The nickel-gold plating-surface is abrasion-resistant and corrosion free and therefore it is often used for components with increased mechanical stress (male).
The resist coated circuit board is first provided with an electroplated nickel layer> 3μm as a diffusion barrier (preventing that the subsequent gold gradually "disappears" by diffusion). After the nickel plating followes by the actual galvanic golding. Gold layer between > 0.4μm to 2μm are deposited. This depends of the purpose. For plugs the number of jacking cycles is applied.
0.4μm 20 jacking cycles
0.7μm, 50 jacking cycles
1.3μm, 200 jacking cycles
2.0μm, 500 jacking cycles
With additions such as cobalt etc. (will also "Hard Gold" called) th egold layer can be deposited without a nickel diffusion barrier.