> One of our process engineers is contemplating changing the etcher chemistry.
> Potential changes include NaCl or sodium chlorate in traditional cupric
> chloride etching chemistry. Before initiating an evaluation of these
> changes, I would appreciate any responses to the following:
> 
> Can anyone share any experiences (positive or negative) with using sodium
> chloride in cupric chloride etchant in order to increase etch rate? Are you
> currently using NaCl and if so, have you found any degredation of equipment
> due to corrosion? Any other comments?

The purpose of the NaCl is to provide not just an increased etch rate
but to provide a uniform etch speed which should typically be
approximately 1oz copper removed per board per minute under spray. The
NaCl is used as both a catalyst and a buffer. If properly controlled
using a Vis-U-Etch colorimetric contoller, your etcher components will
last for years and years. The reason for the degradation of etcher
components such as titanium conveyor axles is due to too much free HCl
present or in other words, out of balance cupric chloride. When an ORP
type controller is used, it looks at Oxidation Reduction Potential,
Specific Gravity and Normality of Acid. The problem with this type of
control is that the ORP numbers can be relied on but the Specific
Gravity changes and the Normality is not on a linear scale so it can not
be relied on either. With two changing variables out of three all you
really wind up doing is baby sitting the ORP controller. Since MOST
people have frequent, daily problems with ORP controllers (ie. frequent
release of Chlorine gas indicating an out of balance etchant), this is
not a reliable way to control cupric chloride. The ONLY constant with
cupric chloride that can be counted on is the color of the etchant which
is only correct when it is a clear emerald green. For those that like
the numbers game, the Vis-U-Etch controller typically maintains an ORP
reading within 20mv at around 580mv to 600mv. Provided you mix your
Chlorate/Chloride oxidizer solution properly and consistently, your
copper content will be approximately 27oz/gallon(US). The Specific
Gravity will be in the range of 38-40 degrees Baume but hold steady at
one point in that range. The Normality will typically stay around .8N.
Since this method of control is not dependant on an exact input of
copper, you don't have to run scrap through or change the calibration
every time you change your production habits. Once a controller is
calibrated, it should accurately introduce Acid/Oxidizer regardless of
how fast or slow copper is added.

> In the same vein, are there any Cupric etchers out there using sodium
> chlorate as the oxidant as opposed to hydrogen peroxide? Again, any
> positive/negative impacts?

The cost of using Hydrogen Peroxide is approximately double that of
Chlorate. Also, Peroxide is not very stable and therefore hard to keep
"fresh". The Chlorate/Chloride mix does not go stale as easily though
mixing more than a one week supply is not recommended.

> Thanks to any and all comments and responses.
> Dave Rooke
> Circo Craft - Pointe Claire
> 

If you would like complete information on the Vis-U-Etch system, we can
be reached at:

Phil Culpovich
Oxford V.U.E., Inc.
PO Box 4221
Sunland, CA 91041-4221
USA

tel. 818-353-4714
fax. 818-353-1024
http://www.oxfordvue.com
e-mail: [log in to unmask]

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