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Effects of under bump metallization and nickel alloying element on the undercooling behavior of Sn-based, Pb-free solders

Published online by Cambridge University Press:  31 January 2011

Moon Gi Cho ,
Sung K. Kang ,
Sun-Kyoung Seo ,
Da-Yuan Shih  and
Hyuck Mo Lee
Moon Gi Cho
Affiliation:
Department of Materials Science and Engineering, KAIST Yuseong-gu, Daejeon, Republic of Korea 305-701
Sung K. Kang
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
Sun-Kyoung Seo
Affiliation:
Department of Materials Science and Engineering, KAIST Yuseong-gu, Daejeon, Republic of Korea 305-701
Da-Yuan Shih
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
Hyuck Mo Lee*
Affiliation:
Department of Materials Science and Engineering, KAIST Yuseong-gu, Daejeon, Republic of Korea 305-701
*
a) Address all correspondence to this author. e-mail: [email protected]
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Abstract

A significant reduction of the undercooling of Sn-based solder alloys was previously reported when they were reacted with various under bump metallurgies (UBMs). In the present study, new experiments have been designed and carried out to understand the undercooling behavior of various Cu- and Ni-doped solders on Ni UBM. Two competing mechanisms were further investigated that include the formation of intermetallic compounds (IMCs) at solder/UBM interface and the change of solder composition because of the dissolution of Ni UBM into solder. Two types of IMCs, including both Ni3Sn4 and Cu6Sn5 that were formed at the interface, were correlated with the undercooling of Sn–0.2Cu and Sn–3.8Ag–0.2Cu solders. In addition, the compositional changes of various Sn-based solders after reactions with Ni UBM were analyzed. On the basis of the experimental results, it was found that the significant reduction in undercooling is primarily caused by dissolved Ni atoms from Ni UBM and the concurrent formation of Ni3Sn4 IMC in the solder matrix. Finally, the beneficial effect of Ni dissolution is thermodynamically favorable as confirmed by the thermodynamic calculations and differential scanning calorimetry measurements with various Ni-doped solder alloys.

Keywords

Differential thermal analysis (DTA)MicrostructureNi
Type
Articles
Information
Journal of Materials Research , Volume 24 , Issue 2 , February 2009 , pp. 534 - 543
Copyright
Copyright © Materials Research Society 2009

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