Emily:

I get in on this discussion a bit late, and consequently do not know if you
are  discussing Cupric Chloride, or Ammoniacal etching.

Either way though, the normal way that etching is controlled is to establish
a set of chemical parameters that give you good etching, and maintaining
those parameters.  When you do this, you can be assured that the etching will
remain the quality that you measured.

However, this is much easier to do with Cupric Chloride that with Ammoniacal,
because you literally can control all the variables in Cupric Chloride, with
existing control equipment.  Further you have much better control of the
ingredients going in to your sump.

One of the things that I have found disturbing (and my knowledge of this is
only in the US, you are located in Taiwan, I recall?) is that the replenisher
for ammonical etchant used to vary significantly, and although it always met
the manufacturers specification, the manufacturers specs were so large that
virtually anything from pure water, to pure ammonia would have met the
manufacturers specs.

Further, at this time, it is not possible, I believe, to monitor and control
all the variables in Ammoniacal etching.  You can control water/copper
through Baume'. And of course you can measure and control pH, but the other
key issue is the Cuprous/Air content, and this, to my knowledge is never
measured.  Some of the people at Atotech have done some research on measuring
the ORP (Oxidation Reduction Potential), just like is done with Cupric
Chloride etchant, which is a monitor of the Cuprous/Air levels, and have
reported good success (verbally), but I do not believe this is commercially
available.

One way to deal with the Cuprous/Air issue is simply to use WAY too much air,
which has the downside of evaporating the ammonia out of the system, but you
compensate for that with a pH monitor/control, and inject anhydrous ammonia.

You can see more about etching at our website www.pcBfab.com

Hope this helps.

Rudy Sedlak
RD Chemical Company

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