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14 pages, 5056 KiB

Open AccessArticle

Short-Pulse Laser-Assisted Fabrication of a Si-SiO₂ Microcooling Device

by Alexandros Mouskeftaras, Stephan Beurthey, Julien Cogan, Gregory Hallewell, Olivier Leroy, David Grojo and Mathieu Perrin-Terrin

Micromachines 2021, 12(9), 1054; https://doi.org/10.3390/mi12091054 - 30 Aug 2021

Cited by 3 | Viewed by 2811

Abstract

Thermal management is one of the main challenges in the most demanding detector technologies and for the future of microelectronics. Microfluidic cooling has been proposed as a fully integrated solution to the heat dissipation problem in modern high-power microelectronics. Traditional manufacturing of silicon-based [...] Read more.

Thermal management is one of the main challenges in the most demanding detector technologies and for the future of microelectronics. Microfluidic cooling has been proposed as a fully integrated solution to the heat dissipation problem in modern high-power microelectronics. Traditional manufacturing of silicon-based microfluidic devices involves advanced, mask-based lithography techniques for surface patterning. The limited availability of such facilities prevents widespread development and use. We demonstrate the relevance of maskless laser writing to advantageously replace lithographic steps and provide a more prototype-friendly process flow. We use a 20 W infrared laser with a pulse duration of 50 ps to engrave and drill a 525 μm-thick silicon wafer. Anodic bonding to a SiO₂ wafer is used to encapsulate the patterned surface. Mechanically clamped inlet/outlet connectors complete the fully operational microcooling device. The functionality of the device has been validated by thermofluidic measurements. Our approach constitutes a modular microfabrication solution that should facilitate prototyping studies of new concepts for co-designed electronics and microfluidics. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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12 pages, 4740 KiB

Open AccessArticle

Integrated Double-Sided Random Microlens Array Used for Laser Beam Homogenization

by Wei Yuan, Cheng Xu, Li Xue, Hui Pang, Axiu Cao, Yongqi Fu and Qiling Deng

Micromachines 2021, 12(6), 673; https://doi.org/10.3390/mi12060673 - 9 Jun 2021

Cited by 15 | Viewed by 3715

Abstract

Double microlens arrays (MLAs) in series can be used to divide and superpose laser beam so as to achieve a homogenized spot. However, for laser beam homogenization with high coherence, the periodic lattice distribution in the homogenized spot will be generated due to [...] Read more.

Double microlens arrays (MLAs) in series can be used to divide and superpose laser beam so as to achieve a homogenized spot. However, for laser beam homogenization with high coherence, the periodic lattice distribution in the homogenized spot will be generated due to the periodicity of the traditional MLA, which greatly reduces the uniformity of the homogenized spot. To solve this problem, a monolithic and highly integrated double-sided random microlens array (D-rMLA) is proposed for the purpose of achieving laser beam homogenization. The periodicity of the MLA is disturbed by the closely arranged microlens structures with random apertures. And the random speckle field is achieved to improve the uniformity of the homogenized spot by the superposition of the divided sub-beams. In addition, the double-sided exposure technique is proposed to prepare the rMLA on both sides of the same substrate with high precision alignment to form an integrated D-rMLA structure, which avoids the strict alignment problem in the installation process of traditional discrete MLAs. Then the laser beam homogenization experiments have been carried out by using the prepared D-rMLA structure. The laser beam homogenized spots of different wavelengths have been tested, including the wavelengths of 650 nm (R), 532 nm (G), and 405 nm (B). The experimental results show that the uniformity of the RGB homogenized spots is about 91%, 89%, and 90%. And the energy utilization rate is about 89%, 87%, 86%, respectively. Hence, the prepared structure has high laser beam homogenization ability and energy utilization rate, which is suitable for wide wavelength regime. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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11 pages, 5965 KiB

