Boron nitride filled epoxy with improved thermal conductivity and dielectric breakdown strength

The present work aims at studying epoxy-matrix composites using boron nitride (BN) as filler for thermal management in electrical applications. Several factors were investigated: the combination of micro- and nano-sized particles, the use of a silane coupling agent (SCA) as well as different dispersion techniques. Composites containing from 10 w% up to 20 w% of filler were manufactured by conventional casting. Several concentrations of nano-sized particles and SCA were considered. The ball-milling (BM) method was used to create an effective dispersion of the filler in the matrix. Thermal conductivity measurements were performed on the samples as the core of the study along with a morphological analysis, dielectric spectroscopy and breakdown strength measurements. The thermal conductivity of the neat resin shows up to a fourfold increase for the composite containing 20 w% of BN, which is among the highest improvements ever reported in literature at this BN content. High concentration of SCA has a significant positive effect on the thermal conductivity of the material while ball milling proves to be an efficient method in breaking the large aggregates present in the nano-powder. Moreover, the addition of BN results in an increase of the breakdown strength of the host matrix (about 10%) accompanied by improved robustness (less scattering of the measured values), both very important factors for any electrical application.