BIMATERIAL INTERFACIAL CRACK-GROWTH AS A FUNCTION OF MODE-MIXITY

The mechanical integrity of many electronic devices and their componen ts is determined by the strength of the interfaces between dissimilar materials. Therefore, the knowledge of interfacial strength is importa nt to the design for reliability of these devices, A few examples are die/die attach interface, lead-frame/molding compound interface, and c opper/resin interfaces in multilayer printed circuit boards, Failure o f these interfaces results in reduced reliability and performance of s uch electronic devices, Two important issues are raised in terms of ap plying the interfacial fracture to the bimaterial interface reliabilit y prediction, The first issue is the quantification of strength (fract ure toughness) in such interfaces as a function of mode mixity, The se cond issue is the computing of actual energy release rate (a generaliz ed crack driving force) and comparing it with the measured fracture to ughness 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 interfaci al fracture mechanics for the delamination growth The proposed numeric al scheme was verified by three examples: a DCB unidirectional composi te 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 an d after delamination growth, Good agreement between testing and predic tion has been achieved.