• Journal of the Microelectronics and Packaging Society
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• v.22 no.4
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• pp.37-46
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• 2015

In this paper, the heat transfer characteristics of PCB (Printed Circuit Board) with cabon CCL (Copper Claded Layer) were studied through experiments and numerical analysis to compare of PCBs with conventional the FR-4 core and heavy copper cores. For study, samples are producted with HDI (High Density Interconnection) PCB of mobile phone with variations of thickness of core materials and grades of carbon material to evaluate heat transfer characteristics respectively. From this research results, heat transfer characteristics of the carbon core was rather low than heavy copper, but better than FR-4 core. In addition, even though the carbon and heavy copper core contributed on the heat transfer characteristics as their thickness increases, FR-4 cores disturbed heat transfer characteristics as it's thickness increases. Therefore, carbon core is recommendable to improve the heat transfer characteristics of the PCB because heavy copper core has much disadvantages such as increasing of wear of drill, the weight of PCB, and manufacturing cost by additional insulation materials for electrical insulation.

• Korean Journal of Computational Design and Engineering
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• v.21 no.4
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• pp.389-396
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• 2016

The necessity for environment-friendly material development has emerged in the recent automotive field due to stricter regulations on fuel economy and environmental concerns. Accordingly, the automotive industry is paying attention to carbon fiber reinforced plastic (CFRP) material with high strength and stiffness properties while the lightweight. In this study, we determine a shape of lower control arm (LCA) for maximizing the strength and stiffness by optimizing the thickness of each layer when the stacking angle is fixed due to the CFRP manufacturing problems. Composite materials are laminated in the order of $0^{\circ}$, $90^{\circ}$, $45^{\circ}$, and $-45^{\circ}$ with a symmetrical structure. For the approximate optimal design, we apply a sequential two-point diagonal quadratic approximate optimization (STDQAO) and use a process integrated design optimization (PIDO) code for this purpose. Based on the physical properties calculated within a predetermined range of laminate thickness, we perform the FEM analysis and verify whether it satisfies the load and stiffness conditions or not. These processes are repeated for successive improved objective function. Optimized CFRP LCA has the equivalent stiffness and strength with light weight structure when compared to conventional aluminum design.

• Macromolecular Research
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• v.17 no.5
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• pp.319-324
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• 2009

A new $\pi$-conjugated polymer, poly[(2-methoxy-(5-(2-(4-oxyphenyl)-5-phenyl-1,3,4-oxadiazole)-hexyloxy))-1,4-pheny1ene-1,2-etheny1ene-alt-(10-hexyl-3,7-phenothiazine )-1,2-ethenylene] (PTOXDPPV), was synthesized by the Heck coupling reaction. The electron transporting unit, conjugated 1,3,4-oxadiazo1e (OXD), is attached on the main chain via linear 1,6-hexamethylenedioxy chain. The band gap and photoluminescence (PL) maximum of PTOXDPPV are 2.35 eV and 565 nm, respectively. These values are very close to those of po1y[(2,5-didecyloxy-1,4-phenylene-1,2-etheny1ene )-alt-(l0-hexyl-3,7-phenothiazine)-1,2-ethenylene] (PTPPV), which does not have OXD pendant. The estimated HOMO energy level of PTOXDPPV was -4.98 eV, which is very close to that of PTPPV (-4.91 eV). The maximum wavelength of EL device based on PTOXDPPV and PTPPV appeared at 587 and 577 nm, respectively. In the PL and EL spectrum, the emission from OXD pendant was not observed. This indicates that the energy transfer from OXD pendants to main chain is occurred completely. The EL device based on PTOXD-PPV (ITO/PEDOT/PTOXDPPV/AI) has an efficiency of 0.033 cd/A, which is significantly higher than the device based on PTPPV (ITO/PEDOT/PTPPV/AI) ($4.28{\times}10^{-3}\;cd/A$). From the results, we confirm that the OXD pendants in PTOXDPPV facilitate hole-electron recombination processes in the emissive layer effectively.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.7-12
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• 2020

