Study On Thermal Properties And Mechanical Properties Of Graphite Flake/Cu Composites

With the development of electronic information technology and the increasing power density of electronic components,the heat per unit area of integrated circuits of increases continuously,and efficient thermal management materials have become a key for guaranteeing performance and reliability in electronic devices.Traditional electronic packaging materials,e.g.Cu,Cu/Mo,Cu/W and Al/SiC composites,are no longer sufficient to satisfy the requirements of heat dissipation for the most recent power electronic devices due to the low thermal conductivity.Therefore,the development of new electronic packaging materials is urgent.Copper matrix composites are becoming prime candidates because of its higher thermal conductivity and attractive mechanical properties.In this paper,natural graphite flake was used as a kind of reinforcement material and copper was used as the matrix,through vacuum hot-pressing sintering,graphite/copper composites with high thermal conductivity were fabricated.The effects of different volume fraction of graphite on the microstructure,thermal expansion coefficient,thermal conductivity and bending strength of the composites were investigated.The results showed that the thermal conductivity of the composites increased as the volume fraction of graphite increased,whereas the trend of bending strength and thermal expansion coefficient was the opposite.When the volume fraction of graphite is 70%,the thermal conductivity in X-Y plane direction of the composite material is up to 676 W/mK,and the thermal expansion coefficient is 7.3×10-6/K,but the bending strength is only 52 MPa,which greatly limits the application of composite materials.Through the analysis,we found that interface adhesion force or binding strength has a direct impact on mechanical properties of composites.In order to improve the mechanical properties of composites.Silicon carbide(SiC),boron carbide(B4C)or titanium carbide(TiC)layer were coated on the surface of the nature graphite flake by the molten salt method,and then the graphite/copper composites were fabricated by vacuum hot-press sintering with SiC,B4C or TiC coated GF and Cu powder.The effects of volume fraction of graphite and coating on the thermal conductivity and bending strength of the composites were investigated.The experimental results show that SiC or B4C or TiC coated on the graphite reduce the thermal conductivity and increase bending strength.Compared with the raw graphite/copper composites,the thermal conductivity of SiC or B4C coated on graphite surface is only slightly reduced,while the thermal conductivity of TiC coating significantly decreases.When the volume fraction of graphite was 70%,the thermal conductivity of SiC or B4C or TiC composites coated on the graphite surface were 610 W/mK,608 W/mK and 526 W/mK,respectively.The bending strength of composites after graphite coating was improved obviously,when the volume fraction of graphite was 70 vol%,the bending strength of TiC coated graphite/copper composites reaches at 103 MPa,B4C and SiC coated were 74 and 75 MPa,respectively.Meanwhile,microstructure features of the coated graphite/Cu composites further illustrates that SiC or B4C or TiC coated on the surface of graphite plays an important role on the fracture model of the graphite/Cu composites.