Copper to resin adhesion characterization for power electronics application: Fracture toughness and cohesive zone analysis

The use of molding compound as encapsulant is nowadays increasing in semiconductor power module applications. The adhesion of package interfaces between copper components and molding compound is one of the key aspect for an improved durability. The presented activity proposes the fracture toughness characterization of copper–resin interface in a power semiconductor package due to different experimental tests and the cohesive zone method to describe interfacial fracture. Double Cantilever Beam (DCB) and Four Point Bending (FPB) tests have been executed on dedicated bi-material coupons. The scope of these trials has been to enhance two different propagation modes based on different ratio between mode-I (opening) and mode-II (sliding) according to a mixed-mode approach. Strain energy release rate (SERR) and mode-mixity have been estimated by a finite element analysis based on the virtual crack closure technique (VCCT) and the crack surface displacement method (CSD). The information about fracture toughness at two different mode mixity have been considered to predict the SERR for every arbitrary mode mixity. Finally, dedicated finite element models based on cohesive elements have been developed and calibrated considering the fracture toughness experimental values and the measured force–displacements behavior during the two considered tests. Dedicated physical analyses have been carried out to validate the proposed method.