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September 2006

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Subject:
From:
Franklin D Asbell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Franklin D Asbell <[log in to unmask]>
Date:
Mon, 18 Sep 2006 19:13:48 -0500
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I've witnessed sporadic poor covered pads but never even considered
verifying their connection via traces to the varied pads.

Typical cause in the majority I observed were poor tin strip/poor predip
(75% of observed) and poor resist develop (15% of observed) with the
remaining undetermined.

Of the observations made above, these were in instances where we confirmed
bath operating optimally.

Is there enough (electrical) activity occurring in these baths where a short
or other board condition would result in robbing plating from those type
areas???

Franklin

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
Sent: Monday, September 18, 2006 7:03 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG

In a message dated 9/18/2006 7:50:57 P.M. Eastern Daylight Time,
[log in to unmask] writes:

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?


To me, this says that there is some "electrical" cause, stronger than the
catalyst that initiates the electroless nickel plating.  Remember, the
catalyst in the ENIG process is a tightrope between getting plating
everywhere (extraneous plating) and not covering some pads (skip plating).
Here you  have skip plating

 If the same net skips board-to-board, likely it is a design issue  where
something is grounded out unintentionally and plating is getting defeated
in one spot. It could be that some via is tented consistantly holding a
poisoning fluid - tin stripper for instance.  If different nets skip on the
panel, then I suspect a more random error - incomplete tin strip, etc. I
guess  it could
be marginally weak catalyst.   I would expect developer residues  to be
random
pads - not all in a single net. Something "electrical" is going on  here.

Denny Fritz
MacDermid

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