High Thermal Conductivity in Epoxy Resin Filled With Low Loading Content of 3D ‐Boron Nitride Framework

The ongoing miniaturization and integration of third‐generation wide‐bandgap semiconductor devices demand advanced thermal management packaging materials. Traditional polymer composites often rely on high filler loadings due to a lack of structured three‐dimensional (3D) networks, resulting in limited thermal improvement and deteriorated dielectric properties. In this study, a gelation–drying strategy was used to fabricate four distinct, continuous three‐dimensional thermal conduction networks within an epoxy resin (EP) matrix. The four networks were constructed using boron nitride (BN) platelets of different sizes (0.2, 2, 5, and 25 μm, respectively). It is demonstrated that the synergy between large‐scale BN fillers and the 3D scaffold enables the establishment of continuous phonon‐matched heat conduction pathways at a low percolation threshold, thereby substantially elevating the thermal conductivity of the EP composites. Benefiting from this unique architecture, the 25 μm 3D‐BN/EP composite achieves an out‐of‐plane thermal conductivity of 0.95 W/(m K) at a low loading of only 10 wt%. This value is 131.7% higher than that of the randomly blended BN/EP, yielding a high thermal conductivity enhancement efficiency of 42.78%. Simultaneously, the composite maintained excellent dielectric performance ( ɛ r = 3.82, tan δ = 0.0172 at 10 6 Hz and 25°C) and good insulation. This BN particle‐size‐regulated 3D network strategy provides a new method for the design of next‐generation epoxy composites for high‐power electronic packaging applications.