Temperature dependence of mechanical properties of individual phases in Sn-3.0Ag-0.5Cu lead-free solder alloy

The commercial Sn-3.0Ag-0.5Cu (SAC) lead-free solder alloy consists of Sn-rich and eutectic phases. The mechanical properties of these individual phases were demonstrated to be a function of the temperature. The nano-indentation equipment assembled with advanced-controlled hot-stage was utilized to examine the mechanical characteristics. The experiments were performed at 60degC, 80degC, 110degC, 130degC and 150degC, respectively. It was found that for both Sn-rich phase and eutectic phase, the mechanical properties, such as hardness and elastic modulus, exhibited the dependence on the temperature. In particular, the creep deformation at the dwell time of constant target load exhibited high sensitivity to the temperature. Generally, the higher temperature resulted in a larger creep deformation, which in turn impacted the strain rate sensitivity of the individual phases. The Sn-rich phase showed larger creep deformation than that of eutectic phase. However, the much larger strain rate sensitivity index value was obtained for eutectic phase at the lower temperature than 150degC. The activity energy of Sn-rich phase was derived based on the relation of strain rates versus temperature.