Hae-Sung Yoon

Aerodynamically focused nanoparticle (AFN) printing: novel direct printing technique of solvent-free and inorganic nanoparticles.

Aerodynamically focused nanoparticle (AFN) printing was demonstrated for direct patterning of the solvent-free and inorganic nanoparticles. The fast excitation-purge control technique was proposed and investigated by examining the aerodynamic focusing of nanoparticles and their time-scale, with the analytical and experimental approaches. A series of direct patterning examples were demonstrated with Barium Titanate (BaTiO3) and Silver (Ag) nanoparticles onto the flexible and inflexible substrates using the AFN printing system. The capacitor and flexible conductive line pattern were fabricated as the application examples of the proposed technique. The results presented here should contribute to the nanoparticle manipulation, patterning, and their applications, which are intensely being studied nowadays.

Defects of wave patterns from tungsten carbide/stainless steel brazed micro-end-milling for printed circuit board machining

The increasing demand for green products and strategies has led to research on reducing manufacturing costs and energy consumptions. In this study, the brazing method was applied to the fabrication of a micro-end-mill for printed circuit board manufacturing, and the machining properties of the fabricated tools were experimentally investigated. A tungsten carbide cutting edge was brazed onto a stainless steel shank using silver filler, and this material rod was fabricated into a micro-end-mill with a diameter of 800 µm. Machining results for this micro-end-mill were observed via scanning electron microscopy, and an abnormal wave pattern was observed on the cutting surface when using the brazed tool. The woven structure of the workpiece is thought to be the cause of this phenomenon; the wave pattern can be removed by controlling the machining conditions. Since the brazing technique is readily applicable to micro-scale cutting tools, it is expected that these results will contribute to improved machining quality when using brazed micro-cutting tools, as well as improved manufacturing efficiency.

Energy Analysis of Micro-drilling Process Used to Manufacture Printed Circuit Boards

Energy savings are becoming a new focus in the industrial sector because of environmental concerns. In order to establish an energy-saving strategy for micro-drilling, it is necessary to consider all aspects of the drilling procedure, including the post-drilling process. This study analyzed micro-drills with diameters of 400 μm. Process parameters, such as the rotational speed of the spindle and in-feed, were controlled, and the energy consumption of each process was measured. Operators can use the results to make decisions on process parameters and whether to perform a de-burring process. Ultimately, an effective energy-saving strategy can be devised for micro-drilling.

Evaluation of Backstitch Tool Path Strategy for Stability and Productivity in Micro-Drilling

Micro-drilling with spacing intervals in the hundred micrometer range is an essential process, however suitable methods are lacking despite efforts to develop useful strategies for precision micro-drilling. For efficiency, printed circuit boards are stacked in several layers and drilled through simultaneously but the process results in misalignment of holes as observed between consecutive layers from top to bottom. The work herein proposes a new tool path strategy in comparison with conventional methods. Hole positioning, drilling thrust force, and duration time were measured and evaluated. This strategy can be utilized in micro-manufacturing process for improving machining stability and productivity.Copyright

A study of tool pattern design for calcified-atherosclerotic-plaque removal robot

Atherosclerosis is a major cardiovascular disease involving accumulations of lipids, white blood cells, and other materials on the inside of artery walls. Rotational atherectomy (RA) is a technique in which a small grinder is inserted into the coronary arteries to ablate plaque and increase blood flow to the heart. High-speed rotational atherectomy, when performed with an ablating grinder to remove the plaque, produces much better results in the treatment of calcified plaque than other methods. The Rotablator, commercial rotational atherectomy device, and other RA tools were developed and used for calcified plaque removal. However, the fabrication processes of the tools are complex and require considerable expenses and time. In this research, a new rotational ablation tool and its fabrication method for calcified atherosclerotic plaque removal is presented. It relies on surface modification to achieve the required surface roughness. Four different types of tool pattern were suggested and the surface of the tools were modified using Nd:YAG laser beam engraving. The ablation experiment was performed on hydroxyapatite/polylactide (HA/PLA) composite which has an elastic modulus similar to that of calcified plaque. The tool performance and reliability were evaluated by measuring the ablation force exerted.

CAD/CAM for scalable nanomanufacturing: A network-based system for hybrid 3D printing

Micro- and nano-structuring have been highlighted over several decades in both science and engineering fields. In addition to continuous efforts in fabrication techniques, investigations in scalable nanomanufacturing have been pursued to achieve reduced feature size, fewer constraints in terms of materials and dimensional complexity, as well as improved process throughput. In this study, based on recent micro-/nanoscale fabrication processes, characteristics and key requirements for computer-aided design and manufacturing (CAD/CAM) systems for scalable nanomanufacturing were investigated. Requirements include a process knowledge database, standardized processing, active communication, adaptive interpolation, a consistent coordinate system, and management of peripheral devices. For scalable nanomanufacturing, it is important to consider the flexibility and expandability of each process, because hybrid and bridging processes represent effective ways to expand process capabilities. As an example, we describe a novel CAD/CAM system for hybrid three-dimensional (3D) printing at the nanoscale. This novel hybrid process was developed by bridging aerodynamically focused nanoparticle printing, focused ion beam milling, micromachining, and spin-coating processes. The system developed can print a full 3D structure using various inorganic materials, with a minimum process scale of 50 nm. The most obvious difference versus CAD/CAM at ‘conventional’ scales is that our system was developed based on a network to promote communication between users and process operators. With the network-based system, it is also possible to narrow the gap among different processes/resources. We anticipate that this approach can contribute to the development of CAD/CAM for scalable nanomanufacturing and a wide range of hybrid processes.

In-Situ Characterization of Nano-Structures Fabricated by Focused Ion Beam (FIB) and Nano Particle Deposition System (NPDS)

Nano particle deposition system (NPDS) had been developed for the creation of micro/nano structures with multimaterials in order to develop the micro/nano devices on the basis of specific localized surface on the multilayer. However, micro structures fabricated by NPDS show different mechanical properties when it compared to bulk material because of its porous and uneven deposition structure. To achieve reasonable mechanical properties of the structure fabricated by nanoscale 3D printing system, it requires in-situ mechanical property test method. Herein, a new approach for in-situ nanomechanical characterization system using microforce sensor and nanomanipulator installed in focused ion beam system. In this research, experimental setup for mechanical characterization was developed and mechanical property test was done in Focused Ion Beam (FIB) system. The specimen was fabricated by FIB milling process, then manipulation and compression processes are operated by this characterization system with real time imaging. The test was done for silver microstructures fabricated by NPDS and results show weaker hardness and smaller young’s modulus than bulk material.Copyright