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An investigation into zinc diffusion and tin whisker growth for electroplated tin deposits on brass

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posted on 13.03.2015 by Mark Ashworth, Geoffrey Wilcox, Rebecca Higginson, Richard Heath, Changqing Liu
It is widely documented that whisker growth is more rapid for tin deposits on brass compared with deposits produced on other substrate materials, such as copper. As a result, studies investigating the effect of process variables on tin whisker formation are often conducted on brass substrates to take advantage of the increased whisker growth rates. Although it has been understood since the 1960s that the increased whisker growth results from zinc diffusion, to date there has not been any detailed analysis of the zinc/zinc oxide distribution at the surface of the tin deposit. Using a commercial bright tin electroplating bath, the formation of zinc oxide at the surface of tin deposits on brass has been investigated. Analyses show that zinc oxide is present on the surface of the deposit within 1 day of electroplating. During storage at room temperature, a network of zinc oxide is formed at the surface grain boundaries, the extent of which increases with time. The critical role that zinc surface diffusion plays in whisker growth for tin deposits on brass has been demonstrated by electrochemical oxidation of the tin shortly after electroplating. This develops a tin oxide film that is thicker than the native air-formed oxide and subsequently serves as a diffusion barrier to zinc surface diffusion, thereby mitigating whisker growth.

Funding

The authors would like to thank the UK EPSRC Innovative Electronics Manufacturing Research Centre for funding this research through the WHISKERMIT programme at Loughborough University. We would also like to acknowledge the contribution to the programme from our industrial collaborators; MacDermid plc, Rolls-Royce plc, Aero Engine Controls, NPL, MBDA UK Ltd., Park Air Systems Ltd. and Gen3 Systems.

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Materials

Published in

Journal of Electronic Materials

Volume

43

Issue

4

Pages

1005 - 1016

Citation

ASHWORTH, M.A. ... et al, 2014. An investigation into zinc diffusion and tin whisker growth for electroplated tin deposits on brass. Journal of Electronic Materials, 43 (4), pp. 1005 - 1016.

Publisher

Springer / © The Minerals, Metals & Materials Society

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2014

Notes

This article is published in the serial Journal of Electronic Materials [Springer / © The Minerals, Metals & Materials Society]. The final publication is available at Springer via http://dx.doi.org/10.1007/s11664-014-2983-y.

ISSN

1543-186X

Language

en

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