Yong-Kyu Cho

Electrorheological Semi-Active Damper: Polyaniline Based ER System

Among various materials suitable for an electrorheological (ER) fluid, polyaniline and its many derivatives based upon modification of oxidation state, dopant and polymerization conditions are of technological interest for their adaptation into ER fluids. This is because they have better thermal stability and smaller density than other potential ER materials. Furthermore, polyaniline is easy to polymerize by oxidation polymerization at relatively low temperature and can be doped from a conducting emeraldine hydrochloride form to an insulating state using simple protonic acids. In this study, we adapted the polyaniline based ER fluids for semi-active cylindrical flow-mode type ER damper. A cylindrical flow-mode type ER damper was chosen in this study because it has similar geometrical configuration to the conventional damper normally used for passenger vehicle. The damping forces measured using a semi-active ER damper with polyaniline based ER fluids were found to be controlled by tuning an applied electric field for different piston velocity.

Magnetorheological (MR) Polishing of Alumina-Reinforced Zirconia Ceramics Using Diamond Abrasives for Dental Application

In this study, ultraprecise polishing of alumina reinforced zirconia ceramics using magneto rheological (MR) fluids and diamond abrasives was investigated. First, alumina-reinforced zirconia composites, containing 0 to 30 vol% alumina, were fabricated by cold isostatic pressing at 150 MPa. The green compacts were then sintered at 1,550°C for 2 h in air. Mechanical properties and microstructures of the composites were observed. Second, a series of MR polishing experiments were performed for composites containing 20 vol% of alumina under various polishing conditions. MR polished surfaces were observed using a scanning electron microscope (SEM) and surface profiler to investigate the variation of the surface integrity. A very fine surface roughness of Ra = 1.960 nm was obtained after 60 minutes of MR polishing using diamond abrasives.

Process Capability Optimization of a LED Die Bonding Using Response Surface Analysis

Abstract In LED chip packaging, die bonding is a very important process which fixes the LED chip on the lead frame to provide enough strength for the next process. This paper focuses on the process optimization of a LED die bonding, which attaches small zener diode chip on PLCC LED package frame, using response surface analysis. Design of experiment (DOE) of 5 factors, 3 levels and 5 responses are considered, and the results are investigated. As the results, optimal conditions those satisfy all response objects can be derived. Key Words : LED chip package, Die bonding(or attaching), Design of experiment, Response surface analysis 본 논문은 지식경제 기술혁신사업(신성장동력장비경쟁력강화사업)의 일환으로 수행중인 ‘LED 패키지 In-line 자동화 시스템 개발’ 과제 연구비 지원으로 수행되었음. * Corresponding Author : Seok-Jae HaTel: +82-11-9092-2753 email: sjha1103@gmail.com접수일 12년 07월 31일 수정일 (1차 12년 08월 22일, 2차 12년 09월 14일, 3차 12년 09월 27일) 게재확정일 12년 10월 11일 1. 서론 LED 칩의 일반적인 패키징 공정은 웨이퍼에 형성된 칩의 양부를 검사하는 웨이퍼 검사 공정, 웨이퍼를 절단하여 낱개로 분리된 칩을 리드 프레임(lead frame)에 부착시키는 다이 본딩(die bonding) 공정, 다이에 구비된 접촉 패드와 리드 프레임의 리드를 와이어로 연결시키는 와이어 본딩(wire bonding) 공정, 다이의 내부회로와 그 외의 구성 부품을 보호하기 위해 봉지재로 외부를 감싸는 몰딩(molding) 공정, 리드와 리드를 연결하고 댐바(dam bar)를 절단하는 트림 공정 및 리드를 원하는 형태로 성형시키는 포밍(forming) 공정을 거치게 된다. 그중에서 다이 본딩 공정은 분할된 칩(die)이 이후 공정에서 견딜 수 있는 충분한 강도의 접착력을 갖도록 칩을 고정시키고 칩으로부터 발생하는 열을 방출시키기 위해 적절한 열전도도 및 전기전도도를 부여하는데 있어 매우 중요한 공정이며, 통상적인 다이 본딩 공정순서를 그림 1에 나타내었다[1,2].

LED Die Bonder Inspection System Using Integrated Machine Visions

In LED chip packaging, die bonding is a very important process which fixes the LED chip on the lead flame to provide enough strength for the next process. During the process, inspection processes are very important to detect exact locations of dispensed epoxy dots and to determine bonding status of dies whether they are lies at exact positions with sufficient bonding strength. In this study, a useful machine vision based inspection system is proposed for the LED die bonder. In the proposed system, 2 cameras are used for epoxy dot position detection and 2 cameras are sued for die attaching status determination. New vision processing algorithm is proposed, and its efficiency is verified through required field experiments. Measured position error is less than X:-29㎛, Y:-32㎛ and rotation error:3° using proposed vision algorithm. It is concluded that the proposed machine vision based inspection system can be successfully implemented on the developed die bonding system.

