Preparation And Properties Of Diamond/silicon Carbide Composites Substrate

Diamond/silicon carbide(diamond/SiC)composites have been considered as ideal materials for electronic packaging due to its high thermal conductivity,low density,and suitable coefficient of thermal expansion.However,the high cost of machining because of its extremely high hardness and brittleness greatly limits its large-scale application.To overcome this problem,this study developed a near net shape forming for diamond/SiC composites substrate by combining tape casting with Si vapor infiltration.In order to solve the issue of low thermal conductivity of the composites prepared by tape casting,the effects on the thermophysical and mechanical properties of the composites were investigated in terms of interfacial structure,matrix microstructure evolution and reinforcing phase particle size distribution,respectively.The effects of diamond and residual silicon content on the dielectric properties of the composites were investigated systematically and the polarization mechanism of diamond/SiC composites in alternating electric fields was revealed.Finally,a low-cost threedimensional diamond/SiC composite preparation process was also initially explored for further reduce the preparation cost,and the results showed that:The SiC precursors added to the tape casting slurry crystallize during the high temperature pyrolysis process and form SiC acting as a binder between the diamond particles,which greatly improves the mechanical strength of the pyrolysis body and is an important reason for inhibiting the deformation of the substrate during densification.The thermal conductivity of composites is affected significantly by mixing mode of diamond with different size.When the content of large diamond remains constant,adding a slight amount of small diamond was found to be effective in improving the thermal conductivity of the composite.However,excess small diamonds added will decrease thermal conductivity due to its high interfacial thermal resistance.The maximum thermal conductivity of obtained diamond/SiC is 469 W/mK when 38 vol.%large diamond and 4 vol.%small diamond were added.Such a result can be attributed to the formation of efficient heat transfer channels within the composite and sound interfacial bonding between diamond and SiC phase.Diamond/SiC substrates with high thermal conductivity are expected to be the next generation of electronic packaging substrates.The significant influence of the chemical composition and microstructure of the diamond surface on the formation of the diamond-SiC interface during infiltration.The newly {111} crystal family was formed on(100)plane by surface atom reconstruction,and the steps were formed on(111)plane,during annealing in vacuum.The diamond undergoes a similar transformation expect that the changes were more drastic,and graphitic clusters appeared on surface when annealing in air.The inhomogeneous nucleation of SiC was found on both(100)and(111)plane of the diamond.Growth of SiC particles on interface are controlled by diffusion-reaction mechanism.The different microstructures on the diamond(111)and(100)faces cause the difference in the growth rate of SiC on the different crystal faces,which results in the SiC on the different crystal faces having completely different microscopic morphologies.Both vacuum and air environment modified diamond enhances the interfacial reaction and facilitates the improvement of mechanical and thermal property,but the graphitic clusters generated on diamond surface after modified in air has a negative effect on the thermal conductivity of composites.The microstructure evolution of diamond/SiC composites after heat treatment and its effect on the thermal conductivity of the composites were investigated.Results showed that the SiC grain size in the composites matrix grows significantly,and the SiC particles are sintered to form a continuous network after heat treated at 1500℃ for 8 h.However,longer heat treatment time will lead to volatilization of residual silicon in the composites and reduce its densities.After heat treatment,the thermal conductivity of the composite is greatly increased,and the maximum value were obtained at heat treatment for 8 h reaching up to 423 W/mK,which is about 40%higher than that without heat treatment.Heat treatment provides a new method for improving the thermal conductivity of diamond/SiC composite.The effects of diamond and residual silicon content on the dielectric property of the composites were investigated.The results show that the real part of permittivity of the composites decreases rapidly and then decreases slowly as the diamond content increase from 0 to 40 vol.%;the real part of permittivity of the composites show a slight increase when the diamond content increase to 60 vol.%.This result can be attributed to the microstructural changes of the SiC matrix caused by the increase of diamond particles.With the increase of residual silicon content,the residual silicon in the composites gradually formed a continuous phase and the real part of the permittivity gradually increased.The imaginary part of the permittivity of the composites has a similar trend to the real part.The imaginary part of permittivity is composed of conductivity loss and polarization loss.For diamond/SiC composites,the conductivity loss dominates in the low frequency range(<400 MHz)and the polarization loss dominates in the high frequency range(400 MHz～1 GHz).The diamond/SiC composites exhibit multiple polarization relaxation phenomena,which are mainly derived from the interfacial polarization of the diamond/graphitized layer,and the graphitized layer/SiC.The study of dielectric properties of diamond/SiC composites is important to promote their application in the field of electronic packaging substrates.A process for the low-cost preparation of three-dimensional connected diamond reinforced SiC composites was briefly developed by injection molding combined with liquid phase silicon infiltration.The diamond particles in the obtained composites were closely arranged along the pores of the template,and heat transfer channels with high thermal conductivity were constructed within the composites.The thermal conductivity of the prepared composites reached up to 298 W/mk at a low diamond volume fraction only 26.4 vol.%.Compared with the previous study,the diamond content was reduced by 31.5%with almost the same thermal properties,which greatly reduced composite preparation cost.The development of the three-dimensional connected diamond reinforced SiC composites preparation process provides a new idea for the development of diamond/SiC composites.