• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.2
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• pp.217-224
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• 2018

The purpose of this study is to evaluate the future potential value of CTE(Critical Technology Element)s that are evaluated to be low in TRA(Technology Readiness Assesment) and to present investment prioritization technologies in defense R&D(Research and Development) based on them. To do this, we used the DEA(Data Envelopment Analysis) method, which is useful in evaluating the efficiency of the organization. Specifically, we suggest a systematic framework to evaluate the future value of CTEs by setting the CTEs derived from the TRA process to DMU(Decision Making Unit)s, the cost and time required to develop each CTE as the input factor of the DEA and the effects of the development of each CTE as the output factor of the DEA respectively. We also conducted an illustrative case study on radar technologies to demonstrate the usefulness of the proposed approach.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.155-167
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a high-temperature cavern thermal energy storage (CTES) operated for a period of 30 years has been investigated by TOUGH2-FLAC3D simulator. As a fundamental study for the development of prediction and control technologies for the environmental change and rock mass behavior associated with CTES, the key concerns were focused on the hydrological-thermal multiphase flow and the consequential mechanical behavior of the surrounding rock mass, where the insulator performance was not taken into account. In the present study, we considered a large-scale cylindrical cavern at shallow depth storing thermal energy of $350^{\circ}C$. The numerical results showed that the dominant heat transfer mechanism was the conduction in rock mass, and the mechanical behavior of rock mass was influenced by thermal factor (heat) more than hydrological factor (pressure). The effective stress redistribution, displacement and surface uplift caused by heating of rock and boiling of ground-water were discussed, and the potential of shear failure was quantitatively examined. Thermal expansion of rock mass led to the ground-surface uplift on the order of a few centimeters and the development of tensile stress above the storage cavern, increasing the potential of shear failure.

• Composites Research
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• v.16 no.1
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• pp.1-12
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• 2003

This study developed SiC$_{p}$/A1$_2$O$_3$$_{f}$/Al composites for electronic packaging to which reinforcements were added with the volume fractions of 49%, 56% and 63% by the squeeze casting method. 0.8 wt. % of the inorganic binder as well as the A1$_2$O$_3$ fiber and SiC Particles with the volume fraction of 1:10 were added to the composites, which were produced in the newly designed mold. For the produced SiC/Al composites, the CTEs (coefficients of thermal expansion) were measured from 30 to 300 and compared with the FEM numerical simulation to analyze the temperature dependent properties. The experiment showed the CTEs of SiC$_{p}$/A1$_2$O$_3$$_{f}$/Al composites that were intermediate values of those of Rule of Mixture and Turner's Model. The CTEs were close to Turner's Model in the room temperature and approached the Rule of Mixture as the temperature increases. These properties analyzed from the difference of the average stress acting between the matrix and the reinforcements proposed in this study.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.76-85
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• 2014

In this paper, the equivalent coefficient of thermal expansion (CTE) of fiber reinforced plastic composite material is investigated with various CTE prediction schemes. Although there are several methods for predicting the equivalent CTEs, most of them have some limitations of are not much accurate when comparing prediction results with test results. In the framework of computational homogenization, a representative volume element is taken from the predefined fiber-volume ratio, and modelled with finite element mesh. Finally, the equivalent CTEs are obtained by applying periodic boundary condition. To verify the performance of the proposed method, the results obtained are compared with those by the existing methods and test results. Additionally, the thermal pointing error analysis for star tracker support structure is conducted and its accuracy is estimated according to CTE prediction schemes.

• Journal of the Korean Data and Information Science Society
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• v.28 no.1
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• pp.119-130
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• 2017

In many literatures on VaR and CTE for multivariate distribution, these are estimated by using transformed univariate distribution with a specific ratio of many kinds of portfolios. Even though there are lots of works to define quantiles for multivariate distributions, there does not exist a quantile uniquely. Hence, it is not easy to define the VaR and CTE. In this paper, we propose the weighted CTE vectors corresponding to various ratio combinations of many kinds of portfolios by extending the researches on the alternative VaR and integrated multivariate CTE based on multivariate quantiles. We extend relation equations about univariate CTEs to multivariate CTE vectors and discuss their characteristics. The proposed weighted CTEs are explored with some data from multivariate normal distribution and illustrative examples.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2000.04a
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• pp.9-15
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• 2000

Flip chip assembly on organic substrates using ACAs have received much attentions due to many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing compatible with organic substrates. ACAs are generally composed of epoxy polymer resin and small amount of conductive fillers (less than 10 wt. %). As a result, ACAs have almost the same CTE values as an epoxy material itself which are higher than conventional underfill materials which contains lots of fillers. Therefore, it is necessary to lower the CTE value of ACAs to obtain more reliable flip chip assembly on organic substrates using ACAs. To modify the ACA composite materials with some amount of conductive fillers, non-conductive fillers were incorporated into ACAs. In this paper, we investigated the effect of fillers on the thermo-mechanical properties of modified ACA composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of non-conducting fillers, dynamic scanning calorimeter (DSC), and thermo-gravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), and thermo-mechanical analyzer (TMA) were utilized. As the non-conducting filler content increased, CTE values decreased and storage modulus at room temperature increased. In addition, the increase in tile content of filler brought about the increase of Tg$^{DSC}$ and Tg$^{TMA}$. However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. It was observed that reliability results were significant affected by CTEs of ACA materials especially at the thermal cycling test. Results showed that flip chip assembly using modified ACA composites with lower CTEs and higher modulus by loading non-conducting fillers exhibited better contact resistance behavior than conventional ACAs without non-conducting fillers.ers.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.1
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• pp.41-49
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• 2000

