Qiao Liang

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

A cyanide-free alkaline copper deposition bath was developed using methylene diphosphonic acid(MDPA,H4L) as a complexing agent for Cu2+.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]2-.MDPA was found to be more likely to form complex species with Cu2+ than 1-hydroxyethylene-1,1-diphosphonic acid(HEDPA) from pH 7 to pH 10.At pH 9,[Cu(H3L)(H2L)]-and [Cu(H2L)2]2-were reduced to Cu at the cathode.Compared with the HEDPA system at 10 ℃ the peak potential shifted to more negative values and the rate of diffusion was faster.