I'm investigating ways of making a capacitive sensor that will operate in very moist environments, potentially even submerged. What I need is a way to make some conductive plates in a specific arrangement that are electrically isolated from each other and from the environment.
One of the options I'm looking at is to use a PCB. I would put the plates in the proper arrangement on both sides of an FR4 board using polygon pours and then cover the whole thing with soldermask. There would be no components on the PCB at all. The entire board, except for the external contacts (outside of the moist/wet sample), will be soldermasked.
Questions:
- Will the soldermask block the moisture effectively, preventing the plates from forming an electrical contact even in the case of prolonged submersion?
- Will the FR4 remain dry? Or will it soak up water, leading to an electrical contact between the plates?
- If this is not the case, is there anything I can treat the board with to make it waterproof?
Let's say for the sake of argument that I will be using seeedstudio's Fusion PCB service.
Best Answer
Yes FR-4 itself is waterproof ("near zero water absorption" according to Wikipedia).