on Mon, 07 Aug 95 09:26:00 GMT, Maurice Dore * <[log in to unmask]> asked:

>I have a mixed technology board - bottom side smt  power supply which is 
>failing. I suspect that the failure is due to the unreliability of 
>decoupling ceramic caps.
>On reworking the caps they tend to crack.
>I have subjected them to thermal shock tests and they seem to retain their 
> integrity.
>Any suggestions? Is it a vendor problem (which seems unlikely) only?
>Thanks in advance.

Are these chip caps?  Is a soldering iron being used for the re-work?
Ceramic chip caps are suceptible to fracturing from the thermal stress from
soldering with an iron.  Heating one end induces a differential mechanical
stress in the cap which is relieved by fracturing in the cermaic.  The
failure may be immediate or may only show up with a DWV electrical test.

-Gregg Klawson
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