A failure criterion for debonding initiation between molding compounds and copper leadframes in plastic encapsulated integrated circuit (IC) packages is proposed. The leadframe pullout test is used to evaluate the bond strengths between molding compounds and leadframes in plastic encapsulated IC packages. The normal and shear stress fields along the interface are analyzed using the finite element method. An average stress approach is employed for the interface failure criterion and the tensile and shear interface bond strengths are obtained from the experimental failure loads. In a parametric study, the effects of specimen loading geometry, moisture, and surface contamination of copper leadframes on the interfacial bond strengths are specifically analyzed. The results show that the interface bond strengths determined for the two specimen geometries are consistent.