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74 PCB007 MAGAZINE I DECEMBER 2022 Temperature Temperature is also a parameter that should be controlled for consistent etch quality. e higher the temperature, the faster your reac- tion rate will be. e temperature of the etcher bath tends to have little effect on etch fac- tor and only improves etch rate; thus, cupric etchers are typically run at the highest possi- ble temperature. e standard temperature to etch at is 130°F. Controlling temperature is also simple because it is done through the etching equipment by monitoring the temper- ature with probes that will activate or deacti- vate the machine's heating and cooling systems as needed. Oxidation-reduction Potential Oxidation-reduction potential (ORP) is a major factor to monitor with CuCl 2 . ORP can be understood as a measurement of how ready your etchant is to etch metal. It does this by measuring the ratio of Cu +2 ions (from CuCl 2 ) and Cu +1 ions (from CuCl—the spent form of the etchant). As you etch, the Cu +2 ions will decrease and the Cu +1 ions will increase, and thus the ORP value will drop. A low ORP is a sign that you need to add reagents to perform regeneration so that the Cu +1 ions will be con- verted back to Cu +2 . ere are three main ways that you can perform this regeneration; if you wish to know more, please see my November 2022 column, "Cupric Chloride Regeneration Options." ORP is measured via an ORP probe that pro- vides a value in the units of millivolts. If you are curious where the millivolts value comes from, the equation is shown in Figure 3. If you are a person who does not like math, no worries; what you mostly need to under- stand is that the ideal ORP range for CuCl 2 is Figure 1: A standpipe (clear glass tube) on a piece of Chemcut equipment. This standpipe is equipped with a specific gravity controller (gray device in the middle of standpipe). Figure 2: A basic ORP probe set-up for a beaker test.