Finite element modeling of interface fracture in semiconductor packages: Issues and applications

The application of finite element models for the prediction of interface fracture parameters such as strain energy release rate and mixed mode stress intensity factors is examined in this paper. The comparison between fracture results obtained from 2D models and related 3D (generalized plane strain) calculations is of particular interest. These results show that for thermal cycling problems, one cannot anticipate 3D fracture results based on 2D calculations alone, i.e. plane stress, plane strain, and axisymmetric models. On the other hand, it is shown that the 2D models are quite adequate for modeling interface fracture in the case of pressure loading on the interface, e.g. pressure due to water vapor expansion during solder reflow. The fracture results presented in this paper were obtained using special enriched crack tip elements that contain the analytic asymptotic displacement and stress field. Issues concerning compatibility and convergence are shown to be important for accurate interface fracture calculations. Enriched crack tip elements for two and three dimensional elements are shown to provide highly accurate results for simulation of debonding in semiconductor packages subjected to thermal cycling and/or moisture absorption.