Microstructure control of unidirectional growth of eta-Cu6Sn5 in microbumps on < 1 1 1 > oriented and nanotwinned Cu

Abstract

Anisotropic microstructure is becoming a critical issue in microbumps used in 3-D integrated circuit packaging. We report here an experimental approach for controlling the microstructure of eta-Cu6Sn5 intermetallic compound in microbumps by using < 1 1 1 > oriented and nanotwinned Cu pads as the under-bump-metallization. By electroplating arrays of large numbers of < 1 1 1 > oriented and nanotwinned Cu pads and by electroplating the Sn2.3Ag solder on the pads, we form eta-Cu6Sn5 in the reflow at 260 degrees C for 1 min. The eta-Cu6Sn5 showed a highly preferential growth along the < 0 0 0 1 > direction. As reflow time is extended, the preferred texture of eta-Cu6Sn5 changed to {2 (1) over bar (1) over bar 3}. The results indicate that we can control the uniform microstructure of eta-Cu6Sn5 intermetallic by controlling the microstructure of the Cu under-bump-metallization. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.