Brightener «Cupracid BL» in acid copper baths (Atotech)

Importance of the Topic

Acid copper plating baths are widely used in printed circuit board manufacturing and decorative metal finishing. Brightener additives such as Cupracid BL strongly influence deposit appearance and functional properties. Reliable monitoring of brightener concentration ensures consistent bath performance, high deposit quality, and reduced waste through timely maintenance.

Objectives and Overview of Study

This application note demonstrates a rapid voltammetric approach for quantifying Cupracid BL in acid copper baths. The aim is to establish a simple, accurate method using cyclic voltammetric stripping (CVS) coupled with a linear approximation technique (LAT) calibration for routine quality control.

Methodology and Used Instrumentation

The method employs a rotating disk electrode (RDE) system operated in CVS mode. No pre-treatment of the plating bath sample is required. An intercept solution is prepared by mixing a virgin make-up solution (VMS) with a small volume of suppressor and the plating bath sample. Key parameters:

• Working electrode: Pt-RDE with Pt tip for CVS.
• Auxiliary electrode: Pt wire.
• Reference electrode: Ag/AgCl/KCl (3 mol/L) with intermediate KNO3 saturation electrolyte.
• Rotation speed: 2000 rpm.
• Potential range: 1.575 V → –0.25 V → 1.575 V.
• Voltage step: 0.006 V; sweep rate: 0.1 V/s.
• Calibration: Linear approximation of stripping charge versus Cupracid BL concentration.

Main Results and Discussion

Calibration curves show a linear relationship between the net stripping charge (Q–Q’) and Cupracid BL concentration over the evaluated range. The peak potential for copper stripping appears consistently around 0.2 V. Reproducibility tests indicate relative standard deviations below 5 %, demonstrating method precision. Interference from common bath constituents (CuSO4, H2SO4, NaCl) was negligible under optimized conditions.

Benefits and Practical Applications

• Rapid analysis without sample pretreatment.
• High sensitivity and good reproducibility.
• Suitable for on-site or in-line monitoring of plating baths.
• Enables early detection of additive depletion, reducing defective deposits.

Future Trends and Applications

Advances may include integration into automated plating control systems, miniaturized sensor probes for continuous in-bath monitoring, and extension of the LAT-CVS approach to other organic additives. Data connectivity with plant control software could further optimize bath maintenance schedules.

Conclusion

The presented LAT-CVS method offers a straightforward, reliable tool for quantifying Cupracid BL brightener in acid copper baths. Its simplicity and precision make it a valuable addition to QA/QC protocols in electroplating operations.

Reference

Atotech Application Note V-136: Determination of brightener "Cupracid BL" in acid copper baths by linear approximation technique using cyclic voltammetric stripping, Version 1.0.