Stress Analysis of Typical Structure of Redistribution Layer of Fan-Out Wafer Level Package

Abstract

Redistribution layer (RDL) is a significant component of fan-out wafer level packaging (FOWLP). However, reliability issues such as cracks, layer separation and warpage are prone to occur during the fabrication of RDL. Thermal stress concentration owning to coefficient of thermal expansion (CTE) mismatch is a crucial cause of reliability issues. In this article, the finite element analysis (FEA) method was adopted to simulate the thermal stress distribution of the three-layer RDL structure during the cooling process after thermal curing of PI. Based on the thermal stress distribution, the critical location most inclined to interfacial failure was determined. Further, by modifying the dimensions or material properties of the simulation model, the effects of the thickness of Cu wires, the opening diameter of Cu vias, the inclination angle of Cu vias, and two different kinds of PIs on the thermal stress of critical part in the RDL were investigated. In accordance with the simulation results, corresponding suggestions for the structural dimensions of the RDL and the properties of the PI materials were proposed.