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]>
To:     <[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]>



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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