Effective material properties and thermal stress analysis of epoxy molding compound in electronic packaging

In this study, the coefficient of thermal expansion (CTE) and the elastic modulus of epoxy molding compound (EMC) are measured using fabricated specimens and then the measured values are compared with the predicted values by theoretical equations (such as dilute suspension method, self consistent method, Hashin-Shtrikman´s bounds, Shapery´s bounds and others). The measured values are distributed within the upper and lower bounds of predicted values. The measured elastic modulus and the CTE of EMC approach close to the predicted values by self consistent method and upper bound of Shapery´s equation respectively. Two-dimensional (2-D) and three-dimensional (3-D) finite element analysis are performed using the measured and analytically predicted values. Finite element method (FEM) analysis indicates that firstly the EMC with eighty weight percentage of filler shows less thermal stress when package is cooling down and relatively high thermal stress when package is heating up. Secondly the stress concentrations at the edge sections about two times higher than the interfaces and at the vertex parts about 1.4 times higher than the edge sections are observed.