Hello Steve,

in between I've read most of the available reports related to the your link.
Nearly all reports point out that the tin cover on mechanical parts have
been the base for tin whisker growth:

       << DirecTV 3 ......  Boeing 601-model satellite ...... 
          being caused by the growth of metal filaments in a relay ..... <<

       >> Galaxy VII Lost ..... failures in Boeing 601 satellites........
          tin whiskers grow in the vacuum of space on internal
          tin-plated relay latching switches..... <<

(a lot of reports on the 601 - bad luck for Boeing products)

       >> report by Gordon Davy1, Northrop Grumman Electronic Systems,
          Baltimore, MD: "Relay Failure Caused by Tin Whiskers" << 

... and a lot more reports decribing the same.

Interesting are the two Westinghouse reports:
       # diode lead as base of a whisker
       # mechanical part of a potentiometer

The link

        >> Patriot Missile:  Anoplate WWW Site:
           Suspected tin whisker related problems (Fall 2000) <<

gives explanations under which conditions tin whiskers will grow and this is
due to my knowledge as well. Tin covered mechanical parts will be able to
produce tin whiskers if mechanical stress ist introduced to them. In all
those cases the tin cover was made by galvanic processes but not by melting
tin on a copper or brass metal sheet. It is also well known, that the risk
of tin whiskers out of tin on copper (or alloys containing a high percentage
of copper) is much higher than whiskers out of tin on a nickel barrier.

It is reported that even out of Sn60Pb40 you may have some tin whiskers if
the conditions are given. 

The only report which not basicly refferes to a mechanical part is one of
the two mentioned Westinghouse reports. There the anode lead of a diode was
diagnosed to be the root of failure. In this very case it would be
interesting to know whether the whiskers have been grown out of the lead at
it's bend or not.

So in my oppinion the risk of tin whiskers on an printed board assembly with
electronic components (not regarding electromechanical parts !) is quite
low, especially when produced using reflow soldering. Then most of the
stress on components leads and the tin coverage - if there has been some
stress - will be removed. And the copper lines on the board themselves
normally cannot be mechanically stressed. An additional method to be more
aware of tin whiskers is to use gold over Nickel as metal plating on the
board - we have experience with this for about 15 years and thousands of
boards with very good results.

I would like to know what's your thinking on the points mentioned before.

Regards

Wolf-Dieter Schmidt
Industrial Engineering
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> -----Original Message-----
> From: Steve Gregory [mailto:[log in to unmask]] 
> Sent: Monday, April 21, 2008 5:22 PM
> To: (Leadfree Electronics Assembly Forum); SCHMIDT, WOLF-DIETER - PFHO
> Subject: RE: [LF] The Cost of EU RoHS: $32.7B
> 
> 
> Hi Wolf!
> 
> Here's a link you might want to look at:
> 
> http://nepp.nasa.gov/whisker/failures/index.htm
> 
> Steve

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