I have two guesses Re: fuming with high copper levels. Guess 1: ORP reading becomes less sensitive as copper levels get higher, requiring more Cu(I) to trip ORP adder point. This may encourage a slow control response, allowing overdosing of oxidizer. Guess 2: Conductivity controllers are set up on a narrow response to conductance in a very specific mixture where the only significant variable is HCl. High Cu may add to the conductivity and cause acid to fail to add. This will definitely throw the system out of balance, either causing overadd of oxidizer (liberating gas when some HCl is added) or some other phenomenon. I may be able to be more complete with more detailed operation info. Marshall Gurian Coates ASI e-mail: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FAB:Cupric Chloride Etchant Author: [log in to unmask] at internet Date: 8/13/96 9:33 AM 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. * *************************************************************************** *************************************************************************** * 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. * ***************************************************************************