Tin plating may be used on circuit boards as a lead free solderable surface.
 It is subject to 3 problems: tin whiskers, tin pest and slivers.

Tin whiskers appear after plating in several hour to several years and are
caused by compressive stressed plating or external compressively conductors.
 Some plating baths are grow whiskers while others do not. The worst subtrate
for whisker growth is brass with a possibility when on copper and nil when on
nickel. See S.C. Britton, Tin Research Institute 1974.  Later research in
Japan, mainly by T. Sonada in Plating and Surface Finishing in J Sur. Fin
Japan and J. Metal Fin. Japan 1990-1995 provide much of the information on
plating and tin whiskers.

Tin pest or alpha-tin forms at low temperatures(0 to -50 deg.C) only if the
surface is seeded with alpha tin.  See R. M. MacIntosh, Journal of Tin
Research, No 72 (1966).  Decreased by codeposit of antimony or bismuth. 

Breakaway tin slivers can be reduced by using a more ductile tin plate or by
reflowing, MP 232 deg C. or plating over nickel.

All problems are decreased by applying a solder mask that prevent tin
whihiser from growing through, prevent accidental seeding surface with alphas
tin, and capture slivers.

Some fabricators strip tin from all but the lands and others plate a nickel
underplate and using the Santa Clara process plate only the lands that are to
be soldered with tin.

Phil Hinton 
Hinton PWB Engineering 
[log in to unmask]