Design,construction And Performance Study Of Continuous Thermal Conductivity Paths For Thermal Interface Materials

With the rapid development of technologies such as electronic devices,microprocessors and integrated circuits,the power consumption and integration of electronic components are getting higher and higher,and heat dissipation has increasingly become a bottleneck limiting their development.Thermal interface materials are the key materials connecting the heat source and cooling system,and are of great importance to the thermal management of the system.In order to meet the thermal management requirements of high-power electronic devices,adding high thermal conductivity particles to thermal conductive materials to construct continuous and efficient thermal paths or networks is a hot topic of research at home and abroad.This thesis aims to construct a new type of thermal interface material with continuous thermal conduction paths to improve the heat conduction efficiency and more effective thermal management of electronic devices.The specific research results are as follows:（1）The thermal conductivity（T_c）of carbon fiber（CF）along the one-dimensional（1D）direction is as high as 1100 W m^-1 K^-1,while its T_c in the radial direction is less than 10 W m^-1 K^-1.Therefore,the thermal conductivity of carbon fibers exhibits various anisotropies and is highly dependent on the orientation of CF.The polydimethylsiloxane（PDMS）/short carbon fibers（SCFs）/aluminum（Al）spherical particles（PDMS/SCFs/Al）composites were first prepared.Then,the SCFs were arranged in horizontal（0°）,inclined（45°）,and vertical（90°）directions using a convenient"pie rolling"method that does not depend on any specific apparatus.The vertically oriented SCFs together with Al spherical particles create an effective three-dimensional（3D）network of thermal conductivity with T_c up to 10.46 W m^-1 K^-1through the plane and 4.13 W m^-1 K^-1 in the plane.anisotropic thermal conductivity is also verified by the Hot-disk method.Also,finite element simulations were used to study the working mechanism and thermal conductivity of the oriented SCFs and Al spherical particle composites.In addition,the surface temperature of the composite material during heating and cooling was observed using an infrared camera.A temperature drop of 16℃ was obtained when SCF-90 was used as the TIM between the laptop chip and the heat pipe,indicating that the vertically oriented carbon fiber-based 3D network successfully achieved efficient heat transfer.（2）Gallium（Ga）-based liquid metal（LM）has a high thermal conductivity(16.5W m^-1 K^-1),however,the surface tension of LM is too high to effectively wet a solid surface,and LM leakage will lead to device short circuits.The high surface tension also makes it difficult to mix LM and fillers well to prepare composite pastes for thermal interface applications.We found that the contact angle of LM on the surface of boron nitride（BN）sheet can be decreased from 133°to 105°by doping with tungsten（W）nanoparticles,which indicates that the surface tension of LM can be reduced by doping with W nanoparticles.It was found that the order of addition of LM,W and BN affects the final morphology of the composites,and the paste composite（LM+W-BN）can only be obtained by mixing W nanoparticles with LM first（LM+W）.LM+W-BN exhibited a high T_c of 14.49 W m^-1 K^-1,and the stability of LM+W-BN under pressure,high temperature,thermal shock and high humidity was also investigated in detail.In light emitting diode（LED）modules,LM+W-BN showed excellent thermal management capabilities.This approach has also been extended to improve the thermal conductivity of other liquid metal composite thermal pastes,including carbon fiber and graphene.