Electronic – Cleaning circuit boards for high impedance

high-impedancepcb

Colleagues,

EEG signals typically have high source impedance. Amplifiers in the EEG circuits have high input impedance too. The signal is DC-coupled to the amplifier.

One problem is that leakages across the surface of the board can distort the signal. Guard rings help prevent that. Contamination on the PCB increase leakages. So, I would like to clean the contamination. Could anyone recommend a procedure for that and what solvents to use?

The board is FR4 with solder mask and silk screen. SMT components.

Cleaning will be done in an industrial facility, which is equipped for handling and disposing solvents. We have fume hoods.

UPDATE: Just added a bounty to this question. What I'd like to get is a fairly detailed procedure. Just throwing names of chemicals at this question will not count.

UPDATE: Bounty period had expired. Still looking for the procedure. Didn't get answers I could award the bounty to.
The tips which got posted so far might be useful for somebody in the future. More tips about board cleaning here (parallel thread on another forum).

UPDATE: Found more systematic insight into PCB cleaning (here and here).

Best Answer

This may be deemed a comment more than an answer, but just as important as which solvent (if any) to use -- we wash our boards with critical circuitry in RO (reverse-osmosis) water because it is free of salts + other contaminants -- make sure the boards are dried thoroughly.

Surface-mount chips often have a very thin gap between the chip and the board which can act as a capillary to retain water for days. So drying thoroughly is important. I'm not sure what works best, but in one case we put our circuit boards in a thermal chamber at a high temperature (probably 60-80 C; I forget) and low humidity for a day to drive off the water.