| LED is highly respected as a new generation of green light around the world,it hascharacteristics of low-carbon environmental protection, energy conservation and stability,long life. The rising of high-power LED, is quickly breaking into the traditional lightingmarket, became a new light for industries.However, the high-power LED in the current market has low energy conversionefficiency,makes about85%of the energy dissipating in form of heat.Poor heat dissipationmakes the LED chip operating temperature too high to work,and LED lifetime discounting.The low thermal conductivity of conventional heat dissipating material,can not meet the needsof high-power LED heating. Thermal expansion coefficient mismatch with the chip.GradientGr/Al is lightweight,and has thermal-physical property,while improving cooling ofhigh-power LED,it also ensures a certain degree of mechanical strength, which is graduallybeing taken seriously by high-power LED industry.The task is constituted by three subjects:LED packaging and thermal-analysis;Preparation of Gr/Al;Preparation of gradient Gr/Al.In this paper,the LED packaging technology and it’s heat dissipation has been studied.Through mathematical models, ANSYS modeling and thermal analysis,life experiments,it hasbeen validated that, based on current packing technology,it’s possible to reduce LED chipoperating temperatures, improve heat dissipation and it’s life of high-power LED with usinggradient materials for it’s radiator.In terms of preparation Gr/Al,graphite’s low solubility in aluminum and flake graphiteeasily penetrated into the layered under pressure have been studied.By comparing,we use thischaracter to made anisotropic Gr/Al,namely make molten aluminum into graphite along thedirection of layer under pressure.Experimental demonstration,with this method we can makedense homogeneous Gr/Al with70%graphite,a density of2.346g/cm3， the thermalconductivities are λ//=566.767W/(m·K) and λ⊥=289.154W/(m·K), the thermal expansions areα//=12.0543×10-6·K-1(50-150℃) and α⊥=12.2763×10-6·K-1(50-150℃),better than LED heatsink materials used now.Through a series of experiments,we analyzes the factors affecting Gr/Al,mainly on thealuminum,graphite,die-casting parameter,stripping process and the sealing material.Wefinally chose ZL104as experiment aluminum, in order to improve fluidity, meltingtemperature is750℃-780℃, natural flake graphite with particle size of32-50mesh. Whengraphite particles are less than80mesh,it’s not perfect to make high volume fraction isotropicGr/Al.Higher the graphite volume fraction is,the thermal-physical is better,the more unevenlevels are, the performance gap within two side is smaller. Graphite’oxidation weight loss canbe negligible under750℃,1h.Referring to the press machine’s data,the composite material obtained under15Mpa was the best.Micro-speed is related to aluminum infiltrated area, time,distance,which must be obtained through calculation. Before casting, external mold must becoated by particles release agent-sealing material-semisolid release agent,and it should bedrying at95℃,for1h.Then, preheated the mold in high temperature unde700℃to ensure thepenetration of molten aluminum environments.Finally,we chose the method of changing volume fraction to form gradient.We can makedifferent volume fraction in one graphite prefabricated blocks,by the design of the rammolding and prefabricated blocks surface.then,we made die-casting experiments.Also,weconducted gradient Gr/Al experiments with graphite and aluminum powder mixed,we havesuccessfully prepared gradient Gr/Al. |
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