Effects of hygrothermal ageing and thermal shock on reliability of interfacial adhesion between black oxide coated copper substrate and epoxy resin

Black oxide is a conversion coating applied onto the Cu substrate to improve the interfacial adhesion with polymeric adhesives. A comprehensive study was made to characterize the black oxide coating and the corresponding interfacial adhesion with various types of polymeric resin, aiming to optimize the oxide processing conditions. The reliability of adhesion performance of the coating was evaluated before and after accelerated hygrothermal ageing, such as temperature cycling, pressure cooker test, and moisture sensitivity test followed by thermal shock. The moisture resistance of the substrate with black oxide coating was much higher than the bare Cu substrate, during both the moisture absorption and desorption processes. Thermal cycling alone did not change significantly the adhesion performance of any of the substrates studied. Pressure cooker test was detrimental to adhesion performance of oxide coated Cu substrates. Nevertheless, the residual interfacial bond strengths were consistently much higher for the black oxide coated substrates than the bare Cu surface. Significant delamination occurred between the bare Cu and the moulding compound after the moisture sensitivity test followed by thermal shock, whereas there was virtually no delamination on the black oxide coated samples under the same ageing condition, confirming the higher reliability of interfacial adhesion performance for the latter

Moisture barrier characteristics of organoclay-epoxy nanocomposites

The moisture diffusion and barrier characteristics of epoxy-based nanocomposites containing organoclay are investigated. The effects of different types of organoclay modified with different compatibilizers, including a quaternary alkylamine-modified montmorillonite (KH-MT), a quaternary ammonium-modified montmorillonite (Cloisite 20A) and an octadecylamine-modified montmorillonite (I30P), on moisture barrier and thermomechanical properties are specifically studied. The moisture absorption and diffusion behaviours were different depending on the type of organoclay: the moisture absorption rates of the Cloisite and I30P systems were much lower with associated lower diffusivity than the KH-MT system or the neat epoxy, due to the higher interlayer distance and more uniform distribution of organoclays, which in turn allowed a longer diffusion path of water molecules in the nanocomposite. The moisture diffusivity of nanocomposites decreased with increasing clay content for all organoclays. The corresponding moisture permeability was lower in the order of nanocomposites containing I30P, Cloisite and KH-MT organoclays. The moisture permeability showed a systematic decrease with increasing clay content, which agrees well with the prediction based on the simple tortuous path model. Increase in effective penetration path due to the very large aspect ratio of the silicate layers was responsible for the reduced moisture permeability. The glass transition temperature was much higher for the I30P nanocomposite than the neat epoxy resin, whether dry or wet condition. It decreased linearly with increasing moisture content. The CTE decreased with increasing clay content for all conditions studied. (c) 2004 Elsevier Ltd. All rights reserved

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

The reliability of adhesion performance of bare Cu, as-deposited and surface-hardened black oxide coatings on Cu substrates was studied. The interfacial adhesion with a polyimide adhesive tape and an epoxy moulding compound was measured using the button shear and tape peel tests after hygrothermal ageing in an autoclave, high temperature ageing and thermal cycles. Moisture adsorption and desorption studies at different aging times suggested that the black oxide coating was effective in reducing the moisture adsorption. The bond strengths for all substrates remained almost unchanged after thermal ageing at 150 degrees C for 8 h. Thermal cycling between -50 degrees C and 150 degrees C for 500 cycles reduced by about 20\% the button shear strength of the as-deposited black oxide substrate, but it did change much the bonding performance of the bare Cu substrate. Hygrothermal ageing at 121 degrees C/100\% RH in an autoclave was most detrimental to adhesion performance because of the combined effect of elevated temperature and high humidity. The reduction in button shear strength after the initial ageing for 48 h was 50-67\%, depending on the type of coating. In all accelerated ageing tests, the residual interfacial bond strengths were consistently much higher for the black-oxide-coated substrates than the bare Cu surface, confirming a higher reliability of black oxide coating. Fracture surfaces analysis of tape-peeled bare copper substrates after 500 cycles of thermal loading revealed a transition in failure mechanism from interfacial to cohesive failure. In contrast, the failure mechanism remained unchanged for black-oxide-coated substrates. The observations made from the button shear and tape peel tests were generally different because of the different fracture modes involved