Inge,
I was also surprised. We do a substantial amount of ENIG especially with the RoHS mandate. With all the alternative finishes available we've seen a mix of everything with lead free solder being at the forefront. Regarding everyone else's inquiries... Here's a little more information that may help identify the root cause. 
      The color of the "un-plated" pads are a charcoal/brown color.
      The nets that do not plate are random through out the parts as well as random in nature from pc to pc in our production panel.
      This order was pattern plated (tin used for etch resist) but in the past we have seen this on panel plated boards
           (dry film resist used  for etch resist) no tin used prior to mask.
      The via hole sizes are normally on the small size (.012 and smaller). This particular job has finished vias of .006 (drilled at ..010). 
      The board thickness is .062.  
      On all jobs the vias are covered with LPI mask.
      Not every job has this problem.
      We have not, at this point, x-sectioned any holes but will do so when we get the panels back.
 
I think I answered most questions that were asked. I really appreciate all the responses. It's quite interesting. I'm really glad to hear this has been seen else where and  prove I'm not going crazy. Now to isolate the problem and fix it.
Dan
>>> "Ingemar Hernefjord (KC/EMW)" <[log in to unmask]> 09/19/06 05:32AM >>>

I've seen all answers on your question. I'm surprised that ENIG has such
a low part of the total market, just some 3%, while HASL has more than
60%. See tart statistics which I send to Steve's wall. The statistics is
from McMurdy.
Inge


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Skweres
Sent: den 18 september 2006 23:54
To: [log in to unmask] 
Subject: [TN] ENIG

We have, at times, had an outside plating service have difficulties with
plating of ENIG on our bare boards. The interesting anomaly we have
encountered is lack of plating on certain pads. They tell us there is
something on the surface of the pads but when they return the panels to
us we micro etch (copper looks beautiful) and all pads look similar in
appearance. We even took a panel and coated immersion white tin with out
problems. This tells me that there isn't any thing on the surface of the
copper. There is one thing I did leave out. The pads that aren't taking
ENIG all happen to be in the same net. Has anyone encountered this? It's
almost like there is a charge being created in certain nets not allowing
the ion exchange to happen. Could it be entrapped chemistry within vias?
Any help and/or direction would be greatly appreciated.
Thanks,


Dan Skweres
Engineering Manager
Bartlett Manufacturing
Phone:847-639-2102 Ext.#230
Fax:847-639-8838


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