Thickness-driven efficacy: The role of conformal coating thickness in electrochemical corrosion protection

This study evaluates how conformal coating thickness influences corrosion resistance in miniaturized hearing aids exposed to moisture, bias voltages, and sweat. ENIG-plated copper pads were coated with either a UV-cured acrylate urethane (Coating A) or a solvent-based modified alkylate resin (Coating B), chosen to analyse how distinct polymer chemistries and thickness influence moisture ingress and electrochemical degradation. By integrating electrochemistry, copper ion quantification, and both surface and cross-sectional scanning electron microscopy with energy-dispersive X-ray spectroscopy, this study establishes a multi-modal framework for diagnosing coating failure. Unlike prior studies relying on isolated electrochemical methods or purely morphological/chemical analyses, this approach bridges kinetics, dissolution, and microstructures responding to recent calls for multi-scale characterization. In addition to confirming known limitations in UV-cured and solvent-based acrylic systems, scanning electron microscopy analysis result evidence unique failure morphologies such as sweat ingress channels, granular decohesion, and volcano-like rupture. These features offer direct evidence of bottom-up failure in ultra-thin coatings, challenge conventional blistering and acrylic degradation models, and emphasize the role of localized phase separation and pressure-driven rupture in electrolyte ingress.