Interfacial Diffusion Behavior And Microstructure Evolution Of Cu/Sn/Cu Materials For Electronic Packaging Under Electric Field

3D integrated circuit is a trend of the current microelectronics industry.In the electronic packaging of 3D integrated circuit,the diameter of the inverted welding bump is about 100?m,and it is expected to be reduced to 1?m with the further development of miniaturization.At this time,the current density through the solder joint will reach 10⁴ A/cm²,which will lead to more prominent Joule heating effect.Further local melting of the low melting point solder bump will be one of the main failure modes for solder joints.The main bonding product of the high service temperature solder joint prepared by the bonding technology is the intermetallic compound phase(IMC phase)with high melting temperature.Because IMC phase has the characteristics of hard and brittle,small growth length and too thin IMC layer will lead to insufficient bonding strength of the flip solder joint,and too thick IMC layer will lead to hard and brittle solder joint.Therefore,the subjective control of IMCS layer is of great significance to the electronic pack-aging industry.Different from the traditional analysis method,which can only carry out static analysis due to the high temperature environment of metal solidification process and the opacity of metal itself,the synchrotron radiation in situ observation technique is used to study the influence of sample temperature on the interface diffusion behavior of Cu/Sn/Cu diffusion couple and under the influence of a series of different electric fields.The influence of electric field type and current density on the growth morphology and microstructure evolution of Cu₆Sn₅ in Cu/Sn/Cu diffusion couple is studied.First,based on the third generation synchrotron radiation light source(SSRF)in Shanghai,for suitable for synchrotron radiation resistance furnace assembly debugging difficulty,incon-sistent with the introduction of the electric field radiation,unable to real-time adjustment in the process of synchrotron radiation imaging problems,we design a dedicated portable for syn-chrotron radiation resistance furnace,sample electricity devices and peripherals system,to solve the above problem well.Secondly,using the designed synchrotron radiation device,it is found that the interface reaction process of Cu/Sn/Cu diffusion couple is different at 260?,300?and 340?.At 260?and 300?,the growth of Cu₆Sn₅ has incubation period,but at 340?,there is no incubation period.With the increase of the sample temperature,the higher the initial energy of the diffusion couple,the shorter the incubation period of the interfacial reactionAt the same sample temperature,the length of Cu₆Sn₅ increases with the extension of dif-fusion time.At the same diffusion time,the length of Cu₆Sn₅ increases with the increase of the sample temperature.At the beginning of Cu₆Sn₅ formation,the growth rate of Cu₆Sn₅ quickly reached the peak and fluctuated with time.At the same time,the linear regression analysis shows that the growth of Cu₆Sn₅ in the Cu/Sn/Cu diffusion couple is mainly controlled by the receptor diffusion,and the growth kinetics is in accordance with the parabolic law,that is,L=kt^1?2+b.Finally,the inhibition effect of the bidirectional pulsed electric field on the growth of Cu₆Sn₅ interface in Cu/Sn/Cu diffusion couple and the mechanism of the effect of the intensity of the bidirectional pulsed electric field on the inhibition effect were studied by using the elec-tric field introduction module and the real-time observation technique of synchrotron radiation.It was found that the bidirectional pulsed electric field forced the precipitation of Cu₆Sn₅ in the Sn solder as a plate,and a small amount of Cu atoms dissolved in the Cu substrate on both sides.The promoting effect of direct current field on the growth of Cu₆Sn₅ in Cu/Sn/Cu diffu-sion couple from anode to cathode direction was studied by using the real-time observation technique of synchrotron radiation.It was found that the growth rate of Cu₆Sn₅ increased sig-nificantly with the increase of current density,and the dissolution of Cu atoms appeared on the Cu substrate at the cathode side.The dissolved amount of Cu atom is directly proportional to the current density of the direct current field and the precipitation amount of Cu₆Sn₅ in the diffusion couple.At the same time,the influence of DC electric field on the average length of Cu₆Sn₅ interface growth in the diffusion couple and the mechanism of the influence effect with the change of current density was observed by using the real-time observation technique of synchrotron radiation.It is found that the DC electric field can significantly increase the average growth rate of Cu₆Sn₅ interface in the wave phase and slightly increase the average growth rate in the stable phase.The improvement effect increases with the increase of current density,but does not change the overall trend of the curve.