Post-mold cure process simulation of IC packaging

Epoxy molding compound (EMC) is a common material used in IC packaging. One of its defects is warpage. Warpage could be a serious issue for some IC encapsulation processes. To alleviate the warpage problem during encapsulation, post mold cure process (PMC) is the most common strategy used. However, there are still no adequate tools or models to simulate the post mold cure process. Since EMC behaves like a viscoelastic material during post mold cure process, a viscoelastic model must be considered. The object of this paper was to construct a correct viscoelastic model, and then to input this model into a software package. This study adopted a dualistic shift factor Maxwell Model to simulate the post mold cure process. With this model, the amount of warpage after PMC process could be predicted. With dynamic mechanical analyzer (DMA) testing, the Generalized Maxwell model and Williams-Landel-Ferry (WLF) equation of fully cured EMC under different temperatures could be derived. Then, the partially cured EMC was tested by DMA. The viscoelastic properties of partially cured EMC were considered to have the similar behavior as temperature. Thus, a new model considering partially cured EMC as a cure induced shift factor similar to temperature shift factor could be derived. This model then became a model with dualistic shift factor Maxwell model. With some modification of structure analysis tool such as ANSYS, this dualistic shift factor Maxwell model could be applied and predict the post mold cure behavior of EMC. The results of calculation showed reasonable agreement between experiments and simulation.