Towards decoupling chemical and mechanical adhesion at the electroplated metal/polymer interface via precision surface texturing

Abstract

Electroplating is the most widely used method for coating metals on polymers, the adhesion of which is ensured by chemical and mechanical interactions of their surface. Unfortunately, the relative contributions of these factors to the overall adhesion was debated over the past century with no quantitative arguments. This study decouples the contribution of polymer chemistry from other adhesion factors by using non-interlocking micro-textures with variated actual surface area. We used state-of-the-art photolithography to micro-texture nine molds with 2, 4 and 6 µm wide and 2, 4 and 6 µm tall pillars (1) hot embossing to replicate the pillars on the ABS polymer (2), electroplating to deposit copper on the textured and etched ABS polymer (3), and peeling test to measure the adhesion strength (4). In the absence of mechanical interlocking, the measured adhesion can be fully ascribed to the surface-amplified chemical adhesion between the metal and the polymer. In result, the chemical adhesion appeared linearly proportional to the actual interfacial area, yet it contributed only a minor fraction (1/7) to the overall adhesion strength in electroplating with classical chromic acid etching. Evidently, chemical adhesion is not the dominant factor in polymer electroplating.