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November 2005

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TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord <[log in to unmask]>
Date:
Sun, 13 Nov 2005 11:25:41 -0500
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TechNet E-Mail Forum <[log in to unmask]>, - Bogert <[log in to unmask]>
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- Bogert <[log in to unmask]>
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November 13, 2005

Thanks for all the good information.  What type capacitor would you recommend as a replacement for the tantalum chip capacitor?
  ----- Original Message ----- 
  From: Ingemar Hernefjord<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Sunday, November 13, 2005 11:02 AM
  Subject: [TN] Seeking Tantalum Chip Capacitor Reliability Information


  Monsigneur Bogert

  Here are some links to good papers about tantalum failure modes and also
  about reliability calculations. If you read these carefully and follow
  the instructions, you have

  1. become a tantalum expert 
  2. tools for making a safer design

  Good luck!

  Ingemar Hernefjord
  Ericsson Microwave Systems

  https://www.avx.com/docs/techinfo/failure.pdf<https://www.avx.com/docs/techinfo/failure.pdf>

  https://www.avx.com/docs/techinfo/eqtant.pdf<https://www.avx.com/docs/techinfo/eqtant.pdf>

  https://www.avx.com/docs/techinfo/bsctant.pdf<https://www.avx.com/docs/techinfo/bsctant.pdf>

  https://www.avx.com/docs/techinfo/tantimp.pdf<https://www.avx.com/docs/techinfo/tantimp.pdf>

  https://www.avx.com/docs/techinfo/rmtant.pdf<https://www.avx.com/docs/techinfo/rmtant.pdf>

  https://www.avx.com/docs/techinfo/thrmtant.pdf<https://www.avx.com/docs/techinfo/thrmtant.pdf>



  -----Ursprungligt meddelande-----
  Från: TechNet [mailto:[log in to unmask]] För Ingemar Hernefjord
  Skickat: den 12 november 2005 17:47
  Till: [log in to unmask]<mailto:[log in to unmask]>
  Ämne: [TN] SV: [TN] Seeking Tantalum Chip Capacitor Reliability
  Information

  We have had problems with exactly same cap one year ago, they broke down
  electrically, even exploded! I think you have a derating problem.
  Reported failures had to do with inrush current and heat dissipation
  (internal losses). We used recommended formulas for calculating correct
  application of series resistors, peak voltage, max reverse voltage etc.
  Finally, we gave up and did this: two in parallel, another two in
  parallel and these in series. Clumsy, yes, but we have had no problems
  since that. I've written a report, let's see if I can find it. 

  Of course, various brands show different failure rates. We performed
  accelerated life test on two new brands. Some hundreds of each, max DC
  voltage at room temperature. 1 kOhm in series for each cap in order to
  follow leakage current and avoid direct shorts. While our standard cap
  began to show failures after 1 day (!!) and showed several failures to
  1,000 hs, the other brand had <1 uA leakage all the way! All old caps
  were sent for destruction and the new brand was introduced immediately.
  BUT, as I said, this was a tough design with high demands on the caps,
  so we still got some, but very few, failures. And as the application is
  military, no failures are accepted the first five years in field. The
  above described parallel/series version has worked perfectly now for one
  year, not one single failure reported even after tough environmental and
  electrical testing.

  Inge

  -----Ursprungligt meddelande-----
  Från: TechNet [mailto:[log in to unmask]] För - Bogert
  Skickat: den 12 november 2005 14:26
  Till: [log in to unmask]<mailto:[log in to unmask]>
  Ämne: [TN] Seeking Tantalum Chip Capacitor Reliability Information

  November 12, 2005

  Folks, we are experiencing large number of failures of tantalum
  surface-mount chip capacitors (CWR06 style).  The capacitors are a
  modified version of MIL-C55365 parts to give an extended CV range.  The
  parts are modified 35 Volt rated parts to yield 22 microfarad, 50 volt
  rated parts.  Reverse peak voltage for these parts is 2.5V at 85C and 5V
  at 25C.  The failed parts were installed correctly.  We checked voltage
  ratings, ripple current, etc. and all are OK for the application.

  There is a problem with board layout since the vendor hand soldered the
  parts to the board by applying soldering iron directly to the top
  surface of the capacitor rather than to the pad area (the capacitor
  manufacturer indicated this is not recommended).  This is because the
  layout was flawed since the land area was not larger than the part so
  the pad could not be heated via the soldering iron.  The vendor
  subsequently changed method of soldering to implement pre-heat and
  reflow soldering and no longer uses hand soldering.  However, even with
  these changes, the parts are still failing.

  This part is a commercial version of a MIL-C-55365 part.  The vendor
  does no burn-in electrical screening testing on the parts so we suspect
  our failures may be due to the normal bath-tub curve in that we are not
  weeding-out premature failures.

  Does anyone have reliability data showing what failure rates can be
  expected for these type capacitors for both non-electrically screened
  tested vice electrical screened tested parts.  Also, what are the most
  likely failure modes for this type part and what are the failure 
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