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Etching solution process control

December 1, 2010

our solution for etching:
- dissolve in 10 l of demineralised water at 20° C, 6 kg of FeCl3.6H2O
- add carefully 200 ml of HCl (Chloric acid, 36% concentration)

Process:
Dip the wire mesh in the solution for 30 (+5/-0) seconds at (20° C, 68° F).

my questions are:

1.How to maintain the concentration of solution and what standard is used, BAC? PMS?
2.How to monitor the temperature.

LYNN LIN
Auditor - China

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With use, the ferric chloride [on eBay or Amazon] concentration will rise and the HCl concentration will drop.

You can analyze for the acid content with a titration using a proper indicator. You can analyze for total chloride and subtract the chloride from the acid to get the ferric chloride [on eBay or Amazon]. This will require removing a calculated amount of solution and adding HCl to bring it back up to level. A few times, it might require a small water addition.
You need to establish limits for both chemicals.

Temperature can be measured with an appropriate temperature measuring device. Normally, this will be a thermocouple with a thin teflon covering of the tip.

The tank should have some method of agitation, with pumped being a normal method.

Normally, you will not use HCl that is that concentrated. It costs too much, and has noxious fumes when making additions.

James Watts
- Navarre, Florida
December 3, 2010