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March 2003

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Subject:
From:
David Douthit <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 20 Mar 2003 19:25:40 -0700
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Kenny,

The short answer is a high humidity and temperature cycle test.
The long answer includes the Tg of the coating material, expected field environmental conditions,
warranty times, and methods of measuring resistance.

The use of high humidity must involve temperatures above the Tg of the coating with long soak times (>2hrs).
Lowering of the temperature to about 10 to 15 degrees C and soaking creates liquid water films above 80% Rh.

Takes measurements in both directions. Are you going to use a standard ohm meter (bad idea, not enough voltage). The
best method is
to apply the normal operating voltage and take measurements (voltage drop, current flow).

Readings will vary with time and temperature.

I hope this helps.

David A. Douthit
Manager
LoCan LLC

"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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