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March 2003

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 21 Mar 2003 11:45:36 +0200
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Ken

Once coated, I believe the only test likely to be revealing in the
relatively short term is the pressure cooker test.

Put some water in an autoclave or a domestic pressure cooker and suspend
the circuit to be tested well above the water level. Seal and bring to
the boil (~120 deg C). Leave for 24-48 hours, making sure the water
never boils dry.

Take out the circuit and check under 10 x magnification for vesication,
blistering or mealing. Any hygroscopic and potentially dangerous
residues trapped under the coating will be revealed.

A very simple and revealing test.

Brian

Bloomquist, Ken wrote:
> I have a question regarding a test for flux contamination on conformally
> coated boards.
>
> I know all about testing uncoated boards but was wondering if there are any
> tests for type UR coated boards?
>
> Does a temperature soak do any good at bringing problems to the surface?
>
> Does baking cause any remaining flux to become conductive?
>
> Does a humidity/temperature soak do any good?
>
> What were looking for is a parallel electrical path that might reduce the
> value of a small SMT resistor.
>
> Thanks in advance,
>
> KennyB
>
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