Fabrication of Microchannels

Techniques for the fabrication of microstructured channel systems will be discussed below, where the focus is on their applicability for future mass production rather than providing detailed information about the techniques. 

Micro-milling was frequently applied in many early applications and it is definitely a useful tool for experimental work and rapid prototyping, but is certainly not a choice when considering future mass production. 

Punching is a cheap technique suitable for mass production. To achieve a sealed microchannel system, the punched plates need to be separated from each other by unstructured plates. To the knowledge of the author of this book only cross-flow heat-exchangers can be fabricated out of punched plates, because the channel systems 

At present, corrugated metal foils fabricated by rolling are already being applied in the field of automotive exhaust gas systems. The metallic monoliths fabricated this way achieve channel dimensions in the sub-millimetre range and are actually microtechnology . 

Laser ablation is frequently applied in many industrial applications. However, for the fabrication of microchannels of several hundred micrometre depth the method appears not to be cost competitive. For smaller channel dimensions in a region well below 100 pm, laser ablation might well be a cost competitive option, especially for small scale applications. 

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Only very few studies with alternative materials and fabrication methods have been published. Ekstrom et al. [35] demonstrated the feasibility of structuring inexpensive polymeric materials by means of a microfabricated master for the production of microchannel systems. The structured polymer film was mechanically clamped between two glass plates to form a closed channel system. Recently, a similar route for the fabrication of microchannel chips that relies on casting of an elastomeric polymer material against a microfabricated master has been presented by Effenhauser et al. [36] (see Sect. 3.4). 

Figure 3 show the assembled microchannel setup, within the PMMA block, and the installed thermocouples at both the lower (Fig. 3a) and the upper (Fig. 3b) plates. The employed technique allowed for the fabrication of microchannels up to 20 pm of plates spacing and uncertainty of 2.0 pm. 

FIGURE 51.1 Schematic diagram of the general processing steps involved in the fabrication of microchannel structures using sacrificial materials. 

FIGURE 51.2 Fabrication of microchannels in a polymer substrate using E CSLs and solvent bonding (additional details are in the text). 

Fabrication of MicroChannel Plate Heat-Exchanger Reactors ... 

Fabrication of microchannels by laser ablation of polymer, PMMA (a) schematic diagram of the laser beam, the laser ablated groove, including the... 

Tonkovich, A. L. Y, Roberts, G. L, Fabrication of a stainless steel microchannel microcombustor using a lamination process, in Proceedings of the SPIE Gonference on Micromachined Devices and Gompo-nents IV, pp. 386-392 (September 1998),... 

Recognizing that the reforming reaction is mass transport limited, the reforming catalyst has been fabricated in microchannel forms which results in significant (factor of 3-5) reduction in the size of the reformer. 

Fabrication of catalyst immobilized microchannel reactors usually needs expensive, complex, and multistep methods. On the eontrary, reactors with simple structures (Figure 5) can also perform effieient hydrogenation reaetions. Yoswathananont et al. [21] reported an effieient hydrogenation reaction in a continuous flow system by the use of a gas-liquid-solid tube reactor. 

Plastic materials have gained importance in microfabrication due to their ease of molding, inexpensiveness, and disposability. Some workers have used these substrates for fabrication of microchips. Pethig et al. [78] and Roberts et al. [79] used laser ablation as a direct method for creating microchannels in plastic chips without the need for fabrication. The methods used an UV excimer laser to bum the microchannels onto the polymer substrate, moving in a predefined,... 

T. Yang, S. Y. Jung, H. Mao, and P. S. Cremer, Fabrication of phospholipid bilayer coated microchannels for on chip immunoassays, Anal. Chem. 73, 165-169 (2001). 

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