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July 2003

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 1 Jul 2003 18:30:36 +0100
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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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