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압축 및 인장 응력 하에서의 FCC 나노 와이어 안정성에 관한 연구
임영태(Young Tae Im),김성엽(Sung Youb Kim),엄윤용(Youn Young Earmme) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The properties of nanowires can be different from those of bulk materials due to the effects of surface. In this paper, using the molecular statics simulation with the embedded-atom method potential, the stability of FCC nanowires under uniaxial compression and tension was investigated. Ni and Pd nanowires with a square cross-section and surface orientations of [100], [010] and [001] were created with initial atomic positions corresponding to the bulk face-centered-cubic crystal structure. The length and the cross-section area of the nanowires were varied. The atoms in the wire were then relaxed to a minimum energy state at 0 K. The simulation results show two kinds of instabilities : partial slip and phase transformation. Comparing the simulation results with Hill criterion, it is found that nanowires become unstable before the system meets Hill criterion under compression and elastic constants and the deformation mode are in a good agreement with Hill criterion under tension.
압축 응력 하에서의 금 나노 와이어 안정성에 관한 연구
임영태(Young Tae Im),엄윤용(Youn Young Earmme) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The structure and properties of nano scale materials can be different from those of bulk materials due to the effects of surface. In this paper, using the molecular statics simulation with the embedded-atom method potential, the stability of Au nanowires under uniaxial compression was investigated. Au nanowires with a square cross-section and surface orientations of [100], [010] and [001] were created with initial atomic positions corresponding to the bulk face-centered-cubic crystal structure. The length and the cross-section area of the nanowires were varied. The atoms in the wire were then relaxed to a minimum energy state at 0 K. The simulation results show three kinds of instabilities : buckling, twinning and phase transformation. Comparing the simulation results with the theoretical ones of the critical buckling load proposed by Euler, it is found that the buckling occurs at a much higher load than the Euler buckling load. A new model predicting the instability for the buckling as well as the twinning and the phase transformation is now under study.
급속 열처리시 실리콘 웨이퍼의 온도분포와 슬립 현상의 해석
이혁,유영돈,엄윤용,신현동,김충기,Lee, Hyouk,Yoo, Young-Don,Earmme, Youn-Young,Shin, Hyun-Dong,Kim, Choong-Ki 대한기계학회 1992 대한기계학회논문집 Vol.16 No.4
본 연구에서는 텅스텐 할로겐 램프를 이용한 급속 열처리 장치로 웨이퍼를 가 열할 때 시간에 따라 변하는 웨이퍼의 2차원 온도 분포와 온도 구배에 의해 발생하는 열응력을 실리콘 웨이퍼의 결정방향에 따라 다른 값을 갖는 탄성계수를 고려하여 계산 하고, 슬립의 발생 시기, 웨이퍼의 가열속도와 슬립량의 관계, 그리고 웨이퍼에 발생 한 슬립의 진전 특성에 대하여 살펴보고 실험결과와 비교하였다. A numerical solution of temperature and thermally induced stress in a wafer during rapid thermal processing (R.T.P) is obtained, and an analysis of onset and propagation of slip is performed and compared with experiment. In order to calculate temperature distribution of a wafer in R.T.P system, heat conduction equation that incorporated with radiative and convective heat transfer model is solved, and the solution of the equation is calculated numerically using alternating direction implicit (A.D.I) method. In dealing with radiative heat transfer, a partially transparent body that absorbs the radiation energy is assumed and this transparent body undergoes multiple internal reflections and absorptions. Two dimensional (assuming plane stress) thermoelastic constitutive equation is used to calculate thermal stress induced in a wafer and finite element method is employed to solve the equation numerically. The stress resolved in the slip directions on the slip planes of silicon is compared with the yield stress of silicon in order to predict the slip. The result of the analysis shows that the wafer temperature at which slip occurs is affected by the heating rate of the R.T.P system. It is observed that once slip occurs in the wafer, the slip grows.
