Experimental characterization of copper-encapsulant interfacial fracture toughness for a peripheral array package

摘要

The objective of this study is to predict the propensity of interfacial delaminations that may inhibit the performance of a novel surface mountable, high I/O electronic package. Incorporation of such predictions in the design phase of the package can lead to judicial selection of materials and geometric parameters such that the occurrence of interfacial delamination based failures can be avoided. This, in turn, leads to significant cost savings and shorter time-to-market due to the shortening of the prototyping and qualification testing phases. The focus of the present study is the prediction of potential delaminations at the encapsulant-backplate interface in the Very Small Peripheral Array (VSPA~(TM)) package during manufacturing. The delamination growth prediction is based on the comparison of interfacial fracture parameters obtained from the numerical simulations to appropriate critical values determined experimentally using controlled fracture toughness tests. In this paper, the fracture toughness of the encapsulant/backplate interface is characterized using a fracture toughness test that requires extremely simle test specimen, fixture and loading geometries. The critical interfacial fracture toughness and the fracture mode mixity are determined using closed-form and finite element analyses of the test specimen geometries, taking into consideration the effects of thermo-mechanical residual stresses resulting from the test specimen fabrication process. Furthermore, an experimental characterization of the encapsulant material is also conducted in order to assess the effects of its thime- and temperature-dependent thermo-mechanical response on the fracture toughness of the encapsulant-backplate interface.