Effects Of Adding Methods Of Sintering Additives On Microstructures And Properties Of AIN Ceramics

Rapid development of electronic technology requires high-performance electronic packaging materials. The traditional Al2O3ceramic substrates are not able to meet the requirements of the high-power, high-performance devices any more. Due to high thermal conductivity, low dielectric constant and low thermal expansion coefficient closed to those of the Si, GaAs semiconductor materials, A1N ceramics are believed to be new-generation electronic packaging materials. Therefore, research on the fabrication, microstructures and properties of the A1N ceramics is very important. In this study, novel adding methods of the sintering aiditives were introduced to produce the A1N ceramics, and microstructures and properties of the ceramics were also investigated in order to make up for the deficiencies of the currently-used A1N ceramic fabricating techniques.It is known that uniform distribution of the sintering additives in the A1N powder is necessary to produce high-quality AJN ceramics. Presently, in the fabricating process of the A1N ceramics, the sintering additive oxide powders are directly added. The disadvantage of this method is that the sintering additives can not homogeneously distribute in the A1N powder. Segregation and shortage of the sintering additives in the A1N ceramics takes place in different regions, resulting in the degragation of the properties of the A1N ceramics. In the current work, the A1N powder was homogeneously mixed with the nitrates of the sintering additives desolved in ethanol. During calcinating, the nitrates decompose into the oxides of the sintering additives, and uniformly enwrap the A1N particles, which can activate the sintering of the A1N ceramics.When the CaO-Y2O3sintering additives added as the Ca, Y nitrates, CaO and Y2O3react firstly with AI2O3in the AJN ceramics to form CaAl4O7and Y3Al5O12, respectively. When the A1N ceramics sintered at1700℃, these two binary-oxides are combined to form CaYAl3O7. As the sintering temperature risen further, CaYAl3O7then decomposes into the binary oxides above. As the A1N ceramics sintered at1800℃, the calcium aluminate almost volatilizes completely, only Y3Al5O12is survived. The adding methods of the sintering additives have great effects on the sintering densification process of the A1N ceramics. When the sintering additives added as the dehydrated nitrates, the A1N ceramics are dense with the well-grown A1N grains and well-distributed second phases. The bending strength and thermal conductivity of the AIN ceramics are both higher than those of the A1N ceramics sintered by adding the oxide sintering additives with the same composition. Moreover, as the AIN ceramics sintered at1725℃by adding1wt%Y2O3and1wt%CaO, the AIN grains are of regular polyhedron in shape, the second phases are small in amount, and segregate at the triple grain boundaries. The bending strength of the AIN ceramics arrives at398.0MPa. The fracture mode of the A1N ceramics is mainly of intergranular fracture mixed with a small amount of cleavage fracture. As sintered at1700℃by adding2wt%Y2O3and2wt%CaO, the microstructure of the AIN ceramics is fine, the A1N grain size is about4μm, and the thermal conductivity of the AIN ceramics arrives at136.7W/(m-K).