Anand Parameters for Eutectic Tin-Bismuth Solder

After the introduction of lead free solder in the packaging industry, there has been ongoing research to find solder alloys that have a low melting point. Boards having solders that reflow at a lower temperature would not only reduce the overall operating cost but also reduce board warpages and reduce damages to sensitive components. The most common low temperature solder is the eutectic tin-bismuth solder with a composition of 42Sn-58Bi. For this study, cylindrical samples of eutectic solder were reflowed in a reflow oven. The reflowed specimens were then subjected to isothermal uniaxial tensile tests at temperatures of 25, 50, 75, and 100 °C at strain rates of 10^-3, 10^-4, and 10^-5 sec^-1. The results from the tensile tests were then used to predict the nine Anand Parameter Coefficients. The Anand model is widely used to predict the stress-strain characteristics of viscoplastic materials and is incorporated in commercial finite element software such as ANSYS. The Anand predicted curves were then compared with the experimental tensile curves to determine the model’s ability to accurately predict the stress-strain behavior at any particular strain rate and test temperature. Finally, the obtained Anand Parameters were used to predict the reliability of a BGA package had it been made of SAC305 solder balls and eutectic solder paste.