Investigation of indium solder interfaces for high-power diode lasers

In order to optimize the soldering process of laserbars onto heatsinks with Indium solder, several investigations have been made. First the growth of Indium oxide film is examined. With this knowledge four different reduction materials are selected. Formic acid as a wet chemical reduction, a plasma activated Hydrogen/Argon gas, a gas enriched with formic acid, and a protective layer of Gold were investigated and compared for an optimized reduction of the oxide film of the Indium solder. A cross section of the solder interface after the soldering process is made in order to see the distribution of the metals. High diffusion of the solder with its contact partners is a sign of a good connection. Enough pure Indium has to be available after the soldering process in order to use its creek properties to reduce the mechanical stress in the laserbar.