Authors: Snugovsky, L.; Snugovsky, P.; Perovic, D. D.; Rutter, J. W.

Source: Materials Science and Technology, Volume 25, Number 10, October 2009 , pp. 1296-1300(5)

Publisher: Maney Publishing

Abstract:

The term "spalling" refers to the formation in a solder joint of a second layer of intermetallic compound, in addition to and separate from the usual single layer that normally forms on the substrate. It has been observed in Pb-free solders of the SAC type when used in conjunction with a nickel finish. Explanations offered to account for this phenomenon have been based on thermodynamic phase equilibria observed in isothermal sections of the Sn corner of the Cu–Ni–Sn system at temperatures 20°C or more above the solidification temperature of the solder, and without regard to reactions that occur at low temperatures, during freezing. Recent measurement of the liquidus projection of the Sn corner of the Cu–Ni–Sn system as shown the occurrence of a ternary quasiperitectic reaction in the composition range in which "spalling" is observed. Evaluation of the effect of this quasiperitectic reaction shows that its operation during freezing of the solder can account for the "spalling" phenomenon.

Keywords: QUASIPERITECTIC REACTION; "SPALLING"; SAC SOLDER ALLOYS

Document Type: Short Communication

DOI: http://dx.doi.org/10.1179/174328408X396023

Affiliations: Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, ON, M5S 3E4, Canada

Publication date: 2009-10-01

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