Dave:  In the world of PCB fabrication, your problem is called "shadow plating".
Rudy Sedlak
RD Chemical Company

--- On Thu, 3/5/09, Dave Connitt <[log in to unmask]> wrote:
From: Dave Connitt <[log in to unmask]>
Subject: [TN] ENIG Question
To: [log in to unmask]
Date: Thursday, March 5, 2009, 12:09 PM

Hello All,
I have a question regarding a strange situation regarding reflow
soldering ENIG finish boards.
We have seen a few boards that have what seems to be gold "washing "
down between pads and creating shorts. This seems to come and go. This
is a flex circuit that is placed on a pallet to go through our SMT line.
One other bothersome issue is that we are having difficulty getting
proper solder stencil alignment across all the flexes in the pallet. I
am pushing to have the flex "panelized" from the vendor to increase
positional accuracy but the jury is still out on that.
I suspect these two issues are related. If the solder gets deposited
"off pad"slightly could the washing process be moving some of the
gold
in between pads? I attached an example.
Has anybody come across this?
If so, what was the solution?
 
Thanks,
Dave Connitt CID+

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