In this study a process-dependent viscoelastic model is developed for considering the constitutive relationship of an epoxy molding compound. The process dependence is realized by incorporating the phenomenological models for the cure kinetics, the cure-dependent volume shrinkage, and the cure-dependent viscoelastic stress relaxation modulus into the constitutive model for the molding compound. The cure-dependent viscoelastic model is incorporated into numerical finite element analysis to simulate warpage of an overmolded chip scale ball grid array (BGA) package under uniform cooling from reflow to room temperature. The simulation results are compared to Shadow Moiré experimental data for validating the modeling methodology. Additional finite element analyses are performed to investigate the influence of molding compound constitutive behavior (temperature-dependent elastic or viscoelastic) on the package warpage prediction, and to consider the package warpage evolution during the post-mold curing (PMC) process.