Rolf Wüthrich

Physical principles and miniaturization of spark assisted chemical engraving (SACE)

Keywords: SACE ; glass micro-machining ; microengineering ; robotics ; [SACE] ; Micro-factory Reference LSRO-CONF-2006-028View record in Web of Science Record created on 2006-06-06, modified on 2017-05-10

Integration of gold nanoparticles in PDMS microfluidics for lab-on-a-chip plasmonic biosensing of growth hormones

Gold nanoparticles were synthesized in a poly(dimethylsiloxane) (PDMS) microfluidic chip by using an in-situ method, on the basis of reductive properties of the cross-linking agent of PDMS. The proposed integrated device was further used as a sensitive and low-cost LSPR-based biosensor for the detection of polypeptides. Synthesis of nanoparticles in the microfluidic environment resulted in improvement of size distribution with only 8% variation, compared with the macro-environment that yields about 67% variation in size. The chemical kinetics of the in-situ reaction in the microfluidic environment was studied in detail and compared with the reaction carried out at the macro-scale. The effect of temperature and gold precursor concentration on the kinetics of the reaction was investigated and the apparent activation energy was estimated to be Ea*=30 kJ/mol. The sensitivity test revealed that the proposed sensor has a high sensitivity of 74 nm/RIU to the surrounding medium. The sensing of bovine growth hormone also known as bovine somatotropin (bST) shows that the proposed biosensor can reach a detection limit of as low as 3.7 ng/ml (185 pM). The results demonstrate the successful integration of microfluidics and nanoparticles which provides a potential alternative for protein detection in clinical diagnostics.

A systematic characterization method for gravity-feed micro-hole drilling in glass with spark assisted chemical engraving (SACE)

Gravity-feed drilling is the most commonly used method for micro-hole drilling in glass with spark assisted chemical engraving (SACE). This paper proposes a method allowing the systematic characterization of this drilling method. The influences of voltage, tool shape and force are investigated. It is found that SACE gravity-feed drilling shows two regimes depending on the drilling depth. During the first 200–300 µm, the discharge regime, controlled by the number of discharges inside the gas film, allows fast drilling (up to about 100 µm s−1). For deeper depths, the drilling is controlled by the hydrodynamic regime in which the drilling speed is limited by the flow of the electrolyte inside the micro-hole resulting in slow drilling of typically 10 µm s−1. Furthermore, it is shown how the gas film build-up time is limiting the drilling speed.

The current signal in spark-assisted chemical engraving (SACE): what does it tell us?

Spark-assisted chemical engraving (SACE) is a promising micro-machining technology for the low-cost machining of holes and channels in non-conducting materials, such as glass and some ceramics. Despite the complexity of SACE due to the interdependency of thermal, electrochemical and mechanical effects, the key data of the machining process can be obtained from only a few signals. Possible process surveillance signals are analysed and discussed. In particular, the current flowing between the electrodes is analysed. It is shown that various information can be deduced from it, such as qualitative indications of the local electrolyte temperature, differentiation between machining and non-machining and the distinction between the presence and absence of a gas film. However, so far no direct link between the current and the instantaneous material removal rate could be found. Experimental results are presented and the possibility of active process control based on current measurement is discussed.

Toward a better understanding of glass gravity-feed micro-hole drilling with electrochemical discharges

Spark-assisted chemical engraving (SACE) is a flexible, simple and inexpensive method for machining electrically non-conductive materials. SACE is particularly interesting because of the high drilling speed that can be achieved compared to other micromachining technologies. In this paper, the issue of drilling speed decreasing from 100 µm s−1 to 10 µm s−1 for micro-hole depths more than 200–300 µm is analyzed. To understand better the material removal mechanism, with the target to eliminate this limit, a model for the material removal mechanism as a hybrid mechanism combining local heating and chemical etching is presented and compared with experimental data. The comparison between the model and experiment allowed the estimation of the machining temperature to be around 600 °C.

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

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

Geometrical characterization of micro-holes drilled in glass by gravity-feed with spark assisted chemical engraving (SACE)

/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.

Improving the material removal rate in spark-assisted chemical engraving (SACE) gravity-feed micro-hole drilling by tool vibration

Spark assisted chemical engraving (SACE) is an unconventional micro-machining technology for glass processing based on electrochemical discharges. SACE gravity-feed drilling is discussed and the material removal rate, quality and geometrical dimensions of drilled micro-holes in glass as a function of the drilling depth are characterized optically. Depending on the machining voltage and drilling depth, four different kinds of micro-hole qualities are obtained from holes with well-defined sharp contours to holes affected by thermal cracks. Based on these results a qualitative model for SACE machining by gravity-feed is given.

Spark assisted chemical engraving (SACE) in microfactory

Spark-assisted chemical engraving (SACE) is an unconventional micro-machining technology particularly suited for glass processing, taking advantage of electrochemical discharges. This technology distinguishes itself by its simplicity and flexibility, the possibility of machining high aspect ratio structures, the excellent surface qualities and the non-utilization of expensive clean room facilities. As the process is a serial one, the material removal rate becomes an important issue. It is shown that, by adequate tool vibration, it is possible to improve the mean material removal rate in gravity-feed drilling by a factor of 2. Micro-holes in glass with a depth of 300 µm are drilled in less than 10 s.

A Numerical Study of Suspension Injection in Plasma-Spraying Process

Spark assisted chemical engraving (SACE) is a method for 3D microstructuring of glass or other non-conductive materials with high aspect ratio and smooth surface quality. It is applicable for rapid prototyping of microfluidic devices, for MEMS interfacing and similar applications. Typical feature size is in the hundreds of micrometres, down to a few tens of micrometres. It is a table-top technology requiring no clean rooms and no masks and with very modest space usage. It is thus well suited for microfactories. This paper gives a basic introduction to SACE and some machining examples.