Fracture characterization of copper-polyimide interfaces in multi-layer RDLs under varying curing profiles and loading rates

The interfacial integrity between polyimide (PI) and copper (Cu) is a determinant factor for the reliability of multi-layer redistribution layers (RDLs) in the advanced electronic packaging, where interfacial delamination can lead to catastrophic electrical failure. This study systematically investigates the interfacial mechanical behavior of PI-Cu structures under varying curing temperatures and shear rates. Through a combination of experimental shear testing, scanning electron microscopy, and finite element analysis (FEA), the evolution of interfacial strength and failure mechanisms was characterized. Experimental results demonstrate a monotonic decrease in shear strength as the curing temperature increases. Notably, within the different Curing temperature range, the interface exhibits pronounced plastic deformation post-peak strength, signifying a glass-to-rubber transition. While curing temperature significantly impacts adhesion, the shear rate was found to have a negligible effect on the ultimate strength of the PI layer under identical curing conditions. SEM fractography reveals a distinct honeycomb-like morphology at 200 °C, contrasting with the relatively smooth fracture surfaces observed at lower temperatures (50 °C–150 °C), which accounts for the degraded bonding strength at elevated temperatures. Furthermore, a Cohesive Zone Model (CZM) was implemented in FEA to capture the rate-dependent deformation and failure progression. The simulation results show high fidelity to experimental data, providing a predictive tool for evaluating interface performance under diverse processing conditions. This work elucidates the correlation between thermal processing history and interfacial reliability, offering critical guidelines for optimizing RDLs manufacturing processes in advanced packaging.