LIGA
Electrochemical finishing of nickel microstructures
S. Kissling, K. Bade
Forschungszentrum Karlsruhe, Institut für Mikrostrukturtechnik, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
Abstract
One method to manufacture high aspect ratio metallic microstructures is the LIGA technique. The acronym LIGA stands for the German words for lithography, electroforming and moulding. A resist layer (e.g. PMMA) is structured using deep X-ray lithography. The resist is developed and the resulting mould is filled with metal by electroplating. Though electroplating is an essential part of the LIGA process there are still challenges concerning the deposit surfaces. Nevertheless, extremely precise metal structures can be manufactured. In particular, the sidewall surface quality can be in the sub-micrometer range. But due to irregularities during the deposition process, resulting in rough or wavy surfaces, the emerging surface does not meet required tolerances. For this reason, a finishing process is necessary. Electrochemical techniques such as electro- or plasmapolishing have been evaluated. Electropolishing, a common anodic dissolution technique widely used in industry to obtain smooth, bright and burr-free surfaces, as well as plasmapolishing, also a technique based on the anodic dissolution are presented. First results of both an electropolished and a plasmapolished nickel microstructure are reported.
| 120 reads | Approaching a sub-micron capability index using a Werth Fibre Probe System WFP
Richard Thelen (a), Joachim Schulz (a), Pascal Meyer (a), Volker Sailea (a)
(a) Institute for Microstructure Technology, Research Centre Karlsruhe, 76646 Eggenstein, Germany
Abstract
Reproducibility and precision of LIGA structures has been claimed in many publications, founded mainly on brilliant pictures. Because of the poor accessibility to the sidewalls many publications are based on surface measurements without including information about z depending aspects [1] and focus on reproducibility as measured close to the top.
Often this neglects operator’s influence, short time and long time reproducibility, environmental effects on the CMM and others. Tactile optical metrology might help to overcome 2D measurements. Repeatability of tactile optical metrology at IMT was proven to be less than 0,3 μm over some months using ultra fine probes with less than 25 μm diameter. In addition DoE was used to determine the minimum deviation for best possible machine settings. Standard Deviation between 50 and 30 nm was measured. Compared to that, uncertainty remains about 1-2 μm for 3D measurements even with z maximum restricted to 1 mm [2]. Not enough to measure sub-μm product variation that is a typical benefit of LIGA products.
Investigations were started at the Research Centre Karlsruhe to find out more about the effects influencing the measurements to explain why repeatability and capability do not match. Interaction between sample and sensor was the main reason. This was simulated and the results were used to reduce the uncertainty of the system. IMT elaborated a new strategy that improves the capability of a coordinate measurement machine CMM with tactile optical sensor for LIGA parts with sub μm variation.
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