Papers by Author: Eun Sang Lee

Abstract: Nitinol consists of nickel and titanium. Nitinol is one of the shape memory alloys, which changes the crystal structure at a certain temperature and is restored to a memorized form. Because of these unique features, it is used in medical devices, high precision sensors, and aerospace industries. However, Nitinol is a traditional method of processing, resulting in thermal deformation and residual stress after processing. Therefore, the electrochemical machining (ECM), which does not produce residual stress and thermal deformation, has emerged as an alternative processing technique. This study used artificial neural network (ANN), which are the basis of AI, to replace conventional design of experiments (DOE). This method was shown to be more useful than conventional method of design of experiments (RSM, Taguchi) by applying artificial neural network to electrochamical machining (ECM) and comparing root mean square errors (RMSE).

Abstract: Micro/nanoscale diamond cutting tools used in ultra-precision machining can be fabricated by precision grinding, but it is hard to fabricate a tool with a nanometric cutting edge and complex configurations. High-precision geometry accuracy and special shapes for microcutting tools with sharp edges can be achieved by focused ion beam (FIB) milling. However, in the FIB milling process, the surface properties of the substrate (such as a diamond substrate) are affected by the amorphous damage layer caused by the FIB gallium ion collision and implantation and these influence the diamond cutting tool edge sharpness and increase the processing procedure. In this study, to reduce the diamond cutting tool edge sharpness and processing procedure, FIB milling beam current and tilting angle characteristics of single-crystal diamond were investigated, along with method for decreasing the FIB-induced damage on diamond tools by platinum (Pt) coating on the diamond substrate. Experimental results revealed that optimize beam current, tilting angle and platinum (Pt) coating could lead to relatively few processing procedure and sharp cutting tool edge. The obtained results are an endeavor to enhance the controllability of the diamond cutting tool FIB milling.

Abstract: In recent years, developments in the semiconductor and electronic industries have brought a rapid increase in the use of large size silicon. However, for many companies, it is hard to produce 400mm or 450mm wafers, because of excesive funds for exchange the equipments. Therefore, it is necessary to investigate 300mm wafer to obtain a better efficiency and a good property rate. Wafer final Polishing is one of the important methods in manufacturing of Si wafers and in thinning of completed device wafers. This research investigated the surface characteristics and optimum condition of applied pressure, polishing speed and slurry-mixed ratio to achieve the optimum condition of wafer final polishing by Taguchi method. By using optimum condition, it helps to achive an ultra precision mirror like surface.

Abstract: The polishing is one of the important methods in manufacturing of silicon wafer and in thinning of completed device wafer. Generally, getting a flat surface such as a mirror is the purpose of the process. The wafer surface roughness is affected by many variables such as the characteristics of the carrier head unit, operation, speed, the pad and slurry temperature. Optimum process conditions for experimental temperature, down-force, slurry ratio are investigated, time is used as a fixed factor. This study will report the evaluation on surface of wafer by dependent of varying platen, chuck rpm, temperature variation, and oscillation which affect it has on the surface roughness. In this experiment, it is determined the optimum condition for polishing silicon wafers. By using optimum condition, it helps to achieve an ultra precision mirror like surface.

Abstract: Electropolishing, the anodic dissolution process without contact with tools, is a surface Treatment method to make a surface planarization using an electrochemical reaction with low current density. Stainless steel can be put various applications which require purity and high precision surface of products. The aim of this study is to investigate the characteristic of electropolishing effect for stainless steel workpieces. In order to analyze the characteristics of electropolishing effect, surface roughness and micro-burr size were measured in terms of machining conditions such as current density, machining time and electrode gap. The tendencies about improvement of surface roughness by electropolishing for stainless steel workpieces were determined.

