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|High-Speed Indium Electrodeposition: Efficient, Reliable TIM Technology|
|Keywords: Indium, electrodeposition, thermal characterization|
|Due to its low melting point (156°C) and high thermal conductivity (82 W/m•K), indium is used extensively as a thermal interface material (TIM). Current technology applies pre-formed pieces of indium, but production issues arise from the required inspection, handling, and fluxing steps. Yield and performance suffer from the purity and interfacial shortcomings of a foil-based technology. On the other hand, electrolytic deposition may produce high purity indium deposits with good interfacial characteristics. We have developed a high-speed process to plate pure indium which satisfies the requirements for thermal interface management. The development of an indium electrolyte is challenging while the reduction potential of In3+ compared to hydrogen is only -0.34V vs. SHE. This means that hydrogen formation will take place prior to indium electrodeposition. Corresponding organic additives are required in the electrolyte in order to suppress the hydrogen generation on the cathode surface; meanwhile these chemicals should enhance the Indium electrodeposition. Here we present a new indium plating process based on an acidic electrolyte with high current efficiency at a minimum of 95%. With this electrolyte it is possible to work up to 20A/dm2. Uniform deposits of a few microns up to several hundred micron thicknesses can be achieved at a plating rate of 100 microns per hour. For good adhesion to standard nickel-plated substrates, an adhesion layer of gold or nickel is required. Thermal conductivity and thermal expansion of the indium deposits correspond to literature values for the bulk metal. The plated deposits were characterized and the results will be presented.|
|Nathaniel Brese , Director-Strategic Planning & Technical Marketing
Rohm and Haas Electronic Materials