Polarographic methods of monitoring addition agents in the electroplating of Sn-Pb solders

The electrochemical techniques typically used to monitor organic addition agents in electroplating baths work poorly in Sn-Pb solder plating baths. These electrochemical monitoring methods are based on the principle that additives act through their effects on the kinetics of the metal-deposition reaction, and thus the reaction M
ⁿ⁺
+ ne
⁻
→ M can be used as a probe to determine the additive concentration. The heavy metal ions in solder plating baths readily poison probe electrodes, however, and thus electrochemical methods on solid electrodes are irreproducible and unreliable in these systems. A polarographic technique, which uses a renewable Hg drop electrode, can be used for the quantitative analysis of addition agents in solder plating solutions, even though the chemical identity of these species may not be known to the user of the plating solution.