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Wed, 07 Aug 1996 08:10:44 -0400 |
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by ipc.org (Smail3.1.28.1 #2)
id m0uo7G5-0000ExC; Wed, 7 Aug 96 06:58 CDT |
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| From [log in to unmask] Wed Aug 7 08: |
42:04 1996 |
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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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