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Delamination between copper and epoxy molding compound (EMC) is one of the common failure modes in packages due to relatively weak adhesion at the interface. Delamination is difficult to predict because a package is often with a complex structure design constructed with different materials and under combined normal and shear loading. Development of cohesive zone elements applied in FEM has emerged into the application of cohesive zones as an effective tool for crack propagation simulation. In this study, a methodology to obtain useful parameters for cohesive zone modeling from experimental measurements is proposed. The approach is demonstrated with the adhesive joint between epoxy molding compound and copper that was under residual stresses and applied mixed-mode loading. The proposed approach to determine the traction-separation function does not rely on the uncertainties of crack tip stresses. The predicted load-displacement result is matched with experimental measurement results at the crack propagation region. Package delamination can be predicted by implementing the proposed testing and modeling scheme within the cohesive zone model.