Open AccessArticle

Study of Microwave-Induced Ag Nanowire Welding for Soft Electrode Conductivity Enhancement

by Meng Zhang, Songjia Han, Zhi-Yang Xuan, Xiaohui Fang, Xiaoming Liu, Wu Zhang and Hui-Jiuan Chen

Micromachines 2021, 12(6), 618; https://doi.org/10.3390/mi12060618 - 27 May 2021

Cited by 6 | Viewed by 2297

Abstract

Silver nanowire (AgNW)-coated thin films are widely proposed for soft electronics application due to their good conductivity, transparency and flexibility. Here, we studied the microwave welding of AgNW-based soft electrodes for conductivity enhancement. The thermal effect of the microwave to AgNWs was analyzed [...] Read more.

Silver nanowire (AgNW)-coated thin films are widely proposed for soft electronics application due to their good conductivity, transparency and flexibility. Here, we studied the microwave welding of AgNW-based soft electrodes for conductivity enhancement. The thermal effect of the microwave to AgNWs was analyzed by dispersing the nanowires in a nonpolar solution, the temperature of which was found to be proportional with the nanowire diameters. AgNWs were then coated on a thin film and welded under microwave heating, which achieved a film conductivity enhancement of as much as 79%. A microwave overheating of AgNWs, however, fused and broke the nanowires, which increased the film resistance significantly. A soft electrode was finally demonstrated using the microwave-welded AgNW thin film, and a 1.13 µA/mM sensitivity was obtained for glucose sensing. Above all, we analyzed the microwave thermal effect on AgNWs to provide a guidance to control the nanowire welding effect, which can be used for film conductivity enhancement and applied for soft and bio-compatible electrodes. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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10 pages, 3437 KiB

Open AccessArticle

Fast and Accurate Light Field View Synthesis by Optimizing Input View Selection

by Xingzheng Wang, Yongqiang Zan, Senlin You, Yuanlong Deng and Lihua Li

Micromachines 2021, 12(5), 557; https://doi.org/10.3390/mi12050557 - 13 May 2021

Cited by 1 | Viewed by 1771

Abstract

There is a trade-off between spatial resolution and angular resolution limits in light field applications; various targeted algorithms have been proposed to enhance angular resolution while ensuring high spatial resolution simultaneously, which is also called view synthesis. Among them, depth estimation-based methods can [...] Read more.

There is a trade-off between spatial resolution and angular resolution limits in light field applications; various targeted algorithms have been proposed to enhance angular resolution while ensuring high spatial resolution simultaneously, which is also called view synthesis. Among them, depth estimation-based methods can use only four corner views to reconstruct a novel view at an arbitrary location. However, depth estimation is a time-consuming process, and the quality of the reconstructed novel view is not only related to the number of the input views, but also the location of the input views. In this paper, we explore the relationship between different input view selections with the angular super-resolution reconstruction results. Different numbers and positions of input views are selected to compare the speed of super-resolution reconstruction and the quality of novel views. Experimental results show that the speed of the algorithm decreases with the increase of the input views for each novel view, and the quality of the novel view decreases with the increase of the distance from the input views. After comparison using two input views in the same line to reconstruct the novel views between them, fast and accurate light field view synthesis is achieved. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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19 pages, 57919 KiB

Open AccessArticle

Simulation-Based and Experimental Investigation of Micro End Mills with Wiper Geometry

by Timo Platt, Alexander Meijer, Torben Merhofe and Dirk Biermann

Micromachines 2021, 12(5), 496; https://doi.org/10.3390/mi12050496 - 27 Apr 2021

Cited by 1 | Viewed by 3068

Abstract

One of the major advantages of micromachining is the high achievable surface quality at highly flexible capabilities in terms of the machining of workpieces with complex geometric properties. Unfortunately, finishing operations often result in extensive process times due to the dependency of the [...] Read more.

