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방정환,이세형,신의선,김정한,이창우,Bang, Jung-Hwan,Lee, Se-Hyung,Shin, Yue-Seon,Kim, Jeong-Han,Lee, Chang-Woo 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.1
Reflow process conditions were investigated for 0402 electric parts with Sn-3.0Ag-0.5Cu solders. Circle hole shape metal mask with 100 m thickness showed excellent printability. Self alignment abilities were 71% for 1005 chips, 52% for 0603 chips, and 3% for 0402 chips. Average joining strengos were 1990 gf for 1005 chips, 867 gf for 0603 chips, and 525 gf for 0402 chips. As mis-mounting angle increased, joining strength decreased. Considering self-alignment ability, mounting angle had to be under $5^{\circ}$ and contact area of the chips had to be over 40% for Pb-free soldering process for 0402 chips.
증착시 및 플라즈마 후처리에 의한 수소 주입이 투명 박막 트랜지스터에서 산화아연 채널층의 물성에 미치는 영향
방정환,김원,엄현석,박진석,Bang, Jung-Hwan,Kim, Won,Uhm, Hyun-Seok,Park, Jin-Seok 한국반도체디스플레이기술학회 2010 반도체디스플레이기술학회지 Vol.9 No.1
We have investigated the effects of hydrogen injection via in-situ gas addition ($O_2$, $H_2$, or $O_2$ + $H_2$ gas) and plasma post-treatment (Ar or Ar + H plasma) on material properties of ZnO that is considered to be as a channel layer in transparent thin film transistors. The variations in the electrical resistivity, optical transmittance and bandgap energy, and crystal quality of ZnO thin films were characterized in terms of the methods and conditions used in hydrogen injection. The resistivity was significantly decreased by injection of hydrogen; approximately $10^6\;{\Omega}cm$ for as-grown, $1.2\;{\times}\;10^2\;{\Omega}cm$ for in-situ with $O_2/H_2\;=\;2/3$ addition, and $0.1\;{\Omega}cm$ after Ar + H plasma treatment of 90 min. The average transmittance of ZnO films measured at a wavelength of 400-700 nm was gradually increased by increasing the post-treatment time in Ar + H plasma. The optical bandgap energy of ZnO films was almost monotonically increased by decreasing the $O_2/H_2$ ratio in in-situ gas addition or by increasing the post-treatment time in Ar + H plasma, while the post-treatment using Ar plasma hardly affected the bandgap energy. The role of hydrogen in ZnO was discussed by considering the creation and annihilation of oxygen vacancies as well as the formation of shallow donors by hydrogen.
Sn-3.0Ag-0.5Cu 솔더링에서 플럭스 잔사가 전기화학적 마이그레이션에 미치는 영향
방정환,이창우,Bang, Jung-Hwan,Lee, Chang-Woo 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.5
Recently, there is a growing tendency that fine-pitch electronic devices are increased due to higher density and very large scale integration. Finer pitch printed circuit board(PCB) is to be decrease insulation resistance between circuit patterns and electrical components, which will induce to electrical short in electronic circuit by electrochemical migration when it exposes to long term in high temperature and high humidity. In this research, the effect of soldering flux acting as an electrical carrier between conductors on electrochemical migration was investigated. The PCB pad was coated with OSP finish. Sn3.0Ag0.5Cu solder paste was printed on the PCB circuit and then the coupon was treated by reflow process. Thereby, specimen for ion migration test was fabricated. Electrochemical migration test was conducted under the condition of DC 48 V, $85^{\circ}C$, and 85 % relative humidity. Their life time could be increased about 22% by means of removal of flux. The fundamentals and mechanism of electrochemical migration was discussed depending on the existence of flux residues after reflow process.
방정환(Bang-Jung Hwan),박재현(Park-Jae Hyun),윤희욱(Hee-Wook Yoon),이민섭(Min-Sup Lee) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
Driving response and tip-in shock vibration are conflicting performances. To improve driving response, tip-in shock problem should be solved. This study illustrates, tip-in shock’s main cause, transfer mechanism, engine mount roll stiffness compare to competitors. To solve tip-in shock, test and simulations were performed in the aspect of source, engine mount, chassis, driveline. By changing EMS, engine mount, chassis, driveline, The following conclusions were reached, to settle tip-in shock, Engine mount total roll stiffness should be increased, Turbine and Engine rpm difference should be decreased.
