Interface Optimization And Thermal Properties Of Diamond/Copper Composites

Diamond/copper composite is one of the advanced packaging materials with great potential.It is favored by many researchers because of its high thermal conductivity,low coefficient of thermal expansion and moderate density.However,it is difficult to form a good interface with pure copper becuase diamond has special crystal structure and strong chemical inertia.In order to optimize the interface and to obtain the composite with excellent comprehensive properties and to reveal the effect of the interface bonding state on the thermal properties of the composite,two kinds of diamond coating layers with different types and thickness of Cr and W were constructed by magnetron sputtering method in this paper.Diamond/copper composites were prepared by pressure assisted infiltration.The effect of phase composition and thickness of Cr and W coating layers on the interface bonding and thermal conductivity of the composites were studied systematically.The coatings and the interfacial structure of the composite were characterized by XRD and SEM.The relationship between interfacial properties and thermal conductivity of the composites was revealed.The main research results are as follows:?1?The surface of diamond particles were coated with uniform and dense Cr and W coatings prepared by magnetron sputtering,and the coating of 45-1100 nm can be obtained by adjusting the deposition time.After the Cr coated diamond with the thickness of 200 nm?W coated diamond with the thickness of 300 nm?was annealed at 600?-900??900?-1200??,the phase of the two kinds of coating layer changed from metallic simple substance to carbides,and Cr also formed oxides.There is a selective interfacial bonding phenomenon in Cr,W coated diamond during low temperature annealing,and the coating layer can only be bonded well with diamond{100}plane.The bonding between the coatings layer and the diamond crystal faces can be realized by increasing the annealing temperature.?2?The phase composition and thickness of the coating layer have a significant effect on the interfacial bonding and thermal conductivity of the diamond/copper composites.The Cr coating was easy to be oxidized under low vacuum?about 10 Pa?,and the coating layer was shedding in different degrees before infiltration.Therefore the prepared composite exists obvious gap in the interface,and the thermal conductivity of the composites is lower than that of pure copper.While the thermal conductivity of W coated diamond/copper composites increases first and then decreases with the increase of annealling temperature?the transformation of the W coating phase composition?.When the coating phase is composed of a large number of WC and a small amount of W₂C,the interfacial bonding is better,and the thermal conductivity reaches 753 W·m^-1·K^-1.On this basis,the effect of the thickness of tungsten coating layer on the thermal conductivity of the composites was studied.With the increase of thickness?45-476 nm?,the thermal conductivity increases first and then decreases,and the thermal conductivity reaches 943 W·m^-1·K^-1 at about 182nm.?3?After bombarding diamond surface with Ar ion beam and then depositing 300nm W coating layer,Ar ion beam bombardment solves the anisotropy of interfacial adhesion/reaction between diamond and tungsten successfully.With the help of the bombardment,and obtained the diamond/copper composite with the same interfacial phase composition and good interfacial bonding.The thermal conductivity of the material was improved greatly.Compared with the composites with only 300 nm tungsten interface layer,the thermal conductivity of the optimized composites was increased from 642 W·m^-1·K^-1 to 896 W·m^-1·K^-1,and the thermal expansion coefficient decreased from 6.8×10^-6·K^-1 to 5.9×10^-6·K^-1.The further enhancement of the comprehensive properties of the composites mainly comes from optimization of the interface thermal conductivity and interfacial bonding state on the diamond{111}plane.