TiO_2 and SiO_2 filled PTFE composites for microwave substrate applications

摘要

TiO_2 and SiO_2 filled polytetrafluoroethylene (PTFE) composite substrates were fabricated for microwave circuit applications. The total content of TiO_2 and SiO_2 fillers was a fixed value of 55 wt%, and the content of TiO_2 in the PTFE matrix varied from 1 wt% to 9 wt%. The influences of TiO_2 filler loading on the microstructure, density, moisture absorption, microwave dielectric properties and coefficient of thermal expansion of filled PTFE composites were investigated. The distribution of filler was uniformthroughout the PTFE matrix. The dielectric constant (ε_r) showed an increasing trend as the TiO_2 content increased, while the dielectric loss (tanδ) decreased up to 5 wt% TiO_2 filler loading and then slightly increased till 9 wt% TiO_2 loading. Composites showed a similar trend of decreasing moisture absorption, and increasing linear coefficient of thermal expansion (CTE), density as the TiO_2 filler content increased. Our results revealed that the TiO_2 and SiO_2 filled PTFE composites exhibited good dielectric properties (ε_r~2.87, tanδ~0.00075), acceptable moisture absorption (0.2 %), CTE (17 ppm/°C) and tensile strength (7.32 MPa) at filler loading of 5 wt% TiO_2 and 50 wt% SiO_2.