KH550 interface-engineered CST/PTFE composites with balanced dielectric and thermal performance for miniaturized RF substrates in 5G applications

The demand for high-performance dielectric substrates for miniaturized radio-frequency (RF) devices and high-power electronic systems has accelerated the development of polymer–ceramic composites that simultaneously deliver high permittivity, low dielectric loss, and improved thermal conductivity. In this work, γ-aminopropyltriethoxysilane (KH550)-modified Ca 0.60 Sr 0.40 TiO 3 (CST)/polytetrafluoroethylene (PTFE) composite substrates were fabricated through a water-based tape-casting route followed by hot-press lamination, enabling uniform dispersion of CST ceramic fillers within the PTFE matrix. The incorporation of KH550 effectively enhanced interfacial compatibility between the ceramic fillers and the polymer matrix, while systematically increasing CST content improved both dielectric and thermal transport properties. At an optimal CST loading of 60 wt%, the composites exhibited a high relative permittivity ( ε r ) of 11.69 while maintaining a dielectric loss tangent (tan δ ) of 2.16 × 10 −3  at 10 GHz, together with a thermal conductivity ( λ ) of 0.714 W m −1  K −1 , a coefficient of thermal expansion (CTE) of 45.53 ppm K −1 , and an ultimate tensile strength of 15.01 MPa. Finite-element simulations reproduced the experimental trends, indicating that KH550-induced interfacial modification reduces interfacial thermal resistance and facilitates interfacial polarization within the composite system. The resulting CST/PTFE composites therefore exhibit a well-balanced combination of dielectric, thermal, and mechanical properties, highlighting their promising potential as dielectric substrates for high-frequency RF and microwave components in advanced communication technologies such as 5G systems.