Tony,
I agree with Mark. DuPonte published a paper in, I Believe,
PC Fab several years back detailing supersaturation of air
in plating baths where the circulation pump intake was too
high up in the plating bath and was sucking in air from the
air sparge system. The air was then compressed by the
pumping system and ended up as very fine bubbles which
attached to the panels being plated right along the
photoresist/copper boundary. These fine bubbles inhibited
plating where they attached, causing mousebites.
The trick to avoiding this was to move the intake to the
circulation system to a place where air from the sparge
system is not present. I had one shop that actually set up
a separate tank with an overflow weir to accomplish this.
The mousebite did go away.
Mark is right that you may have a leak in your filter which
allows air to get into the circulation lines as well.
One other area you might check is the water rinses after
developing. These should be cleaned periodically because
resist residues can build up there. Also, make sure you
have plenty of water flow through these rinses to assure
good rinsing of developer solution from your product.
I have found that mousebites are not just caused by one area
(developing, plating) but by a combination of factors.
Unfortunately, it sounds like you have a situation where
your plating and resist suppliers aren't cooperating to
solve your problem. They're just pointing fingers (a not
uncommon situation).
Regards,
Dave Sullivan
Rockwell Collins, Inc.
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re: [Fwd: Mousebites/divots]
Author: [log in to unmask] at ccmgw1
Date: 6/27/97 4:47 PM
Tony,
I'm not sure your problem is from super saturation in your plating tanks, but
it could be. The defect usually looks like a circular pit or depression in
the copper trace or pad. It is almost always on one side of the trace,
although I have seen it in the middle in sever cases.
There are two typical causes of air saturation. One: if you have a solution
filtration system that has the intake located close to an air sparger tube.
As the solution is sucked into the filtration system, it pulls air bubbles
in from the tank. These bubbles are compressed under pressure in the pump,
and the solution becomes loaded with air. Since this appears to be a recent
phenomenon, this is probably not the cause.
Two: Your filter pump has developed a small leak, and is sucking air as it
pumps. The result is the same as above. I would start checking here.
There is a simple way to determine if you have an air saturation problem.
Turn off your air spargers for 24 to 48 hours (over the weekend, for
example). This will give the bath a chance to stabilize, and any air in
solution to come out. When you start up the tank on Monday morning, see if
you still have pits on the first load. If you don't, then you probably have
a saturation problem. If you do, look at some other area of the process.
Since you've recently done some carbon treating, you may want to have your
copper vendor run tests on the tanks. CVS and hull cell tests should help
you identify any problems there.
Your dryfilm process sounds pretty good. I doubt HG is causing the pits.
Contact me if I can be of help.
Mark Dowding
Regional Technical Specialist
Insulectro
909-943-5758
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