Bimaterial interfacial crack growth as a function of mode-mixity

The mechanical integrity of many electronic devices and their components is determined by the strength of the interfaces between dissimilar materials. Therefore, the knowledge of interfacial strength is important to the design for reliability of these devices. A few examples are die/die attach interface, leadframe/molding compound interface, and copper/resin interfaces in multilayer printed circuit boards. Failure of these interfaces results in reduced reliability and performance of such electronic devices. Two important issues are raised in terms of applying the interfacial fracture to the bimaterial interface reliability prediction. The first issue is the quantification of strength (fracture toughness) in such interfaces as a function of mode mixity. The second issue is the computing of actual energy release rate (a generalized crack driving force) and comparing it with the measured fracture toughness so as to predict the crack initiation, growth, and failure of electronic devices. This study emphasizes on a unified methodology and demonstrates the feasibility of application of the rigorous interfacial fracture mechanics for the delamination growth. The proposed numerical scheme was verified by three examples: a DCB unidirectional composite beam, a DCB resin/copper beam, and an ENF resin/copper beam. Using a crack closure technique, the energy release rate and mode mixity are evaluated and used to predict the behavior of the specimens before and after delamination growth. Good agreement between testing and prediction has been achieved