Electromigration anisotropy introduced by tin orientation in solder joints

Single-crystal Sn/Cu solder joints with (001), (101), (301) and (100) plane of Sn as the interfaces were prepared for studying the relation between orientation of Sn and electromigration. The growth of interfacial intermetallic compounds was found to strongly depend on the Sn grain orientation. When the c-axis was parallel to the current direction, a severe polarity effect was observed, while the c-axis of Sn off the current direction, the polarity effect became less pronounced. For (101) and (301) orientation samples making a 28.6 degrees and 58.6 degrees angles with c-axis of Sn, asymmetrical IMCs layer growth at the anode interface, downward sloping serrated edges of Cu dissolution groove at the cathode and granular Cu6Sn5 growth at the surface were observed, while these morphological features were not found in (001) and (100) samples making a 0 degrees and 90 degrees angles with c-axis of Sn. It is suggested that when the c-axis of beta-Sn was off the current direction, the direction of Cu atoms diffusion is shifted to the c-axis of tin grain under the electromigration driving force.(C) 2017 Elsevier B.V. All rights reserved.