Effect of 0.05% Cr on intermetallic compound layer growth for Sn-Ag-Cu Lead-free Solder joint during isothermal aging

The growth behaviors of interfacial intermetallic compound for the solder joints of Sn-3.0Ag-0.5Cu/Cu substrate and Sn-3.0Ag-0.3Cu-0.05Cr/Cu substrate during isothermal aging at 150deg for 0, 24, 168, 500 and 1000 h respectively have been investigated. The results showed that the intermetallic compound layer at the Sn-3.0Ag-0.3Cu-0.05Cr/Cu joint is much thinner than that at the Sn-3.0Ag-0.5Cu/Cu joint after isothermal aging for the same temperature and time. After aging for 1000 h, the average thickness of intermetallic compound layer of Sn-3.0Ag-0.3Cu-0.05Cr/Cu solder joint is only about 5.13 mum, which is far less than that of Sn-3.0Ag-0.5Cu/Cu joint at 11.33 mum. The diffusion coefficients of intermetallic compound layer of Sn-3.0Ag-0.3Cu-0.05Cr/Cu and Sn-3.0Ag-0.5Cu/Cu joints are 3.90times10^-18 m²s^-1and 1.16times10^-17 m²s^-1 respectively. The longer the aging time, the more obvious is the effect of Cr inhibiting the overgrowth of intermetallic compound layer of Cu/Solder/Cu joint.