Hey all,

I have just had a few questions raised regarding a customers product and
it's reliability.  Presently, they are potting a control circuitry into a
siliconne rubber mould.  This is sealed and then installed in oven control
systems.  What appears to be happening is, over it's lifetime, for some
unknown reason, the ends of the SMT caps is corroding and giving
intermittant faults.  If you pearce the siliconne rubber mould and press on
the end cap with a probe, it then forms a contact and the fault goes away.
The PCB itself is an FR4 PCB with HASL finish, and has an operating current
of around 6mA.  The product is washed once inside the oven control, but
shouldn't the siliconne rubber protect this sufficently enough???  Since the
rubber is a permeable compound, is it possible for water to make it's way
into the mould and onto the surface of the PCB and then not escape????
Would this lead to the corrosion of the end caps???


Cheers

Mike

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------