David
Sorry, I'm not with you on this one. 20 - 25°C/40-80% RH is a perfectly normal
office-type environment. In my view, a mildly harsh environment starts at about 35°C
XOR a RH > 80% or a harsh one at 30°C AND > 75% RH. Where I live, we have summer temps
up to 47°C with low RH and our car electronics (even radio and window-winders) perform
normally after the car has been sitting in the sun and you cannot touch anything
inside, it is so hot. Last night, in midwinter, the temp dropped to 13°C and there was
an equivalent dew point, indicating 100% RH, with c. 1 mm of precipitation in the form
of condensing dew. Again, external electronics worked fine, including cheap movement
detectors. I cannot be persuaded that either of these conditions are really "harsh", so
much as normal.
The ionic contamination is not part of the environment and a cut and dried figire of
1,5 µg/cm2 eq. NaCl is meaningless without knowing the applications, type of circuitry
etc. In some cases, with low voltage gradients, this level would be perfectly safe even
at 80°C/90% RH. On some HDIS circuits with high voltage gradients, even 1/10 this level
may be dangerous, provoking something akin to Doug Paul's arc welder.
I honestly do not believe one can be categorical about this kind of thing. Perhaps you
would like to expound further as to your reasoning????
Have a good pre-millennial year
Brian
David Douthit wrote:
> Technetters,
>
> I would like some expert opinions on what constitutes a "harsh
> environment".
> In order to stimulate some debate the following is one proposed
> definition.
>
> "Due to the highly competitive nature of the electronics industry and
> costs of coating the issue of whether coating is required or not can
> become a hotly debated topic. The primary issue is "What is a harsh
> environment?".
>
> The following general rules can be considered as the boundary line
> condition for a "harsh environment". There are three minimum conditions
> which must exist in the localized area of the circuitry at the same time
> with or without power applied:
> 1. A relative humidity of 60% or higher.
> 2. Temperatures above 0 degrees C.
> 3. The deposition of ionic contaminates on the circuitry surface which
> will exceed 1.5ug
> of NaCl or its' equivalent per square cm during the expected
> lifetime of the product.
>
> Consideration of these conditions must also include shipping, storage,
> and handling of the product. These conditions are a reference point and
> exceptions are possible. Researching these environments are required to
> determine if these conditions exist."
>
> Thank you for your time.
>
> D. A. Douthit
>
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