Introduction
The analysis of organic additives in electroplating baths by cyclic voltametric stripping (CVS) is a robust method and widely used in the electroplating industry. To ensure that continuously reliable results are obtained standardized daily operation procedures are of highest importance. They all contribute to keep the measuring system at best performance.
This document acts as a guideline through the working day. Procedures are described, which should be carried out when starting up the system, during the working day and when the system is shut down. Further general recommendations and procedures, which do not have to be carried out on a daily basis are described.
The recommendations and descriptions in the following refer to the analysis of acid copper plating baths. For the analysis of other plating baths, e.g. tin, tin/lead or electroless copper plating baths some recommendations may not apply.
Start Up - Procedures at the Beginning of a Working Day
The steps mentioned in this section should be carried out when starting up the system at the beginning of the working day. They ensure that highly reliable and reproducible results are obtained with the first determination.
Dosing Units
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Prepare each dosing unit twice with the respective solution. Then rinse the electrodes and tubing in the measuring vessel well with deionized water.
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Comments
The preparation should be done with a waste beaker instead of the measuring vessel below the measuring head and using port 3 for waste. The electrodes are the dosing tips are rinsed thoroughly with deionized water after preparation to avoid carryover.
Bridge Electrolyte Vessel
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What is the bridge electrolyte vessel and what is it used for? The bridge electrolyte is used to separate the reference electrode from the measuring solution. By using a bridge electrolyte, the measuring solution cannot enter the reference system where it could change the reference potential or damage the reference system. In CVS, the chloride concentration in the measuring vessel has an influence on the analysis. To avoid chloride from the reference system leaking into the measuring solution, KNO3 is used as the bridge electrolyte. The solution (KNO3 = 1 mol/L) is available from Metrohm (6.2310.010).
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Replace the bridge electrolyte in the electrolyte vessel (KNO3 = 1 mol/L) every day. Make sure that no air bubbles are present at the bottom of the electrolyte vessel to avoid contact problems.
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More information on how to handle the reference electrodes in voltammetry can be found in the Metrohm multimedia guide (A.717.0003).
If the maintenance free reference electrode (6.0730.000/6.0730.100) is used, no actions are necessary.
Working Electrode - WE (Pt RDE)
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Daily electrochemical cleaning by conditioning in VMS is the best way to guarantee reproducible results. Before the first analysis on a working day, the working electrode should be conditioned.
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In case of accidental metallization, the WE can be dipped in concentrated nitric acid for a few seconds to dissolve the copper. Then, the electrode is rinsed extensively with deionized water and conditioning is carried out again.
Mechanical treatment of the working electrode is neither recommended nor necessary. This not only includes polishing, but also sonication with ultrasound.
More information on how to handle the rotating disk electrodes in voltammetry can be found in the Metrohm multimedia guide (A.717.0003).
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Conditioning of the WE
- It is recommended to run the conditioning at least once per day after all electrodes are installed and the Dosinos are prepared.
- The Cu stripping peak area reflects the state of the system, provided that the same solutions and voltammetric parameters are used. If the charge is smaller (or higher) than usual, it can be an indicator for Dosino leakage (especially suppressor concentrate), impurities, state of the RDE, wrong reference potential among others. The problem source has to be identified and fixed, before continuing work.
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If conditioning takes too long because the charge does not stabilize, replace the VMS and restart the conditioning. If exchanging the VMS and repeating the conditioning does not solve the problem, please refer to the troubleshooting chapter.
Auxiliary Electrode - AE (Pt Rod)
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The auxiliary electrode does not require regular maintenance.
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Mechanical treatment is usually not necessary. If it is done nevertheless, it should be carried out carefully with a soft tissue. Care should be taken that the Pt rod is not turned.
In case of accidental metallization, the AE can be dipped in concentrated nitric acid for a few seconds to dissolve the copper. Then the electrode is rinsed extensively with deionized water, and a conditioning is carried out.
Check Standard
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Check standards should be determined regularly to verify the system is running properly.
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Comments
A check standard only consists of VMS and known concentrations of organic additives. It does not contain contaminations and breakdown products, which are present in a real sample.
A check standard solution should be freshly prepared before the analysis. Especially brighteners are not stable for a longer period of time in dilute solutions.
The validity of DT calibration curves, intercept values and response curves can be evaluated with a check standard measurement.
The recovery for a suppressor determination should be (100 ± 10)%.
The recovery for a brightener or leveler determination should be (100 ± 20)%.
Additional Support
If you encounter any issues or need additional help, please submit a support ticket through Metrohm Technical Support.
For additional training on any of these topics, explore our Metrohm Custom Training options.