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On the root cause of Kirkendall voiding in Cu3Sn

Published online by Cambridge University Press:  04 February 2011

Liang Yin  and
Peter Borgesen
Liang Yin*
Affiliation:
Universal Instruments Corporation, Conklin, New York 13748
Peter Borgesen
Affiliation:
Department of Systems Science & Industrial Engineering, Binghamton University, Binghamton, New York 13902
*
a)Address all correspondence to this author. e-mail: yinl@uic.com
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Abstract

Soldering to Cu interconnect pads with Sn-containing alloys usually leads to the formation of a layered Cu3Sn/Cu6Sn5 structure on the pad/solder interface. Frequently, microscopic voids within Cu3Sn have been observed to develop during extended thermal aging. This phenomenon, commonly referred to as Kirkendall voiding, has been the subject of a number of studies and speculations but so far the root cause has remained unidentified. In the present work, 103 different Cu samples, consisting of 101 commercially electroplated Cu and two high-purity wrought Cu samples, were surveyed for voiding propensity. A high temperature anneal of the Cu samples before soldering was seen to significantly reduce the voiding level in subsequent thermal aging. For several void-prone Cu foils, the anneal led to significant pore formation inside the Cu. In the mean time, Cu grain growth in the void-prone foils showed impeded grain boundary mobility. Such behaviors suggested that the root cause for voiding is organic impurities incorporated in the Cu during electroplating, rather than the Kirkendall effect.

Keywords

SolderingDiffusionElectrodeposition
Type
Articles
Information
Journal of Materials Research , Volume 26 , Issue 3 , 14 February 2011 , pp. 455 - 466
Copyright
Copyright © Materials Research Society 2011

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