• Journal of the Microelectronics and Packaging Society
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• v.18 no.2
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• pp.11-15
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• 2011

Heat transfer equation is first reviewed and then governing equation of moisture diffusion. Analogy scheme is applied to analysis the moisture absorption problem of polymers. It make possible to numerically analyze the diffusion problem for single medium by using commercial finite element code if it is under the isothermal loading condition. It is extended to special multimaterial system by introducing pressure ratio function, whose moisture characteristics of materials are proportional to temperature only. The weight changes of silicon-nonconductive-polymer joint model due to moisture absorption is measured and been very close to the numerical results as for single media with boundary condition with zero concentration, but yields numerical errors as for multisystem media.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.701-706
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• 2015

In this study, experimental and computer simulation results are compared and analyzed. Three-dimensional (3D) fabricated matrices from an MJM 3D printer were joined with poly-acetate thermoplastic polymers using a diode laser. A power range of 5-7 W was used to irradiate the boundary of two polymers. The heated polymers flowed into the matrices of the 3D fabricated structure, and reliable mechanical joining was achieved. Computer simulation showed the temperature distribution in the polymers, and flow direction was estimated based on the flux and temperature information. It was found that the more than the minimum energy threshold was required to effectively join the polymers and that two scans at low-speed were more effective than four scans at high speed.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.3 s.40
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• pp.39-45
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• 2006

This study was investigated the thermal properties of underfill with various epoxy resins using thermal analysis methods such as differential scanning calorimetry (DSC), thermo gravimetry analysis (TGA), dynamic mechanical analysis (DMA) and thermo-mechanical analysis (TMA). And, the adhesion strength of the underfills/FR-4 substrate was evaluated. The glass transition temperature (Tg) of underfill which was composed the cycolaliphatic epoxy resin was lower than that of underfill which was not composed the cycolaliphatic epoxy resin. The thermal degradation of underfill was composed of two processes, which involved chemical reactions between the degrading polymer and oxygen from the air atmosphere. The coefficient of thermal expansion (CTE) of underfill which was composed the cycolaliphatic epoxy resin was higher than that of underfill which was not composed the cycolaliphatic epoxy resin. The excessive curing temperatures caused a weak boundary layer of epoxy resin, which resulted in a deterioration of mechanical properties in the epoxy resin and thus led to poor adhesion property between the underfill/FR-4 substrate.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.1-11
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• 2002

The suitable turbulence model is found to be required in the course of establishing a proper analysis methodology for thermal stripping phenomena which are shown in strong temperature variation area such as reactors and propulsion devices. Three different turbulence models of $\kappa$-$\varepsilon$ model, modified $\kappa$-$\varepsilon$ model, and full Reynolds stress(FRS) model, are applied to analyze unsteady turbulent flows with temperature variation. Three test cases are selected for verification. These are vertical jet flows with water and sodium, and parallel jet flow with sodium. Analysis yields the conclusion that 3-D computation with FRS betters others. However, modified modeling is required to improve its heat transfer characteristic analysis. Further analysis is performed to find momentum variation effects on temperature distribution. It is found that the momentum increase results increase of fluid mixing and magnitude of temperature variation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.567-578
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• 2015

Single droplet-wall collision heat transfer characteristics on a heated plate above Leidenfrost temperature were experimentally investigated considering the effects of impact velocity. The collision characteristics of the droplet impinged on the heated wall and the changes in temperature distribution were simultaneously measured using synchronized high-speed video and infrared cameras. The surface heat flux distribution was obtained by solving the three-dimensional transient heat conduction equation for the heated substrate using the measured surface temperature data as the boundary condition for the collision surface. As the normal impact velocity increased, heat transfer effectiveness increased because of an increase in the maximum spreading diameter and a decrease in the vapor film thickness between the droplet and heated wall. For We < 30, droplets stably rebounded from a heated wall without breakup. However, the droplets broke up into small droplets for We > 30. The tendency of the heat transfer to increase with increasing impact velocity was degraded by the transition from the rebounding region to the breakup region; this was resulted from the reduction in the effective heat transfer area enlargement due to the breakup phenomenon.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.79-84
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• 2005

An experimental investigation for impingement of under-expanded, axisymmetric jets on a flat plate has been conducted, and the surface pressure, the adiabatic wall temperature distributions on the plate have been measured in detail. For the explanation on the wall temperature distributions, the total temperature distributions along a free jet have also been measured with total temperature probes. In this study, the under-expansion ratio and the nozzle-to-plate distance have been considered as experimental parameters. Depending on nozzle-to-plate distances, different distributions of adiabatic wall temperature are shown by the energy separation at a jet edge and a impinged surface. Also, the recovery factor on a stagnation point decreases significantly due to the isolation of fluid particles in a central region.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.612-618
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• 1998

