Durability of bimetallic‐adhesive laminate with ethylene–acid copolymer adhesives

A broadband multicoaxial cable has been developed, based upon the use of ethylene copolymer thermoplastic adhesives to bond tin‐plated steel to copper. The characteristics of the adhesive and the integrity of the bond formed between the dissimilar metals were of prime interest. The copolymers of ethylene examined as adhesives were ethylene–acrylic acid (EAA) and ethylene–methacrylic acid (EMAA). The influence of high humidity on the durability of bimetallic laminates of copper or aluminum with tin‐plated steel and ethylene–acid copolymer adhesives has been studied. Infrared spectrometric and differential thermal analysis data had shown that a contributing cause to failure of bonds between EAA copolymers and copper is the solubilization of an underlying weak copper oxide layer under condition of the test. Electrolytic chromate‐treated copper and immersion chromate‐treated aluminum bonded to degreased tin‐plated steel resulted in joints having comparable durability under stress and humid environments. These results reflect the durability of tin–tin bonded specimens. These materials engineering studies have shown that ethylene–acid copolymer adhesive, properly used and stabilized, can be employed with confidence in adhesive joints.