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Mesoscopic Model Construction And Thermal Performance Optimization For Graphite/Resin Thermal Interface Materials

Posted on:2024-01-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:X L WuFull Text:PDF
GTID:1521307376484084Subject:Materials science
Abstract/Summary:PDF Full Text Request
The continuous development of microelectronics industry leads to the increasing of chip density,and heat dissipation becomes one of the bottleneck of chip technology improvement.Thermal interface material has outstanding thermal conductivity,and is used between chip and heat sink to improve the heat dissipation of chip.However,the thermal conductivity of traditional thermal interface materials has been unable to meet the development of modern microelectronics industry,and it is urgent to further improve the thermal conductivity.In order to effectively improve the thermal conductivity of thermal interface materials,the use of new high thermal conductivity filler has become a trend.Graphite fillers,such as natural graphite,and graphite nanoplatelets,have high thermal conductivity,However,there are two main difficulties in the use of graphite filler.On the one hand,the filler is randomly dispersed,which can not effectively build a thermal conduction path;on the other hand,the filler is seriously wrapped in polymer,resulting in a large amount of interface between the filler and the polymer matrix.These two factors limit the improvement of thermal conductivity.Therefore,in view of the above difficulties,this paper firstly constructs a mesoscopic model of thermal interface materials,using finite element methods to explore the way to improve the thermal conductivity of thermal interface materials,aspect ratio,orientation and continuity of filler,etc.And this paper explores all this influence on the thermal conductivity of thermal interface materials for the subsequent preparation and application in low,medium and high chip power density.Follow-up the thermal interface material is fabricated via freeze-drying,coating and hot pressing method.The specific work is as follows:Firstly,the finite element simulation method was used to study the influence of the aspect ratio,orientation angle and the degree of continuity of the filler on the heat transfer effect of the thermal interface material.The finite element simulation was also used to explore the orientation angle of the filler from 0o,30o,60o to 90o on the heat transfer effect of the thermal interface material.The effect of filler continuity degree on heat transfer of thermal interface materials was also investigated.The finite element results show that the the cross-plane thermal conductivity of the thermal interface material is the highest when aspect ratio of filler is highest,and the results also show that the thermal conductivity is the highest when the filler volume is 8.4%with the filler orientation angle of 90o.The finite element results also show that when the filler volume is 7.2%,the better continuity of the filler is,the better heat transfer performance of the thermal interface materials prepared is.This conclusion has guiding significance for the preparation of thermal interface materials.Secondly,according to the finite element simulation,the graphite nanoplatelets was chosen for fabrication.The thermal conductivity of the thermal interface material was improved from the orientation angle of filler.the graphite nanoplatelets were extruded through ice crystal growth and finally vertical aligned via ice crystal as a template.Then the polymer with low elastic modulus was filled to give the thermal interface material outstanding compression performance and dimensional stability.The effects of temperature gradient direction and cooling rate on ice crystal growth were studied.The mechanical properties and thermal conductivity of the thermal interfacial material were characterized.The results show that(1)when the cooling rate decreases from 36 oC min-1 to 0.36 oC min-1,the degree of supercooling decreases,the nucleation rate of ice crystals decreases,the growth rate and volume of ice crystals increase,and the extrusion ability of ice is stronger,and the thermal conductivity of the prepared thermal interface material is higher.(2)The vertical and horizontal temperature gradients can regulate the growth morphology of ice crystals and improve the vertical orientation of graphite nanoplatelets.(3)The thermal interface material has a low elastic modulus,ranging from 56.7 k Pa to153 k Pa,and the thermal conductivity can reach 3.15 W(m·K)-1.The thermal interface material is suitable for low power chip.Thirdly,in order to further improve the thermal conductivity of the thermal interface material,the graphite nanoplatelets(GNP)/polyurethane(PU)thermal interface material with high thermal conductivity was prepared by the process of coating and hot pressing,and the orientation of the graphite nanoplatelets during coating and hot pressing was studied respectively.The experimental results show that:(1)the orientation morphology of graphite nanoplatelets is affected by solvent evaporation rate during film drying.(2)By using polarization Raman and effective medium model,it is calculated that the interface thermal resistance between graphite nanoplatelets and polyurethane is smaller under low temperature drying.(3)GNP/PU thermal interface material has excellent thermal conductivity of 26.3 W(m·K)-1.Compared with commercial thermal interface materials,the temperature of the chip can drop by 42.3 oC showing outstanding heat transfer performance,and is suitable for medium power chip.Finally,from the perspective of heat transfer mechanism,when the discontinuous filler is dispersed in the polymer matrix,the filler is bound to be wrapped by the polymer matrix,and the interface thermal resistance between the filler and polymer permanently exists.The interface thermal resistance is bound to affect the overall heat transfer performance of the thermal interface material.In this paper,continuous pyrolytic graphite film(PGS)was used as filler to prepare PGS/PU thermal interface material by the coating and hot-pressing method,and the continuous thermal conduction path in the thermal interface material was constructed.This can greatly reduce the thermal resistance of the interface and improve the thermal conductivity.The thermal conductivity can reach 118.5W(m·K)-1.In the actual heat transfer test,it shows excellent heat transfer performance,and is suitable for high power chip.
Keywords/Search Tags:thermal interface materials, vertical orientation, continuity, interface thermal resistance, heat transfer performance
PDF Full Text Request
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