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September 2006

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Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Tue, 19 Sep 2006 08:47:10 -0400
Content-Type:
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If my memory is correct I think Nick Biunno (Hadco) presented a paper a
few years ago at an IPC meeting indicating that induced charge on
various nets would cause "skip plating" and "Black Pad Failures".  One
of the suggestions was to have all nets connected to an edge plated
ground so that were wasn't a charge and then route off the edge plating
after plating.  At the time we also joked about making the boards with
all isolated pads (i.e., no nets) and then throwing the boards away
after plating because there was no circuitry.


Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Tuesday, September 19, 2006 7:27 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG

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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