Interface Stress Analysis Based on Warpage Characterization in a Flip-Chip Package

For the package structure, the internal components of the package need to be collaboratively deformed when the temperature changes and the package's surface will be commonly expressed in a concave or convex shape, i.e., warpage will happen in the package. The warpage of the package is usually easier to obtain through experimental characterization. Considering that the stress and strain inside the package are closely related to the warpage of the overall structure, it is theoretically feasible to calculate the internal stress distribution in the package through accurate and complete warpage information. As a result, it might be used for evaluating the potential failure risk in the package in advance. Especially, it will be very valuable for some expensive packages to evaluate the internal stress without damaging the package. However, the related research is still lacking. In this paper, we combine finite element analysis (FEA) and experiment to accurately record and reproduce the warpage evolution during the whole process of temperature changing. Then accurate material property and boundary conditions are obtained in FEA. After that, the interface stress of thermal interface material (TIM) and underfill are analyzed in detail. This study provides a new method for evaluating the failure risk of thermal-mechanical stress of materials in the package and may also be applied for stress analysis in other package structures.