Effect of a Trace of Bi and Ni on the Microstructure and Wetting Properties of Sn-Zn-Cu Lead-Free Solder

The microstructure and melting behavior of Sn-9Zn-2Cu (SZC) lead-free solder with 3 wt pct Bi and various amount of Ni additions were studied. The wetting properties and the interfacial reaction of Sn-Zn-Cu with Cu substrate were also examined. The results indicated that the addition of 3 wt pct Bi could decrease the melting point of the solder and Ni would refine the microstructure and the rod-shape Cu5Zn8 phase changed into square-shape (Cu, Ni)5Zn8 phase. The addition of Bi, Ni greatly improved the wettability of SZC solder. In addition, the interfacial phase of the solders/Cu joint was typical planar Cu5Zn8 in SZC-3Bi-lNi alloy.