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\$ – Stefan Wyss 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\$ – Stefan Wyss 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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