Mechanical properties of Sn-Bi-Ag low-temperature Pb-free solders

We designed low-temperature tin-bismuth-silver (Sn-Bi-Ag, SBA) solder by CALculation of PHAse Diagram (CALPHAD)-type thermodynamic calculations using the PANDAT software and performed corresponding key experiments. The goal is to suppress bismuth (Bi)-rich phase width growth, while keeping their low melting temperatures. This study shows that CALPHAD calculations make a good agreement with experimental results in phase fraction, melting point, and paths of solidification. As for the tensile properties of the SBA solder in as-cast, high yield strength (YS), high ultimate tensile strength (UTS), and slightly better elongation than the conventional Sn-58Bi solder were obtained. After being thermally aged, higher strength and same elongation level of Sn-58Bi were observed.