Hi Steve,

My opinion is that the pits were caused by gassing in the copper bath
(which probably occurred on initial contact in the tank).  The pits are
only on one edge of the trace (indicating that gasses were trapped by the
resist).  You said that they were only on one side of the board, which
could be due to the copper area differences from side to side.  It's
desirable to go into a copper bath "hot", meaning that they should see
amperage right away.  Amperage should be set low enough so it's pulling
current, but not so high as to cause burning or gassing.  If one side of
the board is high in copper area and this side is lower (or the areas
showing the pits are isolated areas) it's possible that the current was too
high when the boards entered the tank.  Gas would have been trapped by the
photo resist and a pit would form.

I would rule out air saturation in the tank since the pits were only on one
side of the board.  And I would probably rule out etch-resist breakdown,
since that is normally not circumferential.  But to be certain about the
etch-resist, I would X-section a pit and see how deep it goes.  My guess is
that it starts at the base laminate.  If it's an etch-resist problem the
pit will not be as deep.  Maybe only half way through the plated copper.  A
base laminate starting point indicates an obstruction to copper plating;
gas, residues, air pockets.

Mark Mazzoli






At 11:33 AM 10/6/00 -0400, you wrote:
>Hi Ya'll!!
>
>It's picture time again! Got some boards in at incoming inspection that are
>really weird looking Go to:
>
>http://www.driveway.com/share?sid=e25a88c4.8e904&name=Pictures
>
>Look at Pits.jpg and Pits2.jpg...very, very strange! Never have seen
>something like
>this before...and it's only on the backside of the board? What could cause
>this?
>
>Looking in the IPC-A-600F, it only talks about reductions in conductor width
>of more than 20% (for class-2), but doesn't talk about reductions in
>thickness by pits such as these...it's hard to tell if they've gone all the
>way through the trace because the pits are filled with solder mask and you
>can't see all the way down to the bottom of the pits.
>
>Common sense tells me that these boards are rejectable...am I right?
>
>-Steve Gregory-
>
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