I have come across similar incidents, and "guess" that the decoupling capacitors have been installed with reversed polarity. The capacitors do not always burst into flame when power is supplied - it may take some time - and if the equipment is not powered up for very long while it is being built and tested in the factory, it can show up in the field.
Proves the need for "integrated circuit packages, transistor packages, optocoupler packages, capacitors and other small parts to be mounted on material of flammability class V-1 or better". (IEC950, clause 4.4.3.3) John Crabb, Product Safety Engineer, NCR Financial Solutions Group Ltd, Dundee, Scotland. > -----Original Message----- > From: pe...@itl.co.il [SMTP:pe...@itl.co.il] > Sent: 05 November 1998 22:17 > To: emc-p...@ieee.org > 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: pe...@itl.co.il > Visit our Website: http://www.itl.co.il > > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
