A new methodology for the characterization of fracture toughness of filled epoxy films involved in microelectronics packages

Abstract Fracture toughness is regarded as an important fracture criterion for materials when fracture mechanics is applied to assess the reliability of microelectronics packages. Fracture toughness of a filled epoxy is related to material, process and test conditions. Plane-strain based characterization methodologies have been successfully developed to characterize fracture toughness of bulk filled epoxy materials. However, those methodologies may not be applicable for filled epoxy films, due to the differences in stress-state and degree of curing in the films when compared to bulk specimens. In this paper, strain energy release rate was proposed to be a representative for the description of the fracture behavior of filled epoxy materials. Based on linear elastic fracture mechanics and microdigital image speckle correlation technique, a plane-stress based fracture toughness characterization methodology, including theoretical model, measurement facility, experimental approach and analysis method, was developed. With the methodology, the fracture toughness of a silica filled epoxy film, which is widely used in microelectronics packages as an underfill material, was characterized over a wide temperature range (−40 to 200 °C). The fracture toughness of the film was found to have a nonlinear relationship with testing temperature, i.e., the temperature dependence in the low temperature range is much lower than that in the intermediate temperature range, but is higher than that in the high temperature range.