Finishing with NiAu is really interesting alternative for non-lead coating. NiAu is better than other finishing
because it's more durable (very long period of storage).
NiAu is most used for soldering in higher temperatures. In such layer, thickness of nickel is around 5µm,
gold layer around 0,1-0,2µm.
Unfortunately it is the most expensive method of non-lead covering.