Don't run the acrylic through a water wash. High pressure jets typical in
SMD cleaners can punch through the coating (similar to sandblasting) and
delaminate it in flakes that clog filters and DI resin beds.
Use a no clean paste or wire solder with no liquid flux to do the rework,
then you don't need to clean. Rosin or synthetic resin may compromise
application of the new coating, but that is specific to application method,
coating and specific flux.
At previous employers, we repaired through acrylic all the time with no
problems using burning, local stripping, complete chemical stripping or
mechanical abrasion to remove the coating. All worked for certain
components and didn't work well on others.
ARIC PARR
Sr. Manufacturing Engineer
Eaton Corp
1400 S. Livernois
P. O. Box 5020
Rochester Hills, Mi 48308-5020
[log in to unmask]
248 608 7780
Fax: 248 656 2242
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG, on 5/17/99 5:59 PM:
To: Aric Parr@01635@Lectron_RH,
EatonWHQ@CorpMail@WHQCleveOH[C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG],
Dean Jones@01635@Lectron_RH, Luis Arevalo@Automotive Eng@AACOCarolStrmIL
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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