This paper presents the numerical simulation for encapsulating IC with epoxy molding compound using finite element method (FEM). This simulation is aimed at the useful guide to material design for material designers.The resin viscosity is described by a constitutive equation model which is derived from a function of time, temperature and shear rate. Viscosity of some kinds of resin were measured with capillary rheometer. These resins are quantified by the functionwhich is simplified by the power law model and some of them has a negative value of the constitutive equation's non-newtonian factor. The model was used for numerical simulation. The FEM model of flow was studied for two typical types of packages, thinsmall outlined package (TSOP) and general purpose packages, quad flat package (QFP). To recognize the numerical simulation results, experimental results were obtained through the short shot method. We estimated the relationship between the occurrence of "penetrate void" in a molding process and the viscosity of resin and between the void and thickness of packages from the simulation results. From this estimation, it turned out that the void occurrence absolutely relates to the number of the constitutive equation's non-newtonian factor. Some kinds of resin viscosity can be simplified by the power law model with a negative value of the factor. The void occurs easily as the number of the factor becomes negative and the void occurs easily at the edges of the package as the thickness of package increased. In consequence one of the material design guide was shown.
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