Brain,
correct me if I am wrong. Environmental exposure classification for
electronic packaging are well defined based on my knowledge (can't remember
the document name...it has been used so much..almost a "grandfather" clause).
1.0 year round filtered air conditioning with humidity control (I believe it
is the old mainframe room, like your ship room)
1.1 year round air conditioning (non-filtered) with humidity control
1.2 air conditioning (non-year-round) with no humidity control (possibly,
most office environment in North America)
1.3 no air conditioning or humidity control with normal heating and
ventilation (possibly for some developing country office)
2.0 with normal ventilation but uncontrolled heating and humidity
2.1 year round exposure to heat, cold, humidity, moisture, industrial
pollutants, and fluids (pulp and paper industry, for example)
3.0 outdoor environment with moisture, salt spray, and weathering (automobile?)
4.0 aircraft environment (uncontrolled)
Look like your control computer is designed based on 1.0, not 3.0. I would
not surprise it failed. Check the Statement of work (SOW) or critical item
design (CID) of the computer. If there is a requirement for the cross
classess design: e.g. performance 99% under class 1.0 and repair and
overhaul (R&O) 1% under class 3.0 should be spelled out under the
performance requirement. (or, design using high level classification, which
I prefer=define the worst environment)... Few month ago, i believe there is
a discussion about the commercial computer failed at mil environment, i
believe it is the same school of thoughts = without understanding the design
limitation of the unit (a proper designed laptop should have class 2 in
mind, but, in reality, it is not always ture...With warranttee of 1 year,
extendable to 3 years and possible cheap replacement rather than repair for
non-critical usage, it is cost effective for mass production part= design
for life cycle need is fulfilled). It is scary for something like the
"strategic computer" event...(I am sure nothing happened!)
my 2 cents.
jk
At 09:19 AM 1/1/00 +0200, you wrote:
>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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