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Enhanced stress relaxation of Sn–3.8Ag–0.7Cu solder by electrical current

Published online by Cambridge University Press:  31 January 2011

Zhongguang Wang
Affiliation:
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Jian Ku Shang*
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801
*
b)Address all correspondence to this author. e-mail: qszhu@imr.ac.cn
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Abstract

The stress relaxation responses of the Sn–3.8Ag–0.7Cu joints following exposure to electrical currents were examined to investigate the effect of electromigration on the reliability of solder joints. It was found that the stress relaxation rate was enhanced for the Sn–3.8Ag–0.7Cu solder joints subjected to a current density of 2 × 104 A/cm2. Sn hillock formation was observed in situ on the surface of the solder joint and the increase of the hillock volume was obtained as a function of the current application time. Analysis of the vacancy flux indicated that the variations of the vacancy concentration with the electromigration time from the calculations agreed with the growth kinetics of the hillocks observed in the experiments. By modeling the stress relaxation as a climb-assisted dislocation glide process, it is shown that the vacancy accumulation induced by electromigration enhanced the dislocation climb rate, resulting in a large increase of the stress relaxation rate.

Type
Articles
Copyright
Copyright © Materials Research Society 2010

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