Establishment and Accuracy Assessment of Structural Equivalence of Fan-out Reconstitute Wafer for Asymmetric Warpage Prediction

Asymmetric warping is an annoying phenomenon causing defects and reducing process yield of wafers and it must be prevented. Traditionally, full-scale 3D finite element simulations are usually used for addressing this concern. However, its highly computational cost makes this approach less effective and cannot provide analytic prediction to address the problem in a universal manner. Thus, a semi-analytical formulation is conducted in this work in responding the above-mentioned concerns. However, the semi-analytical formulation is only suitable for an ideal bi-layered structure for predicting the bifurcation state. In reality, a fan-out wafer is a highly heterogeneous structure. Therefore, it is important to perform structure and material equivalences for converting the original highly complex 3D structure into a bi-layered structure with equivalent uniform materials for conducting semi-analytical prediction. In this work, four material equivalence approaches are hired for finding the equivalent material properties. Their effectiveness would be evaluated by comparing the bifurcation temperature of their corresponding equivalent bi-layered structure and the original full 3D model. According to the comparison result, the material equivalence using energy method achieves the best result with the standard solution. Thus, it would be recommended for conducting future model simplification. Furthermore, structure equivalence is also taken into consideration for compensating the discrepancy in bending stiffness between the full and the simplified models for better warpage prediction. The simulation results indicated that the differences on bifurcation temperature and warpage between these two models can be reduced to 4.6 and 11 percentages with a computational cost reduction of 72 times. It is expected that such a cost-effective model would be very useful for packaging performance evaluation during early design stage.