What makes you think a highly conductive powder is inert for electronics?
This.
Toner powder is a terrible idea.
Buy actual electronic potting compound and be done with this homebrew silliness.
I said to try toner because, among other reasons, one of its chief design characteristics is the high electrical resistance needed for electrostatic transfer. I’ve seen circuit boards packed with the stuff and it’s a complete PITA but not because it’s shorting. It builds up and cakes hard and then flies off in chips.
I also used to service equipment at a factory making metal wool products, mostly household dishwashing steel wool pads, some familiar brands with blue soap, but other things like bronze wool for rodent-proofing caulks and rubber: rats don’t like gnawing the long lasting bronze. Now THAT place was a nightmare for conductive fibers getting into everything.
I bow to your superior experience. Thanks for the corfection.
I am going to second @Francis_Vaughan and recommend a proper potting compound made for this purpose.
If the board is going to see any significant temperature swings you want a compound with a coefficient of thermal expansion that matches the PC board material or else you risk breaking connections on the board, especially if there are any SMD devices.
Good thinkin’
The device will be used in all temperatures that people work in, from 110º to -20º f.
You’re probably OK if you stick with a product that specifically says it is meant for use on printed circuit boards. The one that @Francis_Vaughan suggested is nice in that it is (1) specified for PC board protection and (2) is relatively inexpensive and available in small quantities.
Well,Marv, I am leaning in that direction.
Would something organic as simple as flour work?