Mechanical properties versus temperature relation of individual phases in Sn–3.0Ag–0.5Cu lead-free solder alloy

The non-homogeneous Sn–3.0Ag–0.5Cu (SAC305) lead-free solder alloy consists of Sn-rich (β-Sn) and eutectic phases. The mechanical properties of these individual phases were demonstrated to be a function of the temperature. The nanoindentation methodology was utilized to examine the mechanical properties at 60 °C, 80 °C, 110 °C, 130 °C, and 150 °C, respectively. It was found that for both Sn-rich phase and eutectic phase, the hardness and Young’s modulus exhibited the dependence on the temperature. Moreover, the creep deformation which occurred at the dwell time of sustained loading was quite sensitive to the prescribed temperature. Basically, the higher temperature resulted in a larger creep deformation. This in turn caused the variable strain rate sensitivity of the individual phases, which was extracted by Mayo–Nix approach. The Sn-rich phase showed larger creep deformation than that of eutectic phase. However, a greater strain rate sensitivity index value was obtained for eutectic phase at the temperature regime (25–130 °C). The derived activity energy implied that for both β-Sn and eutectic phases two rate-controlling processes took place during the creep deformation, in which the transition temperature is around 130 °C.