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Metallic large area mold inserts (LAMIs) are essential for the replication of polymer microfluidic devices. Successful molding of micro- or nanoscale features over large areas is dependent on improving the dimensional control of the mold inserts, particularly those fabricated by electrodeposition using the LIGA or UV-LIGA processes. A systematic approach to controlling the internal stress of the nickel deposits, which was essential for predicting the final flatness of the LAMIs prior to electroplating, was carried out. The internal stress of the nickel deposits from a nickel sulfamate solution was estimated using a bent strip stress measurement method after maintaining electroplating chemicals and conditions and reducing contamination. Over-electroplating of the nickel LAMIs was performed on SU-8 electroplating molds on 150 mm diameter Si wafers. Detailed characterization of the nickel LAMIs to determine the relationship between the overall flatness of the LAMIs and the internal stress identified a suitable process window in terms of the current densities (10–20 mA/cm2) and the internal stress (−8.3 ∼ −3.0 MPa) for the high quality nickel LAMIs with an overall flatness of 100 μm.

Micro production technologies are a driving factor in today’s continuous effort of developing new, highly functional products. The need for increased functionality is met by decreasing the size of individual components as well as consequently miniaturizing components for non-electronic properties including optical, mechanical, and fluidic functions. An important factor in this approach his the right material for a given task and the ability to shape it into the desired geometry as well as to combine micro components in a cost-effective way to build more complex modules and micro systems. One micro production technology that meet several of the above mentioned needs is the LIGA process, a combination of three major fabrication processes — x-ray based micromachining or deep x-ray lithography (DXRL), electroplating, and molding. In x-ray lithography the unique properties of synchrotron radiation, especially high intensity of collimated x-ray photons, permit patterning of extremely precise, very tall primary microstructures up to several millimeters in height with micrometer lateral dimensions and sub-micrometer details (so-called High-Aspect Ratio Microstructures, HARM). These microstructures are attractive for mechanical and optical components in MEMS (MicroElectroMechanicalSystems) devices. While x-ray lithography is crucial to achieve a primary microstructure with superior features, the use of synchrotron radiation is limiting the material choice to only a few polymer materials, so-called x-ray resists. Additional processes including electroplating and molding, however, open up a huge selection of engineering materials such as metals, ceramics, and also a large number of polymers and allow MEMS engineers to combine structural and material properties to build the next generation MEMS devices. This paper is primarily focusing on the DXRL process. Process fundamentals including equipment and infrastructure, x-ray masks, resists, typical structure geometries as well as patterning accuracy will be discussed. A few examples will illustrate ongoing efforts of commercializing this technology and also indicate future areas of applications.Copyright © 2004 by ASME

Micro gas chromatograph (GC) separation columns were fabricated and tested. Rectangular columns with high aspect ratio have inherent benefits over traditional tubular columns and can easily be integrated into a GC sensor system for rapid chromatographic analysis. The 2 m long, 50 μm wide, 500 μm tall columns were fabricated out of electroplated nickel through deep X-ray lithography using the LIGA technique. Critical fabrication issues including reproducible fabrication of compact footprint, deep columns and sealing of the metal columns were addressed. Experiments were conducted to establish the relationship between column head pressure and flow rate. Methane samples analyzed using hydrogen as a carrier gas on uncoated columns showed very little dispersion suggesting that there was no internal leakage in the columns. The sensor performance data compares well with other micro GC sensor systems.Copyright © 2004 by ASME