In the early days of ENiG we saw this condition. The condition presented itself on edge tabs where two or three of the same tabs in each PWB were not accepting nickel and they were part of the same net.  It usually the same edge tabs in each board and the pads were dark. This was attributed to the bath producing, or inducing, spurious electrical potentials between different nets.  Even though this is an electroless system there may be isolated nets that have current induced through a chemical action.  The supplier of the bath resolved the problem and the resolution was not shared as the chemistry was proprietary.

I would connect the offending net to an adjacent net and see if the problem grew or reduced.  Possibly you could solder a jumper and cover the interconnections with plater's tape. It would be a great experiment and I hope you would share the results.

Paul Reid
PWB Interconnect Solutions

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dan Skweres
Sent: Monday, September 18, 2006 5:54 PM
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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