polishing

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.

T Dobrev, D T Pham and S S Dimov
Manufacturing Engineering Centre, Cardiff University, Cardiff, CF24 3AA, UK

Abstract

Electro-chemical polishing is a process of improving micro smoothness, micro topology, and material brightness by anodic dissolving of the substrate in an electrolyte with an external source of electricity. The resulting surface improvements depend on the uniformity of the material microstructure, the lack of surface inclusions, and the consistency of the surface finish all over the target area. In contrast, laser milled structures are mostly concave features; their roughness is usually higher than that achieved on the other surfaces of the component, and also there is a significant presence of foreign or recast particles on them. Thus, it is important to investigate systematically the effects of electro-chemical polishing on microstructures machined by laser milling.

The paper discusses the effects of electro-chemical polishing on the surface finish of laser milled features. Although ECP displayed some limitations when polishing micro features, it still managed to achieve almost 30% improvements in omparison to the initial roughness after laser milling. Another benefit is that the process also improves the edge quality of the laser machined structures by removing the burrs.