Investigation of warpage in wafer-level molding : measurements and FE analysis

Abstract

Novel 3D packaging technologies which require large area mold embedding are being developed in order to achieve further minimization and cost reductions. Compression molding using epoxy molding compounds is one technique being considered for wafer-level encapsulation. However significant warpage in molded wafers is a critical issue which may hinder successive processes from being carried out. Cases of both symmetric (spherical) and asymmetric (cylindrical)-shaped warpage have been reported in wafer-level compression molding trials on blank wafers. This paper presents finite element models of the molded wafer, with and without embedded dies, which take into account the observed complex multi-state warpage characteristics. Molded wafer warpage measurements were carried out in order verify the applicability of the small and large deformation theories for layered plates, to deduce the cure shrinkage molding compound properties and to validate the finite element model of the molded blank wafer. The latter was used to analyze possible factors (nonplanar mold layer thickness, anisotropic wafer elastic properties) leading to asymmetric warpage. The numerical model will thus enable the prediction of the optimum process and material conditions for the warpage to be minimized together with the expected deformation of the molded wafer model with embedded dies.