The Sandwich Structure of a Polyimide/PTFE Composite Film Designed to Achieve a Low Dielectric Constant and Excellent Thermal Performance at High Frequency

As 5G technology rapidly progresses, the demand for insulating dielectric materials with low dielectric constants, minimal dielectric loss, and enhanced thermal and mechanical properties has become increasingly critical. In order to combine the advantages of both fluoropolyimide (FPI) and polytetrafluoroethylene (PTFE), this study successfully developed an FPI/PTFE/FPI composite film with a sandwich structure that seamlessly integrated a commercial hydrophilic PTFE porous fibrous film and FPI. This structure capitalizes on the permeation effect of the FPI wet film to significantly improve interfacial interactions compared to traditional sandwich-structured composites. Consequently, the composite films have an excellent combination of properties. When the proportion of PTFE reaches 50%, the composite film remains stable across high-frequency bands (8.2 to 12.4 GHz), with an impressively low value of 1.5 at 9 GHz. The composite film also exhibits exceptional electrical breakdown strength (385.2 kV mm–1), tensile mechanical robustness (σb = 64 MPa, E = 2.1 GPa), thermal stability (Td5% = 496.1 °C, Tg = 306.2 °C), and a low coefficient of thermal expansion (51.7 ppm/K). Notably, the composite film still maintains good hydrophobic properties, with a water contact angle of 81.2° and a water absorption rate of 3.1%. This research also details an efficient coating method to fabricate flexible dielectric films, proposing a strategy for the development of advanced insulating materials suitable for high-frequency and high-speed communication applications.