The Study Of Metallizing Cladding Onto Diamond

The speedy development of the electronic industry has strict requirements regarding heat dissipation in electronic packaging materials. When the traditional packaging materials such as W-Cu,Mo-Cu or SiC/Al are not adequate to cool the increased heat generation in very large scale integrated circuit, diamond/copper composites are considered to be the most prospective thermal management materials owing to its excellent thermal conductivity, suitably low coefficient of thermal expansion for semiconductor materials and a lower density. At present, Two major problem faced by fabricating the diamond/copper composite material are:1) The inertia of physical and chemical properties which originates from saturation and directionality of the strong covalent bonding of diamond crystal results non wetting between diamond and many metallic materials and a high thermal resistance.2) It is hard to ensure a internal density in diamond/copper composite when strengthening phases volume fraction higher than a certain value makes the bridging effect between diamond particles. Especially for hot pressing method, the stress imposed on compound powder is much less than that of high temperature and high pressure method, thus decreasing the density of the composites. The present paper deals with a study comprising of the interfacial metalization of diamond and molten copper infiltrating into a porous diamond perform spontaneously.Synthetic diamond crystals with particle sizes of170/200meshes are modified by strong carbide forming elements such as W, Mo, Cr and Ti to ameliorate the interfacial bonding between diamond particles and molten copper efficiently. The surface pretreatment of diamond particles includes:1) W layer is reduced from tungsten sol-gels in hydrogen-heating atmosphere and different W content coated on diamond particles are obtained by adding alcohol to dilute the the sol-gel. The corresponding optimal parameters for a uniform and compact W nanolayer are as follows:the concentration of the sol-gel,0.08g/ml; ratio of diamond particles weight gain,(2.94-3.03)%. Many times of failed pressureless infiltration experiments shows that W nanolayer reduced from the sol-gel would not achieve ideal interface condition what the pressureless infiltration method required because of limitation of itself. 2)Temperature plays a major role in carbonization reaction in the molten salts method, where the mol ratio of NaCl:KCl is set to be0.506:0.494. At lower temperature, the carbon atom can not to form carbide with transitional elements for lack of enough energy to migrate vertically. The compaction of diamond/copper composite is hardly to be assured if some exposed areas exist on the diamond particles’surface. Further increasing the temperature to a certain value, trace amount of carbide are formed in the transitional zone, which is favorable for the interfacial bonding between diamond and coating and high interface conductance. This is the optimum experiment condition expected. However, the density of coating decreased appreciably with excessive heat. It is found that the optimized temperature for surface pretreatment of diamond particles are carbide molybdenum,1000℃; Cr,700～1000℃and Ti,700～1000℃respectively. The thickness of layer ranging from tens to hundreds nanometer can be accurately manipulated by controlling the plating temperature and time.3) Tungsten layer coatings with thickness range from100～200nm are applied to diamond grains at temperature of1000℃for60min, which gets close to the predicted result by Andrey M.Abyzov. Carbide forming elements with content of O10%are added to loose working mixture preventing sintering of it and promote a reaction in diamond surface under vacuum condition by the diffusion method.4) Nickel is selected as a coating on the diamond filler for copper matrix infiltration due to the good wettability between nickel and copper. In this article nickel layer is coated on the surface of diamond particles by electroless plating. However, nickel and copper are practically mutually soluble in high temperature and during the infiltration of the matrix metal, nickel diffuses into the matrix and do not enrich at the interface of diamond/copper composite material to form transitional layer.The composite obtained by pressureless infiltration method contains some pores internally which severely impacts density and other performance of it and need further exploration.