Warpage Estimation of a Multilayer Package Including Cure Shrinkage Effects

Warpage and residual stresses in plastic electronics packages are partly due to the shrinkage of the epoxy molding compound during the cure stage and partly due to the mismatch in thermal expansions during the cooling stage. Here, we present a simple but robust way of estimating the warpage part due to the curing effects. The main assumption of our analytical model is that the molding compound remains in the rubbery phase during cure. Using this model, we derive expressions for the effective cure shrinkage and the stress-free temperature. The effective cure shrinkage is a single parameter that can be used as an intrinsic strain value in numerical simulations, which then allows accounting for the curing effects. The solutions are benchmarked with both experimental warpage curves from the literature and with full numerical simulations on a four-layer package consisting of lead frame, die attach, die, and the molding compound. Both comparisons show that our analytical predictions are well capable of accurately predicting cure-induced warpage in multilayer systems.