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. 2012 May 25;336(6084):1007-10.
doi: 10.1126/science.1216511.

Unidirectional growth of microbumps on (111)-oriented and nanotwinned copper

Hsiang-Yao Hsiao  1 , Chien-Min Liu, Han-wen Lin, Tao-Chi Liu, Chia-Ling Lu, Yi-Sa Huang, Chih Chen, K N Tu
Affiliations

Unidirectional growth of microbumps on (111)-oriented and nanotwinned copper

Hsiang-Yao Hsiao et al. Science. .

Abstract

Highly oriented [111] Cu grains with densely packed nanotwins have been fabricated by direct-current electroplating with a high stirring rate. The [111]-oriented and nanotwinned Cu (nt-Cu) allow for the unidirectional growth of Cu(6)Sn(5) intermetallics in the microbumps of three-dimensional integrated-circuit packaging; a uniform microstructure in a large number of microbumps of controlled orientation can be obtained. The high-density twin boundaries in the nt-Cu serve as vacancy sinks during the solid-state reaction between Pb-free solder and Cu and greatly reduce the formation of Kirkendall (or Frenkel) voids.

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