Microstructure, hardness, and shear behavior of Sn3.0Ag0.5Cu–Sn58Bi composite solder joint

In this study, Sn3.0Ag0.5Cu-Sn58Bi (SAC-SnBi) composite solder joint was obtained by two-step soldering process. The microstructure, hardness, and shear performance of the composite solder joint were investigated in comparison with the eutectic Sn58Bi (SnBi) and SnAgCu (SAC) solder joints. Experimental results showed that the SAC-SnBi had similar intermetallic compound (IMC) morphology and thickness with the SAC solder joints. Compared with the eutectic SnBi solder, the large Bi-rich matrix transforms into tiny Bi-rich grains in the SAC-SnBi solder bulk. Tiny Bi-rich grains, Cu₆Sn₅, and Ag₃Sn distribute uniformly in the composite solder bulk. As the SnBi bulk melts into the SAC solder during the second soldering process, the formation and growth of large β-Sn dendritic in SAC solder is suppressed in the composite solder. Therefore, the SAC-SnBi composite joint shows higher hardness and shear strength than the other two. (paper)