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are still needed. Microstructural variations and the importance of these variations in determining the mechanical performance of LIGA deposited MEMS devices are of particular interest for two reasons. The as-deposited structures often contain columnar grains and are far from the thermodynamically stable equiaxed microstructure that is found in bulk nickel alloys. Variations in processing conditions may result in significant variations in the as-deposited microstructure; moreover, elevated temperature exposure can be expected to alter the microstructure and properties of the as-deposited devices. To date, a limited number of investigators have measured and reported values for the Young's modulus, yield strength and ultimate tensile strength of LIGA nickel films, see for example the works of Mazza, Dual and colleagues [2,3], Sharpe et al. [4-6] and Christenson et al. [7]. Published values of the Young's modulus of the films tested in these studies are somewhat inconsistent. Several authors [2,3] have reported Young's moduli of the LIGA materials that are consistent with the modulus of 207 GPa for bulk polycrystalline nickel [8], but others [4-7, 9] have reported significantly lower moduli. The yield and ultimate strengths of the LIGA nickel films reported in these studies are in closer agreement. However, Christenson et al. [7] have reported significant variations in the strength of LIGA fabricated nickel electroforms that were deposited with current densities between 20 and 80 mA/cm2 . The latter study

197 Mat. Res. Soc. Symp. Proc. Vol. 605 © 2000 Materials Research Society

suggested a grain size dependence, but more comprehensive microstructure-properties studies are still needed. The present study is motivated by the need to assure reliability and quality assurance of a U.S. Navy MEMS-based underwater safety and arming (S&A) device, that is spring-supported by electroplated nickel structures. Microstructural variations caused by unintentional variations in the processing parameters or by exposure to elevated in-service temperatures may lead to undesirable variations in the mechanical performance of the LIGA nickel components. In order to investigate the importance of such variations, the grain size and morphology of nine "asprocessed" and three "annealed" LIGA nickel films have been measured using cross-sectional optical microscopy and the results of these microstructural observations have been correlated with mechanical properties that were measured using microsample tensile testing. 2. EXPERIMENTAL PROCEEDURES Nine LIGA nickel microsamples that were fabricated in one large batch, but in separate electrodeposition baths, under nominally identical processing parameters. These samples were fabricated in the second LIGA fabrication run for the Naval Surface Warfare Center, Indian Head Division by Cronos Integrated Microsystems (formerly MCNC, MEMS Technology Applications Center); a detailed description of the sacrificial LIGA process used for MEMS S&A device fabrication is contained in Fan et al. [9]. Three film