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How do I determine the minimum and maximum humidity allowed for a PCB mounted with IC's? (Without having to use some sort of humidity chamber) EDIT: During operation.

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  • \$\begingroup\$ For the ICs you should find the humidity tolerance in the datasheet \$\endgroup\$
    – clabacchio
    Mar 23 '12 at 9:37
  • \$\begingroup\$ Ah okay, does this also apply when they are mounted? (I mean creepage distance ect.) \$\endgroup\$
    – JakobJ
    Mar 23 '12 at 9:52
  • \$\begingroup\$ Hmmm. Can't seem to find the humidity defined in any of the datasheets.... \$\endgroup\$
    – JakobJ
    Mar 23 '12 at 9:55
  • \$\begingroup\$ I don't know your parts, but if you look in this datasheet there is a section dedicated to moisture sensitivity....and also in this \$\endgroup\$
    – clabacchio
    Mar 23 '12 at 10:04
  • \$\begingroup\$ Hmmm. It just says something about baking ect., which I think is related to production. I need to know operating humidity, sorry for not being clear on that. \$\endgroup\$
    – JakobJ
    Mar 23 '12 at 10:12
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While there are standards for humidity testing, much will depend on your application. High humidity levels will cause leakage currents between nets. For very low power boards this may influence the circuit's operation, while for power boards (currents in the amperes range) the effect may be negligible.

Note that humidity tests are often done with a salt spray. This not only increases conductivity, but also has a corrosive effect. The salt may also deposit on small mechanical parts which may cause them to get stuck.

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  • \$\begingroup\$ +1 also for salt spray test: I may need to use it :) \$\endgroup\$
    – clabacchio
    Mar 23 '12 at 10:46
  • \$\begingroup\$ @clabacchio - You'll definitely need it if your device will be used near the seaside or on sea. \$\endgroup\$
    – stevenvh
    Mar 23 '12 at 10:47
  • \$\begingroup\$ I don't plan that, but I may need to simulate some limit conditions, and this (even though somehow destructive) may help (I have a question about faults - would you like to receive some upvotes? :P) \$\endgroup\$
    – clabacchio
    Mar 23 '12 at 10:50
  • \$\begingroup\$ Hmmm... I just need to know the boundaries \$\endgroup\$
    – JakobJ
    Mar 23 '12 at 12:17
  • \$\begingroup\$ There is no way to tell the boundaries without testing, and testing will only give you a statistical approximation of the boundary. Minimum humidity is irrelevant. You must either test for the maximum humidity or seal your electronics from changes in humidity (which itself comes with a host of other problems eg heat dissipation). \$\endgroup\$
    – spearson
    Mar 23 '12 at 13:47

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