A practical die stress model and its applications in flip-chip packages

Failure induced by die cracking is one of the concerns in flip-chip packaging design and reliability study. In this paper, a thermal stress model called bi-material plate (BMP) model for analyzing flip-chip packages is developed. The analytical model, which has a closed form solution, is validated by finite element method and extensive experimental measurements for applications in flip-chip packages. Using this model, die stress and curvature can be determined effectively. It offers a significant advantage in estimating the die stress and package reliability in the process of selecting and evaluating the design and material parameters for the flip-chip packages. From this model, it is evident that the curvature and the bending stress are independent of die size if the edge effect is neglected. Further more, the bending stress is independent of absolute die thickness if substrate to die thickness ratio is kept the same. The die curvature and the bending stress have simple correlation in certain range of thickness ratio.