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This sounds very similar to a process I've used for removing acrylic conformal coating (Humiseal 1B31 & 1B73).

I agree with what Charles already said 100%. In addition to dissolving the silkscreen printing (argh!) you may see the RTV get an attacked.

As with any manual operation, success will depend on goal-oriented workers. The process goal should be to completely remove the coating as quickly as possible. Duh - that would costs them less money to do and you get the card sooner. A single soak to strip the coating can take a very long time to work. How long does your OEM expect the process to take? Using an appropriate brush to manually remove softened coating can speed things up. We also used several (3 - 4) pans in a cascade wash - start with the dirtiest solution first and keep transferring to cleaner ones. I'd also want to know, how many assemblies they expect to clean before replenishing a bath? (I've seen assemblies soaking in totally loaded solutions, a huge ring of conformal coating surrounding the bath and the assembly workers are "stuck" because the coating isn't coming off.) Your OEM may want to try using a UV light as an in-process check for coating residue before the final clean - especially electrical contacts. I needed a forceful spray (something like 15 - 30 psi, 0.5 gallon/hour) to get stripping solution under components and flush the coating out. They'd want to do a spray process in a fume hood because conformal coating/stripper solution doesn't taste good - trust me. And as you know, the Omega meter test won't be valid unless the alcohol can dissolve any remaining stripper residue into solution.

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Folks, I am seeking technical help on the pros/cons of removing Humiseal Type 1A33 conformal coating (MIL Spec Type UR) using Humiseal 1063 Stripper Solvent, or any other solvent that can remove the coating by dipping. We are returning boards from the field for a significant amount of rework where removal of coating by conventional means such as by soldering iron or spot application of solvents is not practical. The boards are FR4 base material (0.063 to 0.125 inch thick) with all parts being plated-thru-hole military specification parts. There are parts such as connectors and numerous Integrated Circuit sockets where the stripper material could get into. There are also a significant number of teflon insulated stranded wire jumpers that are fastened to the board using RTV covered over with conformal coating. The OEM plans on dipping the complete board in a pan of Humiseal 1063 liquid and leaving it sit till the coating is dissolved. Cleaning will then be done using alcohol with DI water applied manually followed by automatic cleaning via in-line cleaner using solvent and DI water. Omega Meter type ionic test will then be done on sample basis to verify the ionic contamination has been removed (Humiseal 1063 stripper is highly conductive).

Has anyone out there removed conformal coating using Humiseal 1063 stripper or other solvent dipping process. If so, please advise if you found the process technically acceptable, and please provide specific process details, including the post cleaning method used. I would appreciate an answer as soon as possible.Thanks.

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Bechtel Plant Machinery Inc.