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Date: | Fri, 21 Jun 96 10:13:18 MST |
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Hi Fred,
I will keep it short, and only reply to one of the topics...
>SMT Components on the Solder-side of a PWB...
The one issue that I haven't seen anyone f/b to you yet is
utilizing 1206 0.1 uF caps on the solder-side of a PWB that
will be processed using Wave-Flow soldering process.
We have had many failures in previous years with bottom
mounted .1/1206 caps, where they have been fracturing from
the heat cycling of the wave solder. After extensive
cross-sectioning, and intense Vendor work, we found that the
massive layer count in a .1/1206 (& sometimes an 0805) was
the Culprit. Just too much packed into a small area.
These problems were solved by either reducing the values to
a .01 or a .047uF cap, or by duplicating caps where you
still needed the higher capacitance.
I know that we have since discovered that most vendors have
resolved these issues with their discretes, but we decided
it was much safer to design away from this value where
possible. This reduces the chance of a low quality vendor
being selected that may still have potentially poor part
integrity.
hope this helps...
Les Beller
EchoStar
"DISH Network...
...Where everthing comes on a dish"
([log in to unmask])
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