Mechanism for Adhesion of Epoxy Resin to Copper Substrate through C-H-Si Amorphous Thin Film

Abstract

With the increase in the power densities of power modules for hybrid vehicles, epoxy-resin-molded components have recently been explored for high-temperature operation that could cause delamination of the resin from the copper substrate because of their different thermal expansion coefficients. Therefore, we propose a method of resin adhesion to the copper substrate using amorphous thin films with inorganic and organic characteristics. The amorphous thin film was deposited on the copper substrate by a plasma- enhanced chemical vapor deposition（C VD）. In the previous work, it was reported that a high adhesive strength of 30 MPa or more was obtained between the resin and copper substrate with a C-H-Si amorphous thin film. To evaluate the influence of the film-forming conditions on the adhesive strength between the resin and copper through amorphous thin C-H-Si films, in this study, films were formed on the copper substrate at different surface roughness and oxidation states, with subsequent comparisons of the adhesive strengths. It was observed that an increase in the surface roughness and oxidation time resulted in increased coverage of the film-formed grains. Additionally, regardless of the microroughness of copper, higher coverage of the formed grains（approximately 200 nm）enhanced the adhesive strength, thus providing a high adhesive strength of about 35 MPa at a coverage of 60% or more. The film-formed grains also had good wettability with the resin. It is presumed that owing to the chemical affinity between the CHx groups of the formed grains, a high adhesive strength of 28 MPa could be obtained even at a low coverage of 15%. These results reveal that the chemical affinities of the film-formed grains of the C-H-Si film with the resin and the anchor effects due to the nano-unevenness of the grains contribute to the adhesive strength between the copper substrate and resin through the C-H- Si film.