with all the good answer you get.  there are good reason for Ni to be  
there.  If you use Au as solder mask - used in old days as cheap  
process, be careful about reliability - any un-dissolved gold might  
give you a headache cause preferential corrosion of exposed Cu if  
solder is not fully covered - of course, depend upon your application  
environment.  Ask your designer what is the intended usage (better  
not be pulp and paper, or gas/oil, any military application).  IMHO.  
my 1.4 cents.
jk
On Jan 27, 2020, at 5:32 PM, Steve Smith wrote:

> Hi All,
>
> I was asked today if nickel is really needed under the gold for  
> plating on copper. I have understood it that the layer of nickel  
> provides a mechanical backing for the gold layer and that it was  
> also needed for the soldering process. Is this correct and is it  
> the only reason it is used?
>
>
> My regards,
>
> Steve Smith
> Design Drafting Group Manager
> Staco Energy Products
>
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