Adhesion Enhancement Between Electroless Copper and Epoxy-based Dielectrics

The adhesion between electrolessly deposited copper and an epoxy-containing dielectric material has been investigated. In particular, the role of mechanical anchoring and chemical bonding in these systems has been examined. The contribution of each of these mechanisms to adhesion has been identified. Probelec, a phenolic-novolac epoxy polymer, and Avatrel, an addition polymerized norbornene polymer with an epoxy side-group, have been tested in this study. Traditional swell and etch treatments have been used to enhance mechanical anchoring through pore-type roughness development on the phenol-novolac epoxy, but were found to be ineffective in roughening the Avatrel surface. The critical difference between the two polymers is the epoxy-backbone (for the phenolic epoxy) versus the epoxy side-group (for the norbornene backbone polymer). In order to create roughness on the Avatrel surface, a novel technique utilizing a blend of Avatrel and Probelec was investigated. This technique created pore-type roughness and enhanced mechanical anchoring on the Avatrel surface. NH₃ plasma treatments were utilized to enhance the chemical bonding contribution to adhesion and produce surfaces with peel strengths of 0.15-0.25 N/mm with minimal roughness generation. Finally, a combined wet-chemical and plasma treatment protocol was investigated to enhance chemical bonding and mechanical anchoring on the same surface. Samples with adhesion greater than 0.5 N/mm with roughness less than 50 nm were produced with both Avatrel and Probelec. Through the use of a combined wet-chemical and plasma-surface treatment the polymer surface has been optimized for adhesion while minimizing roughness.