TiO2 and SiO2 filled PTFE composites for microwave substrate applications

TiO2 and SiO2 filled polytetrafluoroethylene (PTFE) composite substrates were fabricated for microwave circuit applications. The total content of TiO2 and SiO2 fillers was a fixed value of 55 wt%, and the content of TiO2 in the PTFE matrix varied from 1 wt% to 9 wt%. The influences of TiO2 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 uniform throughout the PTFE matrix. The dielectric constant (epsilon (r)) showed an increasing trend as the TiO2 content increased, while the dielectric loss (tan delta) decreased up to 5 wt% TiO2 filler loading and then slightly increased till 9 wt% TiO2 loading. Composites showed a similar trend of decreasing moisture absorption, and increasing linear coefficient of thermal expansion (CTE), density as the TiO2 filler content increased. Our results revealed that the TiO2 and SiO2 filled PTFE composites exhibited good dielectric properties (epsilon (r) similar to 2.87, tan delta similar to 0.00075), acceptable moisture absorption (0.2 %), CTE (17 ppm/A degrees C) and tensile strength (7.32 MPa) at filler loading of 5 wt% TiO2 and 50 wt% SiO2.