A Thermodynamic Modeling Approach for the Design and Development of Low-Temperature Solder Alloys

In recent years, the electronic packaging industry emphasized on low-temperature solder as a strategic focus to mitigate warpage issues during the reflow process. Sn-Bi solder alloys has emerged as potential candidates due to their low melting points and lower costs; however, the presence of large Bi phase fractions in the eutectic Sn-Bi solder introduces reliability issues due to the inherent brittleness of Bi. In this study, a low-temperature Sn47Bi1In2Zn solder alloy with a solidus of 120°C measured by DSC was developed through thermodynamic calculations based on the CALPHAD (CALculation of PHAse Diagram) method using the PANDAT software. The goal of this study is to find a low-temperature solder alloy with the CALPHAD-type thermodynamic calculation methods. Furthermore, we found out that the double addition of In and Zn both decreases the melting point of Sn-Bi alloy, which could be first predicted and illustrated in the vertical section calculation in the PANDAT software. Finally, a low-temperature Sn-Bi-In-Zn quaternary solder alloy was developed.