Hierarchical BN/Al₂O₃ Filler Networks for Enhanced Thermal Transport in Epoxy-Based Non-Conductive Films

Epoxy-based non-conductive films (NCFs) incorporating plate-like boron nitride (BN) and bimodal alumina (Al₂O₃) fillers were developed to improve thermal transport while maintaining the optical and electrical characteristics required for semiconductor-packaging applications. In the designed hierarchical filler architecture, BN platelets act as the primary heat-transfer pathways because of their high intrinsic thermal conductivity and electrically insulating nature. Meanwhile, Al₂O₃ particles with average sizes of 7 μm and 600 nm are introduced to occupy interstitial spaces at different length scales between adjacent BN platelets. The bimodal Al₂O₃ system improves packing efficiency, reduces epoxy-rich regions, and increases the probability of direct filler–filler contact. As a result, more continuous BN–Al₂O₃–BN thermal pathways can be formed throughout the epoxy matrix, facilitating heat transfer across the composite film. The combined use of plate-like BN and differently sized Al₂O₃ particles therefore provides a multiscale strategy for constructing an interconnected thermal network without excessively increasing the filler content. The BN-containing NCF exhibited enhanced thermal transport while maintaining an optical transmittance of more than 66% at 550 nm. This combination of thermal conductivity, electrical insulation, and optical transparency is particularly advantageous for NCF materials used in semiconductor packaging, where thermal management and alignment visibility are simultaneously required. These results demonstrate that hierarchical filler packing is an effective approach for improving the thermal performance of epoxy-based NCFs while preserving process compatibility and material reliability.