Structure Design And Fabrication Of Micro Heat Pipe For LED Modules

As a solid light source,high-power LED has the advantages of high energy efficiency and small volume,and it is a strategic emerging industry supported by the state.It has been used more and more widely in modern society,not only can replace the traditional lighting source,but also can improve the quality of lighting.What’s more,it can be used as the backlight of liquid crystal display and landscape lighting sources to meet people’s need for quality of life.High-power LED has the advantages of high luminous efficiency,low energy consumption,long life and other advantages.As a typical electroluminescent cold light source,more than 60% input power of LED chip is transformed into heat.The LED chip is very small,and the heat accumulation caused the junction temperature is too high thus have a bad effect of light quality and performance.So the effective control of LED encapsulation and reasonable control and stability of junction temperature is the key technology for the fabrication of high performance LED device.The main body of micro flat heat pipe is bond by silicon substrate and glass cover,and micro channel array are fabricated as the wick for providing flowing force of working fluid.In order to reduce the decreased performance of the heat pipe caused by working fluid is easy to dry on evaporation.Three-dimensional reservoir structure is designed and fabricated on the silicon substrate evaporation,which can enhance remain ability of local water film and reduce temperature of LED chip module.The reservoir manufacturing process based on MEMS,combined with wet-dry etching technology of bulk silicon.This reaches continuation of micro channel array and changes the depth of substrate evaporation area.In order to improve the cycle efficiency of working fluid and heat transfer capacity of heat pipe,this paper studies the glass cover of heat pipe modified by low surface energy fluoride.The contact angle of hydrophobic cover plate modified with fluorine silane can up to 116°,which is increased nearly 40° compared with the unmodified glass surface.The hydrophobic surface can improve the speed of working fluid becoming droplet on the inner surface of cover plate,and then quickly fall into the micro channel of substrate to cycle again.This can enhance the heat transfer rate of heat pipe and the maximum power transmission.Aiming at the temperature limit of hydrophobic layer,this paper proposed a method of sealing main body of micro heat pipe used photoresist.The method has an advantage of controllable density.Reliability test is conducted to ensure the normal work of the micro heat pipe.In the process of charging,two methods included the charging by peristaltic pump and the charging by quantitative channel for different heat pipe with different inner volume are used.It has an impact effect on gasification of working fluid in the heat pipe that boiling nuclei exist or not.Preliminary study in this paper about the heat transfer performance using ethanol adding SiO2 nanoparticles was carried out.Different concentrations of nanosized working fluid were charged to provide experimental basis for performance optimization of the micro heat pipe.The testing platform was used to test the heat pipe for LED modules.The results proved that when the input power increasing from 1W to 7W,the temperature of evaporation of ordinary heat pipe can reach to 81 oC,while the temperature of evaporation of heat pipe with reservoir structure is only 72 oC and indicate the improvement of the heat conduction efficiency pipe.The heat pipe with reservoir for LED modules has lower starting power than the normal.Meanwhile,when the two heat pipes are being in a state of working,the heat pipe with reservoir reduced nearly 20 oC and coefficient of thermal conductivity increased by 1.5times.Under the input power of 10 W,the heat pipe with reservoir had been given an equilibration time shortened 60 s and there was an obvious promotion for the thermal cycling.Above all,this paper designed and fabricated the heat pipe for LED modules.Testing results demonstrated that the reservoir structure in evaporation and hydrophobic cover modified by fluoride with low surface energy can both improve the heat conduction efficiency of the micro heat pipes.Meanwhile,two methods included the charging by peristaltic pump and the charging by quantitative channel for improving charging rate.This paper gives an example for heat management of high-power LED and other devices of high flux density and design of sealing structure.