LAUSR

Poly (p‐phenylene benzobisoxazole) (PBO) nanofiber films are promising candidates for next‐generation electronics due to their superior thermal stability, mechanical strength, and heat dissipation capability. However, fabricating high‐quality PBO nanofiber film remains challenging due to its inherent poor solubility and infusibility. Current sol–gel methods for fabricating PBO nanofiber films suffer from the tedious operation, environmental risk, and potential structural defects, thereby limiting their performance and applications. A hierarchical assembly strategy is demonstrated to optimize the fabrication and aggregation structure of PBO nanofiber films through proton‐acceptor solvents such as H 2 O. By controlling nanofiber aggregation and enhancing molecular alignment via external force‐assisted crystallization, high‐performance PBO nanofiber films are achieved with exceptional properties: great in‐plane thermal conductivity (25.85 W·m −1 ·K −1 ), outstanding tensile strength (189.98 MPa), and remarkable thermal stability (T 5% ≈ 517 °C). Remarkably, assembling PBO nanofibers (PBONFs) in high concentration into PBO wet films takes just a few minutes, drastically enhancing preparation efficiency. When applied as flexible printed circuit board substrates, PBO nanofiber films effectively homogenize temperature fields, suppressing local hotspots and reducing surface temperatures by 16.7 °C. This strategy offers a scalable solution for manufacturing high‐performance PBO nanofiber films, demonstrating significant potential for advanced thermal management in next‐generation electronics.