Brightener «Top Lucina α-2» in acid copper baths (Okuno Chemical Industries)

Importance of the topic

Brighteners such as Top Lucina α-2 play a critical role in acid copper electroplating, ensuring uniform deposit morphology, improved brightness and ductility, and minimizing defects in high-precision industrial coatings.

Study objectives and overview

The primary goal of this application note was to develop and validate a rapid, accurate method for determining Top Lucina α-2 concentration in working acid copper baths without extensive sample preparation. The approach combines cyclic voltammetric stripping (CVS) with a modified linear approximation technique (MLAT) to yield reliable quantitative data.

Used methodology and instrumentation

• Electrolyte: Virgin make-up solution containing CuSO₄, H₂SO₄ and NaCl per supplier specifications.
• Intercept solution: 42.812 mL electrolyte + 0.075 mL Top Lucina α-3 leveler + 0.113 mL Top Lucina α-M suppressor + 25 mL sample.
• Working electrode: Platinum rotating disk electrode (Pt-RDE) with Pt tip for CVS; rotation rate 2000 rpm.
• Auxiliary electrode: Platinum wire.
• Reference electrode: Ag/AgCl/KCl (3 mol/L) system with intermediate KNO₃ (sat.)/H₂O (3:1).
• Measurement mode: Cyclic voltammetric stripping (CVS).
• Calibration: Modified linear approximation technique (MLAT).
• Potential program: Start at 1.625 V, sweep to –0.175 V and back to 1.625 V at 0.1 V/s with 0.006 V steps.
• Analytical signal: Copper stripping peak around 0.2 V ± 0.2 V.

Main results and discussion

Cyclic voltammograms displayed a well-defined copper stripping peak whose charge under the curve increased linearly with added brightener concentration. The MLAT calibration yielded a straight-line relationship between the intercept-corrected charge and α-2 level in the range 0–1 mL/L. Precision studies indicated low relative standard deviations (<5%), and the method showed minimal interference from common bath constituents.

Benefits and practical applications

The CVS-MLAT protocol offers several advantages:

• Direct analysis of plating bath without chemical pretreatment.
• High sensitivity and repeatability for routine quality control.
• Compatibility with on-site or automated plating line monitoring.
• Rapid turnaround time for process adjustments.

Future trends and potential applications

Opportunities exist to integrate this electrochemical sensor approach into digital process control systems with real-time feedback. Advances could include multi-additive detection arrays, miniaturized RDE cells for inline monitoring, and machine learning algorithms to predict bath life based on comprehensive voltammetric fingerprints.

Conclusion

The modified linear approximation technique combined with cyclic voltammetric stripping provides a reliable, fast and low-interference method for quantifying Top Lucina α-2 in acid copper baths. Its implementation enhances process control, product quality and operational efficiency in electroplating facilities.

Reference

Okuno Chemical Industries. Application Note No. V-183. Determination of brightener “Top Lucina α-2” in acid copper baths by modified linear approximation technique using cyclic voltammetric stripping. Version 1.0.