Insight into the Influence of Cu6Sn5/Cu Micro-Interface Configuration on Growth Behavior of Cu-Sn Interfacial Intermetallic Compounds in Sn/Cu Solder Joint

Herein, the behavior and mechanism of Cu atom diffusing across Cu6Sn5/Cu interface was researched for analyzing the influence of Cu6Sn5/Cu micro-interface configuration on growth behavior of Cu-Sn interfacial intermetallic compounds (IMCs) in Sn/Cu solder joint. The results indicate that, during Cu atoms diffusing across Cu6Sn5 (001)/Cu (110), Cu6Sn5 (110)/Cu (001), Cu6Sn5 (110)/Cu (111) interfaces, VA2→VA3 stage, VA2→VA3 stage and IA→VA1 stage are the decisive stages, respectively. At those diffusion decisive stages, the difference of average Mulliken population between Cu atom at saddle point and initial state with the surrounding atoms for Cu6Sn5 (110)/Cu (111) interface is 0.62, much greater than that for Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces with average Mulliken population difference of 0.29 and 0.20. Therefore, when Cu atom diffusing across Cu6Sn5 (110)/Cu (111) interface, the magnitude of increase in bonding strength between Cu atoms and the surrounding atoms is the largest, leading that the diffusion rate of Cu atom across Cu6Sn5 (110)/Cu (111) interface is several orders of magnitude smaller than the Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces. As a result, Cu6Sn5 (110)/Cu (111) interface shows the strongest ability for inhibiting Cu atom diffusion, and has the smallest IMC growth rate.