Warpage behavior of the flip chip package in underfill curing process: in situ characterization and numerical simulation

The curing process in which the underfill polymerization into a permanent solid composite is an essential procedure of the underfilling process and is crucial in determining subsequent reliability of the flip chip package. In this study, the deformation behavior of the flip chip package during the underfill curing process has been characterized by 3D-Digital Image Correlation (DIC) method combined with a in situ characterization equipment. Results show that the warpage of both die and substrate of the package increased after the curing process, and compare to the warpage change result from the CTE mismatch when temperature change, the warpage change during the underfill polymerization process is relatively small but not negligible. Further FEA results show that: although the warpage of the package is more severe after underfill curing process, the stress concentration on solder bump is relieved and the maximum stress on the solder bumps decreased; and compare to the package without underfill, the introduction of underfill can still relieve the stress even at temperature as low as -65℃. The conclusions of this paper will contribute to a better understanding of chip-package interactions. It is also meaningful in optimization and reliability evaluation of underfill materials.