On 9/24/20 10:29, John Robertson wrote:

Hi Gianpiero,

Not sure what you mean by "I will try to pass a flux for contacts on the
connectors ". What I would recommend is that you try to polish the pins
or PCB traces for the connectors using a very mild abrasive that won't
damage the gold flashing. Also, watch out for static electricity when
polishing any PCB connectors!

By mild abrasive, something like a pencil eraser. Not sandpaper and
never steel wool. Caig De-Ox-It on a paper towel or Q-tip also works well.

If by flux you mean soldering flux, not a good idea. Flux assists solder
flow, it isn't a contact cleaner or tarnish remover. Many fluxes will
damage electronics if not removed after soldering.