I'd have a cow, if someone coated my shorts around the edges with epoxy.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Tuesday, June 09, 2009 7:12 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating of PCB edges
Way back in the early '70 some jet fighter were having crazing up to 12"
into boards. Fighters diving form high altitude to warm jungle
environment and back to altitude were "pumping" water down the fiber
glass weave resulting in shorts. We did not have a word for it back them
but it was most likely CAF. PWBs had edges dipped in epoxy to prevent
humid air from condensing as water in the glass fibers during the climb
back to altitude.
PR
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Tuesday, June 09, 2009 8:35 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating of PCB edges
Kevin,
I don't know that I would go as far as to say it is a deeply entrenched
military requirement. For the aerospace industry, Boeing, Airbus,
Sikorsky, etc., can be just as demanding in their commercial
requirements as any of our military customers. As my esteemed
colleague, Mr. Hillman, is fond of saying, we don't have a switch on the
solder machine that selects between military solder joints and
commercial solder joints. Same philosophy applies to conformal coating.
We don't coat a military assembly any different (well, in most cases)
than we do a commercial assembly. In fact, because many of our military
boxes are more nearly hermetic in design, vs. the open construction of
commercial boxes, the challenge to the conformal coating is often
greater for the commercial hardware. Our commercial customers put some
pretty odd requirements in their packages when they come to us. Enough
to make me wonder sometimes what they were sniffing when drafting the
design package. Sometimes the customer has wanted us to coat the edges
because they could not give us a tolerance on how close to the edge we
had to be with the coating. Others have indicated that they thought it
gave them greater insurance that the edge of the coating will not
delaminate during thermal cycling if the coating lapped over the edge.
Again, not really traceable to a failure anywhere, but that is what the
customer wants.
Doug Pauls
Rockwell Collins
Kevin Glidden <[log in to unmask]> Sent by: TechNet
<[log in to unmask]>
06/09/2009 07:20 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Kevin Glidden
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Subject
Re: [TN] Conformal coating of PCB edges
Many thanks, as always, to all for responding.
This confirms what I suspected - no real documented industry requirement
or
recommendation, but instead a deeply entranched military "requirement"
that
became somewhat of a standard practice. Of course like anything, there
is
no "one size fits all" rule for all the different applications. In the
end,
a little extra protection can't hurt, with exception of the card guides
and
tight fits.
Thanks,
Kevin Glidden
-----Original Message-----
From: Douglas Pauls [mailto:[log in to unmask]]
Sent: Monday, June 08, 2009 2:24 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating of PCB edges
For our applications, the card guides are metal and are not coated so as
not
to interfere with card insertion into rail guides. Same as you.
I would agree that coating the edges is usually overkill. I would be
hard
pressed to find an example of failures attributed to lack of coating on
an
edge of a board. But it would be too hard to roll that boulder up the
hill.
Speaking as one who has tried it and been flattened by the boulder.
Painfully. Repeatedlly.
Doug Pauls
Rockwell Collins
Keith Calhoun <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/08/2009 12:50 PM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to Keith Calhoun
<[log in to unmask]>
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Subject
Re: [TN] Conformal coating of PCB edges
In my previous employment we built military electronics systems,
airborne and shipboard, and in most cases masked off the board edges
before coating to allow the boards to slide into various types of card
guides or clamps. I never recall a failure attributable to moisture
intrusion through the card edges, and we used to see some amazing
failures in our legacy products.
Keith S. Calhoun
Product Engineer
SoPark Corporation
3300 South Park Avenue
Buffalo, New York 14218
Phone: 716-822-0434 Ext. 237
Fax: 716-822-5062
email: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Monday, June 08, 2009 11:41 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating of PCB edges
Kevin,
For our applications, if the board is coated, the edges of the board are
coated as well, except in certain situations, such as where connectors
are
at the edge of the board. Why? Well, the time honored "we have always
done it this way".
Part of the rationale is that at the board edge, you have the glass
bundles of the laminate exposed and water can potentially wick into
those
glass bundles, creating problems over the long haul. In most cases, I
think that if the boards are routed from the panel, the routing process
tends to seal the edges and conformal coat is not needed. However, if
you
are shearing or punching the board out, then those fibers are not sealed
(in my opinion) and should be coated to seal the edges.
In order for me to change that stance, I would have to have to prove to
our ever skeptical design engineers that not coating a board edge will
never create a problem in any environment for any of the 20-30 years
design life we use on any product we have ever made. Then change an
entire corporate culture.
I am already burned in effigy 2-3 times per week.
Doug Pauls
Rockwell Collins
Kevin Glidden <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/05/2009 10:30 AM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Kevin Glidden <[log in to unmask]>
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[log in to unmask]
cc
Subject
Re: [TN] Conformal coating of PCB edges
No takers on this one, so maybe I will reword it...
How many are requiring conformal coat application to PCB edges, and why?
Thanks!
-----Original Message-----
From: Kevin Glidden [mailto:[log in to unmask]]
Sent: Wednesday, June 03, 2009 1:47 PM
To: [log in to unmask]
Subject: [TN] Conformal coating of PCB edges
Can anyone point me to an industry document where this is mentioned /
required / recommended, or is this left entirely up to choice?
I believe most consider this a good and desirable thing?
How do automated selective spray systems accomplish this?
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