Growth kinetics of Cu–Sn intermetallic compounds at the interface of a Cu substrate and 42Sn–58Bi electrodeposits, and the influence of the intermetallic compounds on the shear resistance of solder joints

This paper explores the growth kinetics of Cu–Sn intermetallic compounds at the interface of a Cu substrate and 42Sn–58Bi electrodeposits obtained from a methane sulphonate bath, and the effect of intermetallic compounds on the shear resistance of solder joints. The growth of the Cu–Sn intermetallic compounds layer [ɛ(Cu3Sn) + η(Cu6Sn5)] during aging exhibits a linear function of the square root of the aging time. The apparent activation energy for the growth of the intermetallic compounds in 42Sn–58Bi electrodeposits on the Cu substrate was 52.48 kJ mol−1. In the early stage of aging, the growth of the intermetallic compound layer contributes to the shear resistance of the solder joints due to the wedge effect of the rough interface between the intermetallic compound layer and the Sn–Bi electrodeposits. However, with further aging, the shear resistance of the solder joint is degraded by the excessive growth of the intermetallic compound layer, which is more brittle than the Sn–Bi electrodeposit layer.