Fatigue Assessment of Solder Bumps on Board Assemblies Affected by PWB Warpage

Abstract

Out-of-plane displacement (warpage) has been a major reliability concern for board-level electronic packaging. Printed wiring board (PWB) and component warpage results from CTE mismatch among the materials that make up the PWB assembly (PWBA). Warpage occurring during surface-mount assembly processes and normal operations may lead to severe solder bump failures. In this research, the effect of PWB warpage on the low cycle fatigue of the solder bumps in plastic ball grid array (PBGA) packages was studied. Finite element modeling (FEM) was used for the strain-based life prediction of solder bumps on board assemblies. In this paper, 3-D models of PWBAs with varying board warpage were used to estimate the solder bump fatigue life for different types of PBGAs mounted on PWBs. In order to improve the accuracy of FE results, the projection moiré method was used to measure the initial warpage of PWBs, and this warpage was used as a geometric input to the FEM. The PWBAs with known PWB warpage were modeled to determine the influence of various levels of initial PWB warpage on the low cycle fatigue failure of solder bumps. The effect of different types of PBGAs with varying locations on solder bump fatigue was studied. Both Sn-Pb and lead-free solder materials were used in this study. The FE models were validated with experimental results obtained using the projection moiré technique. The FE results showed that the initial PWB warpage has significant a effect on the fatigue reliability of solder bumps in PBGA packages.