Direct Observation of Copper Oxidation as a Cause of Delamination at the Interface of Copper and Epoxy Molding Compounds

This paper investigates the interface delamination between epoxy molding compounds (EMC) and copper (Cu) $(\text{EMC}/\text{Cu})$ by applying repeated mechanical stress to assemblies in a bending test, which reflects the multiaxial deformation mode during the thermal shock test. The EMC is bonded onto the Cu-sputtered surface by the thermal compression process. The bending test is conducted under cyclic force between 0 and 450 N with a triangle waveform for $4.5 \min$ per cycle at $250^{\circ}\mathrm{C}$. The delamination area after 500 cycles follows the maximum principal stress (MPS) distribution on the $\mathbf{EMC}/\mathbf{Cu}$, suggesting that MPS leads to the $\mathbf{EMC}/\mathbf{Cu}$ delamination. The cross-sectional SEM image of the $\mathbf{EMC}/\mathbf{Cu}$ shows vertical cracks penetrating the EMC to make the interfacial delamination from the crack bottoms. Oxygen went through the crack, making Cu oxidation in the delamination area. By stark, no oxidation was detected in the $\mathbf{EMC}/\mathbf{Cu}$ bonded area.