Package warpage is a primary concern in a package-on-package. To enhance the accuracy of modeling prediction, viscoelastic parameters, the change of material properties after injection mold cure (IMC) and post mold cure (PMC) temperature and it's time, and cure shrinkage were studied with a dynamic modulus analysis (DMA) and a thermal mechanical analysis (TMA) for a mold compound. A nano-indentation tool was used to characterize a viscoelasticity of underfill material. Material properties obtained from the TMA, DMA and nano-indentation tools were introduced to finite-element-based models. The validation of models was verified with a shadow moire for package warpage.