Kinetics of intermetallic compound layers and shear strength in Bi-bearing SnAgCu/Cu soldering couples

Three lead-free solder alloys, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi and Sn-3Ag-0.5Cu-3Bi, have been used to solder with Cu substrate in the current experiments to investigate the influence of Bi on the kinetics of intermetallic compound (IMC) layer growth and shear strength of the soldering couples. The experimental results indicate that the thickness of IMC layer at the solder/Cu interface increases with aging process. The addition of Bi delays the propagation rate of total IMC layer. For the samples aged at 140 °C up to 500 h, their shear strengths keep at a relative stable level where the fracture occurs in bulk solder side and the addition of Bi improve the strength level, while for the samples aged at 195 °C, the shear strengths decrease continuously with aging time where the fracture occurs along interface between IMC layers and solders and the influence of Bi can be negligible.