LED High Performance For COB Packaging With Application Of AlSiC Substrate

With the development of LED which demands higher power, smaller size and moreintegration, the performance requirements for LED device is increasing at the same time. Asthe traditional substrate can not meet the requirement of the higher and higher power in COBpackaging for its own weakness, AlSiC composite substrate having the advantages of highthermal conductivity and adjustable coefficient of thermal expansion is being applied moreand more widespread in LED packaging. However, the problems of COB light source likelow luminous efficiency and high work calories have limited its development.In this paper, we study the preparation method and properties characterization of AlSiCcomposite substrate. A porous SiC fabricated part is made by compression mold throughwhich we can also learn the effect from the pore-forming material quantity and moldingpressure to the fabricated part porosity. The result shows that the porosity goes up linearlywith the increasing of pore-forming material approximately when its quantity controlledbetween5%and14%, more molding pressure, less porosity. The porosity will be over40%when the pore-forming material reaches14%, which meets the requirement of vacuumpressure infiltration. In addition, analyzing via the microstructure and phase constitution, itcan be realized that AlSiC composite substrate made by the method of vacuum pressureinfiltration where SiC and Al distribute equally and mix uniformly, has a good control to theinterface, no harmful phase such as Al4C3produced in the testing process. The final thermalconductivity of the AlSiC composite substrate could reach171.6W/m¤Kby optimizing initial parameters. Average coefficient of thermal expansion is7.00*10-6℃-1.All those data conform to the LED COB packaging demands.The AlSiC composite substrate will be processed into a patterned leadframe substrateafter the preparation, so as to observe it how to influence the COB luminous efficiency. Setup an optical simulation with SolidWorks and TracePro, and then optimize theseparation distance, dip angle and radius of the inverted taper groove in the patternedleadframe substrate. The optimum parameters we get ultimately are0.75mm inseparation distance,60o in dip angle and0.7mm in radius. At this moment, the simulationresult indicates a higher improved14.99%in luminous efficiency of which the optimumparameter of the dip angle is consistent with the theoretical calculation. Furthermore, wecompare the luminous efficiency of four COB light sources to give a brief overview aboutthese different substrates. They are the patterned leadframe substrate made of AlSiC composite substrate with CNC process and traditional substrate. The result demonstrates thatthe luminous efficiency of ceramic substrate is the lowest, followed by AlSiC compositesubstrate while the patterned leadframe substrate made of AlSiC composite substrate is thebest. And that only compare the COB luminous efficiency of the patterned leadframesubstrate with AlSiC composite substrate, the rate has increased13.68%, quite close to theanalogue simulation result.Beside the results mentioned above, the paper also presents another thermal simulationabout COB LED light source of different substrates with a software of finite element analysisANSYS. The worst COB LED light source heat dispersion is from ceramic substrate. Alsubstrate takes a second place, while the light source made of AlSiC composite substrate isthe best. At last but not the least, we study the heat dissipation of two sizes of COB lightsource, when the chip is in different line spaces. In the situation of a20×20×1.5mm COBlight source in0.25mm line space, the highest temperature is lower than80oC that is exactlyfitting for the packaging requirements, and another advantage is its high reliability. But thehighest temperature of the30*30*1.5mm COB light source is still higher than80oC evenjust in1.5mm line space, so the line spaces or substrate size should be larger to lower downthe maximum temperature of COB light source. The maximum temperature lowers to79.42oC when the line space reaches2mm, while the substrate size has to be40*40*1.5mm if theline space was1mm, only that it will satisfy the demands. And yet, theinfrared thermal imaging test turns out that the COB light source surface temperature is lowerthan115oCof a20*20*1.5mm substrate no matter in which line space. Being in0.25mm linespace, the COB light source surface temperature of a30*30*1.5mm substrate is as high as179.4oC, and the temperatures are all lower than150oC in other line spaces. According to theresearch, the silicone temperature of COB light source is much higher than the chip junctiontemperature. As long as the silicone temperature is lower than150oC, the engineeringapplication requirements will be met. So the line space should be0.25mm when itˉs in aCOB light source of20*20*1.5mm substrate, while the line space should be0.5mm in a COBlight source of30*30*1.5mm substrate.