Sintering Polycrystalline Cubic Boron Nitride Thermal Conductivity Ceramic Under High Pressure

This thesis is to explore a new method for preparing high thermal conductivityceramics substrates applied to electronic packaging. Based on full investigation oftheoretical research and application, the solution is presented that is taking the cubicBoron Nitride (cBN) powder as experimental material and using high-pressuresintering methodto prepare polycrystalline cubic boron nitride (PcBN). The cubiclarge volume press is the experimental platform in this research, to this end, thepressure and temperature in the press cell are calibrated accurately combined thethermocouple thermometry and metal melting point methods. With designingreasonable condition of high pressure sintering, pretreatment for the raw powder andassembly methods, the PcBN ceramics are prepared successfully under6GPa and1500℃.The properties of PcBN ceramics prepared under high pressure are measured,the test items include density, SEM, XRD, bending strength (BS), thermal expansioncoefficient (TEC) and thermal conductivity (TC), then with a comprehensiveanalysis the resulting conclusions of this thesis are as follows:1. Adding moderate metal aluminum and cobalt into cBN powder, the adhesivestrength between crystal grains in PcBN ceramics can be improved greatly. Whilecopper as metal additive, however, an opposite effect is achieved, this result illustratethat the copper is not an effective sintering aids;2. The TEC of PcBN ceramics sintered under high pressure without any metaladditive is depending on the grain size of cBN crystal, increasing with the decreaseof the grain size of cBN crystal, despite this trend, the TEC of this PcBN ceramicsnevertheless match the silicon’s generally. As adding moderate metal aluminum andcobalt into cBN powder, the dependencies disappear, and the TEC of this kind PcBNceramics have very good consistency with silicon;3. The TC of Pure PcBN between40-60W/mK, and this value decease with theincrease of grain size of cBN, the variationtendency conforms to the Goldsmidt-Penn-Parrott model generallywhile the grain size of cBN less than10. The TC ofPcBN ceramics with metal additive come to a high value of above100W/mK,meet the criterion of the high thermal conductivity ceramic. It also describes theappropriate amount of sintering aids can make PcBN ceramics with high thermalconductivity.With high-pressure facility, achieved the goal of sintering PcBN ceramics withcBN powder as raw material in a very short time, overcame the drawback oftraditional methods for preparing ceramics, and the efficiency of sintering isimproved. The PcBN ceramics prepared under high pressure in this work meet therequirements of electronic packaging material either the thermal conductivity,thermal expansion coefficient, bending strength or other indicators. Furtheradjustments of cBN particle size and sintering aids, as well as using hBN as rawmaterial for the preparation PcBN high thermal conductivity ceramic, is the directionof future research.