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Date: 10 Jul 96 22:42:08 EDT
From: "Hans M. Rohr" <[log in to unmask]>
To: "INTERNET:[log in to unmask]" <[log in to unmask]>
Subject: Re: Ammoniacal Etching Speed
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Does anyone have information or data on what chemical control limits are
required (specific gravity, pH, temperature, etc.) to maintain a constant
etcher
conveyer speed for a given copper plating thickness such as 1 oz base and 1
mil
electroplated Cu? We have done a lot of testing and tried a lot of control
schemes. Nothing seems to work reliably. We still etch one piece, measure
the
line width, adjust the conveyor speed accordingly and then run the lot.
Hans Rohr.
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======== Fwd by: Tony King / N ========
Hans,
It may not be the chemical concentrations so much, but the controller used
to maintain the chemistry. Not all controllers are created, the low end
units use a float/sink mechanism, while the better units measure the baume
and use high-tech electronics for automated chemical addition. The high end
units maintain a much tighter range which makes etching more uniform before
and after additions. MacDermid offers a very good higher end controller
which I have used very successfully for years called the MACTROL.
Another approach to consider is the first piece system you presently have.
Based on your average lot size and first piece inspection turn time, match
up the copper weights and process the first piece for the next lot part way
through the preceding lot so that when your first lot is done your second
lot is ready to process, and so on. This would minimize the amount of dead
time by keeping the etcher filled with product. The more an etcher is worked
the better it performs. This system will not prevent the need to adjust
conveyor speed, but does minimize problems. The etcher is a dynamic system
with many interdependent elements which will reach equalibrium if properly
maintained and worked. The standard parameters I use are 23.5 baume, 8.0 to
8.5 pH and a temperature of 125 F.
The single most important control in maintaining the etcher, proper
ventilation due to the impact on pH and chloride concentration !!
Call me if you would like to talk.
Tony King
Elexsys International
603-886-0066
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