Effect of Prolonged Storage on High Strain Rate Mechanical Properties of SAC-Q Leadfree Solder at High Operating Temperature

Electronic devices installed in automotive and downhole drilling applications may be exposed to high temperature and high strain rates during storage, operation and handling, which can contribute to the failures of electronics devices. High temperature shock and vibration loads may be generally in the strain rate range of 1-100 per sec. Applications such as drilling operations may experience temperatures 150°C-200°C. SAC alloys exhibit deterioration of material properties under exposure to high temperatures for sustained periods. There is need for more reliable formulations that can function reliably for sustained periods at high temperature. Recently, several doped SAC solder alloys (SAC-Q (CYCLOMAX), and innolot) have been used in electronic components. SAC-Q are formulated with Sn-Ag-Cu with addition of Bi (SAC+Bi). Adding dopant (Bi, Ni, In, Mg, Mn, La, Ti) to SAC solder alloys can improve wettability, melting temperature, shock and drop reliability and microstructure. In this study, effect of thermal aging (up to 6 months at 50°C) on high strain rate (10 per sec to 75 per sec) mechanical properties for doped SAC lead-free solder alloy (SAC-Q) have been measured at elevated temperatures (up to 200°C). Stress-Strain curves have been plotted over a wide range of strain rates and temperatures for SAC-Q solder alloy. Anand model parameters have been computed from stress-strain curves for different aging conditions.