This study aims to simulate the sinkmarks occurred at rib sections of IC Packges by 2D finite element approach. There are sinkmarks existed in the rib sections where a hot pool might occur during thermoset cross-linking process. Not only the thermal strains but also the volumetric shrinkage of thermoset resin during the solidification have contributions to the residual stresses. In this work, an equal strain model to represent the volumetric shrinkage of epoxy resin was proposed. The elastic modulus during curing was measured and modeled into the finite element analysis. The simulated results were compared with real experimental data and have shown good agreements. The volumetric shrinkage has found to have about three times of contributions to the final sinkmarks than the thermal strains for the epoxy-IC encapsulation. The research presented here has increased our understanding of the thermomechanical behavior of the thermoset transfer molding process.