PBO Fibers‐Reinforced Double‐Layer Heterogeneous Polyimide Composite Film Enabling High‐Frequency Signal Transmission and Thermal Management

ABSTRACT Current technologies for synergistically controlling the low dielectric constant and high thermal conductivity of polymer dielectrics struggle to improve signal transmission quality and heat accumulation issues without compromising material processability. This presents a persistent technical barrier to material innovation in electronics, power systems, and new energy applications. Herein, a double‐layer heterogeneous polyimide (PI) composite film with organic fiber (poly (p‐phenylene‐2, 6‐benzobisoxazole), PBO) is prepared by layered casting and encapsulation process. The ordered “chain network” within the PBO nanofilm and the well phonon matching characteristics with PI facilitate efficient phonon collisions, providing high‐speed pathways for phonon transmission. The 0.10 PNF//IL‐PI film exhibits excellent in‐plane thermal conductivity (λ // = 17.95 W∙m −1 ∙K −1 ) and lower dielectric properties ( k = 2.68, tanδ = 0.008 at 10 6 Hz). Furthermore, it has been fully demonstrated that the film can be used as a patch antenna substrate for high‐quality signal transmission, with a reflection loss intensity of only 4%. Therefore, this design strategy opens new horizons for the development of polymer dielectric materials for cross‐disciplinary integrated applications and provides novel insights for the advancement of high‐frequency flexible electronics.