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From:
- bogert <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, - bogert <[log in to unmask]>
Date:
Tue, 1 Jul 2008 18:14:34 -0400
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text/plain (198 lines)
July 1, 2008

If these parts car not "burned-in'; aka electrical screen testing by the 
part manufacturer, this could be why you are seeing high failure rates.  We 
had similar problem but solved it with electrical screening testing.  Also 
check derating value and circuit CV product to be sure design is OK.


>From: Ioan Tempea <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Ioan Tempea 
><[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [TN] Ceramic Cap Value
>Date: Tue, 1 Jul 2008 11:18:16 -0400
>
>Hi Ken,
>
>We've seen this phenomenon twice in the past 4 months, high rate of ICT
>failure on ceramic caps and had the same issue, replacing the parts
>sometimes worked and sometimes didn't. We even have a painful open case
>on this matter.
>
>I need more clarifications from the group regarding this issue and how
>to get around it.
>
>The paper on aging asks to take the phenomenon into account when
>designing the circuitry.
>Does this mean the high failure rate Ken and I witnessed is borderline
>design?
>
>Can it be marginal testing method also?
>
>Can it be anything else that design or testing?
>
>Thanks,
>
>Ioan
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Bruce Tostevin
>Sent: Monday, June 30, 2008 9:37 AM
>To: [log in to unmask]
>Subject: Re: [TN] Ceramic Cap Value
>
>Ken,
>
>As John Maxwell pointed out, it sounds like you may be seeing the normal
>effects of capacitor dielectric aging.  It's a common stumbling block
>with
>parts at incoming inspection, test, etc.  There's a pretty good one page
>summary with a handy formula at:
>
>http://www.atceramics.com/technicalnotes/circuit_designer.asp
>
>Click on Dielectric Aging Phenonema.  The aging aspects of ceramic
>capacitors are also covered in EIA-521.
>
>A quick way to see if this is what's going on with your parts is to
>preheat
>then a little bit and float a few parts in a solderpot for 5-10 seconds
>and
>remeasure them after they cool. That'll usually bring the value up
>enough to
>confirm the issue.
>
>Bruce Tostevin
>Benchmark Electronics
>Hudson, New Hampshire
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ken Bloomquist
>Sent: Friday, June 27, 2008 5:14 PM
>To: [log in to unmask]
>Subject: [TN] Ceramic Cap Value
>
>Happy Friday,
>
>I need some help understanding how you test for the value of ceramic
>capacitors. We build a board that has some 0603, .470 uF ceramic caps,
>+/-
>10%. The assembly that these parts are on has been having a higher
>failure
>rate at our ICT then we've seen in the past. We tracked the failure to
>this
>cap which had a low reading. We replaced the cap and the unit passed ICT
>just fine.
>
>We measured the cap using our HP 4262A LCR Meter and sure enough it was
>reading low, around .398 uF.
>
>We pulled some new parts off the reel and they read low also ranging
>anywhere from .398 to .425. We suspected that we had a bad reel of parts
>even thought they were from a respected cap manufacturer.
>
>Being curious we tested some more reels from different lot codes and
>found
>the same thing. Being even more curious we tested some other parts from
>the
>same manufacturer and found them to be low by around 5% - 7% and in some
>cases slightly below 10%. We then tested some other parts from a
>different
>manufacturer and they tested low also.
>
>Now we are suspecting our test equipment so we went to an independent
>lab
>and had them tested on an Andeen Hagerling 2500A Bridge. Guess what, we
>got
>the same low readings.
>
>After all that my question is, what are we doing wrong to get such low
>readings on these ceramic caps? It just doesn't seem likely that four
>different parts from three different major suppliers tested on two
>different
>pieces of equipment would all be that far down on the low end.
>
>Any education in capacitor testing and reading would surely be
>appreciated.
>
>Best regards,
>
>KennyB
>
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