Research On Composites For Thermal Interface Materials And Design Of Al/TPG Thermal Conductive Laminated Structure

High performance thermal pyrolytic graphite(TPG)has ultrahigh in-plane thermal conductivity,low density and low hardness,but its weaknesses,such as low strength and welding difficulty,limit it to be used directly for the electronics.However,composite encapsulate technology can be used to improve the usage of TPG,and metal/TPG composites are one kind of ideal thermal management composite materials which have high thermal conductivity,sufficient strength and rigidity,therefore they have become a new research hotspot of the thermal management for electronic apparatus with high heat flux recently.Because the thermal interface materials between metal and TPG are the key to ensure the heat transfer performance and structure reliability of metal/TPG composite struture.To implement the application for metal/TPG composites in thermal management,the preparation and mechanical properties of metal/TPG composites,the mechanical properties and thermal properties of the thermal interface materials,and the design and heat transfer performance of Al/TPG laminated composite are researched.The main results are as follows:(1)The effect of thermal resistance in epoxy/multiwalled carbon nanotube(MWCNTs)composites on the thermal conductivity of epoxy composites were investigated.To improve the interface thermal resistance in epoxy composites,a new process was proposed: using surface silylation modification reduced the interfacial thermal resistance between epoxy resin and filler,and improve the contact thermal resistance between fillers by the click reaction between sulfhydryl(-SH)and vinyl(-C=C).We systematically study the silylation modification and the mechanism of thiol-ene click in MWCNTs/epoxy composite.This paper reveals the relationship between the thermal conductivity of composites and the cooperation silylation modification,thermal initiator AIBN,or the formulations and content of hybrid filler.It is found that have better synergetic enhancement effect when the ratio of SH-MWCNTs to CC-MWCNTs is 3:1.The more hybrid MWCNTs,the greater the synergetic enhancement.(2)Based on the effective medium theory(EMA)and Nan Cewen heat conduction theory model,the relationship between the thermal conductivity of composites with interfacial thermal resistance was analyzed.When interfacial thermal resistance is about 1.5 mm~2·K/W,model predictions are in good agreement with experimental thermal conductivity.(3)The preparation process and thermal conductivity of epoxy/silver coated glass fibers(Ag@GFs)composites were studied.with large L/D ratio and high thermal conductivity were compounded with short-cut quartz glass fiber in a simple electroless silver plating process.The influences of the breeds of glass fiber,L/D ratio,contents,coupling system,process and orientations on the composite property were studied.We research on relationship between the effective thermal conductivity of Ag@GFs with the diameter of glass fibers and silver plating cycle,and the influences of the volume fraction and effective thermal conductivity of Ag@GFs on the expansion coefficient and thermal conductivity of epoxy composites.When the silver content is the same,Ag@GFs have better thermal enhancement on epoxy resin than micron silver powder.Based on the Agari model,a theoretical model for the thermal conductivity of epoxy/Ag@GFs composites were established.(4)A graphene/Ag@GF/epoxy resin three-element composite with high thermal conductivity and low thermal coefficient of expansion used for thermal interface materials(TIM)has been fabricated.The thermal conductivity of composite materials was improved by thiol-ene click reaction.The influence of the volume fraction of graphene and the effective thermal conductivity and content of Ag@GF on the thermal conductivity and thermal expansion of epoxy composite were discussed.The with high thermal conductivity of 1.512 W/(m·K)and the thermal expansion coefficient of 59×10-6 K-1 was used as a high-performance thermal interface material for Al/TPG laminated composite structure.The relationship between storage modulus of the epoxy composite and temperature was studied with dynamic tensile,and the relationship adhesive strength of the epoxy composite and temperature was studied with compressive shear test.(5)Considering thermal interface material,a finite element analysis model for Al/TPG laminated composite structure was established.The influence of the structure of Al/TPG laminated composite,the thickness of Al plate,and the thickness of TIM on the heat dissipation and structure reliability of Al/TPG laminated composite structure were researched,and then a better design of Al/TPG laminated composite was determined.The results from the numerical computation show that when the heat flux is 250 W/cm~2,the improved Al/TPG laminated structure has excellent heat dissipation and structural reliability,moreover it can meet the heat dissipation of high power density electronics with 406.8 W/cm~2.