無電解銅めっき浴中における化学平衡

概要

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The chemical species and equilibria in electroless copper plating baths consisting of copper sulfate, EDTA, glycine, hexacyanoferrate and formaldehyde were investigated by visible-spectrum measurements at 25°C. Chemical species were mainly CuOHL3-, CuL2-, G-, M-, MG2-, HMG-, CuLG3-, CuLfe6-, fe4-, L4- and HL3- at pH11.75∼12.50, where H4L=EDTA, HG=glycine, HCHO+H2O=HM and Fe (CN)4-=fe4-. Glycine and formaldehyde form condensation products such as HMG-, resulting in a decrease in the concentration of free formaldehyde, but the concentration of M-, the electrochemically active species of formaldehyde, increased in the high pH region. Three mixed-complexes were found in the solution: CuL2-, and OH- formed CuOHL3-([CuOHL3-] [H+]/[CuL2-]=10-11.8, molar absorptivity ε730=45); CuL2- and G- formed CuLG3- ([CuLG3-]/[CuL2-] [G-]=101.5, ε730=45.5); and CuL2- and fe4- formed CuLfe3-([CuLfe3-]/[CuL2-] [fe4-]=101.2, ε490=315). The concentrations of CuLG3- and CuLfe4- were considerably lower than the other Cu (II) -EDTA complexes.
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