Aminofunctional silane layers for improved copper–polymer interface adhesion

The aim of this study was to characterize two different copper grades, oxygen-free copper, and phosphorous deoxidized copper, with aminofunctional silane layers on them and to study these silane layers as coupling agents in the injection-molded thermoplastic urethane–copper hybrids. The copper surfaces were as-received and modified, i.e., polished and oxidized. The copper surfaces and silane layers which were grown from solution concentrations of 0.25 and 0.5 vol% were studied with reflection absorption infrared spectroscopy (RAIRS), atomic force microscope (AFM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The adhesive strengths of the copper–polymer joints were measured with peel tests and peeled surfaces were further studied with RAIRS, AFM, and FESEM. On the as-received copper surface, the silane layer was irregular and existed mainly in the surface roughness sites. This was the reason why hybrids manufactured with the as-received copper failed mostly in the silane layer. Hybrids manufactured with the oxidized copper sheets had a uniform silane layer and the hybrids failed mostly cohesively in thermoplastic urethane and had excellent peel strength values. In all silane-treated copper samples, Si–O–Si groups were formed confirming the cross-linking in the silane layer.