Abstract: The polishing process of a silicon wafer is a critical factor in the fabrication of semiconductor. Because a globally planar and mirror-like wafer surface are achieved in this process. The surface roughness in the wafer depends on the surface properties of the carrier head unit along with other machining conditions such as working velocity, polishing pad, temperature, down-force, etc. In this paper, the wafer surface is investigated according to several parameters and experimental data. Experiments were performed to observe the down-force and temperature when the wafer carrier head unit was pressed down onto the polishing pad. A loadcell was employed to obtain the signal of the applied pressure against the polishing pad. Also, working temperature was detected using an infrared sensor. To study on the optimum conditions of machining, monitoring system is coded in Ch and the results of experiment present data using Ch.

Abstract: Since a fine ceramic is possessed of creditable physical and chemical material properties: high thermal resistance, chemical inertness and frictional wear resistance, its applications have been increasing in various industrial fields. Yttria(Y2O3) ceramic, which is formed of cubic crystal structure, has been considered as a light-transmitting material for an optical application and suitable buffer layer in the electronic industry. And its other applications have been increasing recently. For the effective applications of Yttria ceramic, it needs to improve a surface characteristic such as the waviness and surface roughness. The lapping process with in-process electrolytic dressing(IED) method has been performed in the surface machining of high hard-brittle material. IED method is able to overcome the surface machining defects caused by worn grains and unstable chip discharge during conventional lapping process. However, the machining control should be carefully conducted and investigated about each material because its material properties are different each other and exceedingly sensitive. Taguchi method, called robust design, is a useful method for engineering productivity elevation. It is able to search a powerful factor, which influences optimal process design, in accordance with considering noise factors reduction. When diverse factors influence a result according to complex actions each other, it needs to search optimal condition of factors. Response surface design has been widely used in various industrial fields. It helps to solve process design problems in accordance with robust design of process condition.

Abstract: The medical stent is using widely for a surgical operation, because it can reduce the pain of cardiac. When it was developed initially, medical stent was made of stainless steel, however, the TiNi alloy is widely using presently instead of stainless steel. Because, TiNi alloy has not only super elasticity and Smart Material Effect (SME) but also excellent organism compatibility. For these reason, the TiNi alloy is currently highlighted for medical stent material better than other materials. Nevertheless, this TiNi alloy is not suitable to traditional machining process. When the traditional machining process is conducted to the TiNi alloy, it cannot be discharged the machining heat and inner stress. Also, traditional machining process makes a lot of microscopic burrs on the TiNi alloy surface. This microscopic burrs and the rough surface makes injury on vascular, so, it should be necessary non-traditional machining process without defect of traditional machining. In this paper, microscopic burrs on TiNi alloy for medical stent are removed, and surface roughness of the medical stent is evaluated by Electrochemical Polishing (EP) which is one of the non-traditional machining.

Abstract: Polishing is one of the important methods in manufacturing of Si wafers and in thinning of completed device wafer. This study will report the evaluation on abrasion of wafer according to processing time; machining speed and pressure which have major influence on the abrasion of Si wafer polishing, for this, this study design the head unit and analysis head unit. After that, apply to experiment. It is possible to evaluation of wafer abrasion by load cell and infrared temperature sensor. The evaluation of abrasion according to processing condition is selected to use result data that measure a pressure, machining speed, and the processing time. This result is appeared by abrasion in machining condition. Through that, the study cans evaluation a wafer abrasion in machining. It is important to obtain mirror-like wafer surface.

Abstract: It is important to obtain the optimal condition in wafer polishing processing. Polishing is one of the most important methods in manufacturing of Si wafers and in thinning of completed device wafer. This study will report the evaluation on abrasion of wafer according to processing time; machining speed and pressure which have the major influence on the abrasion of Si wafer polishing, for this, this study design the head unit and analysis head unit. After that, this study applies to experiment. The evaluation of abrasion according to processing condition is selected to use result data that measure a pressure, machining speed, and the processing time. This result is appeared by machining condition. Through that, the study can evaluate the abrasion characteristic of wafer in machining.