Study On Surface Metallized Diamond/Copper Composites Fabricated By Spark Plasma Sintering Method In Electronic Packaging Industry

With a high thermal conductivity?TC?and tailored coefficient of thermal expansion?CTE?,diamond/Cu composites can greatly meet the heat dissipation requirements put forward by the rapid development of information industry.However,as a non-carbide forming element,copper has a low carbon affinity which may lead to issues like a weak bonding at the interface with diamond and high interfacial thermal resistance,thus limits its industrial application.This paper intends to pretreat diamond particles with the molten salt bath method and diffusion method,thus prepare diamond/Cu composites with a high TC and adjustable CTE using spark plasma sintering?SPS?method.The microstructure and properties of the coating was investigated by means of SEM,XRD,EDS.The properties,like density,TC,CTE were also measured and compared to the theoretical values estimated by DEM model and Kerner model.Through the research of molten salt bath plating process,we can obtain the following conclusions.With the increase of temperature and the extension of holding time,the layer became more uniform,rougher and thicker.In particular,for chromium coating,under the condition of temperature higher than 900?C,holding time longer than1.0 h,the mass ratio of chromium to diamond higher than 6.72%,the layer which mainly contained carbides could be uniformly and densely covered on diamond particles.For tungsten coating,in order to form a uniform coating on diamond surface,the coating temperature should be higher than 1050?C,holding time longer than1.5h and the layer would contain mainly W and little WC.Through the research of diffusion method plating process,we can obtain the following conclusions.The coating structure of diamond-Cr₃C₂-Cr₇C₃-Cr was observed when plating chromium on diamond surface and the ratio of carbide thickness to metallic layer thickness was about 1:1.5.The microstructure of tungsten coating was porous and not dense.The structure of layer was diamond-W₂C-WC-W and the layer contained little WC,so there was a weak bonding between diamond and the coating,which made it easier to fall off.WO₂ also existed in the composites.The pretreated diamond particles and copper were mixed and fabricated by SPS.Following conclusions were obtained.For Cu/diamond-Cr composites,diamond particles were uniformly distributed in the matrix and the interface bonding was improved.This was because the presence of carbides with a thickness of about 1.0?m could perform as a transition layer and greatly improve the bonding condition.The prepared Cu/diamond-Cr composites had a relatively good performance with a high density of about 97.1%,the TC of406W/?m?K?and CTE close to 9.7?10^-6/K.For Cu/diamond-W composites,the thickness of layer was about 1.5?m and the interfacial bonding was improved to a small extent.But there were still some pores existed in the interface because a large amount of layers fell off during the fabrication process.And the composites with a density of92.5%,TC of 191W/?m?K?and CTE close to 10.0?10^-6/K was obtained.The reason for low thermal conductivity might be that the broken layer existed in the composites as impurities might became scattering centers of phonons and electrons and reduced its free path,which might cause the thermal conductivity to be significantly reduced.By further analysis of composites and referring to DEM model,the subsequent research direction would be further improving the performance of composites by reducing the content of impurities,controlling the structure and thickness of layers.