Phenolic means Bakelite or similar in the context of PCB, it refers to the resin composition.
You can use a sharp knife to remove the residue, if it has not caused corrosion like some fluxes I would leave it alone.
You can use a sharp knife to remove the residue, if it has not caused corrosion like some fluxes I would leave it alone.
Back in the day (circa 1970) we used to 'tropicalise' our pcboards after building and testing. They were for harsh environment conditions where high humidity and heat would corrode lesser boards.
Mainly for Power Stations and oil refineries, Ironbridge, Fawley etc.
Mainly for Power Stations and oil refineries, Ironbridge, Fawley etc.
Is the stuff only on the PCB or is it also on the components and their top surfaces? If it’s only on the PCB it’s probably flux as has been said.
'Tropicalise' would mean something like dipping the boards after assembly and testing in a protective solution, and that means being a bit of a historian to find out what was used originally.
If it is not causing trouble, leave well enough alone.
If it is not causing trouble, leave well enough alone.
Yes it's flux residue (very usual in consumer electronics at the time), and conformal coating was to prevent moisture getting to the sensitive electrics, and in my experience (because of need, application and rework costs), was mainly confined to defence systems.
Just thinking about it, out of all the test equipment I own and that has passed over my bench, probably hundreds of items, I can only remember one single item where the boards were conformal coated. It was a Fluke voltage reference, probably built for the military. AFAIK, nothing else, including high precision stuff, has been coated. I've used the Krylon on some of my own boards, but you need to be aware of the level of cleaning necessary before doing this. Solvents, detergents and good DI water, or the board is better off left uncoated.
Thanks folks. I feel confident now that this was just flux. Feel free to carry on the discussion as it's all very interesting. You've all been very helpful!