3기통 엔진 NVH 개선을 위한 신개념 엔진마운팅 시스템 개발
방정환(Jung-Hwan Bang),김도현(Do-Hyun Kim),윤희욱(Hee-Wook Yoon),이민섭(Min-Sup Lee),이병혁(Byung-Hyuk Lee) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
To reduce fuel cost and vehicle weight, non BSM 3-cylinder engine is increasing, but non BSM 3-cylinder engine has C1 pitch and yaw moment excitation. So compare to 4-cylinder engine vehicle, non 3-cylinder engine vehicle has more NVH problems. In this paper to solve 3-cylinder engine vehicle’s NVH problem, engine exciting force and moment equations were derived. The most effective engine mount design method was selected by engine motion equation analysis. To reduce the engine pitch moment response, engine yaw moment excitation was removed by using outer balancer and the main engine mounts were positioned powertrain pitch axis. To consider engine firing C1.5 roll excitation response, front and rear roll mount span was reduced. The new engine mount system vehicle’s idle vibration was better than 4-cylinder engine vehicle.
방정환(Jung-Hwan Bang),유동열(Dong-Yurl Yu),고용호(Young-Ho Ko),윤정원(Jeong-Won Yoon),이창우(Chang-Woo Lee) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.1
Automotive today has been transforming to an electronic product by adopting a lot of convenience and safety features, suggesting that joining materials and their mechanical reliabilities are getting more important. In this study, a Sn-Cu-Cr-Ca solder composition having a high melting temperature (>230℃) was fabricated and its joint properties and reliability was investigated with an aim to evaluate the suitability as a joining material for electronics of engine room. Furthermore, mechanical properties change under complex environment were compared with several existing solder compositions. As a result of contact angle measurement, favorable spreadability of 84% was shown and the average shear strength manufactured with corresponding composition solder paste was 1.9kg/mm². Also, thermo-mechanical reliability by thermal shock and vibration test was compared with that of the representative high temperature solder materials such as Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb. In order to fabricate the test module, solder balls were made in joints with ENIG-finished BGA and then the BGA chip was reflowed on the OPS-finished PCB pattern. During the environmental tests, resistance change was continuously monitored and the joint strength was examined after tests. Sn-3.5Ag alloy exhibited the biggest degradation rate in resistance and shear stress and Sn-0.7Cu resulted in a relatively stable reliability against thermo-mechanical stress coming from thermal shock and vibration.
방정환(Jung-Hwan Bang),김세준(Sejun Kim),전병선(Byung-Sun Jeon),민홍석(Hong-Seok Min),민경덕(Kyoungdoug Min),송성진(Seung-Jin Song),주영창(Young-Chang Joo) 한국유체기계학회 2002 유체기계 연구개발 발표회 논문집 Vol.- No.-
This paper reports on the development of micro power system component under way at Seoul National University. The need of micro power system is explained and components of micro power system are described. The developments of hydrogen-air micro combustor, micro igniter based poly-silicon heater and micro thruster are described. To manufacture 3-D micro structure the process that manufactures high aspect ratio structures has been developed and optimized. Design, fabrication, and experiment processes are introduced and technical challenges in each phase are described.
수소 및 산소 첨가에 따른 산화아연막의 전기적, 광학적, 구조적 물성
방정환(Jung-Hwan Bang),김원(Won Kim),엄현석(Hyun-seok Uhm),박진석(Jin-Seok Park) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
Effects of hydrogen and oxygen additives on structural, optical, and electrical properties of ZnO films were extensively examined. ZnO films were deposited using RF sputtering by varying the gas mixing ratio of H₂ and O₂. Optical transmittances at visible region, electrical resistivities, and micro-structures of ZnO films were characterized in terms of the kind and amount of additive gases. It was observed that the material properties of ZnO films required for their use in transparent thin film transistors, such as approximately 103Ω㎝ in resistivity and higher than 85% in transmittance, can be achieved by controlling the gas mixing ratio of O₂/H₂ (sccm) in the range of 2/2~2/8.
작동조건을 고려한 자동차용 PEM 연소전지 시스템 성능 시뮬레이션
방정환(Jung-hwan Bang),김한상(Han-sang Kim),이동훈(Dong-hun Lee),민경덕(Kyoungdong Min),김민수(Min-soo Kim),조영만(Youngman Cho) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
The modelingn of PEM (proton Exchange Membrane) fuel cell system consisting of fuel cell stack and BOP (Balance of plant) is presented in this paper. The effects of temperature, pressure (ail, hydrogen). and humidity on the fuel cell system performsnce were mainly investigated using thermo-dynamical and electro-chemical equations. To understand the power distribution characteristics of fuel cell system, the effrcts of operating temperature and air pressure on maximum power and system power were also demonstrated. Through this study, we can get the basic insight into the fuel cell stack and BOP component sizing and it can be used effectively for optimization of the practical fuel cell systems in purpose.