Electromigration And Interfacial Reaction In Cu/Ga Couples

With the continuous development of microelectronics,it becomes more and more intelligent and multifunctional.Room temperature liquid metal has become one of the solutions for flexible electronic interconnection due to its high electrical conductivity,high thermal conductivity,non-toxicity,and non-volatile characteristics.However,the strong corrosiveness and easy oxidation of gallium hindered its further application.At present,the research on the service reliability of gallium-based liquid metals is insufficient.In this paper,the microstructural evolution of Cu/Ga couples at 50 ^oC and 150 ^oC under a current density of1×10² A/cm² was investigated.The results are as follows:1.The wetting area of gallium on copper surface did not change at both 50 ^oC and 150 ^oC with the extension of the reaction time.The presence of oxide film limited the wetting behavior of gallium on copper surface.The intermetallic compound?IMC?is CuGa₂ with square appearance at 50 ^oC.CuGa₂ grain size increased significantly at 150 ^oC and a 1?m thick Cu₉Ga₄ layer was formed between CuGa₂ and Cu substrate.Growth kinetics analysis showed that during the first 6 h of the interface reaction,the IMC growth index was 0.370 and0.373 at two temperatures,which satisfied the t^1/3 rule.IMC growth was controlled by grain boundary diffusion at 50 ^oC and 150 ^oC.2.Current crowding effect appears when current is applied.The microstructure was partitioned after current apply,the grain in middle part is small with scallop-shaped while in edge part is large and flaky.At 50 ^oC,the IMC in whole area is CuGa₂.With the increase of time,the grain size in central area did not increase,and the edge portion increased significantly.The grain size was 3.23?m and 6.70?m in central and edge part after 6 hours.At 150 ^oC,the IMC in central area is CuGa₂,and there is a 1?m Cu₉Ga₄ layer between the CuGa₂ and copper in edge area.The grain size increased significantly compared to 50 ^oC.After 6 hours,the grain size in central area and edge area are 5.50?m and 88.19?m.3.The simulation results show that the Joule heating effect has little effect on interfacial reaction,current crowding effect occurs on sample surface.The partition of microstructure is caused by the electromigration diffusion flux of copper atoms.In electric field,the electromigration flux disrupts the Cu concentration balance between the IMC and liquid front of gallium.Because of this electromigration diffusion flux,IMC grains continue to dissolve,grains change from tetragonal structure to scallop shape and the matrix accelerates dissolution,the thickness of IMC layer reduced.The current density at the edge of the sample is small,this difference in electromigration and diffusion flux causes a large amount of copper atoms to accumulate in the liquid gallium and reducing the concentration gradient of copper atoms in edge area.So the grain growth rappidly,IMC layer is thick and matrix dissolution rarely in this area.