solder Joints Assembled with Lead-Free 

Solder,” Fujitsu Science Technology Journal, 38, 1, June 2002. p. 96-101. 

38
Plumbridge, W. J. “The Solder Programme at the Open University Materials Engineering 

Department: An Update, 2001,” Materials Engineering Department, The Open 

University, UK, <technology.open.ac.uk/materials/mat-hp.html> 

Quan, S., C. Bradshaw, S. Kwiatek. “Properties of Lead Free Alloy and Performance Properties of Lead Free No-Clean Solder Paste,” Presented at IPC SMEMA Council APEX® 2002, 

<www.goapex.org> 

Seelig, K., D. Suraski. “Materials and Process Considerations for Lead-Free Electronics 

Assembly,” <www.aimsolder.com/techarticles/ 

Materials%20and%20Process%20Considerations%20for%20LeadFree%20Electronics%20Assembly.pdf> (accessed November 2002). 

COMPARISON OF ALLOY PROPERTIES 

This section presents samples of comparative alloy data for select performance properties by 

source. These data should not be compared across sources, without referencing back to the 

initial literature source, as performance tests carried out on alloys and metrics used to display 

data often differed. 

NIST and CSM data (Figure 9.1) compare two alloys, SnCu and SnAgCu, with eutectic 

SnPb. Two processes were carried out on the two alloys: water-quenched and air-cooled. 

Although eutectic SnCu exhibited lower elongation than eutectic SnPb, air-cooled SnCu 

exhibited higher elongation than its water-quenched alloy and the SnAgCu alloy through 

both processes. Air-cooled SnAgCu exhibited higher tensile strength than both the alloys, 

whereas its elongation was lower than SnCu and similar to SnPb. 

Figure 9.1. Mechanical Properties

 Key: A = water-quenched average; B = air-cooled 

39
NIST and CSM data (Figure 9.2) also present that the reflow temperature and melting range 

of eutectic SnCu is the highest when compared with three other alloys (see below). Sn3.2Ag-1.1Cu-3Bi is found to have the highest liquidous temperature, whereas all other alloys 

fall between 205-230o

C. Reflow temperatures for all four alloys fall between 230-255oC. 

Figure 9.2. Thermal Properties 

Lau et al. (Figure 9.3) present that eutectic SnCu is lower in tensile strength but higher in 

elongation than SnPb, reflecting its softness and ductility. The tensile strength of SnAgCu is 

higher than eutectic SnPb. SnAgCuBi alloys exhibit a higher tensile strength and a lower 

elongation as compared to eutectic SnPb. 

Figure 9.3. Ultimate Tensile Strength, Yield Strength and Elongation 

40
The exhibit of NIST and CSM data in Figure 9.4 presents that SnPb has the lowest creep 

strength when compared with SnCu and SnAgCu alloys, whereas SnAgCu presents the 

highest creep strength. 

Figure 9.4. Creep Strength 

41
Question 10: 

What are the potential market 

impacts of a switch to lead-free 

solders? 

This section presents the costs associated with the changes in demand for solder metals that 

might result from a shift from lead-based solders to the lead-free solder alternatives considered in the LCA. First, the current use of lead-based solder is discussed. Second, the impacts of a U.S. conversion to lead-free solder alternatives are presented. Finally, market 

summaries are presented for the metals used in lead-free solders. 

CURRENT U.S. USE OF TIN-LEAD SOLDER 

The current quantity of tin-lead solder used in electronic products is not available in the 

published literature. However, potential values of the amount of electronic solder consumed 

in the United States were developed from U.S. Geological Survey (USGS) tin and lead 

consumption data, expert opinion, and estimates of world production of tin-lead solder. The 

estimates of U.S. consumption of electrical solder range from 30 million pounds to 73 

million pounds. Based on research done in 2002, EPA believed the most likely level to be 

between 35 million pounds and 42 million pounds. To avoid underestimating the magnitude of a switch from tin-lead solder to lead-free solder, EPA used a slightly conservative 

estimate of U.S. tin-lead solder consumption of 44 million pounds for this analysis. Worldwide estimates of tin-lead solder use in 2002 are over 176 million pounds. 

IMPACT ANALYSIS OF A U.S. CONVERSION TO LEAD-FREE SOLDERS 

This section evaluates the potential impacts on the U.S. markets for the alternative metals 

that could result from a U.S. conversion from tin-lead solder to four alternative lead-free 

solders. This analysis focuses on a conversion of solders used in electrical applications only, 

excluding uses for building construction, can and container manufacturing, and automobile 

assembly. 

The first step of this analysis is an assessment of the change in quantities of alternative metals 

that might be demanded as a result of a conversion to lead-free solder. The current amount 

of tin-lead solder consumed in electronics products in the U.S., estimated to be 20,000 

metric tons, is used along with the mass-based substitution ratios to calculate the equivalent 

amount of lead-free solder that would be needed as a substitute. For each constituent metal 

in the alternative solders being considered, the analysis calculates the additional quantity 

demanded. 

