Agree, Anil definitely speaks from experience, having here one fellow ex
TATA in Bombay,
the horror stories (perfect antistatic environment as the condensations runs
from tables) are real .
Disagree, Brian , getting puzzled how the hell shall i achieve this high
reliability with this "unwashed" SBGA (2x2 inches square just about) sitting
some .5mm above the board, on my desk .
Hmm, lucky me on no clean, don't envy you the washing machines .
From my limited view i'd say the times of cleaning shall change this
millenium
cu paul
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Saturday, 1 January 2000 18:19
To: [log in to unmask]
Subject: Re: [TN] Harsh Environments?
Anil
Yes! I agree that this does not help. However, a French client of mine has
traced
wind-borne sea salt inland under some weather conditions, so this factor may
be more
serious than is commonly thought.
The strategic computer room of a UK Royal Navy ship, placed right in the
interior of
the structure, is equipped with the most sophisticated air
conditioning/filtering. One
such ship, in dock for refitting, had a fitter wedge the door open for a job
he was
doing where space was limited, for a couple of days during what was reported
as winds
of 3 -4 Beaufort. I was informed that malfunctioning of some equipment
occurred and,
as a safety measure, the totality of the equipment was replaced. This was
reported to
me by an ex-Ministry of Defence employee.
Even worse is salt scattered on roads for ice prevention. The wheels of
passing
vehicles throw up a mist of concentrated brine which spreads everywhere.
I reported these phenomena in my book published in 1986.
Brian
Anil Kher wrote:
> 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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