Suppressor «Solderon ST-200 Primary» in a tin bath (Rohm and Haas Electronic Materials)

Importance of the Topic

The accurate determination of organic suppressors in tin electroplating baths is critical for maintaining deposit quality, controlling throwpower and leveling, and ensuring reproducible plating performance. Suppressor concentration directly affects deposit morphology, brightness and uniformity, making reliable analytical methods essential in industrial surface finishing and quality control.

Objectives and Study Overview

This application note describes a method for quantifying the Solderon ST-200 Primary suppressor in a tin plating bath. The aim is to develop a rapid, sensitive, and dilution titration-based calibration combined with cyclic voltammetric stripping (CVS) on a rotating disk electrode (RDE) to achieve accurate determination over typical production concentration ranges.

Methodology and Used Instrumentation

Sample type: Commercial tin plating bath containing Solderon ST-200 Primary.

Key methodological steps:

• No pre-treatment of the plating bath sample required.
• Dilution titration (DT) in a virgin make-up solution (VMS) matrix comprising Solderon Sn and Pb concentrates and acid HC as per supplier specifications.
• Cyclic voltammetric stripping (CVS) performed under hydrodynamic conditions on a platinum rotating disk electrode.

Instrumentation details:

• Working electrode: Platinum RDE with a Pt tip for CVS.
• Auxiliary electrode: Platinum wire.
• Reference electrode: Ag/AgCl/KCl (3 mol/L) with Solderon acid HC intermediate electrolyte.
• RDE rotation speed: 2000 rpm.
• CVS parameters: Start potential 0.475 V; vertex potentials –0.625 V and 0.475 V; step size 6 mV; scan rate 80 mV/s.
• Calibration by dilution titration with evaluation at Q/Q(0)=0.5.

Main Results and Discussion

The method exhibited a clear linear response of the cumulative charge Q versus suppressor concentration over the working range. The peak current and stripping charge were reproducible, with the copper stripping peak centered near –0.2 V (±0.2 V). Two plotted graphs demonstrated the anodic peak current as a function of potential and the evaluation ratio versus titrant volume, confirming method linearity and sensitivity down to sub-milligram per liter levels.

Benefits and Practical Application of the Method

• Fast, direct analysis without sample pretreatment accelerates process control.
• High sensitivity and reproducibility enable tight suppressor concentration monitoring.
• Hydrodynamic CVS reduces diffusion limits and improves signal stability.
• Applicable for on-site quality assurance in plating bath management.

Future Trends and Potential Applications

• Integration with automated flow-through CVS systems for continuous monitoring of plating baths.
• Extension to other organic additives such as brighteners and levelers by tailoring electrode and potential programs.
• Coupling with chemometric models to predict plating performance from additive profiles.
• Miniaturization using microelectrode arrays for field-portable analyzers.

Conclusion

The presented CVS-DT method provides a robust, rapid, and sensitive approach for quantifying Solderon ST-200 Primary suppressor in tin plating baths. Its simplicity and compatibility with routine plating chemistry make it a valuable tool for industrial electroplating quality control.

References

• Application Note No. V-145, Rohm and Haas Electronic Materials, Version 1.0.