As integrated circuit the way to high density, high power and minor volume develops ceaselessly, how to derive quickly electron yuan the heat that the quantity of heat that parts of an apparatus produces already made research. Epoxy resin is qualitative light, insulation, anti-corrosive and machine easily, the domain is enclosed to having main effect in the electron, but asked for extremely low thermal conductance to restrict its to use range originally. Material of fill of preparation of heat conduction filling heat conduction introducing in polymer matrix is the effective method that improves performance of heat conduction of composite material whole, the article summed up the heat conduction mechanism of material of fill heat conduction above all, discussed the sort of filling and modified method next, to prospective development the trend undertook expectation finally.
Epoxy resin (EP) it is a kind of heat that has stability of admirable and mechanical function, dimension and insulating property solid sex colophony, already was applied extensively at glue sticky agent, pouring the electron such as makings and coating encloses a domain in. But the high speed that follows electronic technology develops, electron yuan the quantity of heat that parts of an apparatus produces is followed thin model change and function promotion shows exponential level to increase, electronic equipment overheat can affect the dependability of the product and service life badly. The thermal conductance with extremely low epoxy resin (make an appointment with 0.2W·(m·K)- 1) to already was not applied to show level electron yuan the use environment of parts of an apparatus, accordingly, the heat conduction performance that how improves epoxy resin matrix is the popular topic of academia all the time.
Through undertaking to polymer matrix molecular structure is designed, increase namely advocate catenary length reduces a catenary to raise change rate, increase polymer crystallization to spend reach crystal dimension and rigid structure introduces in polymer matrix, it is preparation is asked for originally model 3 kinds of of heat conduction material main avenues. In addition, in high polymer matrix filling of conductance of fill high fever has technology with material of preparation fill heat conduction simple, alternative wide with cost cheap wait for an advantage, it is current the most commonly used modified method, the synergism between the sort that studies to its direction basically is centered at filling, appearance, dimension, different filling and best deserve to compare etc.
1.Guide heat engine manages
Normally for, material passes interior certain carry stream child (if the electron is harmonic child) commutative heat energy finishs heat to conduct. relatively at phonon, rate of free electron shift is rapidder, more be able to bear or endure scattering, in efficiency of respect of transmission quantity of heat taller, accordingly, metal and carbolic radical material all show higher heat conduction performance, and the stuff that has mechanism of pure phonon heat conduction if the metallic oxide thermal conductance such as Al2O3 is apparent under metallic stuff, make an appointment with 30W·(m·K)-1 left and right sides. Polymer material is formed by vitreous condition or much brilliant condition for the most part, interior lacks freedom of free electron, phonon to spend not only inferior, still get polar group occasionally polarization influence, the undesirable conductor that is heat (thermal conductance is 0.1 ～ 0.5W·(m·K)-1) only.
Theory of heat conduction access is the most commonly used manage at explaining the heat conduction chance of material of fill heat conduction, namely heat conduction access is formed at the mutual contact between filling and polymer matrix, quantity of heat can pass the method with phonon edge inferior thermal resistance or network to deliver. When content of the filling in the system is inferior, filling particle is dispersedly in polymer matrix, form kind of “ sea - insular ” structure, matrix of edge of quantity of heat - filling - the method of matrix travels, phonon is in filling not joint happening scattering, promotion of composite material thermal conductance is finite. However, increase to some when filling content when specific value, each other begin to contact between filling and form complete heat conduction access, the interfacial thermal resistance between filling is right now far be less than the interfacial thermal resistance between polymer matrix, quantity of heat can be delivered quickly along heat conduction access, composite material thermal conductance increases quickly, namely ” of phenomenon of ooze of “ even more. But newest research makes clear, ” of phenomenon of ooze of “ even more can appear in certain thermal conductance only in extremely tall filling, to most filling character, the 10~103 that thermal conductance is polymer matrix only times, although filling adds a capacity enough tall, composite material thermal conductance also won't appear apparently choppy dot.
2.Filling choice
Preparation is asked for originally model although heat conduction material has a structure agile, thermal conductivity can accuse to wait for an advantage, but preparation technology is sophisticated and reaction can charge a sex poorer, be confined to a lab to synthesize level at present, be apart from industrial production to still have difference. And use filling of high fever conductance to be opposite the modified technology of colophony matrix is relatively mature, and the interfacial property of the form that can adopt logical choice filling, dimension and composite material undertakes fine tuning to thermal conductance. On the choice of filling sort, answer to build heat conduction network to be premise with effective compose, filling of common heat conduction can be divided for the metal kind filling, inorganic pottery and porcelain kind filling and carbon kind filling 3 kinds. Common heat conduction filling and polymer matrix thermal conductance see a table 1.
Express composite material of 1 preparation heat conduction the thermal conductance of commonly used polymer and filling
2.1 metals kind filling
Metal kind filling abides by mechanism of electronic heat conduction, have thermal conductance tall, thermal stability can be good with hot coefficient of expansion low good point, common metal kind filling includes Au, Ag\Cu, Sn to wait, undertake additive with pulverous form normally. The use Cu pink such as Fu Yuanxiang, Al pink E44 of epoxy resin of fill of filling of two kinds of heat conduction in order to determine filling of two kinds of metals is in the thermal conductance of the composite material when the oldest stuff is compared. The result makes clear, the addition that composite material thermal conductance measures along with metallic powder fill and increase, add quality to be colophony matrix respectively when Cu pink and Al pink 4.3 times and 4.6 times when, composite material thermal conductance increases to 0.74 with 1.11W·(m·K)-1. The data of Jasim heat conduction of EP/Al of Al grain preparation that uses average diameter 7.1μm. The result makes clear, when quantity of Al grain fill is 45(w)% , composite material thermal conductance increases to 1.46 W·(m·K)-1, purer constituent epoxy resin rises 117.3% .
