Thermomechanical reliability analysis and optimization for MEMS packages with AuSn solder

Thermal stress formed in the solder of the microelectromechanical systems (MEMS) sensor during the reflow soldering process due to the coefficients of thermal expansion (CTE) mismatch between the different materials. As the package needs to be hermetically sealed to protect the device from outside environmental effects, the local stress concentration would eventually cause cracks in the solder and influence the hermeticity. In this study, we present the thermo-mechanical analysis of the AuSn90 solder with low temperature co-fired ceramic (LTCC) package using Comsol Multiphysics. Thermal residual stress distribution in the solder after the reflow soldering process was simulated. According to the result, the maximum von Mises stress was found and several possible ways for minimizing the stress in the solder and improving the thermo-mechanical reliability were discussed.