Process induced warpage and residual stress in populated ball grid array substrate panel

Abstract

In-process and pre-assembly warpage of printed wiring boards (PWBs) and packages can cause severe problems during component assembly. A numerical experimental hybrid approach is being developed to: (1) analyze the root cause of warpage and associated residual stresses of electronic packages such as ball grid array (EGA) and high density PWB; and, (2) reduce warpage. Advanced material characterization techniques have been applied to determine dimensional changes of a molding compound due to temperature and chemical reactions. Mechanical properties of the molding compound at various temperatures were also tested. The shadow moire interferometry technique is used to measure warpage of a BGA panel. A finite element analysis has also been conducted to investigate the warpage and residual stress evolution during the EGA assembly process. The study shows that the dimensional changes of the molding compound, due to both thermal expansion and chemical shrinkage, and the mismatch between the compound and silicon die/substrate can cause severe warpage.