Driving force of tin whisker growth
In plain words
Thin tin coatings in electronics spontaneously grow hair-like metal filaments that can short circuits, sometimes years after manufacture. What stress or process pushes the atoms into the whisker is not established.
Precise statement
Electroplated Sn films on Cu grow single-crystal whiskers of diameter about $10^{-4}$ to $10^{-3}$ cm and length up to about 1 cm. Determine the driving force (compressive stress from $\mathrm{Cu_6Sn_5}$ intermetallic growth relieved by grain-boundary diffusion under a surface oxide, recrystallization of grains with oblique boundaries, or other contributions) and predict which grains grow whiskers, the incubation time and the growth rate versus stress and temperature. An answer is a model verified on films with controlled stress and microstructure.
What would settle it
Whisker incubation and growth measured on films with independently imposed stress and characterized grain structure, matching a diffusion-and-stress model.
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