Here is ENIG fact that is not widely known at the moment but which some might
I could not understand why I get better TDR and insertion loss results from
solder-mask covered microstrip transmission lines than from otherwise identical
microstrips on the same substrate with soldermask removed and, therefore,
covered with ENIG.
Gold can't be bad, right? As it turns out, even gold coin has two sides to it.
I have found that Shlepnev and McMorrow conducted extensive research and
published data, some of which is presented here
In essence, it's not the "G" that is the problem - it is the "N".
Immersion Gold layer is not thick enough to contain whole of the skin effect
layer (even towards 100GHz) and as signal frequency increases most of the
signal ends up travelling through Nickel.
As Shlepnev commented "Nickel is the most mysterious metal in electronics." It
has significant effect on insertion loss and risetime degradation.
"Significant effect" is posh for "bad."
Some mass PCB manufacturers have been known to apply ENIG before soldermasking.
This causes even more high speed/frequency problems because all of the copper
on the outside layers will have Nickel over it - exposed or not.
Probably not a problem for majority of ENIG users but could cause a headache or
two for unsuspecting.
> Date: Thu, 22 Feb 2018 19:02:25 +0000
> From: Mark Sims <hol...@hotmail.com>
> Yes, have the board done with ENIG gold. It typically adds around $15 per
> run of boards. I do all my boards with ENIG gold... if for no other reason
> than the gold color makes it very easy to determine when your solder paste
> properly covers the pads.
> And, as Charles mentioned, the quality and thickness of the gold can vary
> depending upon the board house. I have used gojgo.com for a lot of boards.
> They do very good, quick work, are well priced, and they seem to have the
> best gold finish.
> Hard gold finish is VERY expensive these days. I've been quoted $250+ for
> setup charges and per-board costs of over $25.
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