Effects Of Sintering Additives On Mechanical Properties And Thermal Conductivity Of AIN Ceramics

As a promising packaging substrate, AIN ceramics attract particular interest due to its specific properties of high thermal conductivity, low dielectric constant, a matching thermal expansion with silicon, good thermo-chemical stability and nontoxic. However, because of the low self-diffusivity coefficient, AIN is difficult to sinter. In order to get the high performance AIN ceramics, the sintering additives are always used. So far, researchers mainly aimed to study the influence of the different sintering additives on the performance of AIN ceramics. There is seldom research focusing on the effects of adding methods of the sintering additive on properties of AIN ceramics, which is important to get high performance AIN ceramics.In this article, AIN ceramics were prepared by the hot-pressing with Y2O3 as a sintering additive added by direct addition and in-situ formation, respectively. The effects of adding methods of sintering additive on mechanical properties and thermal conductivity of AIN ceramics were carried out.The results show that the sintering additive added by in-situ formation is more beneficial to the densification of AIN ceramics due to the homogeneous distribution of Y2O3 in AIN powders. Particularly, when the addition of Y2O3 reaches 2 wt%, the value of Vickers hardness, flexural strength and fracture toughness of the sample sintered at 1850℃can reach up to 15.39 GPa,383.0 MPa and 3.10 MPa-m1/2 respectively. However, mechanical properties such as Vickers hardness and flexural strength decrease with the increase of sintering additive due to the large amount distribution of yttrium aluminates phase in grain boundaries.The thermal conductivities of AIN ceramics increase with the increase of sintering temperature. The sintering additive added by direct addition is more favorable to increase the thermal conductivity of AIN ceramics than that by in-situ formation. Compared with the highest value of 165 W/m·K obtained by in-situ formation sintered at 1850℃with addition 4 wt% Y2O3, the thermal conductivity obtained by direct addition with the addition of 6 wt% Y2O3 reaches to its highest value of 205 W/m·K. This can be explained by the existence of crystal water of Y(NO3)3·6H2O deteriorates the thermal conductivity of AIN ceramics.