Microstructure and drop/shock reliability of Sn-Ag-Cu-In solder joints

The drop/shock reliability of new quaternary Sn-Ag-Cu-In Pb-free solder alloy with increasing amounts of copper was investigated on the basis of their mechanical properties and microstructures in comparison with ternary Sn-1.2Ag-0.5Cu Pb-free solder alloy and quaternary Sn-1.2Ag-0.5Cu-0.4In Pb-free solder alloy as suggested in a previous work. The results showed that Sn-1.2Ag-0.7Cu-0.4In solder alloy has excellent drop/shock reliability compared to Sn-1.2Ag-0.5Cu and Sn-1.2Ag-0.5Cu-0.4In solder alloys owing to the thin IMC thickness and the increased mechanical strength. It was considered that indium addition restrained the IMC growth and increasing the amount of copper promoted the formation of Cu6Sn5 and Ag3Sn phase, which resulted in an increase in the alloy strength.