| With the development of miniaturization,denseness,high frequency and functionalization of electronic components,hot spots and redundant heat in electronic equipment have seriously affected the life and reliability.In 2016,the "Nature" pointed out that "Moore's law" will disappear,if the problem of heat dissipation is unable to be solved.In order to ensure the rapid and sustainable development of electronic equipments,the effective thermal management has become an important issue in the field to be solved,in which electronic packaging materials has become an important part.In practical applications,polymeric composites are favored in electronic packaging to meet the requirements of lightweight,insulation,impact resistance,processing and design.At present,the key scientific problems that limit the thermal conductivity of polymer matrix composites include low intrinsic thermal conductivity of polymer,accurate control of interfacial thermal resistance and effective control of microstructure.Based on the three key scientific problems,breaking through the limitation of low intrinsic thermal conductivity of polymers and realizing the effective regulation of thermal conductivity have become the main goal in the research of polymer packaging materials.Single-crystalline diamond particles are a type of potential fillers for polymer packaging materials due to their high thermal conductivity,good insulation and low price.Therefore,single-crystalline diamond/polymer matrix composites are selected as the research object.Based on the third key scientific problems,three different distributions of diamond are proposed.Reasonable preparation methods are selected to realize the construction of one-dimensional aligned structures,multilayered structures and three-dimensional channel structures.Thermal conductivity and electrical properties of composite materials are studied to lay a foundation for the multi-scale structure design.This work is divided into the following parts:The external magnetic field assisted method was selected to realize the goal of constructing the one-dimensional aligned structure of diamond.The chemical coprecipitation method was used to deposite the magnetic nanoparticles on the diamond particles to solve the technical problem that the diamond does not respond to the external magnetic field.The results show that the obtained composites own columnar "particle bundles" along the direction of external magnetic field,which means that the one-dimensional aligned structure of diamond has been built successfully.Through the adjustment of filling volume,the changing law of columnar "particle bundle" structure is studied.It is also found that the thermal conductivity of composites was obviously improved.The thermal conductivity of composites with the aligned construction of diamonds can reach 1.37 W/m K at a volume ratio of 14%,and thermal conductivity enhancement can reach 250% based on composites with randomly distribution of diamonds at a volume ratio of 5.1%.Although magnetite is introduced,the resistivity of the composite is still in the range of insulation.Building parallel multilayered structures of diamond was selected as the research object.Close-stacked diamond layers were prepared by evaporation self-assembly method,which solve the technical problem that diamond particles layer can be controlled.Hand lay-up and mechanical cutting are used to solve the technical problem that diamond layers distribute along the out of plane direction.It is found that parallel multilayered structures of diamond has been built successfully.The thermal conductivity of the obtained composites is obviously anisotropic.When the diamond content is 24.7 vol%,the out of plane thermal conductivity of the composite reaches 2.0W/MK,which is 335% higher than that of the diamond composite with uniform distribution.The multi-scale model of diamond/silicone composites with parallel multilayered structure is built to study the influence of diamond-layer-thickness on the thermal conductivity of the composites and the mechanism by Finite Element Method on the ANSYS Workbench software.The simulation results were verified by preparing multilayered composites with various diamond-layer thicknesses and diamond loadings.It is found that the reduction of diamond-layer-thickness can effectively improve the through-plane thermal conductivity of multilayered composites.The out-of-plane thermal conductivity of the multilayered composite can reach 2.55 W/m K at a volume ratio of 24.7%,which is 454% higher than that of composites with randomly distribution of diamonds.Meanwhile,the dielectric constant of the composites increases with the decreasing thickness of diamond layers in Ku band,whose variation range is small,and the values is within 3.5.The composites owned very small tan ? values(<0.1),which be used in microwave electronic packaging.The template method was selected to achieve the goal of constructing the three-dimensional thermal transfer paths of diamond.Vacuum assisted filtration method was used to solve the technical problem of three-dimensional deposition of diamond nanoparticles along the template of graphene foam synthesized by chemical vapor deposition.It is showed that diamond nanoparticles are closely packed along the graphene wall,and the three-dimensional structure of diamond particles is successfully constructed.The composites with this structure exhibit better heat transfer performance than that of the composite with a uniform distribution.The thermal conductivity of the composites can reach 0.279 W/m K at a volume ratio of 1.97%,whose enhancement efficiency is 74.33%.Meanwhile,the electrical conductivity of the composites is 0.256S/cm,which is not obviously influnenced by the adding of diamond.Based on diamond/graphene/epoxy composites with the three-dimensional bi-network structure as the research object,the uniaxial compression method of graphene template was used to realize the adjustment of structure density.The results show that the in-plane and out of plane thermal conductivity and anisotropy coefficient of diamond/graphene/epoxy composites with the three-dimensional bi-network structure increase with the increasing structure density,the mechanical properties decrease. |
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