Composite Feedstock Filaments for Fused Deposition Modeling (FDM) of Microwave Interconnects

Improved manufacturing methodology of ceramic-thermoplastic composite feedstock filaments using solvent-assisted dispersion is presented with one of the highest reported ceramic particle filler volume concentration of 50%. Relative permittivity values up to 12.35 along with a low loss tangent of 0.003 have been achieved for newly developed feedstock filaments. They have been employed for fused deposition modeling (FDM) of test specimens for the characterization of complex permittivity, which exhibited dielectric loss tangent in the range of 0.001–0.007 at frequencies ranging from 4 to 12 GHz. This is on par with that of the best microwave laminates. Also, surfactant-assisted ball milling was used to downsize ceramic fillers, while simultaneously applying a surface treatment by a strategically chosen surfactant to improve the interfaces between organic matrix and inorganic particles. The effect of the surfactant surface treatment on the dielectric and loss properties of the composite feedstock materials has been explored, which is compared with analytical model predictions. Two 40-mm-long dielectric rod waveguides (DWGs) were 3-D printed by using an in-house developed composite filament and a commercial counterpart. The former exhibited a much lower attenuation of 0.012 dB/mm as compared to 0.038 dB/mm shown by the latter. Measurements were compared to 3-D electromagnetic (EM) simulation results to extract effective permittivity of DWG fabricated by FDM printing using in-house developed composite feedstock filament, which agrees very well with measured permittivity values.