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I have to design a electronics device that is specified for environmental operating conditions of 0°C to 60°C with 5% to 95% relative humidity (non condensing).

I think the temperature part should be covered with commercial component selection (0°-70° operating temp.), but what about the humidity requirement?

  • Is this humidity specification hard to achieve?
  • Do I need to protect the PCBA with conformal coating?
  • What are the general recommendations for different humidity specifications?

Of course I will need to perform some tests in the climate chamber. But I think there should exist some general guidelines for the design regarding humidity?

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    \$\begingroup\$ What do you mean by non condensing? I don't think conformal coating would be adequate. \$\endgroup\$
    – K H
    Feb 8 at 7:50
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    \$\begingroup\$ I have often seen this "non condensing" addition to relative humidity specifications. I think it means that when you perform tests in the climate chamber, you need to carefully control the climate in order not to reach the dew point. \$\endgroup\$ Feb 8 at 7:54
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    \$\begingroup\$ If you have high impedance analogue and sensitive circuits, at around 0 degC, water will collect on PCB surfaces if there's humidity. So, I'd be tempted to ensure it works down to -10 degC and see what happens when you gradually warm it up through 0 degC. \$\endgroup\$
    – Andy aka
    Feb 8 at 8:53
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    \$\begingroup\$ @Andyaka Thanks for your comment. I have no high impedance analogue and sensitive circuits. It is mainly a digital device. Why do you think that 0°C will be special in term of humidity? When I look at a psychrometric chart, I see no differences to other other temp. ranges. \$\endgroup\$ Feb 8 at 9:13
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    \$\begingroup\$ @StefanWyss - ice that forms on PCB surfaces at below 0 degC starts to melt and becomes more conductive as temperature passes positively through 0 degC and I've had problems with that before that have been cured by varnish/lacquer. \$\endgroup\$
    – Andy aka
    Feb 8 at 9:48
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For an electronic circuit, that specification is almost completely "bog standard". You likely don't have to do anything special to meet it.

Examples of things that are "non-standard" that you might have to take into account:

  1. something that measures a field, capacitive proximity sensing, for instance, since humidity changes the permittivity of the air

  2. something that has a "diffusion interface"--lots of biochemical sensors have a layer that the active species needs to cross and that can be sensitive to humidity

  3. something that has a weird, non-standard package that doesn't hermetically seal the chip

These are unusual unless you're in a specific domain, and you generally know if you are.

Normally where people get burned is that their boards get put in a "condensing" environment even though everything is specified as "non-condensing". But that's not a design problem so much as a specifications issue.

tl;dr Don't sweat it and just do your design.

Good luck.

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