We etch inner layers using Cupric Chloride Etchant. We control the chemistry with ORP and Conductivity probes. The ORP adds Sodium Chlorate and the Conductivity controls HCl adds. We have experienced gas generation (chlorine or HCl fumes) when both the ORP and Conductivity are in control. The gas/fume release occurs when the copper gets as high as 33 - 35 ounces per gallon. Standard procedure is to feed copper into the system when a chemical out of balance situation results in gas generation. Clearly in this case this would be the wrong thing to do. Can anyone explain the chemical reaction behind a release of gas/fumes when the copper is high? *************************************************************************** * 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. * ***************************************************************************