Authored By:
Roger Bernards, Mike Carano, Al Kucera, Thao Pham
OM Group Electronic Chemicals
Maple Plain, MN USA
Summary
Due to the increasing demands placed on acid copper plating solutions to perform via fill plating of blind micro vias it is critical that the plating additives be monitored precisely. This paper presents electrochemical techniques for analyzing additives commonly used in via fill plating baths. The additives, commonly referred to as suppressor, brightener and leveler, all need to be precisely monitored during the production process in order to achieve optimum via fill. Utilizing cyclic voltametric stripping (CVS), these additive types can be monitored with a single analytical instrument when the proper techniques are employed and the measurement procedures are optimized for each additive.
Conclusions
The three primary additives, suppressor, brightener, and leveler, that are commonly contained in via fill plating baths can be independently analyzed by CVS. The suppressor analysis uses only a small amount of plating bath added to a blank solution thus minimizing the influence of the other additives. The optimum procedure for the brightener analysis calls for the plating bath sample to be diluted into a blank solution containing the suppressor rather than running a 100% production bath sample. The production bath dilution and brightener addition amounts need to be carefully set up to give properly spaced data points for the analysis.
The authors have created new techniques for measuring the leveler component in via fill plating baths utilizing the slope of brightener additions as the means for determining the leveler concentration independently of the brightener concentration. Some strong levelers can affect the ability to measure the brightener. Levelers that adsorb onto the platinum electrode can influence the results of the next analysis as well. Special care of the instrument and testing the system with a conditioning method to assure results are proper is a necessary step to insure accurate results with CVS analysis.
Initially Published in the IPC Proceedings
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