Please, don't start putting spec limits on subjective terms. A harsh
environment for the electronics in my desk top computer is mild for my car
and a stroll in the park for my tractor.
If you want to describe environments, use the measurable parameters that are
already widely in use, e.g.:
        Temperature             (degrees C)
        Relative Humidity       (%RH)
        Altitude                        (meters)
        Shake                   (vibration levels, excursion, frequency)
        Shock                   (g)
        Power                   (range, rate of variation, spikes)
        Susceptibility          (electric fields)
        Exposure to water       (drip, rain, submersion)
        Gasses                  (explosive, corrosive)
        Dust, dirt, salt
        More?
Any customer may want a different combination and level of these, but most
design engineers know what the sensible combinations are.
(and specs for local areas of a product are of no use to the end-user, he
wants to know what the complete product can withstand.)

Ahne
A-Laser,
(503)641-9428



-----Original Message-----
From:   TechNet [mailto:[log in to unmask]] On Behalf Of David Douthit
Sent:   Tuesday, December 28, 1999 22:13 PM
To:     [log in to unmask]
Subject:        [TN] Harsh Environments?

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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