Spontaneous Growth of Whiskers on Tin Coatings: 20 Years of Observation

Abstract

Tin coatings and some tin alloy coatings from various plating baths and on several substrates have been kept under observation for spontaneous whisker growth for periods up to 20 years. A review of the results and of information obtained elsewhere suggests that, although assured immunity from whiskers may be difficult to achieve for pure tin coatings, the risks of growth can be greatly reduced by care in selection of type and thickness of coatings and of substrate, and by other measures. Thin coatings, plating on brass without an undercoat and departures from good plating practice all increase risk. Bright, as deposited, coatings are more susceptible than matt coatings although flow brightened or hot dipped coatings have a low risk. Post-plating heat treatment at 180–200°C is useful for some coatings. Alloy coatings are at much lower risk than pure tin coatings, with tinnickel (65% tin) immune and coatings containing lead providing a close approach to immunity.