Monolithic SiC and SiC/C FGM layers were deposited on the graphite substrates by the CVD method and their thermal properties of the two specimens were investigated by thermal shock test for comparison. Temperature profiles and thermal stress distributions on thermal shock test were calculated by a commercially used computer program to see the thermal stress differences inside of two specimens. The specimens coated with FGM were expected to show a efficient relaxation of thermal stresses at the interface and they were not cracked under the actual $\Delta$T=1600 K experimental condition. This result proved that the experimental results were well accorded with the expectation from the theoretical calculations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1541-1550
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• 2001

This paper describes experimental investigations in the direct extrusion of copper clad aluminum rods through conical dies. Composite materials consist of two or more different material layers. Copper clad aluminum composite materials are being used fur economic and structural purposes and the development of an efficient production method of copper clad aluminum composite material rods by extrusion is very important, It is necessary to know the conditions in which successful uniform extrusion ,and sound cladding may be carried out without any defects in the direct extrusion. There are several variables that have an influence on determining a sound clad extrusion. In order to investigate the influence of these parameters on the hot direct extrudability of the copper clad aluminum composite material rods, the experimental study have been performed with various extrusion temperatures, extrusion ratios and semi-cone angles of die. Subsequently, the microscopic inspection of interface bonding is carried out for extruded products. By measuring hardness, along extrusion way of products, a variation of hardness has been discussed. Proportional flow state has been considered by measuring radius ratio of Cu sleeve and Al core before and after extrusion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1297-1303
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• 2012

In this paper, the standard procedures for measuring the moisture sorption properties of thin polymeric materials such as polyethylene terephthalate (PET) by using the thermo-gravimetric method to characterize the moisture diffusion in the polymer are presented, and the sorption properties are quantified. The moisture diffusivity and solubility are characterized to investigate the effect of temperature and humidity on the moisture sorption properties according to the Arrhenius equation. The validation of the obtained sorption properties using thermogravimetry is discussed with the measured permeability based on Fickian diffusion. The nonlinear behavior of the concentration dependent moisture diffusion is investigated experimentally, and the nonlinearity is characterized numerically for the case of having an interface with an inorganic material such as a metal. The Fickian/Non-Fickian model based on the obtained moisture sorption properties is compared and discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.397.2-397.2
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• 2014

유기 발광 다이오드 (OLED)의 상용화를 위해 해결해야할 기술적 문제 중하나는 장수명이다. OLED에 적용된 유기물 층은 수분과 산소에 취약하여 소자 수명을 단축하는 요소로 작용하는데, 이를 해결하기 위해 유기물을 보호하며, 유기물 내로 침투되는 수분과 산소를 제어하기 위한 보호 층의 증착이 필수적이다. 필수적이다. 본 연구에서는, 사이클 화학 기상 증착법(C-CVD)을 이용하여 SiN/SiCN/SiN 구조의 무기 박막을 증착하여 유기물 보호층으로서의 적용 가능성을 제시하고자 한다. 이 때 각층의 두께는 각 각 10 nm이다. 증착된 다층 무기 박막은 비정질 상으로 수분 침투 보호막으로서 적당하다. 다층 무기 박막의 수분에 대한 저항성은 칼슘을 이용한 투과도 변화를 이용하여 측정하였다. 칼슘을 이용한 투과도 측정을 위해 고분자 PEN 필름위에 칼슘을 60nm 두께로 증착 시키고, 이어서 무기물인 SiN/SiCN/SiN의 다층 박막을 확산 방지층으로 증착 하였다. 제작된 소자는 온도 $85^{\circ}C$, 상대습도 85%의 가혹 조건에서 시간에 따른 표면 변화 및 투과도의 변화를 측정하였다. SiN/SiCN/SiN 구조를 갖는 무기 박막 층의 투습도는 3000시간까지는 $3.2{\times}10-5g/m/day$를 유지하였다. 이는 OLED 소자의 상용화를 위한 요구 조건에 근접한 값이다. 그러나 투습도는 측정 시간이 6000시간이 지난 후에 급격 증가하는데 이것은 30nm 두께의 SiN/SiCN/SiN의 확산 방지층에 임계 수명이 존재 한다는 것을 의미 한다고 할 수 있다. C-CVD 기술에 의해 제조된 다층 무기 박막 보호 층의 경계면에서 각 층간의 intermixing 현상이 관측되었으며, 이는 무기물 층의 결함과 핀 홀을 통해 내부로 확산 되는 수분의 침투 경로를 효과적으로 제어할 수 있는 방법이다. 본 연구 결과는 유연 기판 상에 제작된 OLED 소자에 적용 가능한 기술로서 소자 수명의 연장 뿐만 아니라 경량화에도 기여할 수 있는 기술이다.