Unidirectional growth of microbumps on (111)-oriented and nanotwinned copper.
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.
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of China.
Hsiang-Yao
HY
Hsiao
Chien-Min
CM
Liu
Han-wen
HW
Lin
Tao-Chi
TC
Liu
Chia-Ling
CL
Lu
Yi-Sa
YS
Huang
Chih
C
Chen
K N
KN
Tu