Cold atmospheric plasma spraying is used to produce thin coatings of copper and tin between 20-80 μm thickness for use in diffusion soldering. This study presents an alternative process to apply composite solders directly onto power electronic bare dies. The formation of intermetallic phases may be promoted by the homogeneous distribution of the Cu and Sn particles as they are presented not in a layered structure but as a pseudo alloy within the coating. The Cu and Sn powder is mixed in situ using two powder conveyors, enabling adjustable mix ratios. The presented approach has been shown to produce a homogeneous particle distribution within the coating. Furthermore, preliminary experiments indicate the feasibility of the technology for applications in diffusion soldering.

In this study, two different types of power supply are used in order to analyze the influence of the current output characteristics on the electric discharge characteristics. Three different plasma spray guns, namely F4, 9MB and SinplexPro, are studied with the use of different powder feedstock materials (Metco 204C-NS, Metco 71VF-NS, Metco 450NS and Hydroxyapatite C) by measuring the real-time gun voltage and current as well as the frequency spectra of the electric discharge during the spray process. In addition, a metallurgical analysis of the spray coatings is done in order to investigate the influence of the electric discharge characteristics on the spray coating quality in terms of the average coating porosity, hardness, deposition efficiency, degree of oxidation and microstructure.