Thermal and Vapor Smoothing of Thermoplastic for Reduced Surface Roughness of Additive Manufactured RF Electronics

Additive manufacturing (AM) of electronics provides a route for creating customized systems with novel geometries that are not feasible with traditional methods. Standard AM processes such as extrusion can produce substrates on which electrical traces can be deposited. However, the surface roughness of plastic extrusion reduces the effective electrical conductivity and can introduce anisotropy, especially in radio frequency (RF) devices. The roughness can be reduced using vapor smoothing (VS), but solvent absorption changes the surface composition slightly, can be environmentally hazardous, and is not feasible with all thermoplastics. A new method introduced here-coined thermal smoothing (TS)-utilizes a heat source to locally reflow the material, thus minimizing the roughness of the undulating surfaces without the drawbacks of VS. This research work compares the surface roughness impacts of both smoothing processes with profilometry and scanning electron microscope (SEM) images. Both smoothing processes significantly reduce the surface roughness of extruded components by 80% and 90% for TS and VS, respectively. This paper also examines the influence of surface smoothing on high-frequency conductivity of microdispensed conductors (CB028 paste) deposited on the substrates. The measured loss on coplanar waveguides shows an improvement of up to 40% at 7 GHz.