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Fracture and Fatigue Behaviour of MEMS related Micro Materials

: Walter, H.; Dudek, R.; Michel, B.

Proceedings of 11th International Conference on Fracture (ICF XI). CD-ROM : March 20-25 2005, Turin
ISBN: 978-88-903188-0-1
International Conference on Fracture (ICFXI) <11, 2005, Turin>
Fraunhofer IZM ()

Micro-Electro-Mechanical Systems (MEMS) stand for the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. MEMS-materials can be used for a large number of components. These materials show a complex material behaviour due to different mechanical and thermal properties throughout the sandwich, which can influence the mechanical and thermal reliability as well as the life time of it. Filled epoxy resin and electrodeposited metallic thin films are frequently used as MEMS-related materials. However, their mechanical characteristics, which are especially important for Finite Element Analysis (FEA), vary over a wide range. Therefore, for small-dimension samples the theory for bulk materials is oftentimes inaccurate. In this paper, a test method has been developed to determine the fracture toughness of filled epoxy resin with miniature CT-specimens. The investigation of fracture using small specimens is based on analysing crack resistance against stable and unstable crack growth behaviour of standard specimens under quasi-static loading conditions by means of experimental fracture mechanics. The experimentally obtained fracture mechanics parameters will be geometry independent, if they fulfil the geometry criterion of minimal specimen thickness. The critical minimum specimen thickness of epoxy was determined to be 4 mm. Furthermore, a new test methodology will be presented for the determination of the fatigue behaviour of thin copper and nickel films, which is based on bi-material bending. The tests were accompanied by FEA to calculate the cyclic plastic strain of the bending experiments.