Lee,
I don't think you can assume that the cleaning process drying section is
adequate. In many cases, you may have heated air knives blowing away the
water. If you have highly figured assemblies (thick, dense) and low
standoff parts, you cannot assume you got all the water out. Many of your
coatings don't like water when they are applied as a liquid coating, or
while they cure.
Doug Pauls
From: lee Hitchens <[log in to unmask]>
To: <[log in to unmask]>
Date: 03/26/2013 11:40 AM
Subject: Re: [TN] Conformal Coat and Board Edges
Sent by: TechNet <[log in to unmask]>
Can I also ask a question. What is the purpose of baking a PCB before
coating, assuming that the cleaning process drying section is adequate? I
have never really got a good answer to this?
Best Regards
Lee Hitchens
Technical Director
SCH Technologies is a Division of SCH Services Limited
Mob: +44 (0) 7862 25 33 21 www.conformalcoating.co.uk
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Fox, Ian
Sent: 26 March 2013 16:17
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat and Board Edges
No we don't. Since the purpose of the coating is not to prevent moisture
ingress into the board (we all know that happens), but really to prevent
issues with condensation, and since there likely will be no exposed tracks
on the edge, there's no point. We typically have a ground/thermal strip
around the edge of the card anyway so the masking may sometimes cover, or
partially cover the edge. I couldn't tell you how many millions of on wing
hours our assemblies have accumulated over the past 30+ years, but we've
never had an issue in service as a result of uncoated edges, nor in the
umpteen unit qualifications we've carried out. In fact if you carry out
weight gain measurements with high (85%+) humidity exposure the laminate
is
typically saturated after about 4 days and we always run the 10 day
tropical
exposure test
Regards
Ian Fox
Lead Materials and process Engineer
Aero Engine Controls
York Road, Hall Green, Birmingham B28 8LN | Tel: +44 (0)121 607 3763 |
Fax:
+44 (0)121 607 3975
Email: [log in to unmask] | Web: www.aeroenginecontrols.com
Aero Engine Controls is part of the Rolls-Royce Group
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: 26 March 2013 15:43
To: [log in to unmask]
Subject: [TN] Conformal Coat and Board Edges
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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