Surface-modified Li₃Mg₂NbO₆ ceramic particles and hexagonal boron nitride sheets filled PTFE composites with high through-plane thermal conductivity and extremely low dielectric loss

Polytetrafluoroethylene has been widely applied in advanced electronic devices due to low dielectric loss and high thermal stability. Nevertheless, its low thermal conductivity can't satisfy heat diffusion demand under the situation of high-frequency and high-speed signal transmission. The PTFE-based composites filled with hybrid fillers of Li3Mg2NbO6 ceramic particles and hexagonal boron nitride sheets modified by phenyltrimethoxysilane were fabricated. Surface modification enhanced the interface compatibility between PTFE and fillers, thus obtaining tight microstructure and better dielectric properties for the composites. The dielectric properties, thermal conductivity, coefficient of thermal expansion and flexure strength of the composites were researched systematically. When the composites were filled with 40 vol% BN sheets and 10 vol% Li3Mg2NbO6 particles, the high through-plane thermal conductivity of 3.3 W.m(-1).K-1 was obtained, which was 1220% higher than pure PTFE. Meanwhile, the low dielectric constant of 3.9, extremely low dielectric loss of 3.3 x 10(-4) at 9.5 GHz and low coefficient of thermal expansion of 35 ppm/degrees C were also achieved. PTFE-based composites with high through-plane thermal conductivity and extremely low dielectric loss show huge potential for microwave substrates application.