Effect of In addition on the properties of Sn-Au-Cu lead-free solder

In order to improve the mechanical properties of Sn-Au-Cu solder, Indium was added into Sn-Au-Cu solder and five kinds of Sn-Au-Cu-In solders were designed based on cluster-plus-glue-atom (CPGA) model and the melting properties, microstructure, wettability, interfacial reaction and mechanical properties were studied systematically. The DSC results showed that the addition of In reduced the melting point of the Sn-Au-Cu-In solder. The microstructure of Sn-2.85Au-2.34Cu-0.65In solder consisted of white AuSn4 phase, little Cu6Sn5 phase and gray β-Sn matrix, while the other 4 solders consisted of white Au(Sn,In)4 phase, little Cu6Sn5 phase and gray β-Sn matrix. The wettability of five solders on Cu substrate were better than those on Ni substrate. The wettability of Sn-2.81Au-0.89Cu-3.21In solder on Cu substrate was the best; while that of Sn-2.85Au-2.34Cu-0.65In solder on Ni substrate was the best. The shear strength of Sn-2.85Au-2.34Cu-0.65In solder joint was 72 MPa, which was the highest among the five solders.