The source of your sulphur may be the elastomer (rubber) products in contact 
with or in close proximity to your exposed copper.  Sulphur can be used in 
the elastomer cure process and can out-gass, especially if the cure is not 
complete.  Some options to consider may include further curing the elastomer 
or switching to a non-sulphur based elastomer.
 ----------
From: John Loveluck <jol
Subject:  Copper Sulphide corrosion
Date: Wednesday, May 21, 1997 6:06AM



Hi

We have seen failures on a bought-in assembly due to growth of copper
sulphide on the copper traces of a flexible PCB.  The failure occurs at the
base of SnPb solder joints, where the copper traces are not covered by
photoresist.  The whole area of exposed copper and solder joints is covered
by a silicone based potting material.

Unfortunately our supplier is not being very helpful, so I am looking for
clues as to what is happening and how to stop it myself.

The source of sulphur is not known, but there are various rubber components
within the immediate area.

Does anyone have any experience of this type of corrosion system?  If so, I
would appreciate a discussion about the factors involved - in particular,
the role of the potting compound and whether an alternative passivating
material would do a better job.

Thank you



John Loveluck
Group Quality Manager
Tadpole Technology plc
Cambridge Science Park
Cambridge CB4 4RB
Tel: (+44)1223.428200
Fax: (+44)1223.428201

email: [log in to unmask]

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