You could use the table in IPC-SM-785 which lists worst case use environments.
 Step outside that range for the class of product and you could call that
harsh.  I believe Engelmaier is a big proponent of this document.

The work done with COTS (Commercial Off The Shelf) has some information also.
I have a chart that shows temp-humidity curves for the U.S. , world, and mil
specs.

Glenn

David Douthit <[log in to unmask]> 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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