| The third generation semiconductor material represented by Ga N and Si C,have the characteristics of wide band gap,high breakdown electric field,high thermal conductivity and high electron saturation rate,but its service environment is more complex,which puts forward higher requirements for the connection material and connection reliability of the device.Particles with core-shell coatings have proven to be effective in the field of electronic packaging.In this paper,the composite solder prepared after mixing nano-sized and micron-scale Cu@Ag core-shell coated particles and its sintering process are taken as the research direction to provide a reliable connection material and processing for the packaging of third generation semiconductor devices.Cu@Ag core-shell coated particles with average particle size of 50 nm,5μm and 20μm were prepared by liquid-phase reduction method.The results of XRD,TEM-EDS,SEM-EDS show that the prepared Cu@Ag particles have complete coating structure.The effects of three scales of Cu@Ag particle gradation relationship on the sintered microstructure of solder were studied.The SEM-EDS results show that the sintering structure has better densification and less defects when the particle grading relationship conforms to the law of Dinger-Funk stacking theory.The structure is composed of network structure formed by the interconnection of nano Cu@Ag particles,micro Cu@Ag sintering structure and single Ag structure,the sintering necks are formed and connected effectively between the scale particles.Based on the Dinger-Funk theory,the influence of 20μm particle content in the composite solder system on the sintering structure was studied,and the optimal gradation relationship of multi-scale particles in the solder powder system was obtained.The results show that when the content of 20μm coated particles is less,there are more banded pores in the tissue.When the content of particles is 10%,the porosity of the tissue is 23.965%,the content of particles increases to 25%,the porosity decreases to 8.566%with the maximum shear strength reach 29.6 MPa.When the content of particles increased to 30%,the porosity increased to 9.697%.When the mass fraction of particles in the system was 25%～35%,the shear strength decreased,but the strength was still higher than 26 MPa,therefore,the optimal particle scale distribution is M（50 nm）:M（5μm）:M（20μm）=60:15:25.The results show that the joint shear strength of the composite solder at four sintering temperatures is higher than that of the 50nm Cu@Ag solder,the strength of sintering at 280℃is 21.13 MPa and 6.6 MPa respectively,the strength of sintering at 300℃is 29.6 MPa and 14.24 MPa respectively.The high temperature aging test results of composite solder show that the strength of the joint increases slowly in the range of 0～750 h,and the joint performance decreases sharply when the aging time reaches 1000 h,with a decrease of 32.6%.The microstructure,pore distribution and joint strength of Cu@Ag composite solder after sintering were studied.The influence of different process parameters on solder joint was compared and its mechanism was analyzed.The influence of high frequency induction pre sintering process on the properties of composite solder after sintering was discussed.The results show that in the hot pressing sintering process,prolonging the sintering time or increasing the sintering temperature can increase the densification of the sintering structure and the joint strength,but the joint strength decreases when the sintering time exceeds 30 min.In the high frequency induction pre sintering process,increasing the high frequency induction current or prolonging the high frequency action time to 5～10 min will increase the joint connection strength.However,the pre pressure of high frequency induction sintering has a negative correlation with the connection strength,but the solder joint of pressureless sintering can not be effectively connected. |
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