Epoxy molding compound (EMC) is a key constituent in large overmolded panel or wafer. During various packaging thermal processes, the thermal expansion mismatch between EMC and Si die and the shrinkage of EMC due to chemical or physical aging would lead to residual stress and warpage. For accurately predicting warpage in fan-out reconstituted wafer, the viscoelastic constitutive behavior and the physical aging characteristics were investigated. The viscoelastic behavior of the EMC were measured by quasi-static relaxation and creep experiments. Consistency of the viscoelastic behaviors measured from these two experiments were examined and compared to the viscoelastic model constructed from time-harmonic dynamic experiment. From the comparisons of these test results, it was found that the viscoelastic behavior measured by creep and relaxation tests are highly consistent, and the presence of physical aging in the dynamic test specimen delays the viscoelastic relaxation. In addition, physical aging leads to stress-free shrinkage comparable to the chemical-aging induced shrinkage. The chemical-thermomechanical constitutive model was also implemented to simulate warpage evolution of a reconstituted wafer.