Maskless EMM

Electrochemical micromachining (EMM) is a technique designed to generate patterned microstructures in metals and alloys [ 145]. Microfabrication by EMM may involve maskless or through-mask dissolution. Maskless EMM uses the... 

In maskless EMM, there will not be any photoresist mask on the surface of the workpiece sample. Metal dissolution takes place from the desired area of the workpiece in a very selective and controlled way. Highly localized selective metal dissolution from the surface of the workpiece can generate a designed pattern or shape in a 2D or 3D scale. Anodic dissolution in maskless EMM is controlled by the current density, which depends on various predominant machining parameters and anodic reaction pattern. An lEG between the workpiece surface and tool is maintained at a very low value such that stray current effect is minimized. Passivating electrolyte is suitable for maskless EMM due to its ability to form transpassive oxide films and evolve oxygen in the stray current zone. Here, current efficiency varies as a function of the distance from the machining area hence, metal removal is more selective and localized across the zone of the workpiece surface where it faces the tool. 

Different types of EMMs require microtools with different features such as shape and size. For through-mask EMM, the shape of the tool electrode is simple because a mask will mainly restrict the machining area and in turn control the final shape evolution, with a very low aspect ratio. However, for maskless EMM, the shape of the tool electrode will localize the machining area to generate the desired microfeature with a higher aspect ratio. Hence, the shape and size of the microtool are vital factors in the case of maskless EMM. Depending on the types of EMM as discussed in Chapter 4 and shown in Fig. 4.1, EMM tools can also be of various types. 

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