Effect of electric current on grain orientation and mechanical properties of Cu-Sn intermetallic compounds joints

Abstract

Electric current-assisted bonding experiments have been performed on Cu/Sn/Cu joints using an electric current density of 2.0 × 102 A/cm2 at 260 °C. The effect of electric current on the grain orientation of Cu–Sn intermetallic compounds (IMCs) and mechanical properties of Cu/Sn/Cu joints were evaluated. The scanning electron microscopy (SEM) observation indicated that the electric current had obvious polarity effect on Cu6Sn5 growth. The Electron backscatter diffraction (EBSD) analysis revealed that Cu6Sn5 showed a preferred orientation of [0001] direction being parallel to the electric current. On the contrary, the morphology and grain orientation of Cu3Sn were barely influenced under the electric current density of 2.0 × 102 A/cm2. The calculation results indicated that the Cu6Sn5 (0001) plane showed the lowest projection atomic density of 27.9 atoms/nm2. Therefore, the Cu6Sn5 grains with their [0001] directions oriented along electric current could grow faster because of smaller electron wind force and greater Cu atom flux. The results of nanoindentation experiment and shear test also proved that the full-Cu6Sn5 joints formed under electric current had lower Young's modulus mismatch between Cu6Sn5 and Cu3Sn, and had a joint shear strength of 44.87 MPa. The present work offers a method to adjust the texture of Cu–Sn IMCs in the joints for achieving better electrical and mechanical properties.