Ultrasonic-assisted Sintering Process And Reliability Of Cu@Ag Nanoparticles

With the rapid development of the electronics industry,the packaging and testing field have more and more urgent needs for new material systems and packaging processes which can achieve low temperature,high density,high reliability and environmentally friendly power devices,and using metal nanoparticles to achieve low-temperature solid-phase sintering has attracted widespread attention.The Cu@Ag nano-particle stand out from all kinds of materials and have more and more extensive needs because it has taken into account the low cost,low sintering temperature,high conductivity,and high stability.However,in the actual sintering process,the actual application-related issues such as the influence of various process parameters on the joint forming and the service reliability of the joint are still unknown and need to be solved urgently.Through redox and displacement reactions,this article will prepare core-shell structure Cu@Ag nanoparticles with good dispersion and uniformity,with an average particle size of 63 nm.And it has been configured as nano-metal-paste for sintering experiment.The influence of the process parameters in the ultrasonic-assisted sintering and thermo-compression sintering of Cu@Ag nanoparticles on the joint forming has been explored.In ultrasonic-assisted sintering,the sintering degree of the joint will deepen after prolonging the time,but the shear strength will first increase and then become stable,and the joint fracture will gradually show the characteristics of brittle fracture.Increasing the sintering temperature promotes the densification of the sintered structure,but if the temperature is too high,the number of defects will increase and the strength of the joint will decrease.If the ultrasonic amplitude is too small,the particles cannot be sintered,and if the ultrasonic amplitude is too large,it will damage the joint structure,which requires careful adjustment.When the ultrasonic time is 5s,the temperature is 150 ?,and the amplitude is 60%,the shear strength of the joint is biggest,which is 33.07 MPa.In thermo-compression sintering,temperature,time and pressure are all positively correlated with shear strength.The maximum shear strength of the joint is 36.55 MPa by heating at 350°C for 20 min under the pressure of 10 MPa.The sintering process of Cu@Ag nanoparticles has been analyzed.In ultrasonicassisted sintering,the Ag layers are sintered together by dewetting,and Cu is exposed and fully contacted.Cu is sintered with each other under the extremely high energy input to form a dense Cu block.During thermo-compression sintering,only a small part of Cu is sintered,and the weld formation is extremely slow.Reliability tests of ultrasonic-assisted sintered joints and thermo-compression sintered joints have been carried out,the shear strength of the joints have been measured,and the reasons for performance changes have been analyzed.Due to the low degree of sintering,the thermo-compression joint can be sintered more fully during the test,and the strength of the joint is greatly improved after the test is completed.The weld obtained by ultrasonic-assisted sintering produced a large number of welding defects during the test,and the mechanical properties of the joint dropped sharply.Comparing the two test results,we can find the thermo-compression sintering process takes longer time and the joint strength is slightly lower,but it can be used stably for a long time.The craft of ultrasonic-assisted sintering is simple and it can directly provide the joints,whose shear strength is bigger,but the service stability of them needs to be improved.