Preparation And Properties Of Diamond/Copper Composites

In recent years,with severely rising of heat of integrated circuit(IC)along with its high integration scale,so urgent requirement of new materials with high thermal conductivity(TC)and moderate coefficient of thermal expansion(CTE)which match to those of IC materials has been launched.This paper aims to prepare an electric packaging material with high TC with semiconductor materials.Single crystal diamond particles,Cu powders,Ti powders,CuTi alloy powders and W target were used as raw materials.Cu/diamond composites were prepared by pressureless infiltration process and spark plasma sintering(SPS)respectively.The phase composition and microstructure characteristics of the Cu/diamond composites were studied by X-ray diffraction(XRD)and field emission scanning electron microscope(FE-SEM).The thermal conductivity of the Cu/diamond composites was analyzed by thermal conductivity tester.The effects of materials composition on the thermal conductivity of the Cu/diamond composites were studied.Cu-Ti/diamond composites were firstly prepared by pressureless infiltration method at 1300°C.First,phenolic resin and diamond particles were mixed,pressed and heated to prepare a carbonized diamond compact with a porosity of 50%.Then it was embedded in a mixture of Cu and Ti powders,with titanium proportions of 5,10,15,and 20 wt%,respectively.Cu-Ti/diamond composites were obtained by infiltrating of molten Cu-Ti alloy into the diamond preform.The results show that molten Cu alloy cannot spontaneously infiltrate into the porous diamond preform unless the Ti content reaches 10 wt%.An interfacial layer of titanium carbidate is formed between copper phase and diamond particle in the Cu-Ti/diamond composites.With the increasing of Ti content,relative density of the Cu-Ti/diamond composite increases from 83.2% to 89.4%,and thickness of the interfacial layer increases from 0.8μm to 4μm gradually.As the Ti content increases,thermal conductivity of the Cu-Ti/diamond composites increases first and then decreases.When Ti content is 15wt%,the thermal conductivity of the Cu/diamond composite reaches a maximum of only 298 W/(m·K).Diffusion mismatch model and Hasselman-Johnson model were used to estimate the theoretical thermal resistance of the Cu/diamond composites.The highest thermal conductivity reaches 82% of the theoretical value.We also prepare a Cu-Ti/diamond composite by spark plasma sintering a mixture of Cu-1wt%Ti,pure Cu powders,and synthetic single-crystalline diamond particles.The volume fraction of diamond particles in the composites is 50% and the mass fraction of Ti in the matrix was 0.0-1.0 wt%.The results show that an interfacial layer is formed between diamond particle and Cu matrix with the addition of Ti.With the increasing Ti content,relative density of composites increases from 93% to 94.6% and the average thickness of the interfacial layer increase from 300 nm to 1.2μm.As the Ti content increases,the thermal conductivity of the composites increases first and then decreases.The highest thermal conductivity of 529W/(m·K)is obtained when the Ti content is 0.2 wt%,which increased 195% compared with pure Cu/diamond composite.Diffusion mismatch model was used to theoretically estimate the theoretical thermal resistance of the Cu/diamond composites.The highest thermal conductivity reaches 88.6% of the theoretical value calculated by Hasselman-Johnson model.The W-coated diamond/copper composites were fabricated by spark plasma sintering using copper powder and W-coated diamond particles prepared by physical vapor deposition.The results show that with the increasing of coating time,coating area on the surface of diamond particles increases and the composites become denser.Meanwhile,thermal conductivity of the Cu-W/diamond composites increases at first and then decreases with the increasing of coating time.When the coating time is 30 min,the Cu-W/diamond composite with the highest thermal conductivity of 327W/(m·K)can be obtained.The highest thermal conductivity reaches 52% of the theoretical value calculated by Hasselman-Johnson model.Comparing three methods in this paper,spark plasma sintering of Cu-Ti/diamonds composite is the most effective way to produce diamond particle reinforced copper matrix composites.