Fabrication of high aspect ratio microstructure arrays by micro reverse wire-EDM

In this paper, a machining technique to fabricate high aspect ratio microstructure arrays of a total volume less than 1 mm³ is developed. A method for determining the appropriate tension of the micro brass wire of the micro wire-EDM mechanism designed in our previous study is proposed, and a design for suppressing the vibration of the wire is implemented. In addition, a machining approach coined 'reverse wire-EDM' is developed. The micro wire-EDM mechanism is mounted on the worktable rather than on the machine head while the micro workpiece is clamped on the spindle instead of the worktable by a micro chuck. Machining is carried out by a horizontal moving micro brass wire of 20 νm diameter located beneath the micro workpiece to accelerate the removal of debris and to eliminate the heat accumulated in the micro gap during machining. The possible occurrence of short circuit discharge and thermal deformation of the machined part are therefore minimized. Experiments are conducted to machine various high aspect ratio miniature structures including a microstructure array of ten 10 νm sharp-edge lamellae at the tip, a microstructure array of ten 10 νm uniform thickness lamellae and a microstructure array of ten by ten 21 νm squared pillars. It is found that a microstructure array of an aspect ratio more than 33 is satisfactorily and precisely fabricated. The dimensional accuracy and geometric accuracy are less than 0.6 and 1.0 νm, respectively, while the surface roughness R_max is kept within 0.44 νm.