The Study Of Charging And Seal Process,and Thermal Performance Testing On Plate Heat Pipe Substrates With Micro Grooves For High-Power LEDs

With the advantages of high luminous efficiency,long lifespan,energy conservation and environmental protection and so on.LED is gradually replacing traditional light source.Because about 70%of the input power is still converted into thermal energy,and LEDs exist hot spot problem and can only transfer heat in single direction,the increase of junction temperature results in the change of luminescent property and reduction of service life.For high-power LEDs with the input power between 1W and dozens of watt,the increase of input power makes the fever problems more remarkable.In view of the problems that high-power LEDs need efficient cooling,using microgroove flat heat pipes(MFHPs)which are based on the phase change principle to replace the traditional heat dissipation substrate is studied,which can control the increase of junction temperature.If MFHPs can be substituted for traditional plate,the hot spot problem would be reduced and the junction temperature can be controlled effectively.The motive force of working fluid is driven by microgrooves on a silicon wafer,but it is still not clear that the relationship between the flow law of the gas-liquid and the micro-groove structures.Because the inner volume is between 60 and 100μL,a new method should be proposed to improve the charging precision.In addition,a new method should be used to measure the performance of MFHPs accurately and quickly.To solve the above problems in the design,production and testing of MFHPs,the design and improvement of MFHPs with microgroove group structure,the charging and sealing of the working fluid in micro-liter level,and the testing of heat transfer characteristics are studied.The main content is as follows:(1)Based on MEMS processing technology,microgroove group structures in submicron level were designed and fabricated.To improve the capillary traction of microgroove and to take the heat quickly away from heat source,multiple improved structures such as trapezoid,paragraphing parallel and electroforming copper column were designed based on MEMS manufacturing processing,and manufacturing process and sealing methods of heat dissipation substrate of MFHP were elaborated.The changes of pressure temperature,and flow characteristics of the working fluid in MFHPs were studied by numerical simulation,and the emulational results show that the pressure gradient formed along the axial direction is conducive to strengthen the heat transfer and that the optimum filling ratio should be about 40 percent.(2)The charging and sealing methods of MFHPs were studied.The perfusion volume of working fluid for MFHPs is less than 100μL.The oscillation of velocity and pressure makes the precise charging difficult under negative pressure.Through the simulation analysis of the flow characteristics of working fluid,the buffered and isolated charging method using peristaltic pump was proposed to decrease gas slug-liquid plug flow,and it can be implemented that working fluid was charged steadily with maximum deviation of 1.2μL.(3)Because of the phenomenon of the vacuum outgassing and the forming of sealing convex points using polymer materials,cold expansion property of low-melting-point alloy(LMPA)was studied and auxiliary sealing channels were designed.LMPA can be solidified in specific position by controlling temperature gradient,and reliable sealing and no sealing convex point were implemented according to expansive force between LMPA and Si walls.Combining the former charging method,a new charging and seal process was formed,which provides important support for the integrated manufacturing of MFHPs.(4)The thermal performance testing system was developed,and the experimental researches were carried out on the filling ratio,thermal load,micro-groove size and inclination angle.For contact temperature sensor.there exists a thermal balance delay and it is difficult to arrange the sensor on the surface of the LED module,which has an effect on the heat-transfer characteristic test for MFHPs.To solve this issue,a non-contact infrared temperature measuring appliance for MFHPs is designed,and temperature drift caused by LED radiant heat was revised by environmental temperature compensation and the accuracy of measuring temperature was improved by emissivity correction.The results of static and dynamic characteristics show that temperature measurement precision is 1.5℃ and the response time of 95%stable value is approximately 30ms,which provides a basis for dynamic analysis of heat transfer characteristics.(5)The factors including filling ratio,microgroove structural dimensions and working tilt angle were investigated on the effects of heat transfer characteristics.The optimum filling ratio of MFHPs was explored on the basis of simulated and experimental results.Experimental contrasts on the influence factors of microgroove structure dimension,thermal load and tilt angle were implemented,and results show that the improvement of aspect ratio contributes to the backflow of working fluid and to improve the heat transfer capacity,and that the equilibrium temperature of high power LED module integrated with radiate heat dissipation structure substrate is about 40℃,while the equilibrium time is about 60s.Therefore,the junction temperature of high-power LED was controlled effectively.