Mitigating Contact-Constricted Thermal Bottlenecks by Magnetically Programmable hBN Bridge Fillers in Al₂O₃/Epoxy...

Thermally conductive polymer composites often suffer from limited heat transport due to contact constriction in spherical particulate networks. To address this challenge, we report a magnetically programmable bridge-filler architecture that enhances thermal pathways in electrically insulating epoxy systems. In this design, spherical Al₂O₃ serves as a process-friendly primary filler framework, while Fe₃O₄-functionalized hexagonal boron nitride (hBN@Fe₃O₄) flakes act as magnetically addressable bridge fillers that connect neighboring alumina particles and can be oriented along the through-plane direction under an external magnetic field. At a fixed total filler loading of 40 vol%, the Al₂O₃:hBN@Fe₃O₄ ratio of 8:2 provides the most effective balance between bridge-network formation and rheological freedom for alignment, yielding a through-plane thermal conductivity of 2.02 W m^{- 1} K^{- 1}, 72.8% higher than that of the corresponding Al₂O₃-only composite. Finite-element modeling reveals that the hybrid aligned architecture alleviates point-contact-dominated thermal bottlenecks by redistributing heat flux through more continuous bridge-mediated pathways. The optimized composite retains high volume resistivity (4.4 × 10^{1 5} Ω cm) and lower dielectric constant and loss than the Al₂O₃ composite, while package-level thermal tests confirm faster heat transfer. These results establish a generalizable design principle for directionally efficient thermal management in electrically insulating composites with relevance to advanced electronic packaging.