Steve, I am sending you a couple of pictures via a separate email of
recent (last week) tin whiskers seen on a RoHS I.C. on lead-free
product, if you could be so kind as to post them on your website. This
is just one example, I have lots more. The point I am trying to make is
that the whisker issues are becoming widespread, and will eventually
carry over into more COTS parts used in high-rel applications.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 30, 2008 8:34 AM
To: [log in to unmask]
Subject: Re: [LF] tin whiskers / reports of nasa
Hi Wolf!
I don't have any direct experience with tin whisker failures, but as a
production engineer for an EMS company, I wouldn't really know of any
failure unless one of our customers told us about it. We just build
things and ship them. We don't follow the product through their lives
like our customers do.
We also don't build that much lead-free here, but we have the capability
(dual wave solder pots etc.), and it's just because of our customer
base. Most of our customers are either high-rel or military, and forbid
tin plated components.
Another link that talks about more than just relay whiskers is from
CALCE:
http://www.calce.umd.edu/lead-free/tin-whiskers/TINWHISKERFAILURES.pdf
Steve
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of SCHMIDT,
WOLF-DIETER - PFHO
Sent: Wednesday, April 30, 2008 1:27 AM
To: [log in to unmask]
Subject: [LF] tin whiskers / reports of nasa
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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