Warpage simulation for the reconstituted wafer used in fan-out wafer level packaging

Fan-out packaging technology involves processing redistribution interconnects on reconstituted wafer, which takes the form of an array of silicon dies embedded in epoxy molding compound (EMC). Yields of the redistribution interconnect processes are significantly affected by the warpage of the reconstituted wafer. The warpage can be attributed to the crosslinking reaction and viscoelastic relaxation of the EMC, and to the thermal expansion mismatch between dissimilar materials during the reconstitution thermal processes. In this study, the coupled chemical-thermomechanical deformation mechanism of a commercial EMC was characterized and incorporated in a finite element model for considering the warpage evolution during the reconstitution thermal processes. Results of the analyses indicate that the warpage is strongly influenced by the volume percentage of Si in the reconstituted wafer and the viscoelastic relaxation of the EMC. On the other hand, contribution from the chemical shrinkage of the commercial EMC on warpage is insignificant. As such, evaluations based on the comprehensive chemical-thermomechanical model considering the full process history can be approximated by the estimations from a simplified viscoelastic warpage model considering only the thermal excursion.