The second step in the analysis is an assessment of the magnitude and the significance of the 

changes in the markets of the alternative metals. This is done by comparing the change in 

demand for each alternative metal to the current production, consumption, and existing 

stocks of that metal, for the United States and for the world. This comparison reveals the 42
magnitude and importance of the change in the potential demand for each metal. Information on market trends is then used to frame the results in the dynamic context of changing 

markets. 

Table 10.1 presents EPA’s estimates of the change in demand for each metal used for the 

alternative solders. Using the information on solder composition and solder substitution 

ratios, this table converts the quantity of each metal currently used in tin-lead solder (column 1) into the quantity of each metal that would be demanded under the three alternatives 

(column 4). The difference between the two estimates is the change in the quantity of each 

metal that would be demanded if all use of tin-lead solder in the United States were discontinued (column 5) and shifted completely to any one of the lead-free solders. Column 7 

presents the value of the change in metal demand, valued at year-2003 prices (column 6). 

Table 10.1. Additional Quantities Demanded by a U.S. Conversion to


Lead-Free Solder


a

Estimated Baseline Quantity of Tin = 20,000 mton * 63%. 

bThe densities of lead, tin, silver, copper, and bismuth are 11.34, 7.31, 10.49, 8.92, and 9.78 g/cm3, respectively. 

The density of the baseline solder, 63% tin and 37% lead, is 8.801 g/cm3, or (0.37)11.34 + (0.63)7.31. The density 

is used to convert volume (functional unit) to mass. 

c Estimated Post-Conversion Quantity = 20,000 metric tons * Post-Conversion % * Ratio of Alternative to Tin-Lead 

Solder by Mass. 

dEstimated Change in Quantity = Estimated Post-Conversion Quantity - Estimated Baseline Quantity. 

ePrices are as reported in the USGS Mineral Commodity Summaries, 2004. The tin price is the New York 

Composite average price. The silver price is from Handy and Harmon quotations. The copper price is the


London Metals Exchange price. The bismuth price is the price received by domestic dealers.


f Estimated Value of Additional Quantity = Estimated Additional Quantity * U.S. Refined Metal Price in 2003. 

Source: USGS Mineral Commodity Summaries 2004 

43
Table 10.2 shows the magnitude of the change in metal demand under each alternative, 

relative to current U.S. production, consumption, and stocks of that metal. The table 

presents the estimated quantity of each metal that was produced, consumed, or held in 

stockpile in the United States in 2003 (columns 2, 4, and 6). It also shows the change in 

demand for the metals, both by weight (column 1, from Table 10.1 above) and as a percentage of current production, consumption, and stocks (columns 3, 5, and 7). 

Table 10.2. Impacts of U.S. Conversion on U.S. Markets 

a Estimated Change in Quantity (demanded by a U.S. conversion to lead-free solder) from Table 10.1, column 5.


bRefined production quantities exclude mine production; copper scrap production is also excluded.


c Estimated % Increase in U.S. Refined Production = Estimated Additional Quantity / U.S. Refined Production.


dThe reported production quantities are used for tin and bismuth; the production quantities for copper are the


reported refined production quantities; the production quantity for silver is the apparent production.


e Estimated % Increase in U.S. Refined Consumption = Estimated Additional Quantity / U.S. Refined Consumption.


f Estimated % of U.S. Refined Stocks = Estimated Additional Quantity / U.S. Refined Stocks.


Source: USGS Mineral Commodity Summaries 2004. 

A conversion to the SnCu alternative would result in the largest increases in demand for tin 

and copper. Converting to the SAC alternative would result in the largest increase in silver 

demand. The BSA alternative would lead to the largest bismuth demand increase, as well as 

a decline in tin demand. The decrease in demand for lead as a result of any of the conversions would be 12,600 metric tons, with an estimated value of $5,972,322.1 

1

The London Metal Exchange price of lead in 2003 was $474 per metric ton. 

44
If all U.S. tin-lead solder used in electronics applications were replaced by any alternative 

containing Bi, the impact on the market for bismuth could be very large and Bi mines would 

have to increase their output. A conversion to lead-free solder could also have a significant 

impact on silver markets, which would lead to an increase in silver production. Three of the 

lead-free solders use significantly more tin than the current tin-lead solder and one uses 

significantly less. Therefore, the impact of a switch to lead-free solders on the tin market is 

unclear. Copper is used in three of the lead-free solder alternatives, but in very small quantities; therefore, a U.S. conversion to lead-free solder would have almost no effect on U.S. 

copper markets. Existing above-ground stocks would be sufficient to meet this small increase 

in demand for copper. 

45