Research On The Key Fabrication Process Of Ultra-thin Flattened Micro Heat Pipe And Its Equipment Design

The ultra-thin micro heat pipe,which uses the principle of phase change for efficient heat transfer,can be used to solve the heat dissipation problem of high heat flow density chips in smartphones and has been widely used in 4G and 5G smartphones.The wall thickness of the copper tube used in this ultra-thin micro heat pipe is generally 0.1-0.12 mm,which is easily deformed during the manufacturing process and greatly affects the production yield and product performance.Therefore,the core manufacturing process of liquid injection,vacuum and secondary degassing still relies on manual operations to complete.Accordingly,this paper proposes to use a cold welding sealing process and integrated laser welding sealing method to complete the secondary degassing process in situ,and developed integrated equipment to reduce the manual process of this process;and then through the experimental optimization of the liquid injection and vacuum process parameters,the manufacturing efficiency of ultra-thin micro heat pipes is improved and the heat transfer performance is enhanced.The main contents are as follows:Four factors influencing the cold welding sealing process of ultra-thin micro heat pipes were investigated using orthogonal tests,including sealing gap,sealing length,sealing pressure and sealing diameter.Numerical simulations of the one-line cold welding process were conducted and the seal quality was examined by metallographic analysis.The results showed that the effect of seal diameter on the seal gap was the greatest,and the rest were seal pressure,seal length and seal diameter in order.Finally,the seal strength of the ultra-thin micro-heat pipe formed by the new one-line cold welding method was measured by leakage testing through the inflation method.The results showed that the well-sealed ultra-thin micro-heat pipe can withstand air pressure of more than 2 MPa.The development of an integrated laser in-situ welding technology investigates four influencing factors that affect laser welding strength,including laser welding power,pulse width,frequency and welding speed.Through the laser welding of ultra-thin micro-heat pipe burst test,and combined with metallurgical analysis methods to detect gas leakage at the weld or burst process mechanical properties of the tube.The effect of liquid injection rate and secondary degassing process parameters on the heat transfer performance of ultra-thin micro heat pipe was studied.The results show that with the increase of liquid injection rate,heating time and heating temperature,the ultimate heat transfer power increases first and then decreases,and the total thermal resistance of 80 %liquid injection rate is the smallest.And the heat transfer performance of the ultra-thin micro heat pipe is the best when the heating time and heating temperature is 15 s and 140℃.It is also proved that the new one-line cold welding seal integrated with laser in-situ welding process can ensure the quality of heat pipe port sealing.Finally,through the three-dimensional design software to complete the cold welding sealing mechanism,laser in-position welding mechanism,material heating lifting mechanism,frame and other mechanical structure design,and the optimization of cold welding and laser welding and other process parameters integrated into the control program of the equipment,the development of a new automatic two-removal gas removal equipment...