Evaluation of residual stress in flip chip using 3-D optical interferometry/FEM hybrid technique

The residual stress in flip chips was investigated by a hybrid technique of 3-D finite element method (FEM) and 3-D optical interferometry. The residual stress consists of two parts: the chemical shrinkage stress caused by underfill curing and the thermal stress caused by coefficient of thermal expansion (CTE) mismatch and cooling. Warpage and in-plane deformation of the flip chip during the underfill curing and cooling procedure was real-time characterised with an integrated 3-D optical interferometry system. The measurement results were used to evaluate the chemical shrinkage stress and to verify/modify the FEM model for the analysis of thermal stress. It was found that the chemical shrinkage stress under isothermal curing condition is very small in average and negligible. As the difference between the simulated and measured thermal deformation falls within a limited scope, the accuracy of the simulated thermal stress can be guaranteed.