I do use weight gain samples as a method for control on my electroless
copper bath. This gives me a good feeling that the bath is running
consistently on a day to day basis, but is not the total answer. I
process epoxy glass, polyimide glass, polyimide quartz, flex, and
rigid-flex in the same line. I have found, using SEM analysis of
cross-sections, that different materials will exhibit different
thickness' of electroless. For example I always have thinner copper in
the areas of Kapton, Pyralux adhesive, and glass.
Since SEM analysis can not be conducted in a "real-time" mode I use
backlight coupons to verify my coverage. This allows me to verify I
have successfully covered all areas of the through hole. Using a
diamond saw the operator cuts the coupon to size and examines the
through hole using backlight. Although this does not provide date which
lends itself to statistical analysis it does verify an electroless
deposit has been applied which is sufficient to prevent voids.
Hope this helps let me know if I can do anything else. I'll be curious
to read other responses.
Mike McHenry
Senior Engineer
AlliedSignal FM&T
816-997-4918
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______________________________ Reply Separator _________________________________
Subject: FAB: Electroless thickness measurements
Author: [log in to unmask] at INTERNET-MAIL
Date: 3/25/96 10:31 AM
I'd like some advice and comments on electroless copper thickness
measurements.
Here is brief background on my experience.
When I got here, there was no SPC on electroless line. My thought was
first to monitor the end product, Cu deposition. Coupons were attached
(3" by 3") to each basket going through the automated lined. Coupon
weight before and after deposition indicated the amount of copper
deposited.
Once the first SPC charts were made, the chemist started looking for ways
to reduce variability. Getting operators to stop tinkering with the
bath, adding chemicals and fiddling with temperature, seemed to help
some. He found out that reusing the coupons was a bad idea (after
etching away electroless), so now he uses fresh coupons each basket.
So far, the chemist has been able to reduce the range of his control
chart by about 1/3. The question has now come up: how good is our
deposition measurement technique? Supposedly, the coupons bounce around
in the electroless bath and sometimes stick to the panels. The coupons
are loosely attached by stainless wires, so they can, at times , float on
top of the bath.
What do others do to measure electroless copper depostion?
Incidentally, at the last Annual Quality Congress of the American Society
for Quality Control, I heard a speak discuss the effect of uncertainty in
measurement technique on decisions made with SPC charts. My impression
was that the measurement uncertainty could be fairly large in comparison
to the control chart range and mistakes in control chart interpretation
would be rather uncommon. Sorry for the imprecise language. I will go
back to the paper if anyone wants more information.
I told the chemist and the SPC group here that I would ask technetters
about electroless measurements.
Thanks for any feedback.
Louis Hart
Quality Assurance Manager
Compunetics
412-858-6117
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