High-speed indium electrodeposition: Efficient, reliable TIM technology

A new indium electroplating process was developed which provides pure indium deposits suitable as thermal interface materials (TIM) in electronic industry. The main goals of the project were: i.) to develop a stable, high speed indium plating process; ii.) to obtain pure indium deposits with a low melting point (156degC) and high thermal conductivity (82 W/mldrK); iii.) to provide good adhesion to the substrate with a void-free interface. The electrochemical plating bath is based on an acidic electrolyte with copolymer additives. Typical plating conditions are: pH 0.9-1.2, current density 0.5-20ASD, temperature 30-60degC and a metal ion concentration of 30-60 g/l. Uniform deposit thicknesses of a few microns up to several hundred microns can be achieved at a plating rate of 180 microns per hour at a current density of 10ASD. Good adhesion to standard nickel-plated substrates (no delamination or voids allowed) is critical for meeting the thermal and reliability targets. Adherent, void-free deposits were obtained with thermal conductivity and thermal expansion data that correspond favourably to literature values for the bulk metal.