Investigation Of The Effect Of Substrate Grian Refinement To Reaction Of Sn/Cu Interface

Effective Micro-connection has become one of the most critical technical prerequisite and micro-connection is an important part of electronic package.As a main way in micro-connection so far,reliability of soldering is crucial to products.Substrate-solder reaction occured after joint formed.During service,intermetallic compound(IMCs)formed through inter-diffusion and reaction between under bump metallization(UBM).IMCs growth will lead to changes of brittleness and conductivity in solder joints,leading micro connectors fail.The core issue of these changes is around interfacial reaction.Diffusion in the interface lead forming of IMCs.Grain level of substrate has a important effect in diffusion.Pad used in industrial production is electroplated copper(EP Cu),which has much finer grains than HP Cu.HP Cu was widely used in soldering reaction and void formation researches.The role of grain boundaries in the interfacial reaction in current research is still less.The topic aiming at the limitation mentioned above,controlling Cu pads with different grain size while maintaining other conditions the same and making a systematic study of Sn/Cu interfacial reaction and voids formation.In this paper,the physical deposition(Physical VaporDeposition)applied to prepared PVD Cu,and high copper(High Pure Cu),respectively,as Sn/Cu inter facial reaction of the substrates.Reflow and electroplate were used to make Sn/Cu interface and electroplating Sn/Cu(EP Sn/Cu)interface,to study Sn/Cu inter facial reaction and Kirkendall voids;use of field emission scanning electron microscope(FE-SEM)to characterized compound growth state.Analysis and comparison shape and thickness of Sn/Cu inter facial reaction products,fitting Sn/Cu inter facial reaction IMC growth kinetics,get different substrates state inter facial reaction kinetic constants.Micro-voids formation mechanism has been obtained by analyzing the distribution and density of micro-voids in EP Sn/Cu after aging.Results shows that activation energy in wetting reaction decrease as decrease of Cu grain,and micro-voids occurred when aging in 150℃.