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Microstructural Evolution During Electromigration in Eutectic SnAg Solder Bumps

Published online by Cambridge University Press:  03 March 2011

Y.H. Chen,
T.L. Shao,
P.C. Liu,
Chih Chen and
T. Chou
Y.H. Chen
Affiliation:
National Chiao Tung University, Department of Material Science & Engineering, Hsin-chu 30050, Taiwan
T.L. Shao
Affiliation:
National Chiao Tung University, Department of Material Science & Engineering, Hsin-chu 30050, Taiwan
P.C. Liu
Affiliation:
National Chiao Tung University, Department of Material Science & Engineering, Hsin-chu 30050, Taiwan
Chih Chen*
Affiliation:
National Chiao Tung University, Department of Material Science & Engineering, Hsin-chu 30050, Taiwan
T. Chou
Affiliation:
Macronix International Corporation, Ltd., Hsin-chu, 30078, Taiwan
*
a) Address correspondence to this author. e-mail: chih@cc.nctu.edu.tw
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Abstract

Microstructural changes induced by electromigration were studied in eutectic SnAg solder bumps jointed to under-bump metallization (UBM) of Ti/Cr–Cu/Cu and pad metallization of Cu/Ni/Au. Intermetallic compounds (IMCs) and phase transformations were observed during a current stress of 1 × 104 A/cm2 at 150 °C. On the cathode/substrate side, some of the (Cuy,Ni1−y)6Sn5 transformed into (Nix,Cu1−x)3Sn4 due to depletion of Cu atoms caused by the electron flow. It is found that both the cathode/chip and anode/chip ends could be failure sites. On the cathode/chip side, the UBM dissolved after current stressing for 22 h, and failure may occur due to depletion of solder. On the anode/chip side, a large amount of (Cuy,Ni1−y)6Sn5 or (Nix,Cu1−x)3Sn4 IMCs grew at the low-current-density area due to the migration of Ni and Cu atoms from the substrate side, which may be responsible for the electromigration failure at this end.

Keywords

DiffusionElectromigrationPackaging

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Type
Articles
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Journal of Materials Research , Volume 20 , Issue 9 , September 2005, pp. 2432 - 2442
Copyright
Copyright © Materials Research Society 2005

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