Research On The Heat Transfer Character Of Electronic Equipment’s Contact Surfaces

With the development of the microchips, the thermal management for the electronics is facing the rigorous challenges. As the electronics become extremely fast and small, it unavoidably leads to high heat flux. If the high heat flux can’t be removed immediately, electronics will be heated up to very high temperature, which will adversely depress the performance and reliability of the electronic components. However, the interfaces of different materials are the base structure of electronic components. Therefore, enhanced heat transfer across interfaces is an imminent key point in a wide of scientific and engineering applications. The research work of this paper focuses on the heat transfer characters of the solid-solid interfaces of electronic materials. The high-precision measurement method of thermal conductivity and thermal contact resistance, the study of influencing factors on TCR in quantity and the thermal interface material incorporated with nano-copper particles and the mutil-walled carbon nanotubes are all investigated to provide guidance for the thermal management. The main research work of this paper includes the following aspects.1A high-precision method to measure thermal conductivity and thermal contact resistance using reversible heat fluxIn the thermal conductivity and thermal contact resistance (TCR) measurement of solids using traditional steady-state test methods, it is observed that the test thermal conductivity results differ from their standard values when only one directional heat flux is introduced and the measured TCR results are unavoidable to be impacted also by the direction of exerting heat flux. In order to improve the measurement precision, we proposed a method by using harmonic mean value of thermal conductivity and TCR in two directions of exerting heat flux to diminish this effect. Meanwhile, a modified experimental apparatus has been designed and established to high-precisely measure thermal conductivity and TCR of solids. To verify the accuracy of the method, the thermal conductivities and TCRs of samples of99.999%standard pure copper and Elkonite copper-tungsten alloy30W3are measured and discussed in detail.The results indicate that the processing thermal conductivity data well match the reference values, and the present method also has high precision and can be used in a relatively wide range of TCR measurement for solids.2. Research on the influencing factors on TCR of solid-solidThe heat transfer characters between conventional aluminum alloy materials (type:5A05H112,3A21H112,3A21,6061H112and6063) are been investigated through the experimental measurement in detail. The influence on TCR of RMS roughness, micro-hardness value and thermal conductivity of materials are all been discussed. The results indicate that the heat transfer characters is not relate to the RMS roughness in range of commonly manufacture level (<4.5μn), but relate to the flatness, micro-hardness value and thermal conductivity of materials. This exploring work will have merits to study the influencing factors on TCR and to provide guidance for the thermal management.3. Research on the influencing heat transfer characters on fraction of new type thermal interface materialTo enhance heat transfer performance of epoxy resin as a thermal interface material (TIM), multi-walled carbon nanotubes (MWCNTs) and nano-copper particles are incorporated into an epoxy resin to form hybrid composites. The total TCR between the heated and cooled surfaces as well as its components such as the bulk resistance (RBLT) of the TIM, and the boundary resistance (RB) between the TIM and the joint surfaces above and below the TIM of the composite are measured. The influence of the compound in different proportions of MWCNTs and nano-copper particles on the RBLT and the RB is discussed in detail. The results indicate that the total TCR is related not only to the thermal conductivity of the TIM, but also to the other factors such as the property of the filler, the viscosity and the surface morphology of the TIM. Being compared with nano-copper/epoxy composite, for example, the total TCR of the MWCNTs composite can not be reduced in quantity due to the higher RB for the high elasticity modulus of carbon nanotubes and the agglomeration of MWCNTs with nano-particles, although the thermal conductivities of the composites increase with the MWCNTs content. Compared with the total TCR value of19.8-100mm2K/W with the CNT array TIMs, the minimum total TCR can be obtained as11.5mm2K/W (dry self-contact:660mm2K/W) with the composite filled with70wt%nano-copper.