Preparation And Properties Of Diamond/SiC Composites By Silicon Vapor Infiltration

With the development of large-scale integrated circuits,high-performance electronic packaging materials have attracted more and more attention.Among them,diamond/silicon carbide composites are potential electronic packaging materials.It has many advantages such as high thermal conductivity,low thermal expansion,high flexural strength and high hardness.The existing diamond/silicon carbide composites have the disadvantages of high cost and unstable process.In view of this situation,high density diamond/silicon carbide composites were prepared by silicon vapor infiltration method.This method has the advantages of low cost,simple operation and strong controllability.However,as a new method of preparing diamond/silicon carbide composites,there are still many unclear aspects in the preparation process and densification mechanism of silicon vapor infiltration method.Based on the preparation of diamond/silicon carbide composites by silicon vapor infiltration,the technological parameters of the infiltration process were optimized,and the densification mechanism of the composites was mainly studied.At the same time,the microstructures,interfacial characteristics and thermal conductivity,thermal expansion coefficient and thermal shock resistance of the composites were studied,and the thermophysical properties of the composites were reasonably predicted by theoretical model calculation.Research shows:With the increase of compression pressure,the average pore size and porosity of the sample decrease gradually.At different process stages,the porosity decreases gradually from pyrolysis billet,preform to permeation sample,while the average pore size decreases gradually from preform,pyrolysis billet to permeation sample.Silicon in composites will diffuse into diamond,and the diffusion depth will deepen with the increase of permeation temperature.When the permeation temperature reaches 1700?,slight graphitization will occur on the surface of diamond.In order to achieve complete densification of the composites,the pressure of preform should be 50-60 MPa..During the silicon vapor infiltration,the sample should be placed at a height not more than 4 mm away from the silicon surface,and the infiltration temperature should be kept between 1550-1700?,and also the infiltration time should be more than 30 mins.The densification degree of the diamond/silicon carbide composites can reach over 97%.Densification of composites is a simultaneous process of silicon vapor infiltration deposition and reaction sintering of silicon carbide.Among them,silicon carbide is mainly obtained by the reaction of graphite and diamond with silicon.The silicon carbide obtained by graphite reaction has high content and large particle size,while the silicon carbide obtained by diamond reaction has low content and small particle size.The reaction between graphite and silicon produces silicon carbide mainly through the dissolution-precipitation of graphite in silicon,while the reaction between diamond and silicon produces silicon carbide mainly through the solid diffusion of silicon and carbon in silicon carbide.In addition,silicon vapor osmotic deposition includes four steps:silicon melting,formation of silicon vapor pressure,diffusion of silicon vapor in the channel and condensation deposition of silicon vapor on the surface of silicon carbide.The thermal conductivity of the composites increases with the increase of diamond size,silicon carbide content and permeation temperature.The surface of broken diamond has good wettability,and it is easier to react with silicon to form silicon carbide,which reduces the interfacial thermal resistance and improves the thermal conductivity of diamond/silicon carbide composites.When the penetration temperature is 1650?,the content of SiC is 35%,the volume content of broken diamond is 50%at 110 um,and the thermal conductivity of the composites has a maximum value of 518 W·m-1·K-1.When the temperature reaches 1700?,the graphitization of the diamond surface leads to a serious decrease in the thermal conductivity of the composites.The thermal conductivity of the composites was measured by the second iteration method and the existing thermal conductivity model.The results show that when the volume fraction of diamond is less than 30%,the change of thermal conductivity of composites matches H-J model,and when the content of diamond is more than 30%,the thermal conductivity of composites is between H-J model and Agari model.It needs to be predicted by the combination of the two models.The thermal expansion coefficient of the composites is less than 4×10-6·K-1.Large particle size,broken diamond,high volume fraction of silicon carbide and high infiltration temperature will lead to the increase of thermal expansion coefficient of composites.The peak value of diamond in composites was measured by Raman spectroscopy at different infiltration temperatures.The results show that the peak shift of diamond increases with the increase of temperature,which also means that the thermal residual stress in composites increases with the increase of infiltration temperature.The thermal expansion coefficients of composites were predicted by the second iteration method and combined with the existing thermal expansion coefficient models.The results show that CTE values are in good agreement with the predicted values of Turner model at temperature(50?150?),while the measured values of thermal expansion coefficients at higher temperature(250?400?)are in good agreement with the lower bound Schapery model.In addition,the composites exhibit good thermal shock resistance,the flexural strength can reach more than 300 MPa.When the volume fraction of diamond increases from 10%to 60%,the HRA hardness of composites is 84-92.8.The diamond/silicon carbide composites prepared in this study have the advantages of simple process and low cost,and can be used to prepare a variety of samples with different shapes at one time.Compared with other types of diamond reinforced composites,this material has higher desification degree,higher thermal conductivity,lower thermal expansion coefficient,better thermal shock resistance and higher flexural strength.