Volume 7, Issue 8 (September 2010)
Solder Joint Reliability of SnBi Finished TSOPs with Alloy 42 Lead-Frame under Temperature Cycling
Tin-bismuth (SnBi) is a lead-free alternative to pure tin (Sn) lead-frame finish. SnBi finish is considered by some to be a tin-whisker mitigation strategy. In selecting a SnBi finish, the interfacial strength and reliability of solder interconnects formed with select assembly solders must be considered. To characterize the solder interconnect reliability of SnBi finished parts, sets of test assemblies were created with Sn and SnBi finished thin-small-outline-package (TSOP) parts using SAC305 and SnPb solder. Test assemblies were subjected to temperature cycling and interconnect strength tests. It was found that SnBi finish caused TSOP solder joints to have a shorter fatigue life than Sn finish under temperature cycling testing.