The Trend to Low Temperature Solder (LTS) Assembly and the Development Strategy for Tin-Bismuth based High Reliability LTS solder

Component warpage during reflow soldering is limiting the design and application of area arrays packages. With raw material availability, non-toxicity, wettability, and a melting point lower than 200°C, the Tin (Sn)-Bismuth (Bi) system has been widely identified as providing a promising basis for the LTS that could provide a solution to that problem. However, commercial scale implementation of solders based on that system has been limited by the shortage of experimental data on the relationships between microstructure and mechanical properties of these alloys and their long-term reliability. The work reported in this paper goes some way towards filling that gap by providing some insights into the strain-rate sensitivity of Sn-Bi alloys and its implications for the performance of solder joints in long term service.