Thermal fatigue reliability modeling and analysis of BGA socket assembly in system board with preloaded use condition

Heat sink (HS) as thermo-mechanical solution is widely used in modern electronic packaging system including mobile, desktop and server machines to improve and maintain system thermal performance by removing heat away from IC component such as flip chip ball grid array (FCBGA) package and BGA socket. With increased power dissipation need, heat sinks usually carry considerable amount of mass and preload over the components in order to have optimal thermal engagement during operation, which greatly impact reliability performance of BGA solder joint under various reliability tests. Thermal test data show that the most failure locations of BGA balls in BGA socket are located off the package corner that can not be predicted by using traditional strain or energy based metric. Therefore developing a predictive modeling tool with physics based metric in assessing reliability performance of preloaded BGA solder joint still remains a challenge. A nonlinear finite element model including BGA socket and preload heat sink was developed for both standard and system level boards to investigate preload effect on thermo-mechanical reliability performance. Numerical modeling results show that potential failure locations of BGA balls can be identified by maximum principal stress and be correlated well with thermal cyclic validation test. An advanced fatigue life model with mean stress effect and inelastic strain range is also proposed for calculation of initial fatigue life for BGA solder joint