Application of Modified Virtual Crack Closure Method on Delamination Analysis in a Plastic IC Package during Lead-Free Solder Reflow

Abstract

Based on crack closure theory and bimaterial interface crack theory, a new equation for evaluating mode mixity at bimaterial interface crack has been developed. The main objective of this study is to apply modified virtual crack closure method (MVCCM) for the analysis of interface delamination between the leadframe pad and the encapsulant during a lead-free solder reflow process. In this paper the entire thermal and moisture history of a plastic IC package is simulated from the start of level 1 moisture preconditioning (85degC/85%RH for 168 hours) to subsequent exposure to a lead-free solder reflow process lasting about 8 minutes. The transient development of the strain energy release rate due to thermal stress only Gt hygrostress only G h vapor pressure only Gp and combined total strain energy release rate Gtot are computed and studied using modified virtual crack closure method compared with the results using modified crack surface displacement extrapolation method (MCSDEM). With the original MVCCM, the values of total energy release rate still agree well with exact solutions or the solutions using MCSDEM and the error is much less than 5%. At the same time, using the present method phase angles match well with exact solutions under mixed load for analytical case and the solutions using MCSDEM with the effects of temperature, moisture diffusion and vapor pressure for PQFP package during lead-free solder reflow. This is in great contrast to the original MVCCM on the calculation of mode mixity which are far away from exact solutions and the solutions using MCSDEM though the total energy release rates match well with the other solutions