Morphologies and grain orientations of Cu–Sn intermetallic compounds in Sn3.0Ag0.5Cu/Cu solder joints

Morphologies and grain orientations of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at the interface of Sn3.5Ag0.5Cu lead-free solder alloy and copper substrates were investigated by Electron Backscatter Diffraction (EBSD) technology combined with Scanning Electron Microscopy (SEM). Scalloped Cu6Sn5, Cu6Sn5 planes and six-prism shaped Cu6Sn5 IMCs were observed at the interface after 48 h of soldering at 250 °C. Moreover, Cu6Sn5 planes emerged in pairs on top and beside the scalloped Cu6Sn5, and two adjacent Cu6Sn5 planes were with an angle of 120°. Cu3Sn and scalloped Cu6Sn5 IMCs had preferred orientations, and they were Cu6Sn5 (0001)∥substrate surface, and Cu3Sn (1¯00) and (100)∥substrate surface.

► Grain orientations of Cu–Sn IMCs with long time soldering were investigated.
► Preferred orientation of Cu6Sn5 was Cu6Sn5 (0001)∥substrate surface.
► Preferred orientations of Cu3Sn were Cu3Sn (11¯00) and (100)∥substrate surface.
► Cu6Sn5 planes emerged in pairs on top and beside the scalloped Cu6Sn5.