Study on delamination of typical heterogeneous interfaces in redistribution layers in fan-out wafer-level packaging

Fan-out wafer-level packaging (FOWLP) has emerged as a crucial technology for high-density chip integration, with redistribution layers (RDLs) playing an important role in interconnection. However, interfacial delamination within RDLs, driven by the mismatch in coefficients of thermal expansion, poses a critical threat to packaging reliability. In this study, the interfacial delamination behavior of RDLs in FOWLP was systematically investigated. Double cantilever beam (DCB) tests showed that the interfacial fracture toughness decreased significantly with increasing temperature. Specifically, the energy release rate of the Cu/LSF60 interface decreased by 49.6% as the ambient temperature increased from 25 to 260 °C. Thermal cycling tests identified interfacial delamination near the center of the RDL, where pronounced stress concentration was predicted by finite element simulations. To improve interfacial adhesion, several surface treatment technologies were evaluated using DCB tests. Hydrogen plasma surface modification increased the energy release rate of the Cu/LSF60 interface by 12%, whereas citric acid treatment increased that of the Si/LSF60 interface by 90%. Further analysis using X-ray photoelectron spectroscopy and atomic force microscopy indicated that these improvements could be attributed to increased surface roughness, which facilitates mechanical interlocking, and the introduction of polar functional groups, respectively.