The Fabrication of Stainless Steel Parts for MEMs
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The Fabrication of Stainless Steel Parts for MEMs Terry J. Garino, Alfredo Morales1, Thomas Buchheit2 and Brad Boyce2 Ceramic Materials and 2Tribology, Mechanics and Melting Departments Sandia National Laboratories Albuquerque, NM 87185-1411, U.S.A. 1 Microsystems Processing Department, Sandia National Laboratories Livermore, CA 94550, U.S.A. ABSTRACT A micro-molding process was used to fabricate parts in the 0.1 to 10 mm size range from a stainless steel nano-powder. The two types of molds used were both produced from parts fabricated using the LIGA process so that they had precise dimensional tolerance and straight sidewalls. Rigid PMMA molds were made by injection molding and flexible silicone rubber molds were made by casting. Mold filling was accomplished by mixing the powder with epoxy to form a putty-like material that was then pressed into the mold cavities and allowed to cure. After pyrolysis of the epoxy, the parts were sintered in forming gas. The densification kinetics were measured in situ using a video system. Full densification was achieved after 1 hour at 1350°C. The microstructure of the sintered parts was examined using the SEM. The mechanical strength, hardness, dimensional tolerance and surface roughness of the sintered parts were also measured.
INTRODUCTION The two most common techniques for producing parts for MEMs, silicon surface micromachining and LIGA, have limitations. Two limitations of Si micromachining are composition and thickness. The available materials set includes only Si, SiO2, SiC and diamond. Part thickness is generally in micron range. For the LIGA process, the materials set is limited to materials that can be plated such as pure metal and some simple alloys. Plating is a slow process and generates considerable quantities of hazardous waste. Thus an economical technique that could produce parts of more complex metals as well as ceramics and polymeric materials would complement the existing techniques. One technique with the potential to fabricate parts for MEMs with precise dimensional tolerance and with a very broad materials set is micro-molding. In micro-molding, a micro-mold is first fabricated that has cavities that are the shape of the desired parts. The mold cavities are then filled with the material of interest, typically in powdered form. The parts are then released from the mold and sintered to achieve high density and strength. Since it is a batch process, micro-molding has the potential to be low cost, as long as the cost of the molds is not excessive. Previous work has focused on either powder injection molding1-4, a more complicated process, or on filling molds made by deep x-ray lithography (DXRL)5, the same process used to make molds for LIGA, which were therefore relatively expensive due to the cost of synchrotron exposure. In the present work, LIGA was used to make the master from which the molds are made so that precise dimensional tolerance, straight sidewalls and high aspect ratio parts can be produced without the expense of DXRL. B5.19.1
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