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NOVEMBER 2020 I PCB007 MAGAZINE 73 5. Electroanalytical Techniques (Voltammetric) To perform a typical plating bath analysis, a small volume of sample solution (10–100 mi- croliters) is added to a test cell containing 10 milliliters of a supporting electrolyte solution and three specialized test electrodes. Instru- mentation controls the electrical potential of the working electrode, with respect to that of the reference electrode. If, because of the applied potential, compo- nents of the test solution are reduced or ox- idized, a current will be measured between the working electrode and counter-electrode. When the appropriate method is applied, differ- ent bath components are oxidized or reduced, and the current response is proportional to the concentration of the substance being oxidized or reduced. The concentration of a given com- ponent is determined by comparing the sample response to that of one or more standard so- lutions of known concentration. A multicom- ponent analysis is performed by scanning the applied potential while recording the current responses of the sample. Voltammetric meth- ods employing a continuously renewed mercu- ry drop are formally classified as polarography. Employing scanning or pulse potentials in voltammetry can determine copper and form- aldehyde in electroless copper, the gold(I), gold(III) in gold baths, nickel, and cobalt lev- els in hard gold deposits, and tin, lead, sul- fonic acid, and proprietary additives in solder plating baths. The four common techniques of electroanalytical methods are: 1. Voltammogram: Square wave voltammetry measures current as a function of potential. 2. Polarography: Voltammetry at the dropping mercury electrode. 3. Differential pulse polarography (DPP): Forces species in solution to lose or gain electrons (i.e., oxide or reducer) measured versus a reference electrode. DPP determines the concentration of species by measuring limiting current. The limiting current is determined by concentration in solution. 4. Cyclic stripping voltammetry (CVS): A series of forward and reverse voltage scans are applied that alternately plate and strip a layer of the major metal. The electrical charge required to strip the plate is a measure of deposition efficiency, which, under some conditions, can be correlated to additive concentration. Employing scanning or pulse potentials in voltammetry can determine copper and formaldehyde in electroless copper, the gold(I), gold(III) in gold baths, nickel, and cobalt levels in hard gold deposits, tin, lead, sulfonic acid, and proprietary additives in copper plating baths. The fourth most common analytical tech- nique in PCBs is the CVS analysis of copper plating additives. One is an automated labora- tory unit for analysis of multiple plating baths. This technique, developed in the early 1970s by Tench & Ogden at General Dynamics, was crucial in developing high-speed and via filling copper plating. The CVS unit in Figure 10 was Figure 10: A DIY CVS analyzer based on the design of several Asian universities' publications on low-cost instruments to detect diabetes.