Copper Electrodeposition from Non-Cyanide Alkaline Baths Containing Methylene Diphosphonic Acid as a Complexing Agent

Abstract

A cyanide-free alkaline copper deposition bath was developed using methylene diphosphonic acid (MDPA, H4L) as a complexing agent for Cu . The plating bath was investigated using potentiometric titrations, voltammetric curves, and polarization curves. The potentiometric titration gave dissociation constants for MDPA of: pK1=1.86, pK2=2.65, pK3=6.81, pK4=9.04, and the stability constants were: pKML= 10.65, pKML2 = 5.59, pKML3 = 2.50. Three different complex species were present in the bath as the pH increases: Cu(H3L)2, [Cu(H3L)(H2L)], and [Cu(H2L)2]. MDPA was found to be more likely to form complex species with Cu + than 1-hydroxyethylene-1,1-diphosphonic acid (HEDPA) from pH 7 to pH 10. At pH 9, [Cu(H3L)(H2L)]and [Cu(H2L)2] were reduced to Cu at the cathode. Compared with the HEDPA system at 10 °C the peak potential shifted to more negative values and the rate of diffusion was faster.