Electromechanical properties of REBCO CC tapes are known to be limited by defects (cracks) that form in the brittle REBCO layer. These defects could be inherently acquired during the CC tapes' manufacturing process, such as slitting, and which can be initiated at the CC tapes' edges. If propagated and long enough, they are believed to cause critical current degradation and can substantially decrease the delamination strength of CC tapes. Currently, commercially available CC tapes from various manufacturers utilize different growth techniques for depositing the REBCO layers on the substrates in their CC tapes preparation. Their epitaxial techniques, unfortunately, cannot perfectly avoid the formation of particles, in which sometimes acts as current blocking defects, known as outgrowths. Collective research regarding the composition, size, and formation of these particles for various CC tapes with different deposition techniques are particularly uncommon in a single study. Most importantly, these particles might interact in one way or another to the existing cracks. Therefore, systematic investigation on the interactions between the cracks' development mechanism and particles on the REBCO superconducting layers of practical CC tapes are of great importance, especially in the design of superconducting devices. Here, a proper etching process was employed for the CC tapes to expose and observe the REBCO layers, clearly. The scanning electron microscope, field emission scanning microscope, and energy-dispersive x-ray spectroscopy were utilized to observe the interactions between cracks and particles in various practical CC tapes. Particle compositions were identified whether as non-superconducting or superconducting and in what manner it interacts with the cracks were studied.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.69-74
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• 2005

Since the use of CFC and HCFC refrigerants is to be restricted due to the depletion of ozone layer, this experiment applies the $NH_{3}$ gas to study the performance characteristics from the superheat control for improving the energy efficiency. The experiments are carried out for the condensing pressure of refrigeration system from 1500kPa to 1600kPa by 50kPa and for degree of superheat from $0^{circ}$ to $1^{circ}$ by $10^{circ}$ at each condensing pressure. As a result of experiment, 1) As degree of superheat increased, evaporating pressure of the compressor decreased so equilibrium temperature decreased. And specific volume of refrigerant vapors increased so refrigerant mass flow and heat load of the evaporator decreased. 2) An influence of change of condensing pressure on heat load of the evaporator was insignificant. 3) With the identical degree of superheat, change of compressed temperature was insignificant according to each condensing pressure, so there was little change in enthalpy.4) when the degree of superheat is $0^{circ}$C at each condensing pressure, the refrigeration system has the hi띤est performance.

• Tribology and Lubricants
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• v.36 no.1
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• pp.47-54
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• 2020

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT of 400℃) on friction and wear behavior of Ti-6Al-4V alloy prepared by selective laser melting (SLM) were investigated. The objective of this study is to improve the mechanical properties and frictional behavior of Ti-6Al-4V alloy by UNSM treatment. Dry friction and wear tests were conducted using a ball-on-disk method at RT with a bearing steel as the counter ball. Due to the high HT and UNSM treatment, the surface hardness tended to increase and surface roughness tended to reduce. X-ray diffraction (XRD) analysis showed that nanocrystallization structure and compressive residual stress were formed at the surface layer after UNSM treatment at both RT and HT. After UNSM treatment, it was observed that the wear rate was reduced by about 6% for the specimen treated at RT and a 28% reduction for the specimen treated at HT in comparison with the untreated one. Based on scanning electron microscope (SEM) images showed that the damage caused by fatigue wear occurred in the wear track of the heat-treated specimen, and it is believed to be the cause of the highest wear rate. Mechanical properties and wear resistance of Ti-6Al-4V alloy were improved and prospect of industrial application was confirmed. Further research is still required to improve the characteristics of SLM Ti-6Al-4V alloy to the level of wrought Ti-6Al-4V alloy.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.600-605
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• 2010

