Liquid-solid Interfacial Reactions In Fine Pitch Cu/Sn-3.0Ag-0.5Cu/Ni Solder Interconnects

With the development of electronic packaging technology,the solder joint is downsizing,and the solder composition in such small solder joints is more susceptible to the dissolution of substrate and the growth of interface IMC as well,and in turn,the variation in solder composition also affects the interfacial reaction.At the same time,the cross-solder interaction of the heterogeneous substrate shows also more significant as the size of solder joints decreases,and this will strongly influence the reliability of micro-scale solder joints.Furthermore,lead-free mandatory requirements also make soldering technology face greater challenges.In this paper,Cu/Ni cross-solder interaction was studied by Cu/SAC305/Ni linear solder joint at different temperature and different spacing,which explored the effects of temperature and solder thickness on the growth rate and morphology and type transition of IMC on both sides.The reaction process of Cu/SAC305 and Cu/SAC305/Ni chip solder joints was observed by using the real-time imaging technique of synchrotron radiation,so that to further explore the effect of Cu-Ni cross-solder nteraction on the liquid-solid interface reaction,especially the effect of Ni atoms on the growth kinetics and morphology of scallop-like Cu6Sn5 on Cu substrate.The main results are as follows:1.In the Cu/Ni cross-solder interaction,(Cu,Ni)6Sn5 IMC formed on both sides of Cu/SAC305/Ni linear solder joints at 250 oC and 300 oC,and the IMC on Ni side had a faster growth rate than Cu side.At 250 oC,the IMC on Cu side always remained scallop-type,but the IMC on Ni side gradually grew from the needle-type to rod-type.As the temperature increased,the thickness of the IMC decreased slightly at 300 oC.The IMC on Cu side was changed from scallop-type to hexagonal prism rod-type,and the IMC on Ni side also grew from the rod-type gradually into chunk-type,while morphology and grain size of the IMC on both sides were coarser.Atomic flux is the fundamental way of IMC growth.The accumulation of atoms in the interface IMC on both sides depends on the difference between Jin and Jout.The increase in grain size of the interface IMC will decrease the grain boundary area,resulting in a decrease in Jin.Jout remain the same after long-term liquid-solid interface reaction,and at this moment the IMC growth is only controlled by Jin,thus resulting in a slower growth rate.2.With decreasing pitch of solder joints,the Cu-Ni cross-solder interaction in the liquid-solid interface is more significant,which has a serious effect on the morphology and growth of the interface IMC.This resulted in the IMC changing from the scallop-and needle-type into the coarser rod-and chunk-type in a shorter period of time.The average grain diameter increased,but the average thickness decreased.The decrease in grain boundary area results in a reduction in Jin,and the difference between Jin and Jout decreases accordingly,thus resulting in a slower growth rate.3.Compared with liquid-solid interfacial reaction of Cu/SAC305 and Cu/SAC305/Ni solder joints at 221 oC,the Cu-Ni cross-solder interaction was observed and(Cu,Ni)6Sn5 IMC was formed on both sides.With the addition of Ni substrate,the IMC on Cu side gradually evolved from scallop-type to small rod-type.The average diameter of the grains decreased from the initial 18.0 ?m to 5.2 ?m at 20 min.After 1 h of reaction,the average thickness of IMC on Cu side did not change significantly,while the IMC on Ni side grew at a rapid growth rate from the initial 1.16 ?m to 38.6 ?m.