Formaldehyde oxidation, electroless copper plating

Formaldehyde Oxidation during Electroless Copper Plating Studied... 

FORMALDEHYDE OXIDATION DURING ELECTROLESS COPPER PLATING STUDIED BY ONLINE ELECTROCHEMICAL MASS SPECTROMETRY... 

FIGURE 19.9 Extraction of the partial reaction rates for formaldehyde oxidation (o) ((A) measured by DEMS, Figure 19.6A) and copper Cu(II) ion reduction (dotted line) ((B) measured by EQCM, Figure 19.8A) as the difference with the net current (solid line) in the positive-going scan in electroless copper-plating solution (for details see captions of Figures 19.6A and 19.8A). (From Pauliukaite, R. et al., J. Appl. Electrochem., 36, 1261, 2006.)... 

Formaldehyde oxidation rate in electroless plating solution is also higher compared to Cu(II)-free formaldehyde solution. In this case, a nonadditive could be equally explained by the higher catalytic activity of freshly deposited copper metal. 

ED has also been used to improve or maintain the quality of a plating bath and thus eliminate the need for periodic replenishment. An instructive example is shown in Figure 8.9 for the electroless plating of copper onto nonmetallic substrates such as printed circuit boards.10 The process illustrated utilizes an uncharged EDTA-Cu complex where the reduction of copper is driven by the oxidation of formaldehyde to formic acid. The formate ions and the sulfate ions introduced with the make-up copper are undesirable reaction by-products that are removed by ED. NaOH is added to adjust pH sufficiently to ionize the formic acid. The uncharged EDTA-Cu complex remains in the diluate stream, which is returned to the plating tank. 

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