HPMA modified aluminium nitride powder for aqueous tape casting of AlN ceramic substrates

Aluminum nitride (AlN) is considered one of the most desirable materials for integrated circuits and electronic packaging substrates. However, raw AlN powder reacts easily with water, forming Al(OH)₃ or AlOOH on the surface and hindering the development of aqueous tape casting process for preparing AlN ceramic substrates. In this study, hydrolyzed polymaleic anhydride (HPMA) was used to modify AlN powder, which has good water solubility and dispersibility. The AlN powder modified with 5 wt.% HPMA remained stable in water for at least 90 h under magnetic stirring condition and 24 h under ball milling condition, indicating that the HPMA-modified AlN powder has good resistance to hydrolysis. The action mechanism of HPMA is revealed. Firstly, the -COOH of the HPMA polymer and the oxide layer on the surface of the AlN powder underwent a dehydration condensation reaction to form a compound. Secondly, the long chains of the polymer further coated the surface of the AlN powder, forming an anti-hydration layer with a thickness of about 7.0 nm on the surface of the AlN particles. In addition, AlN green sheets were successfully prepared by aqueous tape casting using the HPMA-modified AlN powder without additional dispersants. Subsequently, AlN ceramic substrates were obtained by sintering at 1750 ℃ for 4 h under N₂ atmosphere with a pressure of 0.2 MPa. The relative density and thermal conductivity were tested to be 97.3 % and 122 W·m^-1·K^-1, respectively.