[SI-LIST] Re: Failed Tantalum capacitors - package hermeticity compromised

Any kind of Tan capacitor has a failure rate. if you have to use traditional
Tan capacitor, try to choose rating as high as possible, at leat 2X. Even
with 2X or higher, failure is also possilbe. We ever ran into several
failures, then caused board/chassis burning accident.  The cause is that
MnO2 and Tan metal in traditional capacitor will accelerate burning
(oxygenation) in high temperature. But Organic Tan capacitor, organic will
replace MnO2. so short failure will not cause intenisve burning, usually
safe to the board. I did some experiments on traditional Tan capacitor and
Sanyo PosCAP, PosCAP showed good safety performance. Short failure even
almost did not damage the PCB board.
That's why many companies discarded tranditional Tan capacitor.
Peter zhu
Emerson Network Power

On Wed, Jan 28, 2009 at 12:29 AM, Curt McNamara
<curt.mcnamara@xxxxxxxxxxx>wrote:

> Another factor is in-rush current. If the voltage does not rise slowly but
> is connected
> to a supply which is already active, the voltage rise time can be very
> fast, and the in-rush current
> enough to damage the parts. I have several examples of this here.
>
>
>                                        Curt
>
>
> Curt McNamara, P.E. // principal electrical engineer
> Logic Product Development
> 411 Washington Ave. N. Suite 400
> Minneapolis, MN 55401
> T // 612.436.5178
> F // 612.672.9489
> www.logicpd.com
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> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Salkow, Steven
> Sent: Monday, January 26, 2009 7:40 PM
> To: si-list@xxxxxxxxxxxxx
> Cc: EPICenter pwb-cca Email Forum
> Subject: [SI-LIST] Failed Tantalum capacitors - package hermeticity
> compromised
>
> Content-type: text/plain; charset=us-ascii
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> Recently we have had some tantalum capacitors rated at 16V fail on turn
> of in a 12V circuit. While some percentage of low ESR capacitors
> experience a high surge infant mortality on first turn on unless
> serrated by 50% or more, these capacitor were sent for additional
> electrical screening at an independent test house.
>
> Just as a precaution we decided to also sample test the lot for package
> hermeticity by conducting a bubble test. 25 samples were picked at
> random from the lot of 450 and 100% of these failed bubble test.
>
> Has anyone had this problem before? Has any had counterfeit capacitors?
>
> Steven Salkow
> Lockheed IS&S
> 3130 Zanker Rd, San Jose
> Ca. 95134
> (408) 473-4058
> H: (925) 462-1075
> steven.salkow@xxxxxxxx
> salkow@xxxxxxxxxxxx
>
>
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