Relation between surface preconditioning and metal deposition in direct galvanic metallization of insulating surfaces

Abstract

The relation between surface preconditioning and metal deposition in the direct galvanic metallization of different insulating polymer surfaces by the so-called PLATO technique was studied using electrochemical and surface analytical methods. AFM, XPS and contact angle measurements show that the chromic acid etching of original polymer surfaces leads to an increase of the surface energy and hydrophilicity of polymer substrates due to both surface roughening and the formation of -COOH and/or -COH surface groups. However, decisive for the subsequent surface activation with cobalt sulfide is the increase in surface roughness. The influence of the degree of activation and the electrode potential on the kinetics of Ni metallization was studied by current transient measurements on activated line-shaped structures. The results suggest that the electrochemical reduction of cobalt sulfide to cobalt is a necessary step to induce the process of Ni electrodeposition. Successful Ni metallization could be obtained on ABS (acrylonitrile-butadiene-styrene) and PEEK (poly-ether-ether-ketone) surfaces. The lateral propagation rate, V _x , of the depositing Ni layer depends exponentially on the applied potential and was found to be several orders of magnitude higher than the Ni deposition rate, V _z , in the normal z-direction (V _x /V _z =10²–10⁴). It was demonstrated that the approach involving cobalt sulfide pre-activation can also be applied successfully for metallization of oxidized porous silicon surfaces.