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Reply To: | TechNet Mail Forum. |
Date: | Mon, 5 Jan 1998 07:35:58 EST |
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In a message dated 98-01-04 21:24:44 EST, you write:
> I have a question about some SIR results that I got. I made a few
> consecutive SIR tests on a coupon and found that the ohm reading kept
> on increasing the longer I left the coupon inside the humidity chamber
> (35C, 85%RH). My understanding is that the reading should normally
> decrease with the elapsed time, indicating the lowering of surface
> resistance, right? I ran the coupon for 1 week, at first the ohm
> reading looked OK (~2-5e11 ohm), but at the end of the week the
> reading esceeded 1e12 ohm. I am confused.
>
What you are seeing is fairly common. SIR readings can decrease over time if
you have metal migration and corrosion. Normally, when the readings increase,
it means that you have / had some other surface contaminant that is / was
volatilized during the test. A polyglycol is one such material. The levels
you note would be considered as acceptable by most standards, provided the
measurements were taken correctly.
Doug Pauls
CSL
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