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78 PCB007 MAGAZINE I FEBRUARY 2021 levels in this process will act as a catalytic poison, which then leads to the possibility of voids in the copper deposit. Conductivity Probes One of the least expensive things one can purchase for process con- trol is a conductivity probe. is little unit (looks like a ballpoint pen) costs about $200. is is a great way to monitor the rinse water cleanliness and the rins- ing operation's overall effective- ness. e use of these probes is also an excellent method to measure contaminant build-up in certain chemical processes. An example of a conductivity probe is shown in Figure 4. CVS (Cyclic Voltametric Stripping) While most fabricators rely on Hull cell plating analysis to gain some control of the additives in the electrolytic copper plat- ing solutions, one must resort to a more quan- tifiable means to measure and control for to- day's technology organic addition agents. Cy- clic voltametric stripping is an electrochemical technique used for the measurement of organic additives in plating baths. It is based on the ef- fect that the additives have on the rate of elec- troplating. Regardless of the specific type of organic additive (brightener, leveler, grain re- finer, etc.), its activity is reflected in a change in the plating rate. e analysis is performed in an electro- chemical cell using a three-electrode system, one of which is a platinum rotating disk elec- trode. During measurement, the potential of the platinum electrode is controlled by the in- strument. e potential is scanned at a con- stant rate back and forth between negative and positive voltage limits. A small amount of met- al from the plating bath is alternatively plated onto and stripped off the working electrode as the potential is changed. Dur- ing the scan, the current at the working electrode is measured as a function of potential. e activity of the additive will affect the plating rate of the met- al onto the electrode. e plat- ing rate is determined by calcu- lating the charge required to strip the metal of the working elec- trode. e relationship between the stripping charge and the addi- tives' activity is used to measure the additives and their compo- nents quantitatively. A typical CVS scan for acid cop- per analysis may proceed from 1.5V to -0.225V and back again to 1.5V (Figure 5). During this po- tential sweep, the copper metal will be plated onto the platinum electrode and then again stripped off. e area of the curve under the stripping peak is measured in millicoulombs (mC). Each scan is performed equivalently, and multiple scans are committed to both con- dition the disk and allow for averaging the re- sults from each potential sweep. Figure 4: Conductivity probe, courtesy of Myron L Company. Figure 5: Typical CVS scan showing the stripping peak. The area under the stripping peak curve is the millicoulomb reading obtained for the scan.