Afore-mentioned research make clear, pure metal filling raises thermal conductance place to need specific gravity taller and the effect is finite. In addition, as a result of matrix of polymer of metallic density outclass, bring about metallic powder to be hard in machining a process in colophony matrix dispersive and even, the tall conductivity of metallic powder still can reduce the insulating property of composite material and interpose report performance significantly, restrict its to enclose the application of the domain in the electron.
2.2 inorganic pottery and porcelain kind filling
Inorganic pottery and porcelain kind heat conduction filling has exceedingly good thermal conductivity and insulating property, the domain is enclosed to have distinct advantage in the electron. Common inorganic filling basically contains alumina (6 Al2O3) , nitrogen change boron (BN) , carborundum (SiC) and zinc oxide (ZnO) . Inchoate research discovers, in 31vol%h-BN of the fill in epoxy resin matrix, composite material thermal conductance achieves 2.30W·(m·K)- 1; Go to fill of grain of micron class AlN in epoxy resin matrix, thermal conductance of the composite material when 62vol% fill is measured achieves 4.20W·(m·K)-1, and when the oldest stuff measures 80vol% , thermal conductance rises to 4.50W·(m·K)-1; In tiny ball of 60vol% Al2O3 of the fill in epoxy resin matrix, composite material thermal conductance will achieve 2.70W·(m·K)-1.
Afore-mentioned research make clear, inorganic pottery and porcelain kind the promotion of function of means implementation heat conduction that heat conduction filling often compares through tall filling, this is by force of interaction of the interface between inorganic filling and polymer matrix weaker be caused by. In addition, according to Nielsen model knowable, if filling of micron class inorganic forms place of access of complete heat conduction to need fill quantity to be more than 50vol% . Expensive stuff quantity sacrificed not only the advantage that polymer material machines gently, easily character, still can bring about composite material mechanical function deterioration. Accordingly, undertake to inorganic filling modified enhances his dispersive sex, it is to reduce fill amount, realize industrialized key.
2.3 carbon kind filling
Common carbon kind filling is formed by body of a series of the different that be the same as element, include carbolic accept rice to be in charge of (diamond of rice of CNT) , accept (Xi of ND) , black lead (GR) and carbon fiber (CF) . Carbon kind filling has extremely tall thermal conductance generally and hear resistance and fight pottery and porcelain of oxidation function outclass kind filling. Among them, black lead Xi has highest thermal conductance in all and known material, be considered as the best choice of composite material of polymer of preparation tall heat conduction.
Add rice of accept of Xi of 4(w)% black lead Jarosinski only in epoxy resin piece, composite material thermal conductance relatively matrix rises 132% .
Current, black lead Xi discovers after the researcher studies through a large number of experiments / the actual measurement value of thermal conductance of epoxy resin composite material is far under theoretical value, because black lead Xi issues ability to be able to realize superhigh thermal conductivity in whole structure only,this is, it is difficult to and structure of unique high aspect ratio is returned can make its dispersive in colophony matrix. Accordingly, through reasonable actor chemical art flow is mixed undertake to filling the surface decorates the thermal conductance that waits for a method to all can raise composite material considerably.
2.4 compound filling
Consider to discover, the heat conduction filling that adds onefold sort in polymer matrix makes composite material achieves academic thermal conductance very hard, this is the phonon scattering that causes by the element such as blemish, interface and fill quantity exorbitant the treatment difficulty be caused by that bring about. The heat conduction filling that carries will different figure or kind however undertakes answer after matching, compound filling can reduce the gap in polymer matrix effectively not only, compose builds complete heat conduction access, still can improve filling the dispersive sex in polymer matrix. Normally the method of filling of compound heat conduction includes preparation to mix law and physisorption law in all directly.
Mix a law to basically use the space between filling of different measurement heat conduction to match action in all directly, namely small size filling is OK fill takes the crack between large size filling in, increase the odds that forms access of complete heat conduction. The most commonly used method in physisorption includes electrostatic adsorption or π-π interaction, react through specific action or chemistry the filling of direct will different type undertakes namely compound, make its have specific structure.
The place on put together is narrated, ask for originally in preparation model side of heat conduction data, improve molecular catenary paragraph orderly sex and regularity are the key that raises thermal conductance of epoxy resin matrix. In side of data of preparation fill heat conduction, the heat conduction function of filling is having conclusive effect to the thermal conductance of final composite material, and the interface is the crucial factor that brings about thermal conductance to be worth under theory, accordingly, in recipe design, want to increase the amount of access of complete heat conduction through proper method not only, still should stress improvement the interfacial consistence problem between epoxy resin matrix and filling.
Be based on the research current situation of heat conduction material and development trend, still need to begin the following exploration in research process of future:
(The structure that 1) development analyses heat conduction filling, function is changed and polymer structure is right the influence of function of composite material heat conduction.
(2) perfects the heat conduction mechanism of composite material, build unified and accurate heat conducts a model.
(3) develops the modified step with more taller filling, significant thermal conductivity and combination, implementation exceeds low stuff to measure the tall thermal conductance of next composite material, in order to resolve the restriction of the cost in industrialized production and craft.
