Adhesion of sputtered copper to photosensitive epoxies

Two surface roughening methods, namely O2 plasma etching and ion etching were studied to investigate the adhesion properties of Cu in epoxies. Two photosensitive epoxies were used: a vinyl-ester epoxy (Probimer) and an acrylic epoxy (Envision). Without Cr or surface etching, copper adhered poorly to the epoxies. Chromium, acting as a glue layer, improved the adhesion between the Cu and the epoxies substantially. Even higher adhesive strengths were obtained via plasma etching and ion etching. Microscopic examinations showed that O2 plasma induced more surface roughening than ion etching. Prolonged plasma treatment even degraded Probimer, causing the epoxy coating to lose its mechanical integrity.