The effect of crosshead speed on the joint strength between Sn-Zn-Bi lead-free solders and Cu substrate

The solder joints between Cu/Sn-40Pb/Cu lead solder and Cu/Sn-9Zn/Cu and Cu/Sn-8Zn-3Bi/Cu lead-free solders were studied. The study focuses upon the formation of interface intermetallic (IMC), adhesive strength of the joints and the fracture morphology of the as-soldered soldered joints. For Sn-40Pb, Cu 6Sn 5 IMC was formed. For Sn-9Zn and Sn-8Zn-3Bi solders, two layers were detected. For Sn-9Zn solder, the first layer next to the solder is a Cu 6Sn 5 phase with some Zn dissolve in it. The second layer next to the Cu substrate is γ-Cu 5Zn 8 phase. While for Sn-8Zn-3Bi solder, the first layer is mixture of Cu-Sn + Cu-Zn phase and the second layer is γ-Cu 5Zn 8 phase. Sn-8Zn-3Bi solder has the highest strength followed by Sn-40Pb and Sn-9Zn, respectively, and their strength increases with crosshead speed. The fracture of the solder joints occurs in the elastic strain region or after a small plastic strain with Sn-40Pb solder has the highest strain followed by Sn-8Zn-3Bi and Sn-9Zn solders. The fracture surface of the three solders investigated showed ductile dimple appearance. The addition of 3% Bi increases the tensile strength and ductility of the Sn-Zn-Bi system.