Additive Manufacture of Metal-Ceramic-Joints by means of Selective Laser Melting

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This project deals with the research of additive production of metal-ceramic composites by means of selective laser melting for power electronics. Currently, ceramic circuit carriers are manufactured using DBC- (direct bonded copper) or AMB- (active metal brazing) processes, that are mostly used as power electronic substrate materials. Both processes involve the bonding of a ceramic substrate to a metallic, electrically conductive thin (0.2-0.5 mm) layer, usually in the form of foils. In the DCB process, the two materials are joined by wetting of the molten Cu2O at the bottom side of the copper foil in direct contact with an oxide ceramic (usually Al2O3) in a firing process at approx. 1064 °C. This process results in a cohesive bond, which is necessary in the use of power electronic circuit carriers due to the CTE differences between ceramics and metallization. In the AMB process, titanium additions to a solder alloy (usually Ag-Cu-solders) form a reaction layer during the firing process in contact with ceramic materials. This solder therefore acts as an interface between the ceramic substrate and a metal foil. However, both processes show weaknesses in the areas of flexibility, 3D capability of the metallization and the consumption of resources. In order to finally preserve the conductive structures of the circuit carrier, various lithography-, etching- and washing-processes are necessary, which significantly extend the process chain and additionally harm the environment by using chemicals. Selective laser melting offers an alternative: powder materials can be selectively melted on ceramic substrates at approx. 500 °C in a single process step, which leads to the final metallization. This process can be described as selective laser brazing (SLB). In this research project, Cu-Ti powder is used as metallization material based on the analysis of the state of the art and the extensive preliminary work carried out. Al2O3 will serve as the substrate material. At the beginning of the research project, the melting behaviour of the powder materials without ceramic substrate material will be qualified. However, the main objective of the research is the determination of the wetting behaviour of the powders on the heated Al2O3 with the associated parameter studies. As qualification methods, adhesion tests, current carrying capabilities as well as long-term stabilities of the metallization before and after a thermal post-treatment in inert / evacuated atmosphere are tested. On the basis of EDX and WDX analyses, the core question of the research project - the possibility of a cohesive connection of titanium-containing powder with Al2O3 in the form of the creation of magneli-phases by means of SLB/SLM - is to be answered.