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Interfacial reactions and impact reliability of Sn–Zn solder joints on Cu or electroless Au/Ni(P) bond-pads

Published online by Cambridge University Press:  01 October 2004

M. Date ,
K.N. Tu ,
T. Shoji ,
M. Fujiyoshi  and
K. Sato
M. Date
Affiliation:
Department of Materials Science and Engineering, University of California—Los Angeles, Los Angeles, California 90095
K.N. Tu
Affiliation:
Department of Materials Science and Engineering, University of California—Los Angeles, Los Angeles, California 90095
T. Shoji
Affiliation:
Hitachi Metals, Ltd., Shimane 692-8601, Japan
M. Fujiyoshi
Affiliation:
Hitachi Metals, Ltd., Shimane 692-8601, Japan
K. Sato
Affiliation:
Hitachi Metals, Ltd., Shimane 692-8601, Japan
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Abstract

Sn–9Zn and Sn–8Zn–3Bi solder balls were bonded to Cu or electroless Au/Ni(P)pads, and the effect of aging on joint reliability, including impact reliability, was investigated. For the purpose of quantitatively evaluating the impact toughness ofthe solder joints, a test similar to the classic Charpy impact test was performed.The interfacial compounds formed in the solder/Cu joint during soldering wereCu–Zn intermetallic compounds (IMCs), not Cu–Sn IMCs. One of the Cu–Zn IMCs, γ–Cu5Zn8, thickened remarkably with aging, and eventually its morphology changed from layer-type into discontinuous. The rapid growth of the γ–Cu5Zn8 and void formation at the bond interface led to the significant degradation of the joint reliability due to a ductile-to-brittle transition of the joint. Meanwhile, the compound formed in the solder/Au/Ni(P) joint during soldering was a Au–Zn IMC, above which Zn redeposited during aging. Both the dissolution and diffusion of Ni into the solders were extremely slow, which contributes to negligible void formation at the bond interface. As a result, the solder bumps on the Au/Ni(P) pads were able to maintain the high joint strength and impact toughness even after prolonged aging.

Keywords

ToughnessJoiningMicrostructure
Type
Articles
Information
Journal of Materials Research , Volume 19 , Issue 10 , October 2004 , pp. 2887 - 2896
Copyright
Copyright © Materials Research Society 2004

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