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Date: | Thu, 04 Apr 96 10:09:51 EST |
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I would like to add a few general comments. I have been involved with
electroless copper for a number of years, using most of the methods
available for measurement. SPC of the thickness is frustrating to say
the least. The process is so dynamic & also relies on more than just
the copper bath to influence the thickness (although many of these
variables have only nuance effects).
The measurements vary so much that my real bottom line is:
"I want to know if the bath/line has so much variation from one load
to the next that something has just had a major screwup."
That is, I am looking for those wide swings in thickness from one rack
to another that indicate REAL problems (variation of 30-40 millionths
or more). i.e. Did a replenishment pump die since the last load was
processed? Did someone bump a calibration knob on one of the pumps?
Was the wrong add made? etc.
These are the things that you are REALLY interested in. The thickness
of the Dep copper within 10 or 15 millionths of the target isn't
really going to make much difference to your processing unless you are
already on the verge of etching it out of the holes in your plating
line, creating PTH voids.
Matt Byrne
Hadco, Owego
______________________________ Reply Separator _________________________________
Subject: FAB: follow-up on electroless thickness measurements
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 4/1/96 06:20 PM
Thanks to all who responded to my question about measuring thickness of
electroless copper.
Here are some comments.
1. Coupons must be all the same size, routed, not sheared. Shearing may
not make a big difference, but routing is best.
2. Deposition varies with material: epoxy-glass, polyimide-glass, etc.
My thought is that, with different materials, you may need different SPC
chart for each material. Most of what our plant processes, almost all,
is epoxy-glass, so we can evade this problem.
3. Deposition may vary from lot to lot of the same material. When
setting up an SPC chart, may want to get a mix of lots to use for
coupons. That way, variability in those lots will be included in the SPC
chart even when you don't know what the variability is.
4. Bake the coupon before weighing. Will the copper-clad coupon have
enough water on the surface to make a difference? If the coupon is baked
(and weighed) before deposition, will it not absorb water when it is put
through the wet process?
Thanks again to all who contributed.
Louis Hart
[log in to unmask]
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