Finite element analysis of interface cracking in semiconductor packages

The application of enriched crack tip finite elements for the prediction of interface fracture parameters, e.g., strain energy release rate and mixed mode stress intensity factors, is presented. Of particular interest, is the comparison between fracture results obtained from two-dimensional (2-D) models and related three-dimensional (3-D) (generalized plane strain) calculations. These results show that for thermal cycling problems, one cannot anticipate 3-D fracture results based on 2-D calculations alone, i.e., plane stress, plane strain, and axisymmetric models. On the other hand, it is shown that the 2-D 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. Enriched crack tip elements for 2-D and 3-D elements are shown to provide highly accurate results for simulating debonding in semiconductor packages subjected to thermal cycling and/or moisture absorption.