| With the rapid development of microelectronic technology,electronic packaging has a tendency to be high integration density, high performance, miniaturizatio n and high reliability, which results in a higher request to the electronic packaging materials performance. Because of the high thermal conductivity, adjustable thermal expansion and low density, carbon/metal composite materials h ave attracted much attention in the electronic packaging field. In this paper, the finite element method was used to simulate the thermal performance of the carbon/metal composites. Graphite/copper composites and diamond/aluminum composites were prepared by the vacuum hot-pressing technology and pressure infiltration method, respectively. The surface modification on reinforcement was used to regulate control the microstructure and the characteristic of composite interface, and the influences of interface on thermal properties of composites were studied. The main research work in this paper focuses on the following aspects:（1）Using general-purpose finite element program Ansys, a three-dimensional finite element model with the interface thermal resistance of particle reinforced composites was established to simulate the thermal conductivity of the composites. An outstanding character of the model was that the effect of interface thermal resistance on total thermal conductivity of composites was defined by establishing contact pairs and their real constants. With the help of this outstanding, the model including interface thermal resistance was more practical than the traditional models, and the effect of the interface thermal resistance on thermal conductivity of composites could be better expressed. Based on the model, the effects of interface thermal conductivity, materials properties, particle size of reinforcement and volume fraction on the thermal conductivity of composite was studied. Meanwhile, the influence of materials properties on the thermal expansion of composite was also mentioned. According to the microstructure of diamond/aluminum composite, a further improvement in the model, other three-dimensional finite element model with inhomogeneous interface thermal resistance of diamond/aluminum composites was established. Conbining with the different fracture morphologies of the composites, the evolution of the thermal conductivity had been illustrated. The results shown that the initial improvement of the thermal conductivity c ould be attributed to the reduction of interface thermal resistance on diamond {100} faces. Furthermore, they also pointed out direction of enhancing the thermal properties of composites. Only the interface thermal resistances of diamond {100} and {111} dr amatically reduced, can the thermal conductivity of the composite be close to theoretical value.（2）The effect of interface modification on interfacial bonding and solid state wetting of graphite/copper interface was studied. Surface modification of graphite particles was carried out by mean of magnetron sputtering, and the copper coating was deposited on the particles. The copper coated graphite with different interface modification element were heated to high temperature to investigate the effects of interface modification on suppressing spheroidizing of the copper coating and bonding strength. The result shown that the tungsten element at the interface obviously suppressed the spheroidizing phenomenon and the titanium element at the interface was more efficient to enhance the bonding strength between graphite and copper coating even at low heat treating temperature. If tungsten element is used as the surface modification element, the effect of heat treating temperature on the bonding strengthe is significant. Only the temperature reached 1050 ℃, can the bonding strength be improved.（3） Thermal performance of graphite/copper composites was improved by surface modification method. In this paper, the traditional mixing technology was replaced by electroless copper plating method to realize control the constituents of composite. The composites were synthesized by the copper coated graphite particles directly, and the densification process was accomplished by vacuum hot-press sintering. The composites obtained by the above mentioned route exhibited much more homogeneous microstructure, and a three-dimensional net structure of copper was formed in the composite, which resulted in the improvement of the composite thermal properties. Further more, the surface modific ation which was carried out by magnetron sputtering technology is an efficient method to enhance the solid state wetting between graphite and copper, and the microstructure was much more homogeneous. Meanwhile, the formation of carbide at the interface was conducive to reduce the interface thermal resistance between graphite and copper, and enhance the thermal conductivity of the composites. Combined the two factors, the thermal conductivity of graphite/copper composites was further improved, reached 158W×m-1×K-1. Compared with the graphite/copper composites without tungsten addition, the value was increased by 43.6%.（4） Ion-beam bombarding was used to regulate the selective interfacial reactions between aluminum and different diamond orientations, and the composie exhibited super high thermal conductivity. Through the discussion and calculation of Laplace equation, the result shown that the critical pressure of infiltrating molten aluminum into tapped diamond particles is 40 k Pa under the experimental condition（the size of the diamond is about 200mm and the volume fraction is about 60%） and the pressure would be reduced as the improvement of the wetting ability of molten aluminum on diamond particles. Base on the discussion and the calculated results, the diamond/aluminum composites were manufactured successfully by pressure infiltration process in an in-house designed mould. Without the ion-beam bombarding the selective interfacial reaction between the diamond and the aluminum was obvious. The result shown that an ion-beam bombarding on the diamond particle enhance the graphitization of the diamond surface. Defects and danging bonds promoted the reaction between molten aluminum and diamond surfaces. So the aluminum matrix attached to every diamond orientation surfaces, reducing the interface thermal resistance, and the experimental thermal conductivity of composite was good agreement with the simulation result, reached 713W×m-1×K-1.（5）The influence of coating layer on properties of diamond/aluminum composite was researched. In this paper, tungsten and aluminum nitride coated diamond particles were both attained by magnetron sputtering process, and the effect of style and thickness of modification layer and infiltration temperature on microstructure and performance of composites were investigated. Direct contact between diamond and molten aluminum can be blocked by introduction of the coating layer on the diamond particles, suppressing the formation of Al4C3 phase, and improving the stability of composites in moisture environment. When tungsten was selected as the surface modification element, the composites had the stable thermal properties in a moisture environment through optimizing the infiltration temperature and the coating thickness, and the thermal conductivity reached 632W×m-1×K-1. But with the increase of infiltration temperature the stability decreased, and the thermal conductivity also reduced. Compared with the tungsten coating layer, the aluminum nitride completely prevented the diamond from reaction with molten aluminum, but unfortunately the adhesion of aluminum nitride film on diamond is poor, and the interface thermal resistance increased. The thermal conductivi ty of the composite is only 517W×m-1×K-1. |
PDF Full Text Request