Adhesion Characteristics of Directly Sputtered Copper Seed Layer on Cycloolefin Polymer with Atmospheric Pressure Plasma Treatment

This study explores atmospheric pressure plasma treatment as an alternative to vacuum processes for the direct formation of copper seed layers on smooth cycloolefin polymer (COP) films, targeting next-generation <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6\mathrm{G}$</tex> antenna circuits. The peel strength between the COP film and the copper plating layer increased as the water contact angle decreased, reaching 0.6 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kN}/\mathrm{m}-\mathrm{s}$</tex> urpassing the 0.5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kN}/\mathrm{m}$</tex> threshold required for circuit pattern formation. Failure modes observed during peel tests, including interface failure between the COP film and the copper plating layer as well as substrate failure, were attributed to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Cu}_{2}\mathrm{O}$</tex> formation at the interface and the mitigation of COP surface brittleness. These findings underscore the potential of atmospheric pressure plasma treatment to enhance productivity and reduce equipment costs compared to vacuum-base processes.