Formation of preferred orientation of Cu6Sn5 grains in Cu/Sn/Cu interconnects by soldering under temperature gradient

The anisotropic behaviors of micro solder interconnects have been recognized as a crucial reliability concern due to the continuous trend of miniaturization in high-performance electronic devices. The hexagonal structure η-Cu₆Sn₅ with highly anisotropic phase structure has considerable influence on its growth behavior during soldering and performance in service. In the present work, synchrotron radiation real-time imaging technology was used to in situ investigate the growth behavior of η-Cu₆Sn₅ intermetallic compound (IMC) in Cu/Sn/Cu solder interconnects during soldering under temperature gradient. The microstructure of the Cu/Sn/Cu micro interconnects and the orientation of η-Cu₆Sn₅ IMC grains after soldering were characterized. The electron backscattered diffraction (EBSD) analysis revealed that the η-Cu₆Sn₅ grains showed a preferred orientation, with their [0001] direction being nearly parallel to the direction of temperature gradient. The results pave the way for controlling the orientation of the small number of interfacial IMC grains in three-dimensional (3D) packaging technology.