Dave,
As the literature on Tin Whiskers suggest, 'Pure Tin plating under
Stress' is the main culprit for tin whisker growth, a component joint
does not have the traditional source of stress. The exception is
mounting holes in PCB that have a tin plated land and utilize screws (or
bolts) to fasten the PCB to chassis. The tin plating on land and screw
provides an opportunity for whisker growth.

The main factors for tin whisker growth are - tin plating with brighteners, thin plating < 2 um, no annealing, presence of Zinc in plating and substrate metallurgy with Copper, Brass or Bronze.
_____________________
pratap singh
Tel./Fax: (512) 255-6820
email: [log in to unmask]
www.rampinc.com

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