Run a small bead of epoxy or electronics-grade silicone around bottom of capacitor. Time-consuming, but fairly easy to implement in the short-term. AR probably won't stick to the silicone, but that should not present a severe problem.
Otherwise, never heard of that one before, and we have been using AR, SR, and UR coatings for years with electrolytics, with few if any field failures (none that I have heard, otherwise I would have my hands full with engineering changes...).
HIH and rgds,
Roger M. Stoops, CID
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511
-----Original Message-----
From: Graham Naisbitt [mailto:[log in to unmask]]
Sent: Tuesday, July 01, 2003 1:31 PM
To: [log in to unmask]
Subject: [TN] Leaky capacitors
Good evening Techies
We have a customer who has discovered a "black deposit" underneath an
electrolytic capacitor that has caused a circuit failure. They conformally
coat the assembly using a classic AR coating and claim that the coating
softens the seal on the capacitor. We are awaiting the results of a surface
analysis they are running to determine what the "black deposit" might be.
We believe that the solvents in the coating might be attacking the capacitor
seal causing the leakage, but cannot understand why this should happen on
components from a reputable supplier. The customer has changed the component
supplier, but the problem seems even more severe.
The end product is safety critical Class 3 - folks may die if the product
fails.
Can you good folks maybe shed some light on what might be done to overcome
the problem?
Change the seal on the capacitor and if so, what type of seal should be
used?
Anyone with similar experience?
--
Regards Graham Naisbitt
[log in to unmask]
Cell: 079 6858 2121
Office: +44 (0)1252 813706
Concoat Limited - Engineering Reliability in Electronics
Web: www.concoat.co.uk and www.concoatsystems.com
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