The tracks used as an edge connector are gold coated to improve contact with the female connector: bare Cu oxidizes, and also wears out if they are inserted and removed repeatedly. Au cannot be applied directly to Cu, so electroless Ni + immersion Au (ENIG) is used.
Well, the question is: since Ni has good resistance to abrasion and oxidation, why are never edge tracks plated with Ni only? I don't think it's because of the lower resistivity of Au: with or without Au there are always the microns of Ni in the middle, practically no resistance. And female connector contacts are also Au coated.
Anybody knows? Thank you!
I am NOT answering my question. I am writing here just because I needed a place that is common to all contributions.
My real need was not exactly about edge connectors, but making printed contacts for a sliding switch, this will be to choose tuned circuits for a 'ham' receiver. I aim to make the construction easier for the DIY builder, that's why I looked forward to avoid the gold process, not because of cost but added complexity.
I am delighted to have been quickly and correctly informed in my very first tour into StackExchange. Thanks to everyone!