1 Controlled and Localized Electrochemical Microfabrication …
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depth and width of the processes microchannels. When a moving period is completed,
the spherical tip feeds downward with a controlled layer thickness δ. Then the moving
path is repeated. Thus, microchannels with a higher depth could be fabricated. The
electrolyte electric resistance
R electrolyte
could be expressed as
R electrolyte
= ρ ·d,
where ρρ is the specific electrolyte resistivity, and d is the local separation between
the two electrodes [2]. Because the side gap at spherical end () is smaller than
that face to the shank ( + λ), the electric resistance (ρ · ) at the spherical tip is
smaller than that around the electrode shank (ρ( + λ)). Thus, the EMM rate at the
spherical tip is larger than that around the electrode shank. With the feeding of the
spherical tip towards the workpiece, the taper of the fabricated microchannels could
be reduced. Therefore, the aspect ratio of the microchannel could be improved.
Figure 1.8b shows the microchannel with a depth of 0.25 μm fabricated by layerby-layer EMM using the moving spherical tip as the tool electrode. A layer thickness of 0.1 μm, applied voltage of 4 V, the inter-electrode gap of 1 μm were used.
EMM was implemented at room temperature. As the cross-sectional profile shown in
Fig. 1.8c, a microchannel with an aspect ratio of 0.125 has been fabricated, while the
processed microchannel had an aspect ratio of smaller than 0.1 in the previous study
[22]. Experimental results preliminary verified the possibility of high-aspect-ratio
processing by layer-by-layer EMM with moving spherical tip as the tool electrode.
The following studies would be conducted to investigate the characteristics of layerby-layer EMM while using moving spherical tip as the tool electrode. However,
the achieved maximum machining depth by EMM may be restricted by the spherical diameter, due to the conical shape of the tool electrode shank, as illustrated in
Fig. 1.1c. The taper angle could be deteriorated by the shank part induced stray corrosion. Thus, spherical tool electrode with cylindrical shank of the smaller diameter
is urgently needed to process micro channels with a higher depth, which would be
studied in the following study.
1.4 Conclusions
In this paper, electrochemical micromachining using a moving spherical tip as the tool
electrode has been implemented to fabricate microchannels. Both the mechanisms
and advantages of EMM using the moving spherical tip were analyzed. The electric
field density distribution on the workpiece surface determined the machined profile of
the microchannels, which was verified by the simulation and experimental methods.
An experimental setup for electrochemical micromachining was developed with a
workpiece moving resolution of nanometer scale. Experiments were conducted to
investigate the influences of the applied voltage, initial inter-electrode gap, and spherical tip diameter on the machined depth and precision of EMM. Results showed that
microchannels with smaller gap could be processed with the lower voltage, proper
smaller inter-electrode gap, and smaller spherical tip diameter. Microchannels with
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depth and width of the processes microchannels. When a moving period is completed,
the spherical tip feeds downward with a controlled layer thickness δ. Then the moving
path is repeated. Thus, microchannels with a higher depth could be fabricated. The
electrolyte electric resistance
R electrolyte
could be expressed as
R electrolyte
= ρ ·d,
where ρρ is the specific electrolyte resistivity, and d is the local separation between
the two electrodes [2]. Because the side gap at spherical end () is smaller than
that face to the shank ( + λ), the electric resistance (ρ · ) at the spherical tip is
smaller than that around the electrode shank (ρ( + λ)). Thus, the EMM rate at the
spherical tip is larger than that around the electrode shank. With the feeding of the
spherical tip towards the workpiece, the taper of the fabricated microchannels could
be reduced. Therefore, the aspect ratio of the microchannel could be improved.
Figure 1.8b shows the microchannel with a depth of 0.25 μm fabricated by layerby-layer EMM using the moving spherical tip as the tool electrode. A layer thickness of 0.1 μm, applied voltage of 4 V, the inter-electrode gap of 1 μm were used.
EMM was implemented at room temperature. As the cross-sectional profile shown in
Fig. 1.8c, a microchannel with an aspect ratio of 0.125 has been fabricated, while the
processed microchannel had an aspect ratio of smaller than 0.1 in the previous study
[22]. Experimental results preliminary verified the possibility of high-aspect-ratio
processing by layer-by-layer EMM with moving spherical tip as the tool electrode.
The following studies would be conducted to investigate the characteristics of layerby-layer EMM while using moving spherical tip as the tool electrode. However,
the achieved maximum machining depth by EMM may be restricted by the spherical diameter, due to the conical shape of the tool electrode shank, as illustrated in
Fig. 1.1c. The taper angle could be deteriorated by the shank part induced stray corrosion. Thus, spherical tool electrode with cylindrical shank of the smaller diameter
is urgently needed to process micro channels with a higher depth, which would be
studied in the following study.
1.4 Conclusions
In this paper, electrochemical micromachining using a moving spherical tip as the tool
electrode has been implemented to fabricate microchannels. Both the mechanisms
and advantages of EMM using the moving spherical tip were analyzed. The electric
field density distribution on the workpiece surface determined the machined profile of
the microchannels, which was verified by the simulation and experimental methods.
An experimental setup for electrochemical micromachining was developed with a
workpiece moving resolution of nanometer scale. Experiments were conducted to
investigate the influences of the applied voltage, initial inter-electrode gap, and spherical tip diameter on the machined depth and precision of EMM. Results showed that
microchannels with smaller gap could be processed with the lower voltage, proper
smaller inter-electrode gap, and smaller spherical tip diameter. Microchannels with