The effects of blast lag in abrasive jet machined micro-channel intersections

Abrasive jet micro-machining (AJM) uses compressed air carrying abrasive solid particles to micro-machine a variety of features into surfaces. If the feature sizes are less than the size of the abrasive jet footprint, then a patterned erosion-resistant mask is used to protect the substrate material, leaving exposed areas to define the features. Previous investigations have revealed a ‘blast lag’ phenomenon in which, for the same dose of abrasive particles, narrower mask openings lead to channels that are shallower than wider ones. Blast lag occurs when using AJM on brittle substrates because of the natural tendency to rapidly form a V-shaped cross-sectional profile which inhibits abrasive particle strikes on the narrow vertex at the feature centerline. In this paper, the blast lag phenomenon is studied when using AJM to machine a network of microfluidic channels. It is found that, in some cases, differences in blast lag occurring at channel intersections and within the channels themselves, can lead to channel networks of nonuniform depth. A previously developed surface evolution model is adapted to allow prediction of the onset of blast lag in the channels and intersections and thus explain these differences. Finally, methods to eliminate the differences are discussed.     

光学材料的激光微加工研究进展与应用前景

综述了国内外在光学材料激光微加工方面的研究成果和应用状况，并展望了其发展前景。     

制作微器件的超声电解复合微细加工基础研究

提出一种制造MEMS微器件的新技术——超声电解复合微细加工；设计微细加工工艺系统，进行一系列微细加工基础工艺试验，验证超声电解复合微细加工在微器件制造中的可行性．展示了该技术在提高微细加工精度、效率、表面质量等方面的优势，研究成果对完善MEMS器件制作技术具有重要理论意义与实用价值。     

Modelling of surface evolution in abrasive jet micro-machining including particle second strikes: A level set methodology

A previous implementation of narrow band level set methodology for the modelling of the surface evolution of masked features in abrasive jet micro-machining (AJM) including the effect of mask erosive wear was extended to include the effect of particle second strikes. The model uses a ray tracing/node tracking algorithm to allow the prediction of the effect of particle ricochets from the mask edges and the sidewalls of the machined feature on the resulting surface evolution of high aspect ratio features. Using the model, for the first time, the prediction of the particle second strike effects from inclined masked features is made possible. When compared to previous models that did not account for mask wear and second strike effects, the present model significantly improved the prediction of measured masked micro-channels machined using AJM in glass. When compared to previous particle tracking computer simulations, the present model was found to have a much shorter execution time, and in some cases also showed an improved prediction. The model can be useful in predicting the feature shape in the AJM of brittle targets for aspect ratios greater than 1, and hence for the micro-fabrication of microfluidic and MEMS devices.     

制作微模具的微机械加工技术应用与研究

应用微机械加工技术制作微型模具,再通过微型模具成形微型制件,具有简单、经济、制件质量好及生产效率高等优点.基于制造微模具的微机械加工技术,从加工特点、表面精度和应用场合等方面重点分析了能够制作型腔带有拔模斜度的金属微模具的加工技术——微细特种加工技术和微铣削技术,探讨了微模具制造进一步发展的方向和手段.     

Comparative study of stack interwinding micro-transformers on silicon monolithic

Interwinding planar micro-transformers are developed using micro-machining technique. The transformers with a vertically stack coil structure on silicon monolithic substrate are designed to achieve high coupling and high inductance value in a relatively small coil area. In this work, various types of stack interwinding transformer are fabricated, measured and compared. The results show that the metal-to-metal effect of a multi-layer structure contributes to the significant increase of parasitic capacitances and hence limits the operating frequency. Moreover, the lumped element parameters are analyzed by extracting the measured S-parameter. This investigation can give important information for the future development of three-dimensional RF devices.     

