FEA simulation on the MCP bottom die cracking issue

In a two-die stacked multi-chip package (MCP), cracking was found on the bottom die. Optical and SEM images show that the cracking initiates from the backside of the bottom die, underneath the leading edge of the top die. A model of the package was built using FEA. Thermal loading or mechanical force was applied to the package to simulate the failure situation conditions. The results suggest that the cracking at the bottom die was caused by mishandling mechanical stress and, not by thermo-mechanical stress.