The effect of different post-electroplating surface modification treatments on tin whisker growth

ABSTRACT

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the ‘cracked oxide theory’ was proposed by Tu in 1994. The current study has investigated the effect of both a molybdate conversion coating and a tungstate conversion coating on tin whisker growth from Sn–Cu electrodeposits on Cu, and compared it with that from an electrochemically formed oxide produced from a potassium bicarbonate-potassium carbonate electrolyte. X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of both immersion time and applied potential on the thickness and composition of the oxide film. The XPS studies show that the oxide film formed using either of the conversion coating baths is significantly thicker than that produced from the potassium bicarbonate-potassium carbonate bath. Initial observations suggest that both the tungstate-based conversion coatings and the molybdate-based conversion coatings significantly reduce whisker growth by over 80% for all conversion coating systems compared with a native air-formed oxide and provide improved mitigation compared with the electrochemically formed oxides previously investigated.

KEYWORDS:

• Tin
• conversion coating
• molybdate
• tungstate
• electrochemical oxidation
• electrodeposition
• whisker growth

Acknowledgements

The authors would like to thank Sabrina Yan at the Loughborough Materials Characterisation Centre (LMCC) for her assistance with FIB cross-sectioning. The work formed a partial requirement for completion of a Loughborough University doctorate for author DMH. The paper is based in part on a presentation given at The Eighth Workshop, EMPS-8, ESA, Noordwijk, The Netherlands, 10th-12th May 2017.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

D. M. Haspel http://orcid.org/0000-0002-3097-0150

G. D. Wilcox http://orcid.org/0000-0002-5546-3235

Additional information

Funding

The authors would like to thank both the UK EPSRC Innovative Electronics Manufacturing Research Centre for funding this research through the WHISKERMIT programme and the Loughborough University Materials Research School.