A Comparative Study of the High Temperature Mechanical Behavior of Lead Free Solders

Abstract

Lead free solders are renowned as interconnects in electronic packaging due to their relatively high melting point, attractive mechanical properties, thermal cycling reliability, and environment friendly chemical property. The mechanical behavior of lead free solders is highly dependent on the operating temperature. Previous investigations on mechanical characterization of lead free solders have mainly emphasized stress-strain and creep testing at temperatures up to 125 °C. However, electronic devices, sometimes, experience harsh environment applications including well drilling, geothermal energy, and aerospace engines where solders are exposed to very high temperatures from 125-200 °C. Mechanical properties of lead free solders at elevated temperatures are limited. In this work, we have compared the mechanical properties of two popular Solder alloys, such as SAC305, and SAC_Q at extremely high temperatures up to 200 °C. For each elevated temperature, stress-strain tests were performed at three strain rates (0.001, 0.0001, and 0.00001 1/sec). The experimental results have been compared with the prediction of Anand constitutive model. In addition, high temperature tensile properties of the solders as mentioned above have been compared. Our results show a significant degradation of mechanical properties of lead-free solders at higher temperatures. Comparison of the results between SAC305 and SAC_Q solders has shown that the addition of dopants (e.g. Bi) in SAC_Q solder improves the properties significantly. Good correlations were obtained between the Anand model predicted results and the experimental data over a wide range of temperatures and strain rates.