Measurement of Electroless Plating Rate for Copper and Nickel Baths by Coulostatic Method

Abstract

The coulostatic method was studied for in situ measurement of electroless plating rate of copper from EDTA/HCHO and from Rochelle salt/HCHO baths and nickel from sodium citrate/sodium hypophosphite bath using copper electrodes immersed in stagnant electroless plating bath. Polarization resistance Rnormalp measured by this method showed reproducible inverse relation with deposition rate iELP false(iELP=K/Rnormalpfalse) . The constant K was largely dependent on the type of bath but was little affected by the changes in temperature or concentration of bath components. These characteristics of K results in reproduciblein situ determination of electroless plating rate by this method. Comparing these results with these obtained by the galvanostatic linear polarization method, which also gives Rnormalp , it was shown that good reproducibility of the coulostatic measurements is mainly due to the following two characteristics. First, measured Rnormalp is almost free from solution resistance. Second, the measurement can be finished so rapidly, usually within a few ten milliseconds, that the surface state is little affected by it.

AC Impedance and Coulostatic Studies on Electrochemical Detection of 2‐Mercaptobenzothiazole in a Copper Electroless Plating Bath

“…In the baths without 2-MBT, the log ~-t relations were not completely linear, corresponding to the fact that the complex impedance diagrams were broad arcs. Determination of Rp and Ca values in such cases was performed by analyzing the latter linear part of the log ~-t curve (12,13,23). Although the impedance measurement using FFT and coulostatic pulse perturbation is much quicker than other impedance measuring methods, it still took from several minutes to about 10 min.…”

“…The fact that the concentration of these additives is extremely low, compared with other main components (such as complexed metal ions and reducing agent), makes it difficult to adopt analytical methods for effective surveillance of additives in electroless plating baths. The authors have applied the coulostatic method to detect the electroless plating rate and found that the polarization resistance values are sensitive to changes in the kinetics of the electroless plating reaction (12,13). However, since the polarization resistance for an electrode on which metal deposition proceeds reflects total effects of various factors such as component concentrations (including additives), bath aging, temperature, and so on, such electrochemical measurements are inappropriate for use in detecting the additive effects or concentration selectively.…”

“…of the usual test signal waveforms such as random white noise (20,21), a coulostatic pulse was imposed on the working electrode as an applied perturbation to obtain a frequency dispersion of ac impedance. The coulostatic pulse is a current impulse fed from a condenser of a pulse circuit (12). It rises abruptly to a current value of about V1/R~, where V~ and R] denote the charged voltage of the condenser and the sum of series resistances including the solution resistance and resistors inserted between the condenser and the working electrode (Rlim + RI~ in Fig.…”

The influence of iodate ion additions to the bath on the deposition of electroless nickel on mild steel

“…Suzuki et al described the coulostatic method, where a charged pulse is applied to the electrode to be plated and the potential decay curve is monitored. 13,14 It was shown that the potential decay curve follows the equation…”

“…2IO3 -+ 5H2PO2 -+ 2H +  I -+ 5H2PO3 -+ H2O (13) The extent to which these reactions play a role in the stabilisation (at pH 5) is uncertain. There have been anecdotal reports of IO3stabilisers for use in EN baths, after a period of time in use or in storage, producing Iions (via I2).…”