Chlorine is a gas, which is marginally soluble in water. The more salts, all other things being equal, such as pH, the less soluble the Chlorine. So, you could be creating Chlorine when the Copper is low, and it is soluble enough to not be given off. One key question is do you monitor your ORP, that is to say, actually keep a continuous record of it?? If you are getting serious spikes in an ORP chart, you are creating Chlorine, whether you smell it or not. Another factor, that could be contributing is the viscosity, and thus mixing speed of the etchant. If the Copper is low, the mixing speed of the components is higher, and this will allow the Cuprous ion to come into contact with the Chlorine gas, and react with it, and make it go away, faster. One of the factors that I have seen personally that can contribute seriously to this problem is the type (and horsepower) of the pump making the additions. If the pump is too powerful, and ANY centrifugal pump I have ever seen is too powerful, It will seriously over-add before the ORP sensor tells it to shut off. Best type of pump is a bellows pump, and they should be sized so that they are running a lot of the time that panels are going down the line. Never less than 20% of the time, and more is better, up to even as high as 70% of the time. This ensures slow addition, so that the reactants can circulate around enough to find the Cuprous ion, and not have time to say, "Hey, can't find no Cuprous, I'm history!", and escape to the atmosphere. Also, speaking of mixing, if you are running more than one chamber, you should have some serious horsepower mixing the two sumps. This is best done by pumping from the last chamber to the first, and cascading back. I am going to make a rough estimate that you want one HP of pump circulating for every etcher sump in a line. And that is an absolute minimum. Also, if you have more than one etcher sump, you may want to add Chlorate and HCl at more than one point. If you would like more free opinions, which some have said are worth almost what you pay for them, e-mail, or call. Rudy Sedlak RD Chemical Company 415-962-8004 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************