Study On The Construction Of Three-Dimensional Thermally Conductive Network And Properties Of The Corresponding Epoxy Composites

With the development of the third generation semiconductor technology,the electronic equipment presents the trend of multifunction,miniaturization and integration which results in the greatly improved device power density.As a result,panel warpage,solder joint cracking,device failure,system jamming and other problems,which seriously affect the reliability and service life of the equipment,appeared due to a large amount of heat generated in the equipment.How to dissipate these heat efficiently has become the bottleneck of the next generation electronic devices with high power density.Polymer materials have been widely used in electronic equipments,such as substrate,potting adhesive and interface bonding materials,but their intrinsic low thermal conductivity hinders the heat dissipation.Conventionally,highly thermally conductive fillers have been intensively introduced into polymer matrix to improve heat transfer performance.Nevertheless,excessively high loading of fillers is generally demanded to obtain relatively high thermal conductivity,resulting in significant challenges on deteriorated processing properties,mechanical properties and cost.Therefore,how to achieve high thermal conductivity with small amount of filler is of great significance for electronic devices with high power density.In this work,a series of three-dimensional continuous thermally conductive networks were successfully prepared by using different fillers,like one-dimensional silicon carbide nanowires(SiCw),two-dimensional hexagonal boron nitride(h-BN),hybrid filler of SiCw/BNNS and three-dimensional granular aluminum oxide(?-Al2O3)with the safe,simple,low cost and efficient methods.The corresponding epoxy resin composites with fine continuous filler structure and high thermal conductivity were obtained by vacuum assisted impregnation.The effects of filler morphology,interfacial thermal resistance and network characteristics on the heat transfer efficiency of the composite were systematically researched.These prefabricated three-dimensional heat conduction networks provided fast channels for the transmission of phonons which leads to a good comprehensive performance and excellent thermal management ability.Firstly,silicon carbide nanowire aerogels with spherical holes were prepared by polystyrene(PS)microsphere template method.Silane coupling agent,served as an adhesive,protected the pores induced by the carbonization of template.As a result,SiCw skeleton possessed a very high porosity and high mechanical strength at the same time.Finally,dense epoxy/SiCw composites with continuous heat conduction network were formed by infiltration of epoxy resin.The three-dimensional network greatly improved the heat transfer efficiency,and the thermal conductivity of the composite reached 0.43 W/m·K at a very low loading level of 3.91 vol%,two times higher than pure epoxy.Secondly,h-BN platelets were firstly assembled into boron nitride microbeads via sodium chloride(NaCl)salt-template method during the recrystallization process;then,hollow boron nitride microbeads(BNMB)were obtained after washing.The as-prepared BNMB were further cold compressed to form highly thermally conductive BN skeleton and infiltrated with epoxy resin.Benefitted from the thermally conductive pathways formed by the shells of BNMB,the maximum thermal conductivity of epoxy/BNMB composites reached 17.61 W/m K(in-plane direction),88 times as high as that of the pure epoxy resin,and 5.08 W/m·K(out-plane direction)at the BN loading of 65.6 vol%,showing a great application prospect of thermal management.Then,in order to study the synergistic effect of fillers with different morphologies on the thermal conductivity of composite,a modified vacuum filtration method was used to ingeniously fabricate the thermal conductive framework of SiCw/BNNS with vertical orientation structure.The porosity of the skeleton can be adjusted by controlling the proportion of the hybrid filler.This method significantly improved the out-plane phonon transmission efficiency of epoxy composite that the maximum thermal conductivity reached 4.22 W/m·K.This structure also showed excellent thermal management ability in both theoretical simulation and practical chip sealing test.The dimensional stability of the composite was also greatly improved.Finally,in order to further decrease the interface thermal resistance between fillers,we successfully prepared the three-dimensional porous alumina thermally conductive skeleton with honeycomb structure by using green and safe protein foaming method.High temperature sintering was adopted to realize the lattice fusion of inorganic particles which greatly reduced the contact thermal resistance between fillers.Theoretical simulation showed that,this method reduced the interfacial thermal resistance of the fillers by an order of magnitude compared with the randomly dispersed epoxy resin/alumina composite,and the maximum thermal conductivity reached 2.58 W/m·K,which is 3.6 times of that of the randomly mixed samples at the same filling amount.This strategy paves an effective way for structure design and preparation process optimization of epoxy composites with good thermal performance in electronic packaging applications.