Recent advances in additive manufacturing have allowed fabrication of high resolution, complex geometries with fine features from UV-curable acrylated polymers. Utilizing electroless deposition in conjunction with these manufacturing techniques allows us to leverage the aforementioned benefits and impart electrical and thermal conductivity, a basis for catalytic activity, and improved mechanical properties. Electroless deposition onto 3D-printed polymer acrylates is not well understood and frequently demands a trial-and-error approach to successful metallization of the surface. Plating of these polymer surfaces requires pretreatment steps; there is a lack of knowledge surrounding how these steps affect the coating adhesion and uniformity. Here, we present a systematic investigation into these pretreatment steps with the aim of leveraging quantifiable data to establish best practices. We characterize the effects of alkaline etching on surface roughness and surface chemistry through the use of optical surface topography measurements and XPS, respectively. We utilized Quartz Crystal Microbalance to examine the absorption of Tin (sensitizer) and Palladium (activator) species on the polymer surface. The resulting adhesion strength of the plated metal was measured through peel testing and the coating uniformity was quantified with a coverage fraction parameter. We show that changes in surface roughness of the polymers during the etching step occur at several length scales and time scales, associated with uneven curing degrees in regions of oxygen-inhibited polymerization. We find that the surface concentration of adsorbed sensitizer and activator species is related to the surface concentration of hydrophilic groups produced in the alkaline etching step. We show that the adhesion and uniformity are a function of both surface roughness and surface chemistry. These findings facilitate design guidelines for electroless deposition on 3D-printed polymers, specifically UV-cured acrylates. Further, these design rules allow for a deeper understanding of the role mass transport plays in the metallization of multiscale three-dimensional architectures.

Metallizing complex 3D-printed polymers with electroless deposition: The design rule toolbox of pretreatment steps

ACS Spring 2022

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