Ni-Based Activator for Electroless Copper Deposition: Effect of Metal-Ion Ligand Stability Constant on the Reduction Deposition

Abstract

Electroless plating can achieve the metallization of nonconductive substrate surfaces. Of note, the realization of nonprecious metal catalysis is conducive to promoting the green development of this technology. In this article, a mixture of polyvinyl alcohol (PVA) and nickel chloride is used in catalytic solution by means of a nickel-chelating structure (electron transfer at the O/Ni interface), which simultaneously modifies and activates the substrate surface. Increasing the electron cloud density around nickel cations enhances their catalytic performance. Additionally, trisodium citrate, potassium sodium tartrate, nitrilotriacetic acid, thiourea, and sodium ethylenediamine tetraacetate were elected as coordination agents, and the influence of metal-ion ligand stability constant on the reduction deposition was researched. Coordination bonds can be established between the Cu²⁺ and O/N/S particles of functional groups in the ligands because paired electrons in O/N/S hybrid orbitals tend to occupy empty Cu²⁺ hybrid orbitals and establish coordination bonds. What is more important, the copper–potassium sodium tartrate ligand has the lowest stability constant and reduction barrier. Additionally, the plating solution to join the potassium sodium tartrate as a complexing agent can result in the deposition of a highly crystalline and uniform Cu-plated coating on the surface of the substrate. Hence, reducing the Cu²⁺ reduction barrier (bath stability constant) and enhancing the Ni-catalyzed activity (corresponding electronic structure) will facilitate the achievement of high-efficiency electroless copper plating under nonprecious metal catalysis.