Which, nickel plating has one edge-case, poor high frequency performance -- it is magnetic. I would recommend against using it in a switching converter, say (10s of kHz up). For anything near mains frequency, this is basically irrelevant. ![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif.pagespeed.ce._JElyJQqdB.gif)
Tens of kHz? I thought this was an RF--and I mean GHz--issue? I hadn't contemplated it being a problem at that level. How do ENIG PCBs not have problems?
It's most sensitive at RF, yes. Like a waveguide plated with nickel, and not enough silver over top of it, will absolutely kill the Q. All of the current flow is in the plating.
Down in the MHz, the effect on Q will be minor, because the element's impedance is small compared to circuit impedances. But the skin depth will still be significant: at 1MHz, the skin depth in copper is already small at ~70um, but it's over 10 times smaller in nickel -- and a typical plating thickness is around 12um, so that ain't too great!
Down at 50kHz, it'll easily penetrate the plating, but heating may still be unusually (even objectionably?) high.
A reminder that we mainly use bus bars, in high power converters, because of heat dissipation -- electrical conduction is almost entirely a surface phenomenon, we just use bulk metal parts because they are strong, and effectively carry heat away from that surface.
Heh, wouldn't be surprised if the effect is also lessened somewhat, at high currents, due to sheer saturation. The effect of saturation is to locally increase skin depth.
As for PCBs, ENIG is only over the pads -- SMOBC means traces are bare copper covered by dielectric, no problem there. The pads are slathered in solder, and current flows up the side, much of the nickel area is shielded by the solder blob on top, or the component lead thereupon.
Or in thru holes, the inside is shielded and current flows on the outer surface (the FR-4 side), same idea. So it works out alright for PCBs.
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)
Tim