Influence of copper layer on epoxy acrylate based solder mask surface chemistry and the effect on epoxy adhesion

The influence of the presence of copper on the network formation and the surface chemistry of an epoxy acrylate based solder mask system were investigated, with regards to the application of solder masks on copper layer. The presence of copper within the bulk volume of the solder mask was characterized by utilizing scanning electron microscopy/focused ion beam and energy dispersive X-ray analysis. The copper originates from the copper layer underneath and decreases towards the surface. Differences in the network structure were analyzed by applying infrared spectroscopy in attenuated total reflection mode, which showed no changes in the network structure due to a copper layer underneath. The surface chemistry of two solder masks with different curing agents, amine and anhydride, was investigated for differences caused by changes in the curing behavior depending on copper complex formation. Surface chemistry was analyzed by applying X-ray photoelectron spectroscopy and ti me of flight secondary ion mass spectrometry. Measurable differences in the surface chemistry with regards to copper content are generated due to the copper layer underneath. However, through the optical contact angle method and pull-off test, no differences concerning wetting or adhesion behavior between the solder mask and an epoxy adhesive were observed.