One of the major advantages of micromachining is the high achievable surface quality at highly flexible capabilities in terms of the machining of workpieces with complex geometric properties. Unfortunately, finishing operations often result in extensive process times due to the dependency of the resulting surface topography on the cutting parameter, e.g., the feed per tooth, f_z. To overcome this dependency, special tool shapes, called wipers, have proven themselves in the field of turning. This paper presents the transfer of such tool shapes to solid carbide milling tools for micromachining. In this context, a material removal simulation (MRS) was used to investigate promising wiper geometries for micro end mills (d = 1 mm). Through experimental validation of the results, the surface topography, the resulting process forces, and tendencies in the residual stress state were investigated, machining the hot work tool steel (AISI H11). The surface-related results show a high agreement and thus the potential of MRS for tool development. Deviations from the experimental data for large wipers could be attributed to the non-modeled tool deflections, friction, and plastic deformations. Furthermore, a slight geometry-dependent increase in cutting forces and compressive stresses were observed, while a significant reduction in roughness up to 84% and favorable topography conditions were achieved by adjusting wipers and cutting parameters. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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18 pages, 8933 KiB

Open AccessArticle

Research on the Mechanism of Micro-Water Jet-Guided Laser Precision Drilling in Metal Sheet

by Yinuo Zhang, Hongchao Qiao, Jibin Zhao and Zhihe Cao

Micromachines 2021, 12(3), 343; https://doi.org/10.3390/mi12030343 - 23 Mar 2021

Cited by 17 | Viewed by 2990

Abstract

As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water jet-guide laser processing technology (WJGL) has been gradually applied for its high machining [...] Read more.

As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water jet-guide laser processing technology (WJGL) has been gradually applied for its high machining precision. However, there are a few researches on the heat conduction process of WJGL processing metal materials. Therefore, it is of great significance to study the transient thermal effect of metal materials and the mechanism of material removal to improve the processing quality. In order to explore the heat conduction model of WJGL processing metal materials, this paper is based on the “element birth and death” technique in the finite element method, and the three-dimensional transient temperature field of four typical metal materials (titanium alloy, stainless steel, aluminum alloy, copper) and material removal model are established. Under this model, the removal mechanism of different metal materials and the influence of different process parameters on the temperature field distribution of the material are studied, and the influence of fixed-position drilling and helix drilling on the microporous morphology is compared. The results show that copper and aluminum alloys can obtain a larger depth-to-diameter ratio and a smaller hole taper. Titanium alloy and stainless steel have better hole roundness, lower hole edge temperature, and smaller thermal deformation. Hole roundness error and hole taper decrease with the increase of laser power. The roundness error of each material is reduced to within 10 μm when the laser power is 10 W, and the average hole taper is 8.73°. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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16 pages, 6211 KiB

Open AccessArticle

Laser Spot Micro-Welding of Ultra-Thin Steel Sheet

by Quanhong Li, Zhongyan Mu, Manlelan Luo, Anguo Huang and Shengyong Pang

Micromachines 2021, 12(3), 342; https://doi.org/10.3390/mi12030342 - 23 Mar 2021

Cited by 3 | Viewed by 3233

Abstract

This paper reports a mechanism understanding how to reduce the solder joint failure phenomenon in the laser spot micro-welding process of ultra-thin steel sheets. An optimization method to improve solder joint service life is proposed. In this study, the time-dependent dynamic behaviors of [...] Read more.

