• 마이크로전자및패키징학회지
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• 제31권2호
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• pp.9-15
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• 2024

칩 온 보드(chip on board) 패키지 적용을 위해 프리프레그(prepreg) 표면에 잔류하는 불순물이 봉지재(encapsulant)의 젖음성에 미치는 영향을 규명하기 위해 전자현미경(scanning electron microscope)과 X-선 광전자 분광기(X-ray photoelectron spectroscopy)를 이용하여 미세구조, 조성 및 화학 결합을 분석하였다. 프리프레그 표면에 잔류 불순물이 존재하는 시편의 경우 잔류 불순물이 존재하지 않는 시편보다 접촉각이 28° 높게 측정되었으며, C-O 결합은 4% 낮게 도출되었다. 이는 공정 중 잔류 불순물인 Na, F이 프리프레그 표면에 존재하는 C와 화학 반응을 하여 C-F 결합 생성으로 인해 프리프레그 표면의 C-O 결합이 끊어지면서 프리프레그 표면에너지가 낮아지게 되고 이로 인해 접촉각이 증가하게 되면서 봉지재의 젖음성이 저하되는 것으로 판단된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.410-415
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• 2004

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and $Nos\acute{e}$-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion force and friction force on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.108-111
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• 2004

The polypropylene(PP) fiber is poised as a low cost alternative for reinforcement in structural applications in comparison with other high performance fibers, such as the polyvinyl-alcohol(PVA), polyethylene, carbon and aramid fiber. The mechanical properties of the composite are strongly determined by the interfacial behavior of fiber and cementitious matrix. The crack bridging mechanism contribute to composite toughness from activation of the fiber-matrix interface where energy is dissipated through debonding of the interface and fiber pullout. In this study, therefore, the pullout behavior of PP fibers is investigated. Experimental work includes the investigation of the interfacial properties, and the composite property. The quantification of interfacial properties, the frictional bond is achieved through single fiber pullout test. A study on the effect of inclination angle on fiber pullout behavior is also conducted.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.337-342
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• 2007

In this study, molecular dynamics simulation of nano imprint lithography in which patterned stamp is pressed onto amorphous polyethylene(PE) surface are performed to study the behaviour of polymer. Force fields including bond, angle, torsion, and Lennard Jones potential are used to describe the inter-molecular and intra-molecular force of PE molecules and stamp, substrate. Periodic boundary condition is used in horizontal direction and canonical NVT ensemble is used to control the system temperature. As the simulation results, the behaviour of polymer is investigated during the imprinting process. The mechanism of polymer deformation is studied by means of inspecting the surface shape, volume, density, atom distribution. Deformation of the polymer resist was found for various of the stamp geometry and the alignment state of the polymer molecules.

• 한국자기공명학회논문지
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• 제9권1호
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• pp.67-73
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• 2005

$^{27}AI$ triple quantum magic angle spinning (3QMAS) NMR spectra of several mordenite (MOR) sample were simulated with the point charge model method and compared with experimental 3QMAS spectra. Signal positions from different tetrahedral (T) sites in 3QMAS spectra are mainly governed by local structures of T sites such as T-O-T angles and T-O bond lengths. When preparation methods, cations in addition to Si/Al rations vary, the local structures of T sites in MOR change enough to alter signal patterns in 3QMAS of MOR. This inhibits to study the of Al distribution variation over 4 different T sites in mordenite during process such as dealumination by 3QMAS spectra.

• 대한전기학회논문지:전력기술부문A
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• 제49권1호
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• pp.19-25
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• 2000

This paper describes the sheath induced voltage in underground transmission cable system which will be operated with cable cover protection unit(CCPU). Simulation was carried out to analyze the sheath induced voltage in the real cable system which was installed by 154㎸ CV cable in the case with and without CCPU. The sheath induced voltage will be also analyzed according to the change of grounding method, fault resistance and fault angle. Simulation was performed using EMTP and ATP Draw, the simulation results show whether the CCPU in necessary or not in underground transmission power cable system.

• 대한기계학회논문집A
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• 제29권6호
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• pp.852-859
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• 2005

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and Nose-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion and friction forces on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.

• 한국진공학회지
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• 제7권1호
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• pp.5-10
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• 1998

CAICISS장치를 이용하여 깨끗한 Si(001) 표면에서 재배열하는 dimer의 원자구조를 분석하였다. Si(001) 표면에서 dimer원자가 확실히 buckled되어 있음을 확인하였고, asymmetry(2$\times$1)구조와 c(4$\times$2)구조가 공존하고 있음을 밝혔다. dimer원자의 결합거리는 2.3$\pm$0.1$\AA$이고, buckling각은 18$\pm$$1^{\circ}$였다.

• Macromolecular Research
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• 제15권7호
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• pp.610-616
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• 2007

We developed a coarse-grained force field and have extended it to polystyrene with longer chain length. A systematic method was introduced and was utilized to explain how the coarse-grained force field for polystyrene could be developed from the atomistic simulation in the paper. We elected to use polystyrene with different chain lengths of 20, 40 and 80 monomers in this study. In three cases, we utilized the same new mapping scheme. The coarse-grained force field does reproduce the bond, angle, and radial distribution of the atomistic model. The coarse-grained model proved successful, as shown by analyses of the static and dynamic properties of different chain lengths.

• Bulletin of the Korean Chemical Society
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• 제29권5호
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• pp.963-968
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• 2008

For the [$Cr_2(H_2tmp)_2Cl_4$] compound, simplified models with two bridging methoxo ligands have been studied. The influence of the bridging Cr-O-Cr bond angles on the exchange coupling between metal atoms in the model compound has been analyzed by means of density functional calculations with the broken-symmetry approach. Coupling constant calculated for the full structure is in good agreement with the experimentally reported value, confirming the validity of the computational strategy used in this work to predict the exchange coupling in a family of related dinuclear Cr(III) compounds. The calculations indicate a good correlation between the calculated coupling constant and the sum of the squared energy gap of three pairs of metal $t_{2g}$ OMSOs with a limited variation of the Cr-O-Cr angle. The spin density distribution and the mechanism of magnetic coupling interactions are discussed.