나노 압입자를 이용한 박막/모재 구조의 계면파괴인성치 평가
서병국(Byung-Guk Suh),엄윤용(Youn-Young Earmme) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
A method to measure the interfacial toughness of film/substrate by nanoindenter is proposed. As the thickness of the film decreases, the measurement of the interfacial toughness requires the more sophisticated equipment such as nanoindenter. In this study, the nanoindenter is applied to the substrate near the interface of film/substrate in the direction perpendicular to the normal of the interface, causing the cohesive fracture of the substrate, followed by the interfacial cracking. The specimen of Cu(0.56㎛)/Si(530㎛) are made by sputtering the copper onto the silicon wafer. By scratching the copper surface, we can make the easy interfacial cracking during the nanoindentation. It is found that the averaged values of the interfacial toughness of the Cu/Si is 0.664±0.3 J/㎡. The phase angle of the specimen in this study is ψ ? 36.8° , computed by the method of Suo and Hutchinson.
김성엽(Sung Youb Kim),엄윤용(Youn Young Earmme) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.3
We calculate the variation of the surface stresses according to uniaxial and biaxial strains in face-centered cubic (FCC) metals. In our study, three mainly observed free surfaces of seven representative FCC metals are considered. Employed method is molecular mechanics, in which the interaction of atoms is described by empirical interatomic potentials. As uniaxial strain increases to tensile direction, the surface stresses on {100} and {110} free surfaces decrease monotonously, while those on {111} surface increase. These tendencies are the same regardless of the species of metals and interatomic potentials employed. However, when the system is under biaxial strain, surface stresses change different according to the surface directions, the species of metals, and even interatomic potentials. On {100} and {111} surfaces, heavy metals (Pt, Au) show the opposite variation to light metals (Ni, Cu). In the cases of Pd and Ag, the surface stresses reveal the opposite tendency, depending on interatomic potentials used.
그림자식 모아레를 이용한 PWB의 휨 측정에 관한 연구
이성민(Sung-Min Lee),엄윤용(Youn-Young Earmme) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
PWB warpage is one of the major SMP(surface mount package) failures together with fatigue failure of bonding wires and solder joints in electronic packages. In this study, PWB warpage before and after thermal cycling is measured by shadow moire method whose limited sensitivity is enhanced by a phase shifting technique. PWB specimens tested are made of FR-4 without Cu foil, FR-4 with one-side Cu foil, and FR-4 with two-side Cu foil, respectively. Experimental measurements show that ⅰ) PWB before thermal cycling has some warpage, ⅱ) crosswise directional warpage is larger than lengthwise directional warpage, and ⅲ) PWB of asymmetric structure experiences more serious warpage than that of symmetric structure after thermal cycling as the temperature change in thermal cycling goes higher.
박정순(Park Jeong Soon),임재혁(Jae Hyuk Lim),엄윤용(Youn Young Earmme),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Chip crack analysis is conducted for multichip package subject to molding process and thermal cycling test using finite element method. We investigate the effect of initial vertical crack length on energy release rates of the system, and evaluate the maximum allowable crack length under pressure during molding process. In thermal-cycling test, an initial delamination is assumed between the second chip and a barrier tape, which is located under the second chip. The effect of material properties and multichip geometries on delamination are clarified.
임재혁(Jae Hyuk Lim),한만희(Man-Hee Han),이준연(Jun-Youn Lee),박정순(Jeong Soon Park),엄윤용(Youn Young Earmme),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Prediction of warpage and residual stress in semiconductor chip devices play an important role in chip design. However, there are a few uncertainties in warpage prediction due to unknown patterning material properties, and moisture effect on polymer film. To estimate patterning material properties, we adopt a composite plate analysis and experimental techniques. and measure the warpage of chip after drying at about 250℃ for 30min to remove moisture. In 100㎛, 80㎛ chip cases, finite element analysis result shows a good agreement with measured values, but for 50㎛ and 60㎛ chip cases, there exist a substantial deviation from the measured values due to local deformation from imperfection and defects inherently embedded in the patterning layer and nonuniform bonding between PIcoating and silicon.