Cohesive Zone Modeling of the Polyimide/Silicon Interface in 2.5D Packaging by Nanoindentation Testing

Abstract The polyimide (PI)/silicon (Si) is a critical interface in 2.5D packaging and is highly susceptible to failure due to thermal and mechanical loads. The large thermal expansion mismatch that exists between these two materials poses a challenge for interfacial modeling and reliability predictions. This study presents a method for extracting and calibrating the cohesive zone model (CZM) parameters of the PI/Si interface by nano-indentation testing. Specimens were designed and fabricated to induce interfacial shear deformation during indentation, and the displacement–load (D–L) curves were measured to derive the preliminary CZM parameters. Under the assumption of a bilinear traction–separation law, the key parameters—initial stiffness K0, maximum shear strength τmax, and critical separation displacement δf—were extracted. The finite element simulations were then performed using abaqus to reproduce the experimental D–L response, δf and τmax were further calibrated to improve the agreement between simulation and experiment. The final identified CZM parameters are: K0 = 3.6 × 1014 Pa/m, τmax = 113 MPa, and δf = 4.2 μm. The simulation results demonstrate that the proposed method enables an accurate characterization of PI/Si interfacial behavior and is able to provide a reliable parameter set for future interfacial fracture simulations.