Fabrication Process Investigation And Thermal Performance Analysis Of Micro-diameter Heat Pipe For Printed Circuit Board

With the rapid development of Internet technology and microelectronics technology,5G communication technology with high performance,low delay and high capacity has also been developing rapidly.However,with the increase of 5G real-time data throughput,especially under the development trend of lightness and compactness of the electronic equipment,the heat flux density of the processing chip is increasing,and thus,as its electrical connection carrier,the printed circuit board(PCB)cooling problem has become increasingly prominent.As a high efficiency phase change heat transfer element,micro heat pipe has been widely used to solve the thermal issue in many fields,and the effect is significant.However,to solve the heat dissipation issue of PCB with the thickness of not more than 3.5 mm,the micro-diameter heat pipe with good thermal performance is desired to be developed,that is,the micro heat pipe with the diameter of 2 mm.The wick structure is one of the most critical factors to the thermal properties of microdiameter heat pipes.Five kinds of wick structures and forming methods for the micro-diameter heat pipe are discussed,including the folded screen mesh wick(FSM),the single mesh number double layers screen mesh wick(SSM),the double mesh number double layers screen mesh wick(DSM),the powder sintering copper foam and screen mesh wick(PSSM),the electrolytic deposition copper foam and screen mesh wick(EDSM).The manufacturing process of the fine micro-diameter heat pipe was developed and the process parameters were determined.The samples of five kinds of micro-diameter heat pipes with different wick structures were fabricated.The cross section of the samples was observed by scanning electron microscopy(SEM).The sintering and squeezing state of different wick structures were observed.Forming process and morphological characteristics,and the effect of the shape of the wick on the thermal performance of the micro-diameter heat pipe was analyzed.Based on the capillary limit theory of micro heat pipe,the theoretical heat transfer limit power of the heat pipes with the wicks of SSM,DSM,PSSM and EDSSM are deduced and calculated,the theoretical value are 7.1 W,5.7 W,6.0 W,8.5 W and 7.8 W,respectively.An experimental testing platform is set up to test the thermal performance of the micro-diameter heat pipe with five kinds of wick structures,including the axial temperature distribution,the evaporation and condensation thermal resistance characteristics under different filling ratios and different heating power,and the heat transfer limit power of the micro-diameter heat pipe at the optimal filling ratios;the micro-diameter heat pipes starting characteristics,including the response speed,start time and balance temperature at the heating power of 3 W.The heat dissipation performance of the heat pipe cooling modes for PCB produced by five different heat pipes was tested in different cooling styles.Results show that the optimal filling ratio of micro-diameter heat pipe with the wicks of FSM,SSM,DSM,PSSM and EDSSM are 160%,120%,120%,130% and 90% respectively,and the heat transfer limit power for each sample is 7 W,4 W,5 W,8 W and 7 W,close to the theoretical calculation.With the increase of heating power,the evaporation thermal resistances of the samples increases first,then decreases,and the condensation thermal resistances decreases to 0.1 K/W.At the heat power of 3 W,the start-up times of the five kinds of micro-diameter heat pipes are 220s?230s?215s?224s and 210 s,respectively.Under the condition of natural convection,the heat dissipation effect of SSM heat pipe module is the best,and the thermal resistance is 1.73 K/W.The heat dissipation effect of FSM heat pipe module is the best under the condition of forced convection(2.0 m/s wind speed),with the thermal resistance of 1.24 K/W.