Development of a fatigue-compatible cohesive zone method for a copper-epoxy molding compound bimaterial interface

Abstract

Interfacial delamination is a prevalent failure mechanism in microelectronic packages. While much work has been performed towards understanding fracture of bimaterial interfaces under monotonic loading, investigation focused on the impact of fatigue loading on such structures is still evolving. Microelectronic packaging interfaces experience cyclic loads, and thus may eventually debond during operation. In addition to such fatigue characterization of packaging interfaces, the development of a computationally affordable modeling methodology with predictive capability towards fatigue crack propagation and failure is needed. This present work focuses on copper/epoxy mold compound (EMC) interfacial delamination under fatigue loading both through experiments as well as computational modeling. The performed characterization relies primarily on double cantilever beam tests but also other test configurations such as four-point bend. Finite-element analysis models for both traditional fracture mechanics and cohesive-zone modeling (CZM) has been used. Using fatigue interfacial fracture experiments, an innovative fatigue-compatible CZM modeling framework has been developed. The developed fatigue CZM model was validated against other experimental data. Interfacial fracture failure locus is examined under the context of multiple interfacial fracture tests. Additionally the dependency on fatigue crack propagation trends on mode-mixity is examined.