High-Temperature Lead-Free Solders: Properties and Possibilities

Several candidate alloys have been proposed as alternative solders to high-temperature high-lead solders. None of them, however, can fulfill all the requirements to replace the current high-lead solders. One should understand the properties of the candidate alloys and must carefully apply these solders for high-temperature applications step by step in order to accomplish total lead-free assembly. Three major candidate alloys can be considered as high-temperature solders: Zn-Sn, Au-Sn, and bismuth-based alloys. Each has its own superior characteristics as well as some drawbacks, but all are believed to cover most of the high-temperature applications. There have been other choices appearing as high-temperature interconnections, such as materials based on conductive adhesive technology. In addition, epoxy adhesives filled with metallic solders or nanoparticles with or without silver flakes exhibit excellent stability and can maintain stable interconnection after reflow heat treatment. This paper reviews the latest work on high-temperature lead-free alternative interconnection technologies.