It is called extraneous plating or background plating. 
a) What could be the cause of this?
 Uaually caused by over-catalyst during ENIG process.
b) Any detrimental effect in reliability?
 Sure, it violates the minimum spacing (if luckily without creating hard shorts)
c) Any IPC spec govern this issue?
You can find it in IPC-4552 section 3. 


Best Regards,

Jason Zhao
Zhao PCB International
US 510-468-4412
China 137-74692180

--- On Wed, 9/17/08, Yap, Stella (SMI) <[log in to unmask]> wrote:

From: Yap, Stella (SMI) <[log in to unmask]>
Subject: [TGA] Ni plating on bare laminate
To: [log in to unmask]
Date: Wednesday, September 17, 2008, 6:38 AM



Hi all,
 
 
A PCB supplier submitted the PCB with Nickel plating outside the copper pads.  
 
a) What could be the cause of this?
 
b) Any detrimental effect in reliability?
 
c) Any IPC spec govern this issue?
 
 
 
Thanks,
Stella