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Study of the undercooling of Pb-free, flip-chip solder bumps and in situ observation of solidification process

Published online by Cambridge University Press:  03 March 2011

Sung K. Kang ,
M.G. Cho ,
P. Lauro  and
Da-Yuan Shih
Sung K. Kang*
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
M.G. Cho
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
P. Lauro
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
Da-Yuan Shih
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
*
a) Address all correspondence to this author. e-mail: kang@us.ibm.com
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Abstract

The undercooling of flip-chip Pb-free solder bumps was investigated by differential scanning calorimetry (DSC) to understand the effects of solder composition and volume, with and without the presence of an under bump metallurgy (UBM). A large amount of the undercooling (as large as 90 °C) was observed with Sn-rich, flip-chip size solder bumps sitting in a glass mold, while the corresponding undercooling was significantly reduced in the presence of a wettable UBM surface. In addition, the solidification of an array of individual solder bumps was monitored in situ by a video imaging technique during both heating-up and cooling-down cycles. Data obtained by the optical imaging method were used to complement the DSC thermal measurements. A random solidification of the array of bumps was demonstrated during cooling, which also spans a wide temperature range of 40–80 °C. In contrast, an almost simultaneous melting of the bumps was observed during heating.

Keywords

PackagingSnSoldering
Type
Rapid Communications
Information
Journal of Materials Research , Volume 22 , Issue 3 , March 2007 , pp. 557 - 560
Copyright
Copyright © Materials Research Society 2007

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References

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