Prediction of die failure in copper-low-k flip chip package with consideration of packaging process-induced stresses

In Flip Chip package, the curing process of the underfill polymer will induce extra residual stress and strain fields. For simplicity reasons, in thermo-mechanical analyses, the curing induced stress state was usually neglected by assuming a so-called ldquostress-freerdquo temperature. However, such simplification is not verified, in particular for advanced IC chips such as copper-low-k interconnects, which is very sensitive to the stress level it undergoes. An investigation on the die failure issues in copper-low-k Flip Chip Package with consideration of packaging process-induced stresses was presented in this paper. Firstly, a cure-dependent viscoelastic model was applied to describe the properties of the underfill resin during the curing process and subsequent thermal cycling. Secondly, prediction of die fracture failure probability was conducted. Weibull statistics model was used to describe the probability distribution for the die strength test. Model parameters were obtained by fitting to the test results. Fracture failure probability of the die backside was calculated based on the Weibull statistics model and the stress states induced in the curing processes and test condition. Thirdly, the stress state on the copper-low-k layer was investigated. The results show that maximum stress occurs at top interface of the low-k layer structure. The cure-induced stresses play a significant role on the total stress level. The effect of the packaging process-induced stress cannot be simply neglected.