Method And Mechanism Of Rapid Fabrication Of Cu-Sn IMC Joints By Cu Nanoparticles Composited With Sn

The third-generation wide bandgap semiconductors,led by gallium nitride and silicon carbide,have shown many advantages in the microelectronics field.However,the existing electronic package materials have diffculties to meet the requirements of harsh working environment,like high working temperature(>300 °C).Nanoparticles(NPs)pastes have received extensive attention due to their low sintering temperature and stability in high working temperature.However,Ag NPs are easy-electromigration and Cu NPs is easy to oxidize.These problems limit the development of nanopaste.Therefore,efforts have been made to develop a novel connecting material with low cost,and excellent performance.In this paper,two kinds of copper-tin composite nanopastes were successfully prepared.The first one is Cu@Sn NPs.The small amount of tin on the surface of copper NPs is used to improve the wettability of the pastes and improve the strength of the sintering interface.The second type is Cu NPs mechanically mixed with micro Sn.The nano-scale Cu and liquid tin react rapidly,and the full IMC joints are prepared in a short time,which is a new choice for the connection materials of the third-generation semiconductor..The preparation process of core-shell materials was studied.The effects of factors such as plating composition and reaction environment on particle morphology and copper-tin atomic ratio were analyzed.The study suggested that the plating process is divided into two steps.Thiourea and copper NPs formed a complex in the first step,and took up most of the time.Finally,Cu@Sn NPs having an average diameter of 160 nm were formed.During the sintering process,a small amount of tin on the copper surface acted as a wetting agent.The copper nanoparticles were sintered together by a highfrequency induction rapid sintering method,and the strength could be increased to 23 MPa.The sintering properties of the second materials were studied.It was found that tin in the sintering process melt rapidly and wrapped on the surface of the copper NPs to prevent oxidation effectively.The full Cu3 Sn joint could be prepared in a short time.With the extension of the sintering time,the joint structure gradually developed toward a higher density.The strength could reach 24 MPa after sintering at 330 °C for 10 min,and the strength reached 34 MPa after 60 min sintering.After sintering by highfrequency induction,two kinds of microstructures,Cu85Sn15 and Cu95Sn5,were formed after sintering for 9 s immediately.Columnar-shape Cu95Sn5 formed and inserted in the middle of joint,which greatly improved the strength.The strength didn't show significant changes as the time increased,maintaining between 18 MPa and 20 MPa.