Wolf-Dieter,
I have been studying lead-free electronics, the RoHS and WEEE
Directives, and the like since December 2004, and have already collected
over 12,000 published documents on these subjects, including:
*  235 books.
*  Over 100 Ph. D. and Master's Theses.
*  Over 11,650 reports, papers, magazine articles, etc.
*  Over 240 web pages.

My bibliography of these materials is at 
   http://www.dbicorporation.com/rohsbib.htm
and is some 800 pages long....

To date, I have found *two* documented cases of tin whiskers growing on
tin-lead solders or platings:
*  http://nepp.nasa.gov/whisker/photos/pom/2003dec.htm
*  Liang, J., Dariavach, N., and Shangguan, D., "Tin Whisker Nucleation
   and Growth on Sn-Pb Eutectic Coating Layer Inside Plated Through 
   Holes With Press-Fit Pins," IEEE Transactions on Components and 
   Packaging Technologies, vol. 31 no. 1, pp. 152-158, Mar. 2008. 

I have collected well over 1,000 documents that discuss the growth of
tin-whiskers on lead-free solders and platings.  These include many
cases where unused components are fine, but the same components soldered
to printed circuit boards will grow tin whiskers.

I personally do not trust the quality, reliability, or longevity of
lead-free electronics, because of:
*  Tin whiskers.
*  Tin pest (tin plague, tin leprosy. tin disease, tin blight).
*  Broken solder joints from physical shock.
*  Kirkendall voids.
*  Conductive anodic filaments (CAF).
*  Copper dissolution. 

Before 2006, I would buy electrical and electronic equipment/products
expecting to use them for 3 to 20+ years.  But now I buy new
electronics-- manufactured since early 2006-- only if I figure that I
will recover their total purchase price within 3 months.  I also take
these precautions:
*  Plug lead-free (or suspected lead-free) electronics into AC power
   only when someone will be in the area.
*  Put batteries into battery-powered lead-free (or suspected lead-free) 
   electronics just before using the item, and remove the batteries as
   soon as I finish.

I may be in trouble when my wristwatch quits...

John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE
author of Robust Electronic Design Reference Book, Volumes I & II
dBi Corporation
http://www.dbicorporation.com/

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