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Nanoindentation measurements on Cu–Sn and Ag–Sn intermetallics formed in Pb-free solder joints

Published online by Cambridge University Press:  31 January 2011

R. R. Chromik
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Whitaker Laboratory, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015
R. P. Vinci
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Whitaker Laboratory, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015
S. L. Allen
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Whitaker Laboratory, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015
M. R. Notis
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Whitaker Laboratory, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015
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Abstract

Nanoindentation testing has been used to measure the hardness and elastic modulus of Ag3Sn, Cu6Sn5, and Cu3Sn intermetallics, as well as Sn–Ag–Cu solder and pure Sn and Cu. The intermetallics were fabricated by solid-state annealing of diffusion couples prepared from a substrate (Cu or Ag) and a solder material (Sn or Sn–Ag–Cu solder), providing geometries and length scales as close as possible to a real solder joint. Nanoindentation results for the intermetallics, representing penetration depths of 20–220 nm and loads from 0.7 to 9.5 mN, reveal elastic/plastic deformation without evidence of fracture. Measured hardness values of Cu6Sn5 (6.5 ± 0.3 GPa) and Cu3Sn (6.2 ± 0.4 GPa) indicate a potential for brittle behavior, while Ag3Sn (2.9 ± 0.2 GPa) appears much softer and ductile. Using a bulk Cu6Sn5 sample, Vickers hardness testing revealed an indentation size effect for this compound, with a hardness of 4.3 GPa measured at a load of 9.8 N. An energy balance model is used to explain the dependence of hardness with load or depth, where the observation of an increasing amount of fracture with applied load is identified as the primary mechanism. This result explains discrepancies between nanoindentation and Vickers results previously reported.

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Articles
Copyright
Copyright © Materials Research Society 2003

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