Developments in micro-electron beam welding

At the ISF (Joining and Welding Institute, RWTH Aachen University) the long-established electron beam (EB) welding process is investigated to meet the requirements of the field of micro-applications. A modified LEO ZEISS DSM 962 scanning electron microscope (SEM) is being used as a Micro-EB welding machine. The diameter of the beam in welding mode is about 20 μm, with a maximum beam power of 6 Watt at 30 kV acceleration voltage. The process-specific advantages, such as the inertia-free movement of the tool electron beam, the very small beam diameter, the clean room environment which is due to processing in a vacuum (no shielding gas needed) and the excellent applicability for visual quality control offer the best preconditions for hybrid micro-assembly purposes. If the technology is down-scaled to a micro-level, physical effects occur whose consequences must be met with new approaches of solution. Joining of micro-components presupposes optimal contact conditions. If the micro-components are of a flexible type, those optimal conditions are difficult to implement. The ratio of forces during the joining process and also the low stiffness of the components which is due to the small dimensions require, on the one hand, the application of a suitable handling technique or, on the other hand, a specific beam manipulation strategy. Especially in the field of micro-applications, the possibility to exert influence on the thermal distortion by symmetrical heating and solidification processes is of particular importance. Therefore, the reproducibility of the welded joints is one of the great challenges in the field of microwelding. The investigations and developments done at the ISF show successful results in joining stainless steel sheet materials down to 30 μm thickness and steel wire down to 50 μm in diameter, whereas other materials (Tungsten, Aluminum, Titanium, Nickel) are under investigation.