Study of shear locking effect on 3D solder joint reliability analysis

Abstract

Abstract The fabrication process of WLP (wafer-level packaging) has become more mature, and using the finite element method (FEM) to predict the reliability life of electronic packaging can shorten the WLP design cycles. This study adopted the NSMD (non-solder mask defined) solder joint structure in WLP and used an energy method to predict the solder joint geometry. A fixed mesh size will be determined for the critical region of the solder joint to evaluate the inelastic strain due to the thermal loading in finite element analysis. However, under the influence of the solder geometry of some tested vehicles, especially when the solder contact angle of the lower pad is less than 20 degrees, a shear locking phenomenon will occur at the solder joint. This phenomenon causes abnormal energy transfer. The excessive strain is concentrated on the upper part of the solder joint, resulting in an incorrect estimation of reliability life. Reduced integration can prevent shear locking and has improved strain results compared to full integration. The results of this research demonstrate that the FEM using proper mesh size control and the reduced integration point element in critical regions can deliver accurate reliability life prediction for WLP.