I agree with Joyce. I suspect you more likely have an under-etched copper condition that was not caught prior to plating. That is somewhat common (unfortunately). As Joyce stated, gold layers for ENIG and ENEPIG are extremely thin if deposited per their respective standards. For ENIG, the standard IPC-4553 or 4552, whichever one it is, the maximum thickness for gold is about 5 microINCHES. But an underetched condition typically is very rough around the edges, and when plated over it looks like "rough gold".  The process factors that typically go wrong to create this are several, and they are all listed in detail within IPC-9121, including pictures of the condition you describe. Else, it may not have been immersion-plated, but electrodeposited, which is not ENIG.
No self-respecting electronics manufacturing engineer would be caught without this standard. If you have it and understand most of what is in there, you are even more "dangerous"!  Fabricators will cower in fear as you approach.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo
Sent: Thursday, June 28, 2018 5:36 AM
To: [log in to unmask]
Subject: Re: [TN] Rough Gold causing plating shorts

immersion gold is ion exchange process (correct me if I am wrong).   
only very thin layer can be formed on the surface.  the roughness  
must be underlying layer or substrate plating issue... IMHO.  Not  
sure what actually the supplier of his was saying (it might be lost  
in communication).
The electroless Nickel, unless it is porous (with bubbles or P or  
additive clusters), it usually not rough either...Let me know if you  
guys observe something else in the past...
jk
On Jun 28, 2018, at 3:39 AM, FTL Quality wrote:

> Do you have some pictures to illustrate the issue?
>
> Thanks
>
> -----Original Message----- From: Wayne Showers
> Sent: Wednesday, June 27, 2018 7:57 PM
> To: [log in to unmask]
> Subject: [TN] Rough Gold causing plating shorts
>
> I need a favor in regard to rough gold (ENIG) causing plating  
> shorts.  I need a brief synopsis of which process or processes  
> typically go out of balance to cause this issue.
> Basis: My supplier is indicating electrical shorts attributable to  
> rough gold being the reason for their low lot yields on a rigid  
> flex. Unfortunately, I know enough to be dangerous but not  
> necessarily effective in this realm.