We don't (usually) because nearly all of our CCAs are mounted into frames. Many of the CCAs have a special grade of PWB that wicks heat away from certain components into the frames (certain components are underbonded with thermally conductive epoxy to sink the heat into the PWB), and coating the perimeter and the edge insulates the frames from the PWB. Even "normal" FR-4 slash types will benefit from some heatsinking into guide rails, frames, and wedge-locks if not coated, allowing the CCA to run a little cooler. It's part of my thermal management schemes. Sometime take a look at a thermal image of a CCA during operation, such as a power supply, and note the cold spots around standoffs. Even standoffs can sink away a lot of heat, but not if the coating is on the PWB prior to assembly of the hardware.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
Sent: Wednesday, October 20, 2010 3:15 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coating Board Edges
The reason is that, in the past, coating the edge of the board reduced the risk of delamination in service. No resist present.
ATB - Graham,
Sent from my iPhone
On 20 Oct 2010, at 19:20, Douglas Pauls <[log in to unmask]> wrote:
> Good afternoon all,
>
> I am glad we all appreciate Inge and the time he puts into making this a
> fun and interesting forum. To sum up: Ditto.
>
> I have a question related to conformal coating, a sort of survey. For
> those of you that conformally coat your assemblies, do you coat the edges
> of the boards? Why or why not?
>
> There is an internal debate here and I wanted some other viewpoints before
> offering my own.
>
> Doug Pauls
> Rockwell Collins
>
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