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Electromigration induced microstructure and morphological changes in eutectic SnPb solder joints

Published online by Cambridge University Press:  31 January 2011

A. Lee,
C.E. Ho and
K.N. Subramanian
A. Lee*
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824
C.E. Ho
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824
K.N. Subramanian
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824
*
a)Address all correspondence to this author. e-mail: leea@egr.msu.edu
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Abstract

Simultaneous direct current stressing with thermal aging accelerates the migration of conducting species resulting in significant microstructural coarsening. Because of the synergistic fields influence, such coarsening begins from the anode and propagates toward the cathode. Prolonged current stressing with 104 A/cm2 at 150 °C causes the inter-lamellar eutectic SnPb to become a two-layer structure, with a Pb-rich layer adjacent to the anode and an Sn-rich layer adjacent to the cathode. This mass movement causes hillock/valley formation, and the extents of such surface undulations increase with increases in the time duration of current stressing as well as with the joint thickness. In thinner solder joints these events occur sooner, although the extents of surface undulations depend on the thickness of joints. In addition, Cu present in the substrate and in the intermetallic layer at the cathode migrates to form Cu6Sn5 within the Sn-rich layer, in a region close to the Pb-rich layer.

Keywords

ElectromigrationMicrostructurePackaging

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Type
Articles
Information
Journal of Materials Research , Volume 22 , Issue 11 , November 2007, pp. 3265 - 3272
Copyright
Copyright © Materials Research Society 2007

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References

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