Image courtesy of Ames Laboratory
Molten droplet of Ames Lab lead free solder, an alloy of tin, silver, and copper.
A new alloy was discovered with the required properties for a solder based on analysis of the thermal properties, atomic structure, and composition; the end result was a eutectic alloy, a mixture of tin, silver and copper that melted and froze precisely at one temperature – a temperature lower than the melting temperatures of the individual metals that made up the alloy. This eutectic alloy has superior mechanical and electrical properties other lead-free substitute alloys.
The new solder provided an alternative for lead-based solder that is safer to the environment and is stronger than typical tin-lead combinations. Licensed by more than 50 companies worldwide, Ames Laboratory’s lead-free solder has generated over $2.5B in sales worldwide since it was patented.
Composed of lead and tin, traditional solder has been used for thousands of years to fuse together metal parts. Solder melts rapidly at one temperature, flows easily, and then freezes quickly creating a strong, durable bond making it ideal for assembling electronics. However, lead is a highly toxic material and in the 1990s there was a concern that this might be a substantial new threat to the environment as the lead leaches out of electronic devices buried in landfills. This problem led BES-funded researchers at Ames Laboratory to see if their understanding of how metals interact could be used to identify a replacement for traditional tin-lead solder in order to reduce the potential environmental concerns. Their research discovered a combination of copper, tin, and silver which, when mixed together, has a lower melting temperature than each metal has separately. The new alloy was determined to be an excellent substitute for the lead-containing product – and worked at a temperature that could be handled with standard soldering equipment. The work has been licensed by nearly 50 companies worldwide since 2002. Subsequently, additional research developed slight compositional modifications for special soldering applications. Current work is looking into potential additives to the tin-silver-copper formula to further strengthen the solder to combat the heat that is generated in advanced electronics.
Basic Research: Office of Science Basic Energy Sciences program;
Follow-up Applied R&D: DOE Office of Environmental Management, the Iowa State University Research Foundation, and Nihon-Superior Co, a licensee of the technology.
CM Miller, IE Anderson, and JF Smith. “A viable tin-lead solder substitute: Sn-Ag-Cu,” J. Electronic Mater. 23 595 (1994).
DOE Laboratory, Industry
Technology Impact, Collaborations, EM