Ken, We use 20 tantalum caps in parallel in a military radio and have seen a much higher fallout in our factory testing in the last few years. I believe the cell phone industry placed a major burden on the major capacitor suppliers, who could barely keep up. It appears the quality levels have dipped slightly because of the extra demand. This makes proper derating and series resistance even more critical. ESR comes into play as well when these caps are in parallel. The good caps will also dump their energy into the leaky one, as well as your supply voltage, to burn them up. I agree with John, AVX & Kemet have valuable technical information abstracts on surge failures and construction. They also supply a more surge robust, low ESR, capacitor that can take more abuse if your application requires it. Good luck Jim Carlson Rockwell Collins Reliability Engineer John Maxwell <[log in to unmask]>@ipc.org> on 03/07/2002 02:12:04 PM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to John Maxwell <[log in to unmask]> Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: Re: [TN] Tantalum Capacitor Failure Ken, As a side note, tantalum is like most other valve metals and burns when localized heating gets too high. There is plenty of oxygen (Ta2O5) in the dielectric and extra provided by the manganese dioxide cathode (MnO2) so once failure starts the part consumes itself. Unfortunately one looses the evidence. Over voltage, unrestricted voltage ramp up (that's why vendors recommend a series resistor), reflow profile especially if the part has a polymer cathode or if there is too rapid a cool down after reflow and of course weak parts all are on the list for potential root cause. I suggest getting their recommended application notes along with those from Kemet and AVX and see if thermal or electrical conditions are outside manufacturers recommendations. That analysis should get you down the trail of determining what is happening. John Maxwell At 12:57 PM 3/7/02 -0600, you wrote: >I am wondering if anybody has had similiar issues or can help resolve >a failure we are experiencing. On about 4% of our units at first time >power up 1 of two capacitors that are in parallel are burning up. Upon >replacement the capacitor it to will work fine. >The cap we are using is Vishay Sprague 594D336X9035R2. Since the other >capacitor in parallel is unaffected, I am assuming that it is a Vishay >issue. > >Per Vishay: >The root cause of failure could not be identified. It is requested that the >failure circumstances be reviewed. Failures can occur due to thermal stress >during board mounting, strenuous application conditions, or because of >reduced capacitor capability. There was no specific evidence of reduced >capacitor capability identified. Please be aware, the thermal profile used >for board mounting, and the application conditions (even transient >conditions such as may occur with unregulated power supplies) can affect >product performance. > >Has anyone else experienced a similiar failure or have an opinion? I wish I >could pre-test the caps prior to them burning to supply an intact >capacitor to Vishay for their analysis. > >Please note: When allowed to play its course the cap turned red hot, >unsoldered itself from the PCB and burned a whole in the lab bench! > > --------------------------------------------------------------------------- >------ >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 previous postings at: www.ipc.org > On-Line Resources & Databases > >E-mail 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 > --------------------------------------------------------------------------- >------ --------------------------------------------------------------------------------- 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 previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- 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 previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------