Refinement of the Extrusion Printing Process through Material and Deposition Control Toward the Fabrication of Coplanar Waveguides

Digital printing technologies are increasingly explored as cost-effective alternatives to the conventional lithography process for the fabrication of radio-frequency (RF) transmission structures. In our previous works [1], [2], the feasibility of digitally fabricating coplanar waveguide (CPW) transmission lines using off-the-shelf and commercial dispensing equipment was demonstrated. While these works confirmed the viability of extrusion-based additive manufacturing for RF structures, limitations in feature resolution and dimensional confinement motivated further process refinement. In this study, an improved fabrication approach is presented by integrating a high-solid-content silver nanopaste (CL85), a fine-diameter precision dispensing nozzle and a polished 99.6% alumina substrate. The influence of paste rheology, nozzle geometry, and substrate surface quality on line width accuracy, edge quality, and thickness uniformity is systematically investigated. Optical microscopy and profilometry measurements demonstrate improved geometric precision and repeatability compared to previously reported configurations. RF characterization is still pending, nevertheless, the structural improvements achieved support the advancement of extrusionprinted CPW structures for high-frequency applications.