| Heat dissipation restricted the development of high power electronic devices and its application.Heat accumulation influence the working condition of the devices and decrease its reliability,meanwhile,the life span also shortened.As the fourth generation lighting resource,high power LED,whose lighting efficient reaches 40%,attached great importance by national energy conservation and emission reduction strategy and researches carried out in universities and research institutions,of which heat dissipation is significant constituent part.Mainstream heat dissipation methods are air patenting and water cooling,phase change cooling and thermoelectric cooling also develop rapidly.Heat pipe technology is a kind of high-efficiency passive heat dissipation method integrating material conductivity and phase change cooling,which with no need for extra input energy and the structures are flexible designed to be flat or cylinder,heat transfer directions include horizontal and vertical.Heat pipe have merits that structure is simple and range of applications is wide.Considering integration and flat packaging with LED,this paper aimed to add the excellent heat transfer capacities of Cu to micro heat pipe.How structure patterns,vacuum and filling ratio influence the heat transfer capability is the main research contents.Based on mechanical numerical calculation and FEM simulation results of effect to wick structure by surface tension and capillary force of micro channel,the minimum of structural dimension,the maximum of drag force generated by capillary structure.Photolithograph and electroforming technology have their own range of application and restricted conditions to determine line width of micro structure,from 50?m to 200?m.According to discrepancy of heat flux direction,structural designation is divided into two groups: MHP that transfer transverse,including parallel and trapezoidal wick structures.MVC that transfer longitudinal,including parallel,concentric circles and radiation channels.The negative photoresist SU-8 is appropriate for high depth-to-width ratio situation,the drag force is supported by wick structures and packaged with Cu coverplate followed up.The optimized parameters of electroforming including depth-to-width ratio,current density,solution constituents and additive,height error can be controlled below 10?m while target height is 120?m.Stream guidance and cavity structure of Cu coverplate are fabricated by corrosion forming,packaging with Si wafer by sealant.The volume of vapor chamber within the scope of 100~200?L.To improve the charging accuracy,we use vacuum cold welding and peristaltic pump charging method,which charging errors are lower than 5%.The temperature testing platform collect temperature parameter within vacuum environment and curve plotting as time goes by,the time-temperature analyze demonstrates heat behavior of micro heat pipes.Testing results reveal that smaller occupation ratio strengthen phase change cooling,the capacity of heat transmission of Cu is lower than efficiency of phase change cooling.Trapezoidal wick structure provides imbalance capillary force,with a correct installing direction,differential pressure between evaporator and condenser was enhanced,in favor of backflow of working fluid.The temperature uniformity effect of parallel channel MVC is better than concentric circles and radiation channel MVCs and 30% charging ratio is the best.Cu coverplate with parallel channel is superior to the others,meanwhile,coordination of parallel Cu coverplate and concentric circles has a highest heat dissipation performance,equilibrium temperature of evaporator is lower than 30? while input power is 7W.Based on the theoretical and experimental study shown above,the Cu-Si micro heat pipe exhibited an excellent heat transfer capacity,which provide a feasible solution for high power LEDs.According to the real working condition and restriction,this method can used in thermal management for other high power device by modifying the specific parameters of the MHP. |
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