I did find the paper that started the discussion about the magic thickness being .002" but I still agree with the general rule stated below.

http://nepp.nasa.gov/whisker/reference/tech_papers/2010-Panashchenko-IPC-Tin-Whisker.pdf

I will patiently wait for Dave to come back.

Phil

From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, June 12, 2013 6:10 AM
To: TechNet E-Mail Forum; Bavaro, Phillip @ MWG - TW
Subject: Re: [TN] minimum thickness of Type UR Conformal coat and tin whiskers

Phil,
While this is an answer I "should" know, I don't.  Dave Hillman regularly attends and presents at the CALCE yearly conference on whiskers and so he keeps up on all of that.  At present, my esteemed colleague is bumping his head on rocks, kayaking upside down, on some white water in North Carolina.  He should be back in the office on Monday and will no doubt answer then.

From our discussions, the general rule is still "no conformal coating prevents whiskers".  A thicker coating may cause the whisker to expend more energy punching through and yet more energy to punch through an adjacent coating on a lead (usually resulting in buckling), but I have yet to hear about some magic thickness of any kind of coating that completely mitigates whiskers.  But I could be wrong.

Dave?

Doug Pauls



From:        Phil Bavaro <[log in to unmask]<mailto:[log in to unmask]>>
To:        <[log in to unmask]<mailto:[log in to unmask]>>
Date:        06/11/2013 02:26 PM
Subject:        [TN] minimum thickness of Type UR Conformal coat and tin whiskers
Sent by:        TechNet <[log in to unmask]<mailto:[log in to unmask]>>
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Doug et al,

Is there a disagreement in the industry as to what minimum thickness of urethane is required in order to mitigate tin whisker concerns?

I am hearing that the .003+/-.002" does not provide enough of a minimum thickness and that the number is as high as .004".   I can understand wanting the minimum being raised to .002" but higher than that would seem to make the process much more difficult to control.

I have a potential customer asking if we measure the thickness on the individual component leads which is another can of worms it seems.  We always used flat samples to document our thicknesses.

I did not get to attend this years APEX so I might have missed the latest data.
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