Study On Ultrasound-driven GaInCu Alloy Cu/Cu Bonding At Room Temperature

Low temperature bonding has always been a topic of concern in the field of material bonding,and ultrasonic welding is considered to have the characteristics of low welding temperature,easy operation and high welding efficiency.Ultrasound has a unique acoustic cavitation effect in liquid solder,which can remove surface oxide films,clean the surface of the base metal,enhance the wetting between the solder and the substrate,promote the diffusion of the solder,and provide an environment for chemical reactions.Currently,the solder used for ultrasonic welding needs to undergo at least two solid to liquid transitions,and the welding temperature is at least above 100℃.There is no research on room temperature liquid solder.With ensuring operational performance as a prerequisite,the lower the welding temperature,the better.This avoids problems such as material softening,mismatching of thermal expansion coefficients between heterogeneous materials,and element burning loss caused by high welding temperatures,thereby improving the reliability of the system,reducing energy consumption,and expanding the application field of materials.The emergence of gallium and gallium based alloys seems to show us the direction.Starting from the recently received attention of gallium based liquid alloys,this article has studied a room temperature liquid Ga based alloy solder using its unique properties,including but not limited to its affinity for most metals and low melting point.Ga and Cu can undergo interfacial reactions at room temperature,and the product CuGa₂phase is stable at room temperature and has a small coefficient of thermal expansion,making it a reliable interfacial reaction product.We try to combine gallium based alloy solder with ultrasonic welding to achieve ultra fast connection between pure copper at room temperature.The research results will provide basic reference ideas for further exploration of room temperature welding.The main research results obtained in this article are as follows:（1）A room-temperature liquid solder-gallium based liquid alloy solder,is proposed,which relies on the interfacial reaction between the base metal and the solder as the initial condition and the unique acoustic cavitation effect of ultrasound in the liquid solder as the auxiliary medium,thereby achieving ultra-fast room-temperature connection between pure copper（The connection can be achieved within 0.3 s）.（2）The optimal process parameters suitable for this experiment are determined by orthogonal experiments,and the effects of process parameters on the microstructure and mechanical properties of the weld interface are clarified.It is revealed that the reason for interfacial bonding mainly depends on the metallurgical reaction between the solder and the base metal,which generates a unique and stable intermetallic compound CuGa₂ at room temperature at the interface,thereby achieving reliable connection between the base metals.（3）The effects of natural aging on microstructure and shear strength are revealed.With the increase of natural aging time,the diffusion reaction process is promoted,and CuGa₂ particles continuously precipitate and aggregate with each other to grow.The precipitated elemental In tightens the CuGa₂ particles,filling the weld more completely,and improving the interface structure.A typical interface structure is obtained,which is Cu/CuGa₂+In/Cu.At the same time,with the increase of natural aging time,the shear strength of the weldment is improved.（4）It is found that with the prolongation of artificial aging time,the high-temperature phase Cu₉Ga₄ was first formed at the interface edge near the base metal,followed by the formation of Cu₉Ga₄ phase inside the interface.Under aging for 6 hours,a well bonded interface structure Cu/CuGa₂+Cu₉Ga₄/Cu is formed.Similarly,the shear strength exhibits a slow decrease followed by a rapid increase,and finally a slight decrease.