A Comprehensive Simulation Study on Cu Trace Damage and Cu/Polyimide Interface Delamination of RDLs in Fan-Out Wafer Level Package Under Hygro-Thermo-Mechanical Loads

The current study investigates the influence of moisture on the delamination of Cu/Polyimide (PI) interfaces and cracking of Cu traces within the redistribution layers (RDLs) of fan-out wafer level packages (FOWLPs) containing two dies during the reflow process, utilizing finite element simulation. The crack initiation and the delamination behavior of Cu/PI interfaces are analyzed using the cohesive zone model (CZM) based on interface fracture mechanics. The influences of the number of RDL layers and thickness of Cu traces on interface damage and trace stress concentration are also studied. The findings indicate that crack formation and delamination of interfaces are most likely to occur at the edge of the interface between the top layer of Cu trace and the polyimide in die-to-die (D2D) region. The presence of hygro-swelling stress exacerbates interfacial damage. Moreover, the degradation of the Cu/PI interface intensifies with an increase in the number of RDL layers. While Cu trace is prone to stress concentration at the junction with the pad, the impact of moisture on Cu trace stress at 260 °C is relatively small.