effect of humidity on a PCBs

[Emam]

Hello,

Thank you for helping me.

I have a PCB which works very good in normal conditions (20°C, low humidity).
For some reasons I should use this PCB in a thermal chamber with relatively high degree of humidity.
I figured out that some fucntions are not performed correctly.

Can someone tell me what is the effect of humidity on a PCB?
How can we avoid it?

Thank you and bests regards

 

[Colin Mitchell]

You could have dirt between the tracks and this is causing leakage.

 

[shrtrnd]

Colin Mitchell's observation is a likely cause. There are a lot of other factors that can cause this:
Compositon of the PCB board itself (does it absorb moisture), component susceptability to humidity, actual humidity causing moisture on the board that affects conductivity of signals.
This is the reason why you should test your boards under different environmental conditions to ensure that if you sell a product, it works whether its used in
Finland (cold), Great Britian (wet), or the Middle East (hot and dry).
The number of environmental factors that can cause electronic malfunctions are many.
I know your issue here is in determining why the board malfunctions in high humidity.
You need to check the spec sheets on your board (the board and components) to ensure compatibility with high humidity operation, THEN look at the effects of moisture on the board operation.
Are you using components from quality manufacturers, or inexpensive cut-rate manufacturers?
Are the components sealed from humidity.
If you lack time or resources, try applying a conformal coating to the board, and see if that seals it from environmental (humidity) factors that are interferring with proper circuit operation.

 

[Colin Mitchell]

You may also have a section that has very high impedance.

 

[Emam]

Thank you,
Actually I have found a type of spray (varnish) that I can put on my PCB.
It is a tropicalization varnish.
So I will test it afterwards. I hope it will work better.

Bests regards