Abstract
The role of thiourea as an organic additive in the nucleation and growth mechanism was studied for copper deposition and its application in the decorative electroplating and fashion accessory industries. The bath was designed to reduce the environmental and ecological impacts using methanesulfonic acid as electrolyte as an alternative to alkaline cyanide baths. We evaluated the nucleation and growth mechanism of copper exploiting voltametric and chronoamperometric measurements with a brightener concentration ranging from 0 to 90 ppm. We used the Scharifker–Hills model to estimate the type of nucleation mechanism after progressive addition of thiourea. Scanning electron microscope was employed for surface analysis and morphological characterisation of the nuclei. We verified that progressive nucleation is a key step in the obtainment of a shiny and homogeneous copper film, but an excess of thiourea could cause parasitic adsorption reactions on the surface of the substrate. X-ray fluorescence spectroscopy was used for the thickness determination of the copper deposits and the electrodeposition efficiency correlated to thiourea concentration. Finally, the optimal concentration of thiourea was assessed to be 60 ppm for the used formulation of copper plating.
Highlights
Introduction iationsIn the electroplating industry, copper plating is an important treatment and it is often the first and irreplaceable step in the electrodeposition of metal films for both technological [1] and decorative [2] purposes
We studied a new methanesulfonic acid-based copper bath that would be safer for electroplating plant technicians than alkaline cyanide baths, ready to be upgraded in a white bronze deposition bath and eco-compatible [3]
Thiourea was added in a copper solution that already contained a complexing agent, necessary to tailor copper electrodeposition potential in the case of an upgrade of the bath into a bronze electrodeposition one
Summary
Introduction iationsIn the electroplating industry, copper plating is an important treatment and it is often the first and irreplaceable step in the electrodeposition of metal films for both technological [1] and decorative [2] purposes. Copper is an excellent undercoat for subsequent deposits, since it has good capability to compensate substrate defects that could accelerate corrosion, and its deposition can be chemically tailored to obtain levelled, high thickness bright films. The need to deposit small quantities of precious metals in the field of the electroplating industry and fashion accessories necessarily passes from the possibility of depositing copper or copper alloys (bronzes) with high thicknesses, high efficiency and improved corrosion resistance characteristics compared to the past. This need is fundamental for reducing the environmental and ecological impact for an increasingly eco-sustainable production. This work seeks to improve the copper deposition process, a Licensee MDPI, Basel, Switzerland.
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