Characteristics of Electroless Sn Plating Electrolyte using a Choline Chloride-Based Ionic Liquid

Abstract

In the present study, a choline chloride(ChCl)-based ionic liquid(IL) was used as an electrolyte to confirm the characteristics of electroless tin plating. The effect of the type of additive and reducing agent, as well as the addition of complexing agent and water, on the properties of the ChCl-based IL, including the freezing point, viscosity, conductivity, open circuit potential, and plating thickness, was investigated. The results showed that the crystallization temperature was 25 degrees C when the ChCl-thiourea molar ratio was 1:1, and it decreased to 10 degrees C upon adding the additive, while the conductivity increased and viscosity decreased. Dimethylthiourea was added to promote the electroless plating reaction. Electrolytic tin plating was performed at 70 degrees C using ChCl-thiourea-based IL as the electrolyte. The thickness of the tin-plated layer was 1.5 mu m when malonic acid and dimethylthiourea were used. The addition of a small amount of water increased the plating speed and thickness, and the maximum thickness of 2 mu m for the tin-plated layer was obtained after 30 min. These characteristics demonstrate the potential applications of these environmentally friendly electrolytes for fast, thick, and dense electroless tin plating using ILs at low temperatures.