Preparation And Properties Characterization Of A High Temperature Solder Based On The Cu@Sn@Ag Core-Shell Particles

With the development of electronic devices towards high integration and miniaturization,the power density of the devices increases,leading to a sharp increase of heat production.However,the traditional Si-based semiconductors can not work stably at temperature higher than 175℃.Due to the excellent physical properties,the wide band gap semiconductors represented by Si C have become the most potential alternative materials.However,so far,no suitable solder can make full use of the physical properties of Si C.Therefore,it is urgent to explore a new lead-free high-temperature chip attach material.In this paper,a novel solder based on Cu@Sn@Ag core-shell particles is adopted for short-time interconnection at low temperature and long-term service at high temperature.In this paper,a two-step electroless plating method was used to prepare the Cu@Sn@Ag particles with compact and uniform coatings.After that,the influence of coating thickness on interconnection effect was studied.Due to the coating of Ag,the oxidation resistance of Cu@Sn@Ag particles was better than that of Cu@Sn.Hence,the process of interconnection can take place without gas protection or vacuum.The solder paste was prepared by mixing the Cu@Sn@Ag particles with terpineol,glycol and other organic solvents.After reflow at 250℃under 3 MPa for 15 min,the melting point of the bondline can be increased to 475℃.The results show that the thermal expansion coefficient of the bondline is 15.77×10^-6℃^-1;the resistivity is 4.6±1.4μΩ·cm;the thermal conductivity is 159.97 W·m^-1·K^-1,142.71W·m^-1·K^-1 and 137.28 W·m^-1·K^-1 at 30℃,150℃,250℃;the shear strength is25.8±6.9 MPa and 19.7±6.3 MPa at 30℃and 400℃,respectively.In the harsh environments,the reliability of the bondline composed of the preform based on Cu@Sn@Ag particles was studied.In the water drop test with a bias voltage of 60 V,the short-circuit time of the bondline based on Cu@Sn@Ag particles is 145 s during the process of electrochemical migration.After being stored at high temperature and humidity environment for 14 days,the resistivity of bondline based Cu@Sn@Ag particles increased from 4.6±1.4μΩ·cm to 8.5±3.8μΩ·cm.After aging at 300℃for 15 days,the porosity of the bondline based on Cu@Sn@Ag particles only increased from 6.8%to 10.8%,and the shear strength decreased from 30.5±6.3 MPa to 22.3±5.6 MPa.After 500 cycles of thermal shock,the bonding area of the interface decreased from 99.0%to 84.2%.As mentioned above,the performance of bondline based on Cu@Sn@Ag particles decreased slightly in harsh environments.