Ultralow‐k hollow glass microsphere filled perfluoroalkoxy composites

Perfluoroalkoxy (PFA) composites filled with different volume fractions of hollow glass microsphere (HGM) and HGM/PFA–HGM/HBO3–HGM/PFA sandwich layered composites were prepared by simple dry mixing and hot‐pressing process. The dielectric frequency and temperature response characteristics, thermal expansion coefficient, and mechanical strength were investigated as a function of the loading fraction of HGM fillers. The obtained .6VfHGM/.4VfPFA composite demonstrates ultralow‐k (εr ∼ 1,63@1 MHz; 1.57@10 GHz) with low‐dielectric loss (∼7.2 × 10−4@1 MHz; ∼1.73 × 10−3@10 GHz), water absorption of ∼1.21%, in‐plane thermal expansion coefficient of 42 ppm/°C, and temperature coefficient of dielectric permittivity (τεr) of ∼−92 ppm/°C. The temperature stabilities of dimension and dielectric permittivity for the .6VfHGB/.4VfPFA composite could be substantially improved by forming .6VfHGM/.4VfPFA–.6VfHGM/.4VfHBO3–.6VfHGM/.4VfPFA sandwich–layered composite, which still maintained reasonable dielectric properties and mechanical rigidity with flexural strength of ∼8.1 MPa.