In order to meet the requirements of faster speed and higher packing density for devices in the field of semiconductor manufacturing, the development of Cu/Low k device material is explored for use in multi-layer interconnection. SiOC(-H) thin films containing alkylgroup are considered the most promising among all the other low k candidate materials for Cu interconnection, which materials are intended to replace conventional Al wiring. Their promising character is due to their thermal and mechanical properties, which are superior to those of organic materials such as porous $SiO_2$, SiOF, polyimides, and poly (arylene ether). SiOC(-H) thin films containing alkylgroup are generally prepared by PECVD method using trimethoxysilane as precursor. Nano voids in the film originating from the sterichindrance of alkylgroup lower the dielectric constant of the film. In this study, methyltriphenylsilane containing bulky substitute was prepared and characterized by using NMR, single-crystal X-ray, GC-MS, GPC, FT-IR and TGA analyses. Solid-state NMR is utilized to investigate the insoluble samples and the chemical shift of $^{29}Si$. X-ray single crystal results confirm that methyltriphenylsilane is composed of one Si molecule, three phenyl rings and one methyl molecule. When methyltriphenylsilane decomposes, it produces radicals such as phenyl, diphenyl, phenylsilane, diphenylsilane, triphenylsilane, etc. From the analytical data, methyltriphenylsilane was found to be very efficient as a CVD or PECVD precursor.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.133-140
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• 2002

Phosphogypsum is a by-product from the phosphoric acid process for manufacturing fertilizers. It consists mainly of $(CaSO_4.2H_2O)$ and contains some impurities such as$(P_2O_5)$, 불소$(F_-)$, and organic substances. The annual world production of this material is up to 150 million tons and is up to 1.57 million tons in Korea. Therefore studies describe application of phosphogypsum to daily and middle cover materials in landfill. For this Purpose, experiments were performed to evaluate the engineering properties of the material by sieve analysis, specific gravity, consistency of soil, compaction, CBR, permeability, mi environmental characteristics of leaching test, reactor test. The results of this study are as follows : The mixing and layer conditions of CBR value are 6.2~6.3%, coefficient of permeability is $\alpha$$\times10_{-5}~10_{-6}cm/sec$. And leaching test results are far below than those of regulatory requirement of Waste Management Act, Soil Environment Preservation Act in Korea and RCRA in USA. Therefore phosphogypsum can be used as daily and intermediate cover materials in landfill.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1096_1097
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• 2009

Aluminium doped zinc oxide(ZnO:Al) thin film, which is mainly used as a transparent conducting electrode in electronic devices, has many advantages compared with conventional indium tin oxide(ITO). In this paper in order to investigate the possible application of ZnO:Al thin films as a transparent conducting electrode for flexible film-typed dye sensitized solar cell (FT-DSCs), ZnO:Al and ITO thin films were prepared on the polyethylene terephthalate (PET) substrate by r. f. magnetron sputtering method. Specially one-inched FT-DSCs using either a ZnO:Al or ITO electrode were also fabricated separately under the same manufacturing conditions. Some properties of both the FT-DSCs with ZnO:Al and ITO transparent electrodes, such as conversion efficiency, fill factor, and photocurrent were measured and compared with each other. The results showed that by doping the ZnO target with 2 wt% of $Al_2O_3$, the film deposited at discharge power of 200W resulted in the minimum resistivity of $2.2\times10^{-3}\Omega/cm$ and at ransmittance of 91.7%, which are comparable with those of commercially available ITO. Two types of FT-DSCs showed nearly the same tendency of I-V characteristics and the same value of conversion efficiencies. Efficiency of FT-DSCs using ZnO:Al electrode was around 2.6% and that of fabricated FT-DSCs using ITO was 2.5%. This means that ZnO:Al thin film can be used in FT-DSCs as a transparent conducting layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.459-465
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• 2013

In the manufacturing process of steel plates, materials at high temperatures above $800^{\circ}C$ are rapidly cooled by using a circular impinging water jet to determine their strength and toughness. In this study, the basic heat and fluid flow is solved by using the existing numerical model for boiling heat transfer. Actually, steel undergoes a phase change from austenite to ferrite or bainite during the cooling process. The phase change induces changes in its thermal properties. Instead of directly solving the phase change and the material cooling together, we solve the heat transfer only by applying the thermal properties that vary with temperature, which is already known from other studies. The effects of the changes in the thermal properties on the cooling of steel and the necessity of calculating the phase change are discussed.