Research On Surface Treatments Of Copper Plates In Liquid-cooling Systems

As the integration degree and miniaturization of electronics increases,electronics exhibit increasingly higher heat flux density,which greatly affects the performance and life of electronics.Microchannel liquid-cooled cold plate technology has the characteristics of high efficiency,compactness,and low noise,which can provide greater heat dissipation capacity in a relatively compact area.It is currently one of the most widely used technologies in the field of electronic heat dissipation,and microchannel cold plate is the key component of microchannel liquid-cooling system.As the most commonly used microchannel cold plate materials,copper has the advantage of excellent thermal conductivity,and its surface properties seriously affect the performance of the heat dissipation system.However,there is no systematic research of the effects of different surface treatments on the surface properties and performances of copper plates in microchannel liquid-cooling systems.In response to the above problems,we systematically investigated the effects of four surface treatments-cleaning treatment,passivation treatment,plasma treatment,and chemical modification treatment on the surface properties and performance of copper plates in microchannel liquid-cooling systems.The morphology,structure and chemical composition of the samples were characterized by field emission scanning electron microscope（FE-SEM）,X-ray diffraction technology（XRD）,X-ray photoelectron spectroscopy（XPS）,infrared spectroscopy（FTIR）.The roughness and wettability of the samples were investigated by atomic force microscope（AFM）and contact angle（CA）.The heat dissipation capacity,corrosion resistance and stability of liquid-cooled copper plates were evaluated by heat transfer test,electrochemical test and surface analysis,respectively.According to these characterization and performance results,and the relationship between the surface properties and performance of liquid-cooled copper plate was initially established.The main research results of this thesis are as follows:（1）Four processes were proposed to treat the surface of liquid-cooled copper plate with cleaning treatment（#1）,passivation treatment（#2）,plasma treatment（#3）,and chemical modification treatment（#4）.The characterization results showed:for sample#1,the surface is flat and a small amount of natural oxide exists.The roughness is 19.43nm while the CA of cooling liquid on the surface is 42.0°;for sample#2,the surface is relatively flat and Cu（I）-BTA passivation layer is constructed on the surface.The roughness is slightly increased to 26.88 nm while the CA of cooling liquid on the surface is 73.3°;for sample#3,the surface introduces oxygen-containing hydrophilic groups,and the morphology presents nanoplate array structures.The roughness is further increased to 35.47 nm while the CA of cooling liquid on the surface is reduced to 9.8°,exhibiting super-wetting.for sample#4,the surface is mainly composed of copper stearate agglomerates with low surface energy,and the morphology shows a cluster structure.The roughness is further increased to 71.20 nm while the CA of cooling liquid on the surface is increased to 102.7°.（2）To investigate the heat dissipation capacity of different copper samples,we set up a heat transfer device,and calculate the heat transfer coefficients of liquid-cooled copper plate,which are 1295、1589、2019 and 1661 W/（m²·K）,respectively.Among them sample#3 has the largest heat transfer coefficient and the best heat dissipation capacity.The electrochemical results show that sample#4 treated by chemically modified process has the best corrosion resistance in the cooling liquid followed by sample#2,while sample#3 has worse corrosion resistance.The chemical stability results show that the surface morphology,composition and roughness of samples treated by#1,#2 and#4 processes have little change exhibiting excellent stability,while the morphology and roughness of sample#3 changes slightly due to Cu₂O generated on its surface.（3）Based on the above characterization and performance results,the relationship between the surface properties and performance of liquid-cooled copper plate is preliminarily established:surface roughness and wettability have an important impact on the heat dissipation capacity of copper plate,and the increased surface roughness helps to expand the contact area between cooling liquid and copper plate,which can improve the heat dissipation capacity;the copper surface superhydrophilic to cooling liquid has a stronger heat dissipation capacity,which the solid-liquid interaction is strengthened due to hydrophilic modification.The surface chemical composition has an important influence on the corrosion resistance and stability of copper plate.And the existences of passivation layer and low surface energy substances help to improve the corrosion resistance and stability of copper plate.Therefore,the improved performance of liquid-cooled copper plate can be achieved by adjusting the properties of the microchannel surface/interface of liquid-cooled copper plate.