Effects of moisture and temperature ageing on reliability of interfacial adhesion with black copper oxide surface

This paper reports the recent studies on adhesion performance of copper alloy substrate with bare surface, black oxide coating and black oxide with debleeding treatment. The interfacial adhesion of substrate with polyimide tape and glob top resin were measured after autoclave test (or pressure cooker test, PCT), temperature ageing and thermal cycles based on the button shear and tape peel tests. The failure mechanisms were studied from the fracture surface analysis. Moisture absorption and desorption studies at different aging time were carried out to understand the property changes due to moisture. The results show that the black oxide coating improved significantly the interfacial bond strength in the dry condition. The mechanical interlocking mechanism provided by the fibrillar copper oxide was mainly responsible for it. The interfacial bond strengths for all substrates remained almost unchanged after thermal ageing at 150°C for 8 h. Thermal cycles between -50°C and 150°C for 500 and 1000 thermal cycles exhibited generally a negligible influence or decreased slightly the interfacial adhesion. The hygrothermal ageing at 121°C/100% RH in an autoclave (i.e. PCT) resulted in large reductions in interfacial bond strength after the initial 48 h ageing and tended to level off with further ageing. Fracture analysis of tape peeled bare copper substrates after 500 cycles of thermal loading revealed a transition of failure mechanism from adhesive to cohesive failure. In contrast, the failure mechanism remained unchanged for oxide-coated substrates. The implications arising from the button shear and tape peel tests are different because of the different fracture modes involved. According to the available data discussed above, the PCT is regarded as the most severe test affecting the adhesion performance. Presence of oxide coating minimized the moisture absorption rate when compared to the bare copper surface.