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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Aero Engine Controls is part of the Rolls-Royce Group, whose legal entity is Rolls-Royce Engine Control Systems Limited which is registered in England.
Registered office at Moor Lane, PO Box 31, Derby, DE24 8BJ. Company number 6686268, UK VAT number GB 939 396 075

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