| Copper is one of the most widely used metal materials for human beings.Copper is also widely used in various electronic products.Therefore,the wettability of solder on the surface of copper substrate is an important aspect concerned by people.The microstructure of the substrate surface is an important factor affecting the wetting and spreading process and has the potential to promote the wetting and spreading of solder.At present,the research on the wetting control of substrate surface microstructure mainly focuses on the preparation of superhydrophobic and superhydrophilic surfaces.However,the wetting behavior of solder on the microstructured substrate surface is seldom and controversial: on the one hand,it is believed that the microgroove structure on the substrate surface can provide additional capillary force to promote the wetting and spreading of sold er,but some people also believe that the micro-convex structure on the substrate surface plays a pinning role on the movement of the three-phase line,thus causing the wetting angle of solder on the substrate surface to increase.Therefore,the influence mechanism of the substrate surface microstructure on the wetting process still needs further discussion.Under what conditions can substrate surface microstructure promote wetting and spreading? Under what circumstances can wetting spread be prevented? Thi s will be the main problem to be solved in this subject.Firstly,the nanosecond laser marking machine was used to construct different surface morphologies on the surface of copper substrate,and the wetting behavior of pure tin and pure tin on the surface of microstructured copper substrate under vacuum and live conditions was studied by combining the seat drop method.The wetting spreading mechanism was revealed by observing the microstructure of the interface.In addition,the wetting behavior of gallium indium eutectic alloy on the surface of microstructured copper substrate was studied.The following are the main conclusions drawn from the study:(1)The wetting experiment of pure tin on the surface of microstructured copper substrate was carried out at 250? and 1×10-4Pa vacuum.The microstructure of the substrate surface has an important influence on the wetting process.Pure tin has a good circular symmetrical morphology on the surface of circular and grid texture structures,while orientation spreadin g occurs on the surface of stripe texture structures.The reason for orientation spreading is mainly due to different energy barriers perpendicular to the texture direction and parallel to the texture direction.The wetting angle on the substrate surface with different line spacing decreases with the decrease of line spacing.The reason for the decrease of wetting angle can be attributed to the pinning effect of the micro-convex structure on the threephase line on the substrate surface.Finally,the wettin g angle of pure tin on the surface of microstructured copper substrate also decreases with the increase of temperature.(2)The wetting experiment of flux-assisted pure tin on the surface of microstructured copper substrate was carried out under the condi tion of 250? in real time.Under the action of flux,the wetting angle decreases as the line spacing decreases,but when the line spacing decreases to 50 ?m,the wetting angle is larger than that on the smooth substrate surface.The wetting angle also decreases with the increase of marking times.Under the actual conditions,the flux can remove the solder and the oxide film on the surface of the substrate,so that the solder and the surface of the substrate can be in good contact.After wetting reaches equilibrium,no obvious intermetallic compound is generated at the tin/copper interface,and the microstructure on the copper side remains intact,so additional capillary force promotes wetting and spreading of solder.(3)Ultrasonic-assisted wetting experiment of pure tin on the surface of microstructured copper substrate was carried out at 250 ?.Under the action of ultrasonic wave,the wetting angle decreases with the decrease of line spacing and decreases with the increase of marking times.The solder can be found to flow around the micro-groove structure on the surface of the substrate marked many times,and the contact angle on the surface of the substrate marked seven times reaches 0.Shock wave generated by ultrasonic wave due to cavitation effect can remove oxide film on the surface of solder,and vibration of ultrasonic wave can promote wetting and spreading of solder.After the wetting reaches equilibrium,no intermetallic compound is generated at the tin/copper interface,the microstructure of the copp er side remains intact,and the solder reaches a good wetting state under the combined action of ultrasonic wave and capillary force.(4)The wetting experiment of gallium indium eutectic alloy on the surface of microstructured copper substrate was carrie d out at room temperature.The contact angle of gallium indium eutectic alloy on microstructured substrate decreases with the decrease of line spacing,and the wettability becomes better with the increase of marking times.The wetting angle of gallium indium eutectic alloy on the surface of substrate marked 7 times is 0.The liquid alloy has two driving forces when wetting and spreading on the surface of the microstructured substrate.One is that the driving force of wetting and spreading on the surface of the substrate conforms to Young's equation.The other is that it has additional capillary force when flowing in the microgroove,thus obtaining a smaller wetting angle.The final wetting result is consistent with Wenzel model.To sum up,the microstructure of the substrate surface can effectively control the wetting behavior of solder on the substrate surface.In the wetting process,if the micro-groove structure on the substrate surface is complete,wetting spreading can be promoted.However,the microgro ove structure on the substrate surface can be consumed due to the reaction,which will hinder the wetting and spreading process. |
PDF Full Text Request