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June 2013

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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 17 Jun 2013 12:00:49 -0500
Content-Type:
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Hi Steve - Yes, XY is in the matrix although the question of coverage for 
XY is not an issue. There are a number of studies that show tin whisker 
can grow thru XY conformal coating too. The IPC task has XY in the matrix 
primary for comparison purposes against the other conformal coating types 
- AR, UR, SR, ER. Again, the test is not a tin whisker test but a test to 
understand/characterize conformal coating/application method on components 
in terms of coverage/thickness. 

Dave



From:   Steven Creswick <[log in to unmask]>
To:     <[log in to unmask]>
Date:   06/17/2013 11:45 AM
Subject:        Re: [TN] minimum thickness of Type UR Conformal coat and 
tin whiskers
Sent by:        TechNet <[log in to unmask]>



Dave,

Probably a dumb question, but is parylene in the test matrix somewhere?


Steve Creswick
Sr Associate - Balanced Enterprise Solutions
http://www.linkedin.com/in/stevencreswick
                         616 834 1883



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Monday, June 17, 2013 11:02 AM
To: [log in to unmask]
Subject: Re: [TN] minimum thickness of Type UR Conformal coat and tin
whiskers

Hi gang - sorry for the late reply but as Doug detailed, I was enjoying 
the
SE US whitewater for the last week. As for tin whiskers and conformal
coating mitigation, a conformal coating material captures and contains tin
whiskers but does not eliminate them. There currently is some 
investigative
work in progress under the SERDP organization contracts by Celestica/BAE 
and
Rockwell Collins which will provide some insight on how conformal coating
can alter the tin surface interface reactions thus impact tin whisker
initiation/growth. The 4 mil thickness value that Phil mentioned is from 
the
IPC JSTD 001E Space Addendum criteria and is based on a 12+ year ongoing
investigation by NASA Goddard with a urathane conformal coating material.
There is no consensus on what is the minimum thickness necessary for tin
whisker risk mitigation by a conformal coating material yet -  although 
the
published data does show thicker is better. 
There is also an IPC JSTD 001 task group working on a "State of the
Industry" conformal coating  assessment effort that is ongoing right now
which should provide the industry a baseline of typical coverage/thickness
for various conformal coating materials types/application methods. This
baseline could be used in an effort to develop what conformal coating
minimum thickness would be adequate for tin whisker risk mitigation. So 
the
short answer for Phil's question is there is a flurry of industry activity
trying to provide an answer to his question. Good information takes time.

Dave Hillman
Rockwell Collins
[log in to unmask]



From:   Douglas Pauls <[log in to unmask]>
To:     <[log in to unmask]>
Date:   06/12/2013 08:12 AM
Subject:        Re: [TN] minimum thickness of Type UR Conformal coat and 
tin whiskers
Sent by:        TechNet <[log in to unmask]>



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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