Analysis of Polishing Mechanism and Characteristics of Aspherical Lens with MR Polishing

The aspherical lens was designed to be able to array a focal point. For this reason, it has very curved surface. The aspherical lens is fabricated by injection molding or diamond turning machine. With the aspherical lens, tool marks and surface roughness affect the optical characteristics, such as transmissivity. However, it is difficult to polish free form surface shapes uniformly with conventional methods. Therefore, in this paper, the ultra-precision polishing method with MR fluid was used to polish an aspherical lens with 4-axis position control systems. A Tool path and polishing mechanism were developed to polish the aspherical lens shape. An MR polishing experiment was performed using a generated tool path with a PMMA aspherical lens after the turning process. As a result, surface roughness was improved from

Analysis of Cutting Characteristic of the Sapphire Wafer Using a Internal Laser Scribing Process for LED Chip

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A study on flow coefficient evaluation by shape change of butterfly valve

Abstract Scribing is cutting process to determine production amount and characteristic of LED chip. So it is an important process for fabrication of LED chip. Mechanical process and conventional scribing process with laser sourcehas several problems such as thermal deformation, decreasing of material strength and limitation of cutting region.To solve these problems, internal laser scribing process that generates void in wafer and derives self-crack has been researched. However, studies of sapphire wafer cutting by internal laser scribing process for fabrication of LED chipare still insufficient. In this paper, cutting parameters were determined to apply internal laser scribing process for sapphire wafer for fabrication of LED chip. Then, foundation of cutting condition was established to set up internallaser scribing system through investigation of cutting characteristics by several experiments. Keywords : Internal laser scribing, Laser ablation, LED chip, Pulse laser, Sapphire wafer 본 논문은 산업통상자원부 사업화연계기술개발사업(R8E0사업-투자유도형)의 일환으로 수행중인‘Z-stocked Multi Focusing기술을 적용한 Thick Epi-Wafer 절단용 Laser System 개발’ 과제 연구비 지원으로 수행됨.

A Study on the Analysis of Multi-beam Energy for High Resolution with Maskless Lithography System Using DMD

Abstract Butterfly valves have been used to control the flow rate of various fluids in many industries because it have unique manageability compare to other valves. The flow rate passing through the butterfly valves can be controlled according to the coefficient of capacity calculated by disk angle change. In this study, flow analysis by 3D modeling was performed to derive the coefficient of capacity to evaluate and improve newly developed butterfly valves. Also, required measurement system was established to verify the performance of the valves, and to compare with the calculated results. Key Words : Grooved butterfly valve, capacity of coefficient, Disc Open Angle 본 연구는 중소기업청 산학협력실 지원사업에 의해 수행되었음. * Corresponding Author : Bong-Cheol ShinTel: +82-32-860-7306 email: kenny77b@empal.com접수일 12년 07월 19일 수정일 (1차 12년 10월 09일, 2차 12년 10월 31일) 게재확정일 12년 11월 08일 1. 서론 최근 들어 국내 발전 설비 및 제조 공장의 설비가 증가하고 기존 설비의 유지 보수 또한 증가 하고 있는 추세이다. 이러한 시설에 고온, 고압의 기체 및 유체의 제어를 위해 밸브가 필수적으로 요구되고 있고 용도에 따라 게이트 밸브, 볼 밸브, 글로브 밸브, 버터플라이 밸브 등이 많이 사용되고 있다.[1] 이중 버터플라이 밸브는 기존의 다른 밸브의 비해 크기가 작고 완전 개폐 동작이 빠르다는 장점과 정밀 유체 제어가 가능하다는 장점을 가지고 있다. 따라서 국내 건축 및 플랜트 산업에서는 정밀 유체 제어를 위해 생활 및 공업용수의 급·배수에서 많을 활용을 하고 있다.[2,3]또한 grooved butterfly valve는 고온, 고압의 환경조건에서도 활용되기 때문에 내구성과 신뢰성과 더불어 정밀 유체 제어가 가능한 고품질 밸브가 필수적으로 요구되고 있다. 외국 제품의 경우에는 설계 단계부터 생산단계의 전 공정이 전문적인 인력 및 측정 장비를 이용해 수행되고 있어 밸브의 성능 평가에서 중요한 용량 계수를 각도에 따라 정확히 명시하고 있다. 국내 밸브의 경우 외국의 인건비 상승으로 인해 국내 OEM 방식으로 생산하고 있으며 이러한 방식을 통해 국외로 수출하는 회사를 제외하고는 영세한 규모의 기업환경 조건에

Electrorheological characterization of polyaniline-coated poly(methyl methacrylate) suspensions

Exposure process is the most important technology to fabricate highly integrated circuit. Up to now, mask type lithography process has been generally used. However, it is not efficient for small quantity and/or frequently changing products. Therefore, maskless lithography technology is raised in exposure process. In this study, relations between multi-beam energy and overlay were analyzed. Exposure experiment of generating pattern was performed. It was from presented scan line by multi- beam simulation. As a result, optimal scan line distance was proposed by simulation, and micro pattern accuracy could be improved by exposure experiment using laser direct imaging system.