Microphase Rivet‐Reinforced Interfaces in PTFE Composites: Enabling High Thermal Conductivity and Dimensional Stability for High‐Frequency Substrates

Heat dissipation remains a formidable challenge for polytetrafluoroethylene (PTFE) based high‐frequency substrates, as the integration of thermally conductive fillers like hexagonal boron nitride (hBN) is often hindered by the intrinsic chemical inertness and ultra‐low surface energy of PTFE. Herein, a soluble fluoroalkyl end‐capped polyimide (FPI) precursor is developed. The amphipathic structure of FPI acts as an intermolecular bridge, facilitating the homogeneous dispersion of hydrophobic hBN within aqueous PTFE emulsions. Upon thermal imidization, in situ microphase “rivet” architectures evolve at the filler‐matrix boundaries, replacing fragile van der Waals contacts with robust, mechanically anchored transitional zones. The topological interlocking significantly restricts the long‐range segmental mobility of PTFE chains, yielding an exceptional thermal conductivity of 2.89 W/m·K (a 7.5‐fold increase) alongside an ultralow copper‐matched coefficient of thermal expansion (12 ppm/K). Remarkably, these breakthroughs are achieved while preserving superior dielectric properties (permittivity D k = 2.52, loss tangent D f = 0.00078 @ 10 GHz). This work establishes a universal and scalable blueprint for fabricating extreme‐performance PTFE substrates tailored for the stringent demands of next‐generation 5G/6G telecommunications.