The use of planar fluidic devices for performing small-volume chemistry was first proposed by analytical chemists, who coined the term "miniaturized total chemical analysis systems" (/spl mu/TAS) for this concept. More recently, the /spl mu/TAS field has begun to encompass other areas of chemistry and biology. To reflect this expanded scope, the broader terms "microfluidics" and "lab-on-a-chip" are now often used in addition to /spl mu/TAS. Most microfluidics researchers rely on micromachining technologies at least to some extent to produce microflow systems based on interconnected micrometer-dimensioned channels. As members of the microelectromechanical systems (MEMS) community know, however, one can do more with these techniques. It is possible to impart higher levels of functionality by making features in different materials and at different levels within a microfluidic device. Increasingly, researchers have considered how to integrate electrical or electrochemical function into chips for purposes as diverse as heating, temperature sensing, electrochemical detection, and pumping. MEMS processes applied to new materials have also resulted in new approaches for fabrication of microchannels. This review paper explores these and other developments that have emerged from the increasing interaction between the MEMS and microfluidics worlds.

Microfluidics meets MEMS

Machining with electrochemical discharges is an unconventional technology able to machine several electrically non-conductive materials like glass or some ceramics. After almost 40 years of its first mention in literature, this technology remains an academic application and was never applied in industrial context. The knowledge about machining of non-conducting materials using electrochemical discharge phenomenon is reviewed up to this date with some particular attention to the electrochemical point of view. Some main limiting factors are highlighted and possible solutions are discussed.

Machining of non-conducting materials using electrochemical discharge phenomenon – An overview

Sample pretreatment on microfabricated devices.

The non-traditional machining of particulate reinforced metal matrix composites is relatively new. However, researchers seem to pay more attention in this field recently as the traditional machining of particulate reinforced metal matrix composites is very complex. This research investigates different non-traditional machining, such as electro-discharge, laser beam, abrasive water jet, electro-chemical and electro-chemical discharge machining of this composite materials. The machining mechanism, material removal rate/machining speed and surface finish have been analysed for every machining process. This analysis clearly shows that vaporisation, melting, chemical dissolution and mechanical erosion are the main material removal mechanisms during non-traditional machining. The thermal degradation and the presence of reinforcement particles mainly damage the machined surface. The understanding of electro-discharge, laser beam and abrasive water jet machining is more developed than that of electro-chemical and electro-chemical discharge machining for particulate reinforced MMC.

/pdf/developments-in-the-non-traditional-machining-of-particle-bum48hfw29.pdf

Developments in the non-traditional machining of particle reinforced metal matrix composites

Machining of various electrically non-conductive materials is possible with Spark Assisted Chemical Engraving (SACE) Even though this technology presents several interesting properties like simplicity, flexibility and the possibility to obtain very smooth machined surfaces, it has one severe weakness: reproducible machining can hardly be achieved One of the main limiting factors is the unstable gas film around the tool electrode in which the necessary electrical discharges for machining take place The known facts about this gas film are reviewed and a theoretical model allowing an estimation of its thickness is derived An experimental method for measuring this thickness using the inspection of the current-voltage characteristics of the process is presented Several methods to obtain more reproducible machining are proposed It is demonstrated that decreasing the gas film thickness by changing the wettability of the tool electrode can result in significantly higher machining repeatability

The gas film in Spark Assisted Chemical Engraving (SACE) - A key element for micro-machining applications

A new, versatile architecture is presented for microfluidic devices made entirely from glass, for use with reagents which would prove highly corrosive for silicon. Chips consist of three layers of glass wafers bonded together by fusion bonding. On the inside wafer faces a network of microfluidic channels is created by photolithography and wet chemical etching. Low dead-volume fluidic connections between the layers are fabricated by spark-assisted etching (SAE), a computer numerical controlled (CNC)-like machining technique new to microfluidic system fabrication. This method is also used to form a vertical, long path-length, optical cuvette through the middle wafer for optical absorbance detection of low-concentration compounds. Advantages of this technique compared with other, more standard, methods are discussed. When the new glass-based device for flow-injection analysis of ammonia was compared with our first-generation chips based on silicon micromachining, concentration sensitivity was higher, because of the longer path-length of the optical cuvette. The dependence of dispersion on velocity profile and on channel cross-sectional geometry is discussed. The rapid implementation of the devices for an organic synthesis reaction, the Wittig reaction, is also briefly described.

/pdf/multi-layer-microfluidic-glass-chips-for-microanalytical-mbcqgnlm1s.pdf

Multi-layer microfluidic glass chips for microanalytical applications.

3D micropatterning is done in an electrolyte with electrodischarge assisted etching at the tool tip. Reported are the influence of the percentage of sodium ions in the sample, the applied voltage and the distance between tool and glass sample, and the induced local composition modifications. SIMS analysis has shown the diffusion and extraction of sodium ions, dissolution of SiO/sub 2//sup $/and local substitution of Na/sup +/ with H/sup +/ ions. The study of such aspects will contribute to the control of 3D microstructuring and to the local surface modification.

3D microstructuring of glass using electrochemical discharge machining (ECDM)

Glass substrates were micromachined using electro chemical discharge machining. The developed tool holder allows to scan the substrate surface as well as machining it in a closed loop. The developed control algorithm for drilling holes allows to achieve relatively high machining speeds (up to 30 /spl mu/m/s) and deep structures (up to 1 mm). Micro-channels up to a depth of 100 /spl mu/m were machined in one step with a removal rate of 4.5/spl middot/10/sup 5/ /spl mu/m/sup 3//s. Reported are some examples of machining micro-holes, micro-channels and modification of existing pattering.

In situ measurement and micromachining of glass

Keywords: [SACE] Reference LSRO-CONF-2006-021 Record created on 2006-06-06, modified on 2017-05-10

Study of Spark Assisted Chemical Engraving – Process Technology Data

Keywords: SACE ; glass micro-machining ; microengineering ; robotics ; [SACE] Reference LSRO-CONF-2006-020 Record created on 2006-06-06, modified on 2017-05-10

Study of Spark assisted Electrochemical Etching - Force Measurements

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