High drop test reliability: lead-free solders

Recently, preventing environmental pollution, lead-free (Pb-free) solders are about to replace tin-lead (Sn-Pb) eutectic solders. Sn-Ag-Cu alloys are leading candidates for lead free solders. Sn-Ag-Cu-P was developed last year, but Sn-Ag-Cu-P alloys were not satisfactory to meet severe customer requirements like thermal aging process followed by drop tests. To improve drop test performance after the thermal aging process, a combination of indium and nickel was investigated. After the effect of indium and nickel on Kirkendall voids and Cu₃Sn growth thickness was studied, the weight ratio of indium to nickel was optimized. Based on the results of board level reliability tests, a new lead free solder has been developed. This paper presents the optimum nickel and indium included in Sn-Ag-Cu based solder alloys.