I had also customer with the same case (the EMS is blaming the ENIG).
But I had also cases with real black pads issues.
Just to remind you Werner Engelmaier opinion (against ENIG).
Reuven
נשלח מה-iPhone שלי

ב-4 באוג 2011, בשעה 17:16, Pete <[log in to unmask]> כתב/ה:

> I have a similar interest in your problem, but for a different reason.
> 
> We have used ENiG from the start of the RoHS changeover, and have never had an ENiG problem.  Very careful PWB vendor certification has saved us lots of $$$.  Until recently we have had a captive assembly shop, which was admittedly weak.  The only "ENiG" problem we ever had was their difficulty in learning how to solder BGAs.  That would have been a problem with any finish.  Once they learned, we've been fine.
> 
> But here's the reason for my interest.  I just minutes ago finished reading an analysis on "black pad", which showed no black pad, just bad soldering.  Where ENiG caused the problem is that our new contract manufacturer had a quick excuse for his problem.  We lost a few weeks because they couldn't form an IMC, and right away blamed the ENiG.  
> 
> I have trusted PWB vendors I've used for many years with no issues.  But having some sort of incoming test to give the CM the same confidence might only prove what we already know, but could eliminate the time lost to blaming ENiG.
> 
> ENiG doesn't kill boards, processes do.
> 
> Pete
> 
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