Study On Ultrasonic Bonding Technology Based On Copper Micro-nanocones Arrays

With the development of microelectronic products into high density and integration,3D packaging with high density and miniaturization has becoming the mainstream packaging way.As the core technology,bonding affects the density and size of packaging directly,traditional high-temperature melting bonding technology generates thermal stress,which will greatly reduce the packaging reliability,therefore,low-temperature Cu-Cu bonding technology which is suitable for 3D packaging research has aroused much attention.We have developed a novel ambient ultrasonic bonding method based on Cu micro-nano cone arrays in both sides.After ultrasonic pressure for a short time,Cu cones plated with a very thin Sn or Ag could be inserted into each other,effective bonding interface could be formed with the diffusion of Cu and middle layer.Compared with the traditional bonding,due to the introduction of ultrasonic wave,the bonding temperature and bonding time can be cut down immensely.In this experiment,we used SEM/TEM to test the bonding interface and determine the interface composition.Through the analysis of the interface morphology evolution,the optimum parameters have been chosen as followed:the middle layer 500 nm,pressure 8 Mpa and time 1 s.This article focuses on the ultrasonic bonding mechanism as the middle layer is Sn.The formation and closure of type I and II voids and the micro mechanical behavior of cones are discussed,under the effect of ultrasonic vibration friction,Cu cones could embedded into each other and the deformation could speed up voids closure.TEM analysis proves the deformation and diffusion.The heat treatment process has proved the high reliability of ultrasonic interface,the interfacial morphology and composition haven't changed after a long time heat treatment,the monolayer Cu₃Sn in the interface could increase the mechanical strength of the packaging effectively,so we don't need extra heat treatment to increase the bonding strength.Under the acoustic cavitation of ultrasonic wave,heat effect could speed up the interface diffusion without voids formation,and the morphology of IMC with nanoparticles has proved the acoustic cavitation effect on the bonding interface.The ultrasonic bonding mechanism guide the practical applications.