A new prediction methodology for electromigration-induced solder degradation in a WL-CSP system

This paper proposes a new prediction method for electromigration induced void generation of solder bumps in a wafer level chip scale package (WL-CSP). The methodology is developed based on discretized residual weight method (RWM) in a user-defined finite element analysis (FEA) framework to solve the local electromigration governing equation with the variable of atomic concentration. The local solution of atomic concentration is incorporated in the multi-physics environment for electrical, thermal and stress in both sub-model and global model. The new method takes the advantage of solving the variable of atomic concentration, it avoids directly solving the divergences of the atomic flux, which includes the atomic concentration gradient items and is very hard and challenging to get the solution by traditional method. The simulation results for voids and time to failure (TTF) are discussed and correlated with previous test results. Comparison of the results with and without considering the atomic density gradient for representive nodes is investigated.