Fast Preparation Of Ceramic With High Thermal Conductivity Under High Pressure

This paper is to explore a new method for preparing high thermal conductivity ceramics substrates applied to electronic packaging. On the basis of the research on the preparation of thermal ceramics at home and abroad, cubic boron nitride(cBN) as the main raw material was sintered into polycrystalline cubic boron nitride(PcBN) ceramics under the high temperature and high pressure, and Aluminum nitride(AlN) ceramics, β-Silicon carbide(β-SiC) ceramics and Polycrystalline diamond(PCD) ceramics were also prepared under the same condition. Firstly, thermocouple temperature measurement method and metal melting point method were used to calibrate the cavity temperature and pressure on the experimental platform of TH-V type cubic press. Then the raw powder was pretreated and assembled, and the PcBN ceramic, AlN ceramics, β-SiC ceramics and PCD ceramics were prepared successfully under the 6 GPa and 1500℃.The density, bending strength, thermal conductivity, thermal expansion coefficient and thermal diffusion coefficient of PcBN ceramics, AlN ceramics, β- SiC ceramics and PCD ceramics were tested, it could be concluded from the results and analysis as follows:1. Using the sintering method with high pressure and high temperature, we could quickly achieve the densification of PcBN ceramics, AlN ceramics, PCD ceramics and β-SiC ceramics, and good crystal shape of the grain could be obtained.2. Adding moderate metal aluminum and AlN into cBN powder, the adhesive strength between crystal grains in PcBN ceramics could be improved greatly, so as to improve its bending strength, and fracture characteristics of PcBN ceramics could be changed.3. The thermal conductivity of the PcBN ceramics with 5% metal Al additive increase with the increase of the particle size of c BN, when the particle size was between 8 to 12μm, the thermal conductivity was closed to 100w/mK, and reached the requirements of thermal conductive ceramics with high thermal conductivity. The thermal conductivity of the PcBN ceramics with different content of AlN decreases with the increase of content of AlN. When the content of AlN additive was 5%, and the particle size of cBN was between 8 to 12μm the thermal conductivity of PcBN ceramics reached 90 w/mK, and it basically met the requirements of thermal conductive ceramics with high thermal conductivity. Thus, it was concluded that adding reasonable sintering additive could favor PcBN ceramics to obtain high thermal conductivity.4. The thermal expansion coefficient of PcBN ceramics closed to that of Si by adding Al or AlN into PcBN ceramics.5. The thermal conductivity of AlN ceramics and β-SiC ceramics sintered under high pressure and high temperature were low, but the PCD ceramics could reach 129.5 W/mK, which completely met the requirements of thermal conductive ceramics with high thermal conductivity.In conclusion, we could achieve the sintering of PcBN ceramics, AlN ceramics, β-SiC ceramics and PCD ceramics with cBN, AlN, β-SiC and diamond powder raw material in a very short time by the method with high temperature and high pressure, which overcome the disadvantages of traditional methods for the preparation of ceramics, and improved the efficiency of the sintering. The PcBN ceramics prepared under high temperature and high pressure with high thermal conductivity reached the requirements of ceramics substrate for electronic packaging on the bending strength. The PCD ceramics also had high thermal conductivity, and could be used as a new thermal conductive ceramic material in the future.