EDTA electrolytes for the deposition of antimony coatings

Antimony coatings serve as a cost-effective alternative to tin in manufacturing printed circuit boards, a replacement for toxic cadmium in protecting steel components from marine corrosion, and a means of producing protective-decorative coatings with high reflectivity. These coatings also find application in semiconductor contacts, lithium-ion battery production, and other applications. This review examines the compositions and key process characteristics of aqueous solutions used for the electrochemical and electroless deposition of antimony coatings. These compositions contain the EDTA ion [(OOCCH 2 ) 2 NCH 2 CH 2 N(CH 2 COO) 2 ] 4- , which functions as a ligand, thereby binding antimony(+3) into complexes. EDTA-based electrolytes are characterized by high throwing power and their ability to yield high-quality, bright, and corrosion-resistant antimony coatings. A typical formulation, for instance, operates at a pH of 0.5–0.7 and contains 50–70 g/dm 3 antimony trichloride, 20–30 g/dm 3 disodium ethylenediaminetetraacetate dihydrate, 3.5–4.5 g/dm 3 of OP-10 additive, and 1.5–2.5 g/dm 3 of leveling agent A. Under operating conditions of 18–25 °C and a cathode current density of 1.5–5.0 A/dm 2 , these electrolytes yield light, silvery, bright, and relatively hard coatings. The deposition process is carried out with a current efficiency of 97.6–100.0% and a rate of 18.0–19.2 µm/h. The obtained coatings, with a thickness of up to 100 µm, possess a defective rhombohedral structure. The throwing power of the electrolyte under these conditions is 76–81%. A further advantage of these electrolytes is their relatively low toxicity. In addition, the review summarizes literature data on the complex formation of antimony(+3) with the EDTA ion in aqueous solution and on the structures of crystalline antimony(+3) ethylenediaminetetraacetates.