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심형섭,이성혁,김종민,신영의,Sim, Hyung-Sub,Lee, Seong-Hyuk,Kim, Jong-Min,Shin, Young-Eui 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.3
The present study is devoted to investigate the transient flow and to estimate the filling time fur underfill process by using the numerical model established on the fluid momentum equation. For optimization of the design and selection of process parameters, this study extensively presents an estimation of the filling time in the view points of some important factors related to underfill materials and flip-chip geometry. From the results, we conclude that the filling time changes with respect to the under fill materials because of different viscosity, surface tension coefficient and contact angle. It reveals that, as the gap height increases, the filling time decreases substantially, and goes to the saturated values.
펨토초 레이저가 조사되는 동안의 금속 박막내의 비평형 에너지 전달 현상에 대한 수치해석 연구
沈炯燮(Hyung Sub Sim),李晟赫(Seong Hyuk Lee) 대한전기학회 2007 전기학회논문지 Vol.56 No.2
The present study investigates numerically nonequilibrium energy transfer between electrons and phonons in metal thin films irradiated by ultrashort pulse lasers and it also provides the temporal and spatial variations of electron and phonon temperatures using the well-established two-temperature model(TTM) on the basis of the Boltzmann transport equation(BTE). This article predicts the crater shapes in gold film structures, and compares the results by using two-dimensional energy transport equation. From the results, it is found that nonequilibrium energy transfer between electrons and phonons takes place, and the equilibrium time increases with the increase of laser fluence. On the other hand, above threshold fluence the ablation time doesn't change nearly with increasing fluences. Compared with one-dimensional TTM, it also reveals that the temporal distributions of electron and phonon temperatures at the top surface estimated by using two-dimensional TTM have a similar tendency. The results show that two-dimensional TIM can simulate the crater shape of metals during the irradiation of femtosecond pulse lasers and the absorbed energy is propagated to z-direction faster than to r-direction.
극초단 펄스 레이저가 입사된 박막 구조의 마이크로스케일 열적-광학적 특성 연구
심형섭(Hyung Sub Sim),이성혁(Seong Hyuk Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
This paper is devoted to investigate numerically the microscale thermo-optical characteristics in thin metal and semiconductor films irradiated by ultrashort pulse laser. For metal films, the two temperature model (2TM) is used, and the quantum effects are included. For silicon films, two different models such as the 2TM and the three temperature model (3TM) are utilized and they are compared with each other. In addition, the extended two-dimensional equations of 2TM and 3TM are established for the prediction of crater shapes and ablation depths. For gold films, it is found that thermo-optical properties vary considerably with temperature because of quantum effects during the laser irradiation. For silicon film irradiated by ultrashort pulse laser, it is observed that non-equilibrium state occurs between LO and acoustic phonons for femtosecond pulse lasers because the pulse duration is shorter than LO phonon-acoustic phonon energy relaxation time.