The Effective Cure Shrinkage of Underfill and its Effects on the Reliability of Flip Chip Package

Underfill (UF) is an important material for improving the reliability of flip chip interconnection in advanced packaging. How the curing process of underfill in the packaging process affects the residual stress of the encapsulation is of great significance for packaging reliability evaluation and failure analysis. In this paper, an effective curing shrinkage measurement system has been built by utilizing the Fiber Bragg Grating (FGB) method and the effective curing shrinkage of an underfill material has been measured; the warpage behavior of a Si-UF-Si three-layer structure which was designed to simulate the actual encapsulation has been experimental measured using the 3D-Digital Image Correlation (DIC) method after UF curing, and an finite element model has been built and warpage of the three-layer structure has been calculated based on the measured effective curing shrinkage of UF, results shows that the curing shrinkage and relaxation behavior of underfill affect warpage behavior oppositely and may both contribute to the warpage behavior of the three-layer structure; furthermore, based on the warpage results of the three-layer structure, the curing shrinkage effect of underfill on the residual stress of a FCBGA packaging has been analyzed by FE simulation with modified simulation parameters.