Effect of Multiple Reflowing Processes on Interfacial Reactions and Mechanical Properties between Sn-9.0 wt.%Zn, Sn-3.0 wt.%Ag-0.5 wt.%Cu Solders and Ag Substrate

The effect of multiple reflowing processes on interfacial reactions and mechanical properties of the Sn-9.0 wt.%Zn (SZ)/Ag and Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC)/Ag couples was investigated in this study. The SZ/Ag and SAC/Ag couples were reflowed at 240°C for 10 min in one up to five times. After reflowing, all couples were quenched in icy water and air-cooling conditions. The experimental results revealed that the AgZn3, Ag5Zn8, and AgZn phases were formed in the SZ/Ag couple. The thin AgZn3 layer was observed when the SZ/Ag couple was quenched in icy water. When the number of reflows was increased, a rod-shaped Zn phase gradually became a fine needle-shaped Zn phase. Only the Ag3Sn phase was formed in the SAC/Ag couple. The growth mechanism of the intermetallic compound was diffusion-controlled in both reaction couples. A brittle fracture was observed in the SZ/Ag solder joint. The fracture surface showed the ductile and slightly brittle failure in the SAC/Ag solder joint.