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Investigating Size Effects on Mechanical Properties: Preliminary Work and Results for Thin Copper Foils.
Proceedings of Materialsweek 2001, 1-4 Oct. 2001, International Congress Centre Munich Abstract
Copper is one of the most important materials used in microsystems, mechatronic components and microprocessors. With decreasing dimensions of copper components, e.g. 0.2 µm copper configuration on microprocessors, and increasing application of simulation techniques to determine the reliability of components under working conditions the used material parameters have to characterise the material behaviour as close as possible. Many hints in literature and own measurements indicate an influence of the size of the test specimens on the mechanical properties of many materials used in microsystems, e.g. yield strength, ultimate strength, fracture strain, creep behaviour. For example, tensile tests of micro Ni specimens show an increase of the yield strength and a decrease of the strength of rupture with regard to values for large specimens. The creep of SnPb-eutectic solder material increases by a factor of ten when reducing the tested volume from 785 mm3 to 1.8 mm3. This paper discusses some important issues, which have to be considered in the study of the size effect on the mechanical properties of thin Cu foils, e.g. texture, grain size, and hardness. The main task is to perform experiments with specimens whose dimensions vary while keeping the ratio of thickness and width constant and whose microstructure is comparable. First results from tensile tests (deformation resolution 20 – 40 nm; force resolution 10-5 N; strain velocity 5*10-3 to 8*10-5) of rolled copper stripes, processed out of foils, of varying thickness (20 to 250 µm) are presented. | |||||||||||||
G. Simons, Ch. Weippert, J. Dual, J. Villain: