Material Efficient Additive Manufacturing for Metallization of Stereolithography Printed Waveguides and Passive Microwave Components Using a Custom-Made Silver Ink

Abstract

Stereolithography (SLA)-printed resin is lightweight, cost-effective, and features a smooth surface, making it ideal for waveguide manufacturing. However, metalizing the inner surface of one-piece SLA-printed hollow waveguides presents significant challenges. The current SLA metallization methods, particularly the popular Tollen’s reagent (silver nitrate solution in ammonia) for SLA resin, are material-wasting, due to a large amount of silver particle residuals floating in the reagent. Thus, such metallization process cannot qualify as a material-efficient additive manufacturing (AM). In this work, we present a custom-made silver-ammonia complex silver ink that is suitable for the metallization of the inner walls of the waveguides. Unlike the material wastage in the Tollens’ process, where the chemical reaction for the metallization happens in the bulk solution and causes wastage of silver material, in our proposed method, the chemical reaction happens only at the wet film formed on the SLA-printed component during the heating cycle. In addition, the proposed ink is suitable for low-temperature ( $60~^{\circ }$ C– $80~^{\circ }$ C) curing, and despite the low-temperature curing, the ink demonstrates an excellent conductivity of $1.5\times {10}^{7}$ S/m. Furthermore, the proposed ink is also suitable for other AM methods, such as inkjet printing and spraying, making it suitable for versatile metallization methods for both SLA 3-D-printed objects and planar-patterned microwave components. To validate the concept, multiple waveguide sections, magic-T, horn antennas, and planar microwave components have been fabricated using the proposed ink. Experimental verification of these components confirms comparable performances with their commercial counterparts realized through traditional manufacturing. For example, the fully printed waveguides demonstrate an attenuation constant of 0.015 dB/cm. All of this has been achieved while saving the silver content by around 95% as compared to the Tollens’ reagent metallization method for waveguide plating.