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June 2001

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 28 Jun 2001 12:59:16 +0300
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Jim

It depends a) on the service conditions and b) the required reliability,
as well as the factors mentioned by others. If you have a piece of, say,
oil-prospecting instrumentation that fails in the middle of the
Amazonian jungle and it requires 3 days of pirogue transport to the
nearest helipad, 1 day to get it to an international airport, 15 days
held up in customs, 2 days to get it back to you, 7 days to diagnose,
repair the fault and test it and then the reverse transport procedure,
just because you chose not to clean it, then it isn't going to do your
company's reputation any good. My short answer is that if the goods are
going to work under poor climatic conditions and you cannot afford a
failure in the field, then you may start to believe that not cleaning
could be inappropriate. That having been said, conformally coating over
flux residues is ALWAYS potentially harmful to the health of a product
and anyone who does it without a full risk assessment, based on a full
series of both field and laboratory tests, must do so at his own risk.
Even so, you cannot eliminate variables which can affect the results,
such as a batch of bare boards which arrive in your plant with more
hygroscopic contaminants on the surface than is usually the case and
more than when you did the risk assessment.

At your risk and perils...

Brian

"West, Jim" wrote:
>
> Hi,
>
> Do boards have to be cleaned before you apply conformal coating?  Does it
> depend on what type of flux is used?  Example would be no-clean flux, you
> can apply conformal coating over it right?
>
> Thanks,
> Jim
>
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