Adding to Kathy's great comments about SPC programs, I had some very good
help from some people at Motorola once who showed us that measuring "input"
variables
(such as process temperatures, chemical analysis, etc.) without measuring
"output" results can prove useless.

An example would be places that chart process chemistry analysis without also
measuring the product quality that comes off the line.  For instance, if you
chart all the analysis for electroless copper chemistry but fail to compare
them to backlight readings or, more accurately, weight gains then you'll not
benefit from SPC as much as you could.  True, chemical analysis charting will
alert you to spikes and trends but it won't tell you that even under the best
of circumstances your copper is depositing as you'd like.

Some lines don't lend themselves well to output measurements.  Those are
"spooky" lines to operate.  There are few examples, as most processes have
some definite ways of measuring quality performance.  But lines having input
variable measuring and output measuring are the ones that prove easiest to
control.

Mark Mazzoli

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