Warpage Prediction Methodology of Extremely Thin Package

A novel and systematic methodology to predict the warpage of extremely thin packages is proposed. The geometrical and material inhomogeneities of both die and substrate are included in the prediction methodology. The inhomogeneous thermo-mechanical properties of dies due to the thermal incompatibility between silicon substrate and active/passive layers are inversely extracted from the Shadow Moiré measurements of dies. The inverse problem is solved by combining the Finite Element Model of the simplified layered die and an optimization algorithm. 3D copper trace mapping method is used to build the heterogeneous features of each layer in substrate. The 3D real copper traces from Electronic Computer-Aided Design (ECAD) files are mapped into each block layer of substrate in the proposed methodology. Additional residual stress is applied on substrate. The residual stress is inversely extracted from Shadow Moiré measurement of substrate-silicon couple warpage sample. In addition to the temperature-dependent Young's modulus and coefficient of thermal expansion, molding shrinkage is another non-negligible and intrinsic thermo-mechanical property of epoxy molding compounds (EMC). Equivalent residual stress is used to capture the influence of molding shrinkage on the warpage of extremely thin packages. The residual stress parameter is inversely extracted from Shadow Moiré measurement from Copper-EMC bilayer warpage sample. Our results show that these intrinsic thermo-mechanical properties of die, substrate and EMC become more prominent and start to play a non-trivial role in warpage as package becomes thinner. The proposed methodology provides a robust and practical approach to predict the warpage of extremely thin packages more accurately. We also propose an EMC material selection method for optimizing the warpage of extremely thin packages based on our proposed warpage prediction methodology.