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September 2008

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From:
"Douglas O. Pauls" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 4 Sep 2008 07:59:05 -0500
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I don't think it is an issue of what kind of deposition process you have, 
but more the rigidity and flexibility of the coating.  Silicone conformal 
coatings (though a tool of the Devil) are generally quite flexible and 
elastic.  Acrylics, urethanes and epoxies are in more common use and are 
more rigid.

I would ask the question of why you want to coat the flex circuit in the 
first place?  The conformal coating is not going to add any insulating 
characteristics to a polyimide based resin (Kapton), so you don't really 
gain anything and only set yourself up for failure.  Even Parylene will 
crack and flake if the bending is great enough or repeated enough.  When 
we have flex circuitry here at Rockwell that is soldered to rigid boards, 
we just coat the solder connections, which does not flex, and leave the 
rest of the flex alone.

Doug Pauls




James Mahoney <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
09/04/2008 07:30 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
James Mahoney <[log in to unmask]>


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Subject
Re: [TN] FLEX CIRCUIT AND CONFORMAL COATING






I would not recommend any conformal coating that is spray deposit but I
would consider pyraline coating process after installation. Repeated 
flexing
will cause cracking and peeling off from the Kapton. Also may consider 
some
type of surface prep to rough up the flex material to enhance the bond
strength.



Thank you, 
Jim Mahoney 
Quick Turn Flex Circuits, LLC 
Applications Project Manager 
P# 603-821-6571 
F# 603-821-5723 
M# 603-305-6250 

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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon
Sent: Wednesday, September 03, 2008 5:42 PM
To: [log in to unmask]
Subject: [TN] FLEX CIRCUIT AND CONFORMAL COATING

Does anyone know what IPC spec that addresses if flex circuit between
two rigid boards can or cannot have conformal coating? I found Design
spec IPC 2223 that addresses in paragraph 4.4 that it generally should
be free of conformal coating due to make it stiff or debonding of the
coating. Not sure what coating that is referring.  Any ideas, thanks in
advance, Jon


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