Elastic and Inelastic Properties of Electroplated Nickel Used in LIGA Techniques
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Elastic and Inelastic Properties of Electroplated Nickel Used in LIGA Techniques Basrour Skandar 1 and Delobelle Patrick 2 Laboratoire de Physique et Métrologie des Oscillateurs. UPR 3203 CNRS, 32 Avenue de l’Observatoire. 25 044 F Besançon, FRANCE. 2 Laboratoire de Mécanique Appliquée Raymond Chaléat. UMR 6604 CNRS, 24 rue de l’Epitaphe, 25000 Besançon, FRANCE. 1
ABSTRACT The aim of this paper is a wide investigation at the micro scale of the elastic and inelastic properties of electroplated Nickel, which is extensively used in the LIGA techniques. Using a nano-indentation set-up, we have obtained the Berkovitch's hardness HB and the Young's modulus E. These mechanical properties are affected by the current densities used during the electroplating as well as the nature of the substrates. The roughness Ra was obtained thanks to confocal microscopy and a linear behavior of HB versus 1/ Ra corresponds to a Hall and Petch relation. The yield stress Y0 and the ultimate strength Q have been deduced from the experimental measurements using a Finite Element Method (FEM) .Q has been found sensitive to the deposition conditions. Moreover (Y0+Q) has shown a linear dependence versus the hardness HB. Finally, Nickel microbeams fabricated by LIGA technique have been characterized with a bending test. The data deduced from this method, i.e. E and Y0+Q, are in good agreement with the results obtained by nano-indentation. INTRODUCTION The development of Micro-Electro-Mechanical Systems (MEMS) by Computer Aided Design (CAD) needs an accurate description of the physical properties of the materials involved during the fabrication process. Among these properties, the mechanical characterization of test structures is crucial for improving the fabrication processes [1]. Up to now, three-dimensional microstructures are widely obtained with bulk silicon or quartz micromachining. More recently, the LIGA (Lithography, Galvanoformung Abformung) techniques using X or UV light become more and more important for the MEMS. Indeed, these techniques are attractive because they allow the use of different kind of materials like plastics, metals and ceramics too, and are suitable for high aspect ratio structures. More recently, new UV photoresists have strongly propelled the UV – LIGA. This process is more compatible with conventional microelectronics environment, and is limited to the deep etch UV lithography and the electroplating of metals. At the moment, the Nickel is widely used in the fabrication of metallic microdevices or microsystems [2]. In the first part of this paper, we focused our attention on the Berkovitch's hardness HB of the material and the Young’s modulus E obtained with a nano-indentation set-up. The investigation of these properties have been done towards the preparation conditions namely the current densities J used during electroplating, the nature of the substrates (Copper or Silicon depending on the further applications), and the bath composition. In addition, we have also correlated HB to the roughness Ra obtained thanks to
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