Lead-Free Solder Technology Transfer from ASE Americas
The objective of the workshop "Lead-free Solder Technology Transfer" was to inform the photovoltaic (PV) industry about current trends to phase-out Pb in electronic devices, and to facilitate the transfer of the ASE Americas Inc.'s Sn/Ag solder to other PV manufacturers.
The National Photovoltaic Environmental, Health and Safety (EH&S) Assistance Center
Brookhaven National Laboratory (BNL) operates the National Photovoltaic EH&S Assistance Center, under the auspices of the Department of Energy (DOE), to foster the safe and environmentally friendly operation of photovoltaic facilities and products, extending from R&D to manufacturing and use. The BNL Center undertakes the following activities: a) It directly supports DOE Headquarters, the National Renewable Energy Laboratory (NREL), and Sandia National Laboratory (SNL) to ensure that their facilities and those of their contractors are operated in an environmentally responsible manner. b) It conducts EH&S audits, safety reviews and incident investigations, as needed. c) It assists the photovoltaic industry to identify and examine potential EH&S barriers and hazard-control strategies for new photovoltaic materials, processes and applications before their large-scale commercialization.
The current workshop is guided by this proactive approach to EH&S. It was organized and chaired by Vasilis Fthenakis, BNL. The issue of lead-free solders was raised by the participants of a previous workshop "PV and the Environment" at Keystone, CO in July 1998.
Fthenakis opened the session by welcoming the participants and emphasizing the need for open discussion and collaboration on EH&S issues among all members of the industry. The message he conveyed was that "working together means wining together".
To safeguard the environmental friendliness of photovoltaics, the PV industry follows a proactive, long-term environmental strategy involving a life-of-cycle approach to prevent environmental damage by its processes and products from "cradle to grave." Part of this strategy is to examine substituting lead-based solder on PV modules with other solder alloys. Lead is a toxic metal that, if ingested, can damage the brain, nervous system, liver and kidneys. Lead from solder in electronic products has been found to leach out from municipal waste landfills and municipal incinerator ash was found to be high in lead also because of disposed consumer electronics and batteries. Consequently, there is a movement in Europe and Japan to ban lead altogether from use in electronic products and to restrict the movement across geographical boundaries of waste containing lead.
Photovoltaic modules may contain small amounts of regulated materials, which vary from one technology to another. Environmental regulations impact the cost and complexity of dealing with end-of-life PV modules. If they were classified as "hazardous" according to Federal or State criteria, then special requirements for material handling, disposal, record-keeping and reporting would escalate the cost of decommissioning the modules. Fthenakis showed that several of today's x-Si modules failed the US-EPA Toxicity Characteristic Leaching Procedure (TCLP) for potential leaching of Pb in landfills and also California's standard on Total Threshold Limit Concentration (TTLC) for Pb. Consequently, such modules may be classified as "hazardous" waste. He highlighted potential legislation in Europe and Japan which could ban or restrict the use of lead and the efforts of the printed-circuit industries in developing Pb-free solder technologies in response to such expected legislation.
Japanese firms already have introduced electronic products with Pb-free solder, and one PV manufacturer in the United States, ASE Americas has used a Pb-free solder exclusively in their modules since 1993. Finding a safe, reliable and cost-effective substitute for lead-containing solders is not easy. Tin/lead solder has been the standard solder technology for several decades and extensive knowledge has been gained on the practical and theoretical aspects of its use. The printed circuit and the electronics industries recently embarked on a multi-million-dollar R&D effort to develop such alternatives, focusing on material properties, manufacturing processes, cost of alloys and long-term availability and reliability. Fthenakis outlined such efforts and listed alternatives examined by the electronics industries.
One of the most promising alternatives (for electronics) is the 96.5%Sn/3.5%Ag solder that ASE Americas developed and use. ASE Americas' research and independent field testing showed it is at least as reliable as the standard one. This solder is slightly more expensive than the regular Sn/Pb solder. However, to the audience gratification, Steel Heddle, a solder manufacturer, announced that they will absorb the incremental cost and will supply
96.5%Sn/3.5%Ag at the same price as the conventional Sn/Pb solder ribbon. Another issue is the low TTLC for Ag in California (i.e., 0.5 g / kg of module), but Fthenakis showed that the Sn/Ag solder will add less than 10% of this quantity (i.e., 0.05 g of Ag / kg of module).
The major point made by Fthenakis was that alternatives exist that are both environmentally benign and cost-effective, and that the PV industry can only benefit by being proactive in switching to Pb-free materials, thereby exceeding the expectations of its supporters and averting potential future legislation.
Ronald Gonsiorawski, ASE Americas, gave the major contribution to this workshop. He first described the history of the Sn/Ag solder technology that he developed while at Mobil Solar. His incentive then was to find a better solder in response to failures of conventional Sn/Pb solder contacts at the interface of thick film silver to silicon. Gonsiorawski presented a series of results on thermal bond aging and solder bond strength which showed that the properties of the Sn/Ag solder were superior to those of conventional solder. He then discussed the use of the Sn/Ag solder and described how early problems in processing had been solved. He showed published results on the product's reliability obtained by field testing at the Arizona State University and the Florida Solar Energy Center. He concluded that there are no technical or reliability problems in adapting the
96.5%Sn/3.5%Ag to PV manufacturing, and that, in addition to the environmental advantage of a Pb-free solder, it improves the module's reliability.
After his slide presentation, Gonsiorawski answered questions for about 45 minutes on technical aspects of the Sn/Ag solder technology; the details he gave greatly interested the audience and gained their full appreciation for his expertise and the value of this Pb-free technology. The questions and answers section was recorded and is included in this report.
For a complete workshop report contact:
Brookhaven National Laboratory
Upton, NY 11973
Tel. No. (631) 344-2830
Fax No. (631) 344-4486
Last Modified: June 11, 2008
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