Flip chip assembly on organic substrates using ACAs have received much attentions due to many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing compatible with organic substrates. ACAs are generally composed of epoxy polymer resin and small amount of conductive fillers (less than 10 wt.%). As a result, ACAs have almost the same CTE values as an epoxy material itself which are higher than conventional underfill materials which contains lots of fillers. Therefore, it is necessary to lower the CTE value of ACAs to obtain more reliable flip chip assembly on organic substrates using ACAs. To modify the ACA composite materials with some amount of conductive fillers, non-conductive fillers were incorporated into ACAs. In this paper, we investigated the effect of fillers on the thermo-mechanical properties of modified ACA composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of non-conducting fillers, dynamic scanning calorimeter (DSC), and thermo-gravimetric analyser (TGA), dynamic mechanical analyzer (DMA), and thermo-mechanical analyzer (TMA) were utilized. As the non-conducting filler content increased, CTE values decreased and storage modulus at room temperature increased. In addition, the increase in the content of filler brought about the increase of $Tg^{DSC}$ and $Tg^{TMA}$. However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. It was observed that reliability results were significantly affected by CTEs of ACA materials especially at the thermal cycling test. Results showed that flip chip assembly using modified ACA composites with lower CTEs and higher modulus by loading non-conducting fillers exhibited better contact resistance behavior than conventional ACAs without non-conducting fillers.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.115-124
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• 2015

Thermal energy storage (TES) is a technology that stores surplus thermal energy at high or low temperatures for later use when the customer needs it, not just when it is available. TES systems can help balance energy demand and supply and thus improve the overall efficiency of energy systems. Furthermore, the conversion and storage of intermittent renewable resources in the form of thermal energy can help increase the share of renewable resources in the energy mix which refers to the distribution of energy consumption from different sources, and to achieve this, it is essential to combine renewable resources with TES systems. Underground TES using rock caverns, known as cavern thermal energy storage (CTES), is a viable option for large-scale, long-term TES utilization although its applications are limited because of the high construction costs. Furthermore, the heat loss in CTES can significantly be reduced due to the heating of the surrounding rock occurred during long-term TES, which is a distinctive advantage over aboveground TES, in which the heat loss to the surroundings is significantly influenced by climate conditions. In this paper, we introduced important factors that should be considered in the shape and multiple layout design of TES caverns, and proposed guidelines for storage space design.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.04a
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• pp.35-43
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• 2001

Flip chip assembly on organic substrates using ACAs have received much attentions due to many advantages such as easier processing, good electrical performance, lower cost, and low temperature processing compatible with organic substrates. ACAs are generally composed of epoxy polymer resin and small amount of conductive fillers (less than 10 wt.%). As a result, ACAs have almost the same CTE values as an epoxy material itself which are higher than conventional underfill materials which contains lots of fillers. Therefore, it is necessary to lower the CTE value of ACAs to obtain more reliable flip chip assembly on organic substrates using ACAs. To modify the ACA composite materials with some amount of conductive fillers, non-conductive fillers were incorporated into ACAs. In this paper, we investigated the effect of fillers on the thermo-mechanical properties of modified ACA composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. It was observed that reliability results were significantly affected by CTEs of ACA materials especially at the thermal cycling test. Results showed that flip chip assembly using modified ACA composites with lower CTEs and higher modulus by loading non-conducting fillers exhibited better contact resistance behavior than conventional ACAs without non-conducting fillers. Microwave model and high-frequency measurement of the ACF flip-chip interconnection was investigated using a microwave network analysis. ACF flip chip interconnection has only below 0.1nH, and very stable up to 13 GHz. Over the 13 GHz, there was significant loss because of epoxy capacitance of ACF. However, the addition of $SiO_2filler$ to the ACF lowered the dielectric constant of the ACF materials resulting in an increase of resonance frequency up to 15 GHz. Our results indicate that the electrical performance of ACF combined with electroless Wi/Au bump interconnection is comparable to that of solder joint.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.243-256
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• 2012

Developing efficient and reliable energy storage system is as important as exploring new energy resources. Energy storage system can balance the periodic and quantitative mismatch between energy supply and energy demand and increase the energy efficiency. Industrial waster heat and renewable energy such as solar energy can be stored by the thermal energy storage (TES) system at high and low temperatures. TES system using underground rock carven is considered as an attractive alternative for large-scale storage, because of low thermal conductivity and chemical safety of surrounding rock mass. In this report, the development of available thermal energy storage methods and the characteristics of storage media were introduced. Based on some successful applications of cavern storage and high-temperature storage reported in the literature, the applicabilities and practicabilities of storage media and technologies for large-scale cavern thermal energy storage (CTES) were reviewed.