Adhesion performance of black oxide coated copper substrates: Effects of moisture sensitivity test

This paper reports the adhesion performance of copper alloy substrates with bare surface, black oxide coating and surface-hardened black oxide coating. In view of optimizing the surface hardening process, the shot peening pressure and speed were varied. The interfacial adhesion of the coated substrates with glob top resins and a moulding compound was measured and the failure mechanisms were studied from the fracture surface analysis. Moisture resistance of the substrates was evaluated using the C-mode scanning acoustic microscopy (C-SAM) analysis and the lead pull test. The result showed that the black oxide coating improved the interfacial bond strength with both the glob top resins and the moulding compound. The surface hardening process reduced the total thickness of black oxide coating, but the coating thickness was rather insensitive to the shot peening condition. The interfacial bond strength was in general higher for the as-grown coating than the surface-hardened coating. There were correlations between the interfacial adhesion, the coating thickness and the surface energy of coated substrates: the button shear strength of a glop top resin increased with oxide thickness and substrate surface energy. The moisture resistance of the substrate with black oxide coating was much higher than the bare copper substrate. After hydrothermal ageing, significant delamination occurred between the bare copper and the moulding compound, whereas there was little delamination on the black oxide coated samples.