Comprehensive Analysis of BGA Block Warpage Induced after Post Mold Cure

摘要

The warpage induced after post mold cure (PMC) process is critical for BGA in blocks because it affects the solder ball attach process, and the subsequent package singulation process. In this paper, a comprehensive warpage analysis is performed on BGA block by means of experimental warpage measurement, real-time shadow moire measurement with temperature profile, material characterization of mold compound viscoelastic properties, and finite element modeling of package warpage with consideration of chemical shrinkage and viscoelasticity effects. Accurate temperature and time dependent viscoelastic material properties are required for mold compounds because the curing profile and cooling rate during PMC can be important. Shadow moirt measurements show that the block warpage is the maximum around the T_g of mold compound, not at the room temperature after the PMC or reflow cooling. The validated 3D viscoelastic finite element model explains that the observation in moire is due to the global CTE mismatch between mold compound and substrate. The effect of chemical shrinkage during molding and PMC is significant too. The sensitivity of mold compound and substrate material properties to block warpage is also studied. This finite element model can be a useful warpage predicting tool for future design of BGA in blocks.