Experiments for Obtaining Cohesive-Zone Parameters for Copper-Mold Compound Interfacial Delamination

Interfacial delamination due to mismatch of coefficient of thermal expansion is a prominent failure mechanism of multilayer microelectronic packaging. Current methods for investigating and preventing interfacial delamination rely heavily on interfacial fracture mechanics. Such techniques are effective but also limited because they rely on assumptions about existing cracked geometry. Cohesive-zone modeling is an alternative technique for modeling interfacial delamination that is capable of simulating both crack initiation and crack propagation. This paper presents a methodology for developing a cohesive-zone model for an interface between the copper leadframe and the epoxy molding compound (EMC). Through experiments, the interfacial strength is characterized quantitatively, and load versus displacement data are collected for each experiment. By mimicking these results with a cohesive-zone model, mixed-mode cohesive-zone parameters are obtained. The fully defined mixed-mode cohesive-zone model can be used to simulate interfacial delamination between the copper leadframe and the EMC in any microelectronic package that contains such an interface. Furthermore, the procedure demonstrated here may be employed to characterize a cohesive-zone model for other interfaces in microelectronic packages.