Interfacial fracture toughness test methodology for flip chip underfill encapsulant

An interface crack mixed mode fracture toughness test methodology has been developed in this paper. A compact mixed mode (CMM) fracture test fixture and specimen were employed. Fracture toughness tests for underfill encapsulant bonded specimens with interface cracks were subjected to a wide range of global mixed mode loading conditions. Finite element analysis modeling for an interface crack in the CMM specimen provided the necessary stress intensity factor calibration solution. The results showed that the mode II fracture toughness generally displayed a larger value than the mode I toughness. Failure criteria based on a failure analysis diagram or an effective stress intensity factor were proposed for interface cracks loaded under different mixed-mode fracture conditions.