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December 1999

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Subject:
From:
Anil Kher <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 30 Dec 1999 16:16:25 +0530
Content-Type:
text/plain
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text/plain (134 lines)
Upto 1 km inland of coastal areas and during monsoon there is 50 ppm of salt
in the aerosol owing to heavy surf / winds. This tends to enter the
electronic instrument chasis and can condense at dew point on the PWB.
This environment would be HARSH.
Anil Kher
----- Original Message -----
From: Brian Ellis <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 29, 1999 12:47 PM
Subject: Re: [TN] Harsh Environments?


> 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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