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