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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.
A study on the thermomechanical behavior of semiconductor chips on thin silicon substrate
임재혁,한만희,이준연,Youn Young Earmme,이순복,임세영 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.8
This study is concerned with the deformation or warping behavior of thin layered semiconductor structure comprising a silicon substrate, a pattern layer and a polyimide coating layer with its thickness varying from 100um to 50 um. In contrast with the conventional thick semiconductor structure, today’s semiconductor structure is increasingly thin and therefore the warping is extremely conspicuous, being among the major concerns in the structural design of a chip. In the view of thermomechanical analysis of an extremely thin layer structure considered in the present paper, a few parameters on the deformation should be taken into consideration such as the pattern layer and intrinsic stress. To account for the effect of the pattern layer, we make a well educated guess for the mechanical properties, employing the test results and the CBA (Composite Beam Analysis) theory. In addition, we take into consideration the effect of the intrinsic stress due to moisture absorption on deformation. We show that the chip warpage is accurately predicted when all these are properly considered. Furthermore, we have found that the local instability or wrinkling, associated with the nonuniformity or the inhomogeneity in material properties and bonding quality between any two neighboring layers, appears as one important mode of energy relaxation in addition to the overall warpage when the chip thickness becomes very small.
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.
Saebom Lee,Seung Tae Choi,Youn Young Earmme,Dae Youl Chung 대한기계학회 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.8
A problem of a circular elastic inhomogeneity interacting with a crack under uniform loadings (mechanical tension and heat flux at infinity) is solved. The singular integral equations for edge and temperature dislocation distribution functions are constructed and solved numerically. to obtain the stress intensity factors. The effects of the material property ratio on the stress intensity factor (SlF) are investigated. The computed SIFs are used to predict the kink angle of the crack when the crack grows.
Lee, Saebom,Park, Seung-Tae,Earmme, Youn-Young,Chung, Dae-Youl The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.8
A problem of a circular elastic inhomogeneity interacting with a crack under uniform loadings (mechanical tension and heat flux at infinity) is solved. The singular. integral equations for edge and temperature dislocation distribution functions are constructed and solved numeric-ally, to obtain the stress intensity factors. The effects of the material property ratio on the stress intensity factor (SIF) are investigated. The computed SIFs are used to predict the kink angle of the crack when the crack grows.
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.