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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