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Undercooling and microhardness of Pb-free solders on various under bump metallurgies

Published online by Cambridge University Press:  31 January 2011

Moon Gi Cho ,
Sung K. Kang  and
Hyuck Mo Lee
Moon Gi Cho
Affiliation:
Department of Materials Science and Engineering, KAIST, Gusung-Dong 373-1, Yusung-Gu, Daejeon, Republic of Korea 305-701
Sung K. Kang
Affiliation:
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598
Hyuck Mo Lee*
Affiliation:
Department of Materials Science and Engineering, KAIST, Gusung-Dong 373-1, Yusung-Gu, Daejeon, Republic of Korea 305-701
*
a)Address all correspondence to this author. e-mail: [email protected]
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Abstract

The undercooling behavior of pure Sn, Sn–0.7Cu, Sn–3.5Ag, and Sn–3.8Ag–0.7Cu solder alloys was observed in terms of various under bump metallurgies (UBMs). Four different UBMs (electroplated Cu, electroplated Ni, electroless Ni(P), and electroless Ni(P)/immersion Au) were used. The amount of the undercooling of Pb-free solder alloys was reduced when reacted with electroplated Cu UBM and Ni-based UBMs. The Ni-based UBMs were more effective than Cu UBM in reducing the undercooling of Pb-free solders. When Ni3Sn4 was formed during the interfacial reactions with Ni-based UBMs, the reduction of undercooling was significant, especially for pure Sn and Sn–3.5Ag. The effects of UBMs on the undercooing of Pb-free solder alloys are discussed by comparing intermetallic compounds formed during interfacial reactions with UBMs. In addition, the microstructural changes as well as the microhardness of four solders with or without UBMs are discussed, which could be related to their undercooling behaviors.

Keywords

SolderingMicrostructureHardness
Type
Articles
Information
Journal of Materials Research , Volume 23 , Issue 4 , April 2008 , pp. 1147 - 1154
Copyright
Copyright © Materials Research Society 2008

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