Evolution of interfacial morphology of Sn-8.5Zn-0.5Ag-0.1Al-xGa/Cu system during isothermal aging

The intermetallic compound formation between Sn-8.5Zn-0.5Ag-0.1Al-xGa lead-free solders and Cu substrate under aging was investigated for the Ga contents of 0.05% and 2%. The investigation was conducted by dipping Cu in the solder. The results of investigation indicated that the intermetallic compounds formed were Al4.2Cu3.2Zn0.7, Cu5Zn8, CuZn5 and AgZn3 at the interface in the as-dipped stage. The aging treatment at 150 °C convents the AlCuZn and CuZn5 compound to Cu5Zn8. The Cu6Sn5 compound was formed closing to the Cu substrate after aging for 1000 h. The AgZn3 was decomposed and Ag dissolves in Cu5Zn8 after aging for 500 h. Addition of Ga into the solder also increases the thickness of Cu5Zn8 compound. Long time aging results in the formation of voids and consequently cracks between IMC and solder.