Abrasive jet micro-machining of planar areas and transitional slopes in glass using target oscillation

Analytical models are presented which allow the prediction of the shape, sidewall slope, and depth of abrasive jet micro-machined planar areas and transitional slopes in glass using a novel technique in which the target is oscillated transversely to the overall scan direction. A criterion was developed to establish the minimum oscillation velocity to ensure negligible surface profile waviness in the scanning direction. If the oscillation velocity is sufficiently greater than the scanning velocity, the target receives an approximately uniform energy flux, resulting in a high degree of flatness for both masked and unmasked planar areas micro-machined in glass. It was also found that particle scattering from the mask edge caused the sidewalls of a planar area to be very shallow, on the order of a few degrees. Two methods were investigated to machine planar areas with increased sidewall slope using target oscillation: (i) machining micro-channels adjacent to the planned planar area, and (ii) target oscillation with an obliquely oriented nozzle. Among these two methods, target oscillation with an obliquely oriented nozzle created steeper sidewalls and was easier to implement, but it also caused appreciable mask under-etching. A major distinction between the target oscillation approach and a previously published method that was based on the superposition of the erosion profiles of adjacent nozzle scans, is that the latter is capable of machining an arbitrary surface profile over a large area, whereas the present target oscillation technique is intended only for the machining of flat planar areas at a single elevation. For such applications it is the preferred approach.     

Quad-cantilever microsensors with a low-cost single-sided micro-machining technique for trace chemical vapor detection

This paper presents a quad-cantilever microsensor for on-the-spot detection of ultra-low concentration chemical vapors. Compared with conventional dual-cantilever sensors, the quad-cantilever configuration can form a fully cantilever-formed Wheatstone-bridge that possesses a higher sensitivity of twofold and more balanced condition to compensate for environmental noise like temperature fluctuation or air flow. Besides, the four integrated micro-cantilevers are made of SiO₂, with each having a single crystal silicon piezoresistor fully encapsulated by SiO₂. Thus, the quad-lever sensor achieves a very low signal noise of 0.2 μV. For specific detection, sensitive molecule layer is self-assembled on two sensing cantilevers, with another two as reference. The sensors are micro-fabricated with a single-side process from the wafer front-side. With wet anisotropic etch used to release the piezoresistive cantilevers, the new fabrication technique features low-cost and high-yield. Self-assembled with a novel dual-branch specific mono-layer, about 100 ppt level trinitrotoluene (TNT) vapor has been rapidly and repeatedly detected.     

Abrasive slurry jet micro-machining of holes in brittle and ductile materials

This paper investigated the effects of elasticity and viscosity, induced by a dilute high-molecular-weight polymer solution, on the shape, depth, and diameter of micro-holes drilled in borosilicate glass and in plates of 6061-T6 aluminum alloy, 110 copper, and 316 stainless steel using low-pressure abrasive slurry jet micro-machining (ASJM). Holes were machined using aqueous jets with 1 wt% 10 μm Al₂O₃ particles. The 180 μm sapphire orifice produced a 140 μm diameter jet at pressures of 4 and 7 MPa. When the jet contained 50 wppm of dissolved 8 million molecular weight polyethylene oxide (PEO), the blind holes in glass were approximately 20% narrower and 30% shallower than holes drilled without the polymer, using the same abrasive concentration and pressure. The addition of PEO led to hole cross-sectional profiles that had a sharper edge at the glass surface and were more V-shaped compared with the U-shape of the holes produced without PEO. Hole symmetry in glass was maintained over depths ranging from about 80–900 μm by ensuring that the jets were aligned perpendicularly to within 0.2°. The changes in shape and size were brought about by normal stresses generated by the polymer. Jets containing this dissolved polymer were observed to oscillate laterally and non-periodically, with an amplitude reaching a value of 20 μm. For the first time, symmetric ASJM through-holes were drilled in a 3-mm-thick borosilicate glass plate without chipping around the exit edge.The depth of symmetric blind holes in metals was restricted to approximately 150 μm for jets with and without PEO. At greater depths, the holes became highly asymmetric, eroding in a specific direction to create a sub-surface slot. The asymmetry appeared to be caused by the extreme sensitivity of ductile materials to jet alignment. This sensitivity also caused the holes in metals to be less circular when PEO was included, apparently caused by the random jet oscillations induced by the polymer. Under identical conditions, hole depths increased in the order: borosilicate glass > 6061-T6 aluminum > 110 copper > 316 stainless steel. The edges of the holes in glass could be made sharper by machining through a sacrificial layer of glass or epoxy.     

The gas film in spark assisted chemical engraving (SACE)—A key element for micro-machining applications

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.