Effect of Initial Microstructure on the Low-Pressure Oxidation of Copper

In this study, the formation behavior of surface oxide films through low-pressure oxidation was investigated for conventional pure copper, electrolytic copper foil, and electroplated copper materials. Before low-pressure oxidation, pure copper exhibited a microstructure of coarse equiaxed grains, electrolytic copper foil contained a mixture of coarse and fine columnar grains, and the electroplated copper layer consisted of fine grains. After low-pressure oxidation at 700°C, unlike oxidation under atmospheric pressure, Cu2O films with a particle size of approximately 5 µm grew on the copper substrate in all samples. Furthermore, no detachment or delamination of the oxide films was observed in the cross-cut tape test or the 180° bending test for any sample. These results indicate that, regardless of the initial crystalline structure of the copper substrate, low-pressure oxidation leads to the formation of a dense coating layer composed of large Cu2O grains, which is strongly bonded to the copper substrate. Therefore, the oxide films formed on electrolytic copper foil and electroplated copper materials are also expected to exhibit high bonding strength, similar to conventional pure copper.