Solvent-free water-repellent parylene coating to enhance hydrolysis resistance of aluminum nitride and thermal conductivity of epoxy composites

The utilization of aluminum nitride (AlN) ceramic materials in state-of-the-art electronic devices and semiconductors is rapidly expanding. However, raw AlN is subject to rapid hydrolysis, and its exorbitant storage expense impedes its widespread use. In this study, raw AlN was modified by applying a coating of parylene C using a rotary powder coating machine to improve the hydrolysis resistance and thermal conductivity of epoxy composites. Microscopic mapping images, along with X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry results were used to characterize the AlN powder before and after the coating process, and the mechanism of the hydrolysis resistance was determined. Modification with parylene C affected the hydrophobicity of the AlN surface, with the water contact angle increasing to 144°. The modified powder was not hydrolyzed under 100 % humidity and a temperature of 50 °C. During the heat treatment of the parylene C, the pyrolyzed monomers were polymerized and formed mechanical bonds with the AlN core. The protective 8 nm-thick layer that formed on the surface of the AlN crystal prevented attack by water molecules and hindered the hydrolysis of the AlN. Furthermore, the parylene C structure interacted with an epoxy matrix, which improved the thermal conductivity of the composite. This study investigated a facile but scalable strategy to enhance the anti-hydrolysis property of AlN powder and quasi-isotropic thermal conductivity of polymer composites.