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Subject:	Antw: [TN] Finding cracked capacitors
From:	Guenter Grossmann <[log in to unmask]>
Reply To:	TechNet E-Mail Forum <[log in to unmask]>, Guenter Grossmann <[log in to unmask]>
Date:	Tue, 6 Jun 2006 09:42:15 +0200
Content-Type:	text/plain
Parts/Attachments:	text/plain (63 lines)

Ioan

We use 3 technologies to search cracks in ceramic caps:
1. Ultrasonic microscopy. Works pretty well if the cracks are not too close to the termination and if the structure of the caps is not too inhomogeneous. Otherwise you don't have a flat surface to couple the US into the component or the signal noise ratio ist too bad.
2. Infrared microscopy. Only applicable if you have a connecting path in the crack where you can pump some power though. I already thought once that using a penetrating material with a certain conductivity could help in this measurement but I didn't have the time to look at that in depth.
3. X- Ray. Works with a penetrating liquid that absorbs X-Rays (Boron- Iodine solved in methylene). However, you need to work with 100kV and a detector with a good energy resolution and whenever possible 12bit graphics since the ceramic of the caps is already absorbing a lot of the X- rays. Plus some tricks in handling.

And its still not sure that we find the bastards.

Best regards

Guenter

EMPA
Swiss Federal Laboratories for Materials Testing and Research
Centre for Reliability
Guenter Grossmann, Senior Engineer

8600 Duebendorf
Switzerland

Phone: xx41 1 823 4279
Fax : xx41 1 823 4054
mail: [log in to unmask]

>>> [log in to unmask] 05.06.2006 16:11:04 >>>
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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