Steve,
you are 100% correct. AR coating normally can be removed using semi-aqueous
clean. Special care should be taken regarding the integrity of the
interface of old/new coating area if touch up is being used. Damaged AR
coating may be act like a trap to moisture and contaminents, potentially may
result some corrosion. The major concern is the potentially grow dendrites
at the old/new coating interface (under the new coating but on top of the
old one).
You should contact conformal coat manufacature to define a proper procedure
of rework the PWA.
(it is to my knowledge, you would save time to just remove the coating and
re-coated after rework rather than go through burning, cleaning, rework,
localized touch up).
good luck.
jk
At 05:54 PM 5/17/99 EDT, you wrote:
>Hi ya'll!
>
>We just got a rework job in from a customer where we're gonna change a PLCC28
>out for them, remove it and replace it with another. The board has been
>conformal coated with an Acrylic conformal coating (Humiseal type 1B73 I
>believe...).
>
>I know reworking can be done just by burning through the coating, and then
>cleaning up the pads real good before putting the new part back down. We're
>water soluble, so we're gonna have to run the boards through the cleaner to
>clean the flux residues...and I know that we'll damage the coating when
>putting it through the cleaner. On the boards that I've looked at, the
>coating has been compromised anyway on spots here and there just from the
>handling...acrylic is not too tough.
>
>I told our customer that the coating was gonna be pretty raggy looking when
>he got the boards back from us, and we're not in the conformal coating
>business. But what's bothering me, is that I think they've got some spray
>cans and they're gonna try and touch-up things themselves...against my strong
>recommendations. I think the boards should be stripped of the coating that's
>on there now, baked, and then re-coated.
>
>But like I said, we're not in the conformal coating business, and I've not
>worked much with the stuff anyway. I'm just thinking logically about it...am
>I sweating things too much?
>
>Thanks!
>
>-Steve Gregory-
>
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