Study On The Mechanism And Performance Of Secondary Degassing/seal Welding Of Ultra-thin Vapor Chamber

In order to solve the heat dissipation problem of thin electronic devices under high heat flux density,it is necessary to develop an ultra-thin vapor chamber(UTVC)with thinner thickness and better heat transfer performance.However,the further decrease of the thickness of the UTVC is likely to lead to leakage in the seal welding process,which will affect the service life of the UTVC.In addition,the insufficient seal welding strength will lead to the poor secondary degassing effect of the UTVC,which will decrease the heat transfer performance of the UTVC.Therefore,in order to meet the requirements of high heat transfer performance and long service life of the UTVC,this paper studies the mechanism and performance of the secondary degassing and seal welding of the UTVC with a thickness of less than 0.4 mm,the main research contents are as follows:(1)Through the analysis of the secondary degassing and seal welding mechanism of the UTVC,the secondary degassing and seal welding process method of the UTVC with a thickness of less than 0.4 mm is designed,and the corresponding experimental device is designed and built.Using finite element simulation software,the stress distribution and deformation of the electrode tip and weldment under four different electrode structures are analyzed.The analysis results show that the optimal structure of the electrode tip is 1.5x10 mm.(2)Welding specimens with a thickness of 0.32 mm are prepared,and the influence of welding parameters on the seal welding performance is studied by mechanical performance testing and microstructure observation of the welded joints.The research results show that the increase of welding current will reduce the average hardness of the welded joint.When the welding current is greater than 12 k A,the tensile shear force of the welded joint will decrease with the increase of welding current;the average hardness of the welded joints increases with the increase of electrode pressure.When the electrode pressure is greater than 0.32 MPa,the tensile shear force of the welded joint will decrease with the increase of the electrode pressure;the increase of welding time will reduce the average hardness of the welded joint,but when the welding time is greater than 1.2 s,the tensile shear force of welded joints shows a downward trend with the increase of welding time.(3)A compound parameter experimental group is established to study the influence of the interaction between welding parameters on the seal welding performance;a sealing strength test device is set up to analyze the sealing strength of the UTVC.The research results show that when the welding current is 12 k A,the electrode pressure is 0.28 MPa and the welding time is1.2 s,the mechanical properties of the welded joint are the best,and the sealing strength of the UTVC is the largest.Therefore,welding current of 12 k A,electrode pressure of 0.28 MPa and welding time of 1.2 s are the best process parameters for UTVC seal welding.(4)Heat treatment and grinding processes are used to prepare weldments with different surface hardness and surface roughness.Under the same welding parameters,the influence of the surface hardness and surface roughness of the weldment on the seal welding performance is studied.The research results show that when the surface hardness of the weldment is 90 HV and the surface roughness is 1.5 ?m,the mechanical properties of the corresponding welded joint are the best.Therefore,in order to improve the seal welding performance,the shell of the UTVC can be heat treated(temperature is 550 ?,and the holding time is 3 h)and the sealing part of the UTVC can be ground with 400# sandpaper.(5)A test device for heat transfer performance of the UTVC is designed and built.The effects of secondary degassing process parameters on the start-up performance and temperature uniformity performance of the UTVC are studied.The results show that the secondary degassing can significantly improve the heat transfer performance of the UTVC.The best process parameters for secondary degassing are the degassing time of 45 s,the degassing temperature of 90?100 ? and the length of the collecting section of 55 mm.