You probably already checked this but I'll mention it anyway. With
tantalum capacitors, the normal failure mode is a short circuit. So, I
suppose it's possible that the capacitors are defective or they have
been specified incorrectly. Or, perhaps, 5V capacitors have been
installed at the 12V locations. I would guess that the polarity would
have to be correct or the caps would blow the first time power is
applied. I would check to insure that the voltage rating on the caps is
correct.
If multi-layer ceramic (MLC) capacitors are being used and are failing,
I would guess the problem isn't with the capacitors. I suppose that
undersized power traces on a multilayer board underneath the capacitors
might be a remote possibility.
Max Kelson
Evans & Sutherland
-----Original Message-----
From: [email protected] [SMTP:[email protected]]
Sent: Thursday, November 05, 1998 3:17 PM
To: [email protected]
Subject: Burning Card Module
Dear Members,
I am sure some of you can give me ideas on how to analyze a card
module which in four different occassions caused charring and
smoke within the equipment. In all cases, fire did not spread
and
the charring occurred in all cases, arounf decoupling SMT
capacitors located between the Vcc and ground.
The subject card sits in an industrial type computer within a
GSM
equipment. The card is fed by 5 V and 12 Vdc from the computer
power supply and employs two SE:V interfaces. It employs a
piggy board with a receiver with direct connection to an
external
outddor antenna.
Any suggestions how this may have happened in the field, on four
different occassions and the charring/burning occured around the
decouplng capacitors.
For this let us assume PWB is flame rated 94V-0 and is
Recognized.
Regards,
PETER S. MERGUERIAN
MANAGING DIRECTOR
PRODUCT TESTING DIVISION
I.T.L. (PRODUCT TESTING) LTD.
HACHAROSHET 26, P.O.B. 211
OR YEHUDA 60251, ISRAEL
TEL: 972-3-5339022
FAX: 972-3-5339019
E-MAIL: [email protected]
Visit our Website: http://www.itl.co.il
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