Chinese CK12 capsules and humidity

Recently I have had some problems with a microphone with a Chinese CK12 capsule.
The capsule as such sounds fine (in fact the same as the MP capsules), but when the humidity get higher, the infamous 'noise' begins...
As far as I know, the CK12 (edge terminated) capsules are usually less sensitive for high humidity.
What could be the reason for this humidity problem and how can this be avoided?
I noticed that the connection to the backplate(s) is very close to the brass ring connected to the membrane(s).
Could this be the weakest point?
As a test, I covered the backplate connection with a thin layer of epoxy cement, and as far as I have noticed so far, this improved the situation.
(In fact I didn't have any humidity problems after this at all.)
Is this a common problem? Interested in experiences from other users!

Could there be fine "debris" (like brass filings) behind the membrane?
A slight expansion due to humidity might cause problems in this case?
Wild guess, only based on some earlier (debris) reports.

RuudNL said:

As a test, I covered the backplate connection with a thin layer of epoxy cement, and as far as I have noticed so far, this improved the situation.
(In fact I didn't have any humidity problems after this at all.)
Is this a common problem? Interested in experiences from other users!

Click to expand...

Yes, to avoid humidity problems in CK12 the connection screw and lug for the backplate MUST be covered with low moisture absorption insulator. Acrylic nail polish will work. For best noise performance you need to insulate every Hi Z component connection and make sure you run the capsule leads with lowest parasitic capacitance, possible. In our microphones we insulate even gate of the jfet and all associated parts, as well. The diaphragm should be grounded.

Best, M

Thanks Marik! That confirms my thoughts.