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. 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