I agree with Dougal. I've tried this before and it gets out
of hand very rapidly. There is too much variation in the
incoming laminate (no reflection on our laminate supply
brethren) to run SPC on permanganate weight loss. Plus, if
you have an automatic line, getting down line to pull off
the coupon is something the operator will want to do
reluctantly at best.
My suggestion of things to control on a permanganate bath
are:
1. Permanganate concentration
2. Caustic concentration
3. Manganate levels
4. Total solids
5. Temperature
I assume you are using electrolytic permanganate
regeneration. If you aren't, then I do not believe you will
be able to control this process as it degenerates too
rapidly, which may be (I guess) why you would want to
control by weight loss. Follow Dougal's suggestion. It is
the only way to achieve control of this process.
Regards,
Dave Sullivan
Rockwell Collins, Inc.
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: DESMEAR FOLLOW-UP
Author: [log in to unmask] at ccmgw1
Date: 3/7/97 6:57 AM
Edward Szpruch wrote:
We intend to upgrade our follow - up in desmear process and
implement SPC . We intend to perform weight-loss measurements on uncladed
laminates .
What are the most common figures for FR-4 and modified resins such as
FR-405 ?
Edward, we used to run SPC on weight loss at desmear, but you have to
be very careful, because you will find that every time you change the
batch or supplier of laminate used for your weight loss panels, the
SPC goes into an out of control situation, and the line starts running
above or below the previous average. This is because of the variation
in surface resin on the laminate, and it is this surface resin that is
attacked by the permanganate. The other issue is that you cannot re-use
the coupon, as the surface resin is removed and so the permanganate is
now trying to remove resin from between the glass bundles.
The real key is to use the weight loss panel as a measure during a
DOE to establish the critical factors in the process (incl.sweller)
and then run SPC on those parameters, not the product attributes.
Dougal Stewart
Exacta Circuits
Scotland
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