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June 2006

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Wed, 14 Jun 2006 08:25:25 -0500
Content-Type:
text/plain
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text/plain (207 lines)
Good Mornin' Ramon!

They have! Check out this:

 http://www.avxcorp.com/docs/Catalogs/softterm.pdf

Kind regards,

-Steve Gregory-

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, June 14, 2006 8:08 AM
To: [log in to unmask]
Subject: Re: [TN] Finding cracked capacitors

        It seems to me that it is time for the manufacturers of ceramic
caps to get back to the drawing board and redesign the caps so that this
problems is resolved by getting to the root cause. Some kind of strain
relief termination so that the cap is not susceptible to stresses. I can
think of more than one way to do that but the manufacturers have the
resources in place to make the changes and come out with the best
resolution.
        Ramon 





-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Camille Good
Sent: Tuesday, June 13, 2006 3:03 PM
To: [log in to unmask]
Subject: Re: [TN] Finding cracked capacitors

Using the hot soldering iron approach can cause a number of problems,
many of which have been described in previous posts. I've also seen a
case where a hot soldering iron caused the cracked capacitors to
self-heal (temporarily) - the heat drove out any water that had worked
its way into the cap due to a high-humidity operating environment, and
that in turn got rid of the leakage current problems we were having. At
the time, we didn't know that the issue was a cracked capacitor, so it
was maddening to troubleshoot the product. The product clearly was not
working correctly, but the instant you touched that area of the PCB with
a soldering iron (and there were a number of components all in parallel
with the capacitor) the problem went away and the product started
working fine.

  -Camille



  I saw a product a couple years ago that had problems due to cracked
capacitors. The problem only showed up in high humidity situations,
where the presence of high humidity would cause an increase in the
leakage current of the capacitor. This increased leakage current sucked
away enough power from other components that the part wouldn't work
correctly in certain conditions.
       The worst part was that as soon as we touched that particular PCB
no

Dale Ritzen <[log in to unmask]> wrote:
  Quite a lot has been done in regard to this in the design of
electronic assemblies. There are some pretty good white papers out on
part placement changes during board design that minimize this risk,
especially during depanelization. I used to have one saved aside after
an incident with a customer of ours. I'll see if I can find it and post
same.

The only solid way we were ever successful in finding these was with a
quick touch with a hot soldering iron. The cracked terminus usually pops
off the pad if it has cracked away from the body of the part. Yes, it
does expose the cap to another shot of high temp, but it does ensure
that you detect all cracked caps and get them replaced. Since caps with
cracked terminus typically don't fail consistently during ICT or
functional testing (as they can be in parallel or be making partial
contact to pogo pins which still see a device), the soldering iron
method was our only recourse. But, this is only practical if you have a
consistent problematic area of the board. In a case where the caps may
be located in many areas, trying the soldering iron technique on an
entire board is probably not very timely or cost effective.

Good luck with this. It's a tough one...
Dale Ritzen
Quality Manager
Austin Manufacturing Services

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of John Maxwell
Sent: Monday, June 05, 2006 10:46 AM
To: [log in to unmask]
Subject: Re: [TN] Finding cracked capacitors


Daniel,
Most flex cracks are hidden under the termination at the capacitor
termination/PWA interrface making it very difficult to detect using SLAM
or C-SAM. A quick way to uncover cracks is exposure to humidity & bias
accelerating failure. A few temp cycles ahead of humidity testing will
open the cracks a bit easing humidity entering the capacitor body
accelerating failure.

John Maxwell


>A good acoustic microscope should be able to find these cracks quickly 
>and non-destructively. It is not a cheap tool, though, at $100k-$200k
depending
>on the options.
>
>On Mon, 5 Jun 2006 10:11:04 -0400, Tempea, Ioan
wrote:
>
>
>
>>Hi Technos,
>>
>>a never ending story, ceramic caps that crack, possibly due to
>>
>>
>depanelizing. The damage is not visible, unless the cap is cross
sectioned.
>
>
>>Is there any testing, thermal cycling or something like that, that 
>>could
>>
>>
>show the damage real fast?
>
>
>>Thanks,
>>
>>Ioan
>>
>>

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