This paper reports a mechanism understanding how to reduce the solder joint failure phenomenon in the laser spot micro-welding process of ultra-thin steel sheets. An optimization method to improve solder joint service life is proposed. In this study, the time-dependent dynamic behaviors of the keyhole and the weld pool are simulated, and the temperatures in the keyhole of two different laser pulse waveforms are compared. The results show that laser energy attenuation mode (LEAM) can only obtain shallow weld depth because of the premature decay of the laser power of waveform, resulting in the laser beam that cannot be concentrated in the keyhole. The temperature inside the keyhole of LEAM fluctuates significantly, which shows a downward trend. Due to the existence of the peak power of waveform in laser energy continuous mode (LECM), the large angle of inclination of the wall of the keyhole inside the melt pool is more conducive to the multiple reflections of the laser beam in the keyhole and increases the absorption rate of the laser energy by the base material, resulting in the “keyhole effect”. But the temperature in the keyhole gradually rises, close to the evaporation temperature. A method combining LEAM and LECM to improve the solder joint service life by optimizing the temperature in the keyhole indirectly by adjusting the peak power of the laser pulse waveform is proposed in this study. The experimental results show that the weld depth can be optimized from 0.135 mm to 0.291 mm, and the tensile strength can be optimized from 88 MPa to 288 MPa. The bonding performance between the upper and lower plates is effectively improved. It can reach the required weld depth in a short time and improve the welding efficiency of the laser spot micro-welding process. The simulation results show that the temperature inside the keyhole is well optimized below the evaporation temperature of the material, which can avoid the violent evaporation of the welding process and keep the whole welding process in a stable state. By optimizing the laser pulse waveform, the temperature inside the keyhole can reach 3300 K, and it is always in a stable state than before optimization. The stable temperature inside the keyhole can help to reduce violent oscillation and spattering of the molten pool and improve welding efficiency and joint life. The research can help provide effective process guidance for the optimization of different laser pulse waveforms in the micro-welding process. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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15 pages, 7055 KiB

Open AccessArticle

Microlens Array Fabrication by Using a Microshaper

by Meng-Ju Lin and Cheng Hao Wen

Micromachines 2021, 12(3), 244; https://doi.org/10.3390/mi12030244 - 28 Feb 2021

Cited by 5 | Viewed by 2131

Abstract

A simple, easy, inexpensive, and quick nonsilicon-based micromachining method was developed to manufacture a microlens array. The spherical surface of the microlens was machined using a microshaper mounted on a three-axis vertical computer numerical control (CNC) machine with cutter-path-planning. The results show the [...] Read more.

A simple, easy, inexpensive, and quick nonsilicon-based micromachining method was developed to manufacture a microlens array. The spherical surface of the microlens was machined using a microshaper mounted on a three-axis vertical computer numerical control (CNC) machine with cutter-path-planning. The results show the machined profiles of microlens agree well with designed profiles. The focus ability of the machined microlens array was verified. The designed and measured focal lengths have average 1.5% error. The results revealed that the focal lengths of micro lens agreed with the designed values. A moderate roughness of microlens surface is obtained by simply polishing. The roughness of the lens surface is 43 nm in feed direction (x-direction) and 56 nm in path interval direction (y-direction). It shows the simple, scalable, and reproducible method to manufacture microlenses by microshaper with cutter-path-planning is feasible. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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Other

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13 pages, 1364 KiB

Open AccessPerspective

by Atanas Ivanov, Abhishek Lahiri, Venelin Baldzhiev and Anna Trych-Wildner

Micromachines 2021, 12(10), 1184; https://doi.org/10.3390/mi12101184 - 29 Sep 2021

Cited by 10 | Viewed by 2061

Abstract

This paper provides an overall view of the current research in micro-electrical discharge machining (micro-EDM or µEDM) and looks into the present understanding of the material removing mechanism and the common approach for electrode material selection and its limitations. Based on experimental data, [...] Read more.

This paper provides an overall view of the current research in micro-electrical discharge machining (micro-EDM or µEDM) and looks into the present understanding of the material removing mechanism and the common approach for electrode material selection and its limitations. Based on experimental data, the authors present an analysis of different materials’ properties which have an influence on the electrodes’ wear ratio and energy distribution during the spark. The experiments performed in micro-EDM conditions reveal that properties such as electron work function and electrical resistivity strongly correlate with the discharge energy ratio. The electrode wear ratio, on the other hand, is strongly influenced by the atomic bonding energy and was found to be related to the tensile modulus. The proposed correlation functions characterized the data with a high determination coefficient exceeding 99%. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications: Advanced Micro Processing Technology, Devices and Equipment, Volume II)

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