Intermetallic compound identification and Kirkendall void formation in eutectic SnIn/Cu solder joint during solid-state aging

Abstract

Microstructural investigations were performed on the interfacial reactions between eutectic SnIn solder and Cu substrate during reflowing at 433 K and solid-state aging at 373 K. Cu₂(In,Sn) was identified as the only intermetallic compound (IMC) at the interface, which consists of two sublayers with different morphology, a fine-grained sublayer at the Cu side and a coarse-grained sublayer at the solder side. During solid-state aging, voids were found between these two Cu₂(In,Sn) sublayers but not at the substrate interface, which is also attributed to the Kirkendall effect considering the different diffusion fluxes of Sn or In and Cu atoms in different sublayers.

Keywords:

• diffusion
• intermetallic compounds
• SnIn solder
• interfaces
• Kirkendall void

Acknowledgements

The authors gratefully acknowledge the financial support from the Hundred Talents Program of the Chinese Academy of Sciences, the National Basic Research Program of China (Grant No. 2010CB631006), and the Major National Science and Technology Program of China (Grant No. 2011ZX02602).