Study On The Thermophysical Properties And Reliability Of Gallium-based Liquid Metal

With the rapid development of chip design and manufacturing technology,high-power and high-performance CPU continue to update and iterate.While pursuing high-performance,it also brings huge challenges to the heat dissipation design of the chip.At the current stage,the existence of a thermal interface is an unavoidable problem in chip heat dissipation design,and it is also one of the bottlenecks for efficient heat dissipation.In order to solve the heat dissipation problem of electronic equipment,the development of thermal interface materials with high thermal conductivity has become a research hotspot in the field of thermal management.Therefore,a new heat-conducting material with high thermal conductivity,Liquid Metal(LM),came into being.At the same time,it is of profound significance to prove its thermophysical properties and application reliability,which can provide a scientific basis and theoretical support for the application and promotion of liquid metal in the field of high-performance chip heat dissipation and technical research in the future.In this paper,four gallium-based liquid metals were prepared,and the Ga₆₂In Sn Ag with the highest thermal conductivity was selected through the thermal conductivity test as the research object of this subject,and the main thermophysical properties of the alloy;Through the aging treatment of the produced Cu-LM-Ni sandwich structure under different conditions,combined with the characterization of the material microstructure,the material compatibility with Cu and Ni was studied;then the designed sealed heat dissipation structure was kept at a constant temperature reliability experiments such as constant humidity,high temperature aging,cold and thermal shock,etc.The feasibility of the heat dissipation scheme is analyzed through the experiments of sealing material reliability,sealing reliability,corrosiveness and thermal resistance;finally,the preparation is compared and studied through the CPU burning test thermal conductivity of liquid metal and a commercial thermal grease.The main conclusions of this article are as follows:(1)Through DSC analysis,it is found that the fine adjustment of elements has little effect on the melting point of the prepared liquid metal,but the supercooling degree of the alloy will increase with the increase of the content of gallium element,resulting in a decrease in the freezing point.Through thermal conductivity analysis,it is found that,the addition of trace Ag element can effectively improve the thermal conductivity of liquid metal.CTE analysis in the temperature range of-40?125?reveals that its thermal expansion characteristics are staged.According to the viscosity test,it can be known that it is a non-Newtonian fluid,and the proved viscosity varies as the shear rate increases,it is concluded that the application needs to be applied slowly to reduce the viscosity.According to the results of the wetting experiment,it can be seen that the liquid metal is uniform on the surface of the four solid materials of Si,Si O₂,Cu,and Ni no wetting,reducing the surface roughness of the substrate and increasing the temperature can improve the wettability of liquid metal,but it still cannot achieve wetting fundamentally.Therefore,a method of prefabricating a layer of LM oxide film on the substrate to achieve wetting is proposed.It provides a feasible solution for the liquid metal in practical applications that is difficult to wet.(2)Through the study of material compatibility,it is found that the Cu/LM interface reacts at 60?to form a relatively brittle Cu Ga₂ IMC layer,and this layer grows and continues to form with the increase of temperature,and a small amount of In₂Ag phase appears at 120?.At 150?,the Cu Ga₂ phase will melt in the molten alloy to form enriched phases of Ga,In,Sn,and Cu elements.However,even if the Ni/LM interface is kept at the highest temperature of this experiment for 150h,no obvious reaction will occur.Therefore,when gallium-based liquid metal is used as a heat dissipation material,it cannot be directly contacted with pure copper material,and Nickel plating can be used for protection.(3)Through the gap filling capacity test and the unsealed high temperature and high humidity test results and analysis,it is found that liquid metal may crack,vertically flow out,and severely oxidize in the special working environment such as high humidity,slight vibration,and large temperature difference.Propose and design a heat dissipation scheme for liquid metal as a thermal interface material for chip cooling;at the same time,the preferred sealing material and heat dissipation structure can withstand high temperature and humidity,high temperature aging,and thermal shock reliability tests.The heat dissipation structure effectively protects the liquid metal from being a reaction occurred,further verifying the feasibility of the heat dissipation scheme.(4)Through the thermal resistance test and the CPU burning test results and analysis,it is found that the overall thermal resistance of the sample prepared by the liquid metal after the reliability test did not increase significantly,which once again verified the feasibility of the sealing scheme.During the CPU burning test,the liquid metal exhibits excellent thermal conductivity due to its higher thermal conductivity and lower interface thermal resistance,which is 8°C lower than the CPU empty and full load temperature difference when using commercial thermally conductive silicone grease,a 25% drop.