I suppose that if you have very ragged board edges, liquid water could get in. Then with freeze/thaw cycles, you could have the board delaminate.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Tuesday, March 26, 2013 2:33 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat and Board Edges
Thank you Lloyd. So most of your customers take a "don't care" with a handful on either end saying it MUST be coated, and the other group MUST NOT be coated.
I should have asked the more refined question of whether we intentionally coat or not coat for reliability reasons, rather than a natural artifact of the coating process.
Here is how a conversation goes here on the topic:
Me: Do we have to coat the edge of the board?
Designer: Yes, absolutely, an iron clad requirement.
Me: Why?
Designer: We have always done it that way, so it must be right.
Me: what about when a high density connector is along the edge? Or Card Guides along the edge?
Designer: Well no, of course not. Coating would wick into connectors.
Me: So we must coat board edges, except when it is very inconvenient?
Designer: Right.
I have yet to see an instance where conformal coating along the edge of a board is really value added. All of our boards are routed out, so the edge of the resin is fairly well sealed. So coating does not really provide any additional sealing. Now, if the edge of the board had punched edges, where the resin was not sealed off and the glass fibers are open, I might see the value. On the other hand, those are usually not high reliability assemblies either.
Doug Pauls
From: "lduso - Diamond-MT.com" <[log in to unmask]>
To: TechNet E-Mail Forum <[log in to unmask]>,
[log in to unmask]
Date: 03/26/2013 10:51 AM
Subject: Re: [TN] Conformal Coat and Board Edges
I do not have specific reasons why or why not but I can say of the hundreds of customers we have had for liquid coating, I can think of only a handful that demanded it, and less that strictly forbid it. As a normal process we do not coat the edges unless it has an exposed conductive surface there. I do know of one customer who forbid it for fitment reasons in a case.
Obviously if it is XY or a dip operation we coat the edges.
Lloyd Duso
On Tue, Mar 26, 2013 at 11:42 AM, Douglas Pauls < [log in to unmask]> wrote:
OK, the conformal coat question of the day:
Do you conformally coat the edges of a printed circuit assembly? Why or why not?
OK, that is two questions, or perhaps a half fractional question.....
Doug Pauls
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Lloyd Duso
Diamond-MT
Plant Manager
(814) 535-3505
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