Here is the datasheet for the one that is being used. Thanks for your
help, Jon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls
Sent: Thursday, September 04, 2008 9:32 AM
To: [log in to unmask]
Subject: Re: [TN] FLEX CIRCUIT AND CONFORMAL COATING
Ahh, the ever popular "the contractor screwed up". In my opinion,
debonding refers to the loss of adhesion between the coating and the
flex
surface (like you are seeing), but Gary may have meant it as having the
solvent from the coating actually attack the polyimide construction,
causing the two sides of the flex film to lose adhesion and open up.
So, the answer is the ever popular "it depends". What was the AR
coating
used? I can tell you that we use Humiseal 1B31, which has a carrier
solvent of toluene (mostly) with a little xylene and methyl ethyl ketone
for a nice full bodied aroma with a nice aftertaste. That solvent
combination has not ever attacked the flex that we use. And really, it
is
only an issue when the coating is still liquid. Most manufacturers that
coat acrylics in volume chose a fairly fast evaporating solvent. The
faster it evaporates, the less time there is for attack.
So, what was the AR used? Maybe I can give a better answer knowing
that.
Doug Pauls
"Roberts, Jon" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/04/2008 08:06 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Roberts, Jon" <[log in to unmask]>
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Subject
Re: [TN] FLEX CIRCUIT AND CONFORMAL COATING
Jim and Gary, I forgot to mention in my first email that the product was
only to have the two rigid boards (assemblies) coated. The vendor over
sprayed the AR conformal coating onto and between layers of the flex.
The flex purposely made up of separate layers to make more flexible.
The assembly drawing states the flex be "generally free of coating". I
was trying to find out in the design spec (IPC 2223 paragraph 4.4.2) the
meaning of "debonding of the flex coating". What coating is one of my
question.
Another question is can or will the AR coating actually cause issue with
the flex as Gary Ferrari stated "If it is not compatible, then it could
very possibly break down the material, exposing the circuits beneath and
increasing the risk of adhesion breakdown of the copper to the flexible
substrate."
We are changing the drawing to indicate not to conformal coat the flex
but we have a significant number of assemblies where the coating on the
outside was removed but still have some coating trapped in between the
layers. We can bend the flex and the coating will start to flake off.
Assembly goes into a small box and has not moving parts where the
flaking coating can cause mechanical issues.
I am wording but trying to seek as much information from this forum
which is the best.
Thanks, Jon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of James Mahoney
Sent: Thursday, September 04, 2008 7:31 AM
To: [log in to unmask]
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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