Study On The Preparation Of Micron-Cu@Ag And Nano-Ag Particles Mixed Solder Paste And The Mechanism Of Its Rapid Sintering

Along with the miniaturization of optoelectronic devices,it is crucial to enhance the power density of electronic devices.Third-generation semiconductor materials such as SiC and GaN is widely used in aerospace,space exploration,and other fields due to its excellent performance.The interconnection could endure high temperature is imperative since SiC chips could work stably at a temperature higher than 600 ?.Traditional Sn-based solder could not meet the requirement of servicing at such a high temperature due to its low melting point.Because of nano-effect,nanomaterials have been widely investigated in recent years.Although the preparation and sintering processes of nanosilver particles are well-developed,the high cost,poor resistance of electromigration and chemical migration of nanosilver greatly limit its application.The research of nano copper also has been limited because of its proneness to be oxidized and complicated bonding process.Hence,we prepared a kind of bonding material that is low-cost,easy to store,and able to bond at low temperature and service at high temperature.In this paper,nanosilver particles are prepared by a chemical reduction method.The preparation of micron Cu@Ag core-shell particles is achieved by a displacement reaction.The particle shape,reaction temperature,reactant ratio,and reaction time are controlled to explore the best parameters of the preparation.The solder paste,prepared by mixing core-shell particles with nanosilver particles at a theoretically calculated ratio,is adopted in sandwich structure joints.And the mechanism of the interconnection achieved by electromagnetic induction heating process and the hot-pressing sintering process is investigated by changing the parameters of sintering.According to the experiment,the average diameter of nanosilver particles is 14.33 nm.And the sintering of nanosilver happens at a low temperature of about 238 ?.The micron Cu@Ag core-shell particle prepared with a 6:1 reactant ratio in 10 minutes at60 ? possesses strong antioxidant ability since the insulation of dense nanosilver shell.The porosity in joints is minimized by adopting 3:1 as the ratio of mixing core-shell particles with nanosilver.With the increase of heating power and sintering time,in the electromagnetic induction sintering experiment,the porosity in the joint decreases,and the uniformity gradually improves.The copper substrates are interconnected by sintered necks of nano silver while the output power is 22 kW.While enhancing power to 26 kW,the peak temperature in the joint reaches the melting point of silver,and then the metallurgical connection is achieved.Pressure could ensure the strength of the joint.The solder paste prepared by mixing the particles before drying would form a uniform joint with fewer defects after sintering.The solder paste prepared by mixing particles later is not uniform and would bring more defects.The silver plating on the surface of the micron copper particles could improve the oxidation resistance,and the nanosilver particles could improve the uniformity and compactness of the joint.The shear strength of the joints first increases and then decreases with the prolonging of sintering time.When the power is 22 kW and heating time is 15 s,the shear strength of the solder paste prepared by the first mixing method could reach 40 MPa.When the heating power increases to 26 kW,the shear strength could reach 48 MPa.In the hot-pressing sintering experiment,defects such as the pores of the interface gradually decreases with the increase of temperature and time.However,increasing the temperature and prolonging the heating time would cause the oxidation phenomenon,resulting in the gradual increase of the oxide layer on the surface of the Cu substrate and the micron Cu@Ag core-shell particles.The shear strength first increases and then decreases with the increase of temperature and time.When the heating time is 30 min,the shear strength of the joint sintered at 350 ? reaches the maximum,which is 20 MPa.When the heating time is 60 min,the strength of the joint sintered at 350 ? is only 15 MPa.