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Effect of Zn on the intermetallics formation and reliability of Sn-3.5Ag solder on a Cu pad

Published online by Cambridge University Press:  31 January 2011

Y.K. Jee ,
Y.H. Ko  and
Jin Yu
Y.K. Jee*
Affiliation:
Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 305-701, Korea
Y.H. Ko
Affiliation:
Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 305-701, Korea
Jin Yu
Affiliation:
Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, Daejeon 305-701, Korea
*
a)Address all correspondence to this author. e-mail: youngkun_jee@kaist.ac.kr
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Abstract

Varying amounts of Zn (1, 3, and 7 wt%) were added to Sn–3.5Ag solder on a Cu pad, and the resultant solder joint microstructures after a reflow and isothermal aging (150 °C, up to 500 h) were investigated using scanning electron microscopy, energy dispersive x-ray, and x-ray diffraction, which were subsequently correlated to the results of microhardness and drop tests. Zinc was effective in improving the drop resistance of Sn–3.5Ag solder on the Cu pad, and an addition of 3 wt% Zn nearly doubled the number of drops-to-failure (Nf). The beneficial role of Zn was ascribed to suppression of Cu6Sn5 and precipitation of Zn-containing intermetallic compounds (IMCs). However, the Zn effect was reduced as Cu6Sn5 and Ag3Sn precipitated in a joint IMC layer after prolonged aging. The interface between Ag5Zn8 and Cu5Zn8 was resistant to drop impact, but two other layered IMC structures of Cu6Sn5/Cu3Sn and Cu5Zn8/Cu6Sn5 were not.

Keywords

Chemical reactionDiffusionFracture
Type
Articles
Information
Journal of Materials Research , Volume 22 , Issue 7 , July 2007 , pp. 1879 - 1887
Copyright
Copyright © Materials Research Society 2007

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