• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.79-84
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• 2016

A flexible electronic device deformed by external force causes the failure of a semiconductor die. Even without failure, the repeated elastic deformation changes carrier mobility in the channel and increases resistivity in the interconnection, which causes malfunction of the integrated circuits. Therefore it is desirable that a semiconductor die be placed on a neutral line where the mechanical stress is zero. In the present study, we investigated the effects of design factors on the position of neutral line by finite element analysis (FEA), and expected the possible failure behavior in a flexible face-down packaging system assuming flip-chip bonding of a silicon die. The thickness and material of the flexible substrate and the thickness of a silicon die were considered as design factors. The thickness of a flexible substrate was the most important factor for controlling the position of the neutral line. A three-dimensional FEA result showed that the von Mises stress higher than yield stress would be applied to copper bumps between a silicon die and a flexible substrate. Finally, we suggested a designing strategy for reducing the stress of a silicon die and copper bumps of a flexible face-down packaging system.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.1
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• pp.55-59
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• 2011

Folding endurance, bending fatigue and monotonic tensile tests of 4 kinds of Cu foil on flexible substrate was performed to investigate the relationship between folding or bending endurances and tensile characteristics. The repeated 5.3 or 2.0% strain was applied to Cu foil in folding endurance test or bending fatigue test while monitoring the electrical resistance. Elastic modulus, yield strength, ultimate tensile strength, ductility, and toughness were obtained by monotonic tensile test on the same samples. The Cu foil with higher toughness and ductility showed higher reliabilities in folding or bending fatigue. However, elastic modulus and yield strength did not show any relationship with folding and bending reliability. This is because the failures of Cu foil by folding or bending fatigue were closely related to the fracture energy of metal.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.105-111
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• 2023

Electronic devices have been evolved to be mechanically flexible that can be endured repetitive deformation. This evolution emphasizes the importance of long-term reliability in metal wiring connecting electronic components, especially under bending fatigue in compressed environments. This study investigated methods to enhance adhesion between copper (Cu) and polyimide (PI) substrates, aiming to improve the reliability of copper wiring under such conditions. We applied oxygen plasma treatment and introduced a chromium (Cr) adhesion layer to the polyimide substrate. Our findings revealed that these adhesion enhancement methods significantly affect compression fatigue behavior. Notably, the chromium adhesion layer, while showing weaker fatigue characteristics at 1.5% strain, demonstrated superior performance at 2.0% strain with no delamination, outperforming other methods. These results offer valuable insights for improving the reliability of flexible electronic devices, including reducing crack occurrence and enhancing fatigue resistance in their typical usage environments.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.2
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• pp.94-100
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• 1988

Recently with the rapid development in marine and shipbuilding industries such as marine structures, ship, and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics was closed up an important role in mechanical design. In this study, the 5086 Al-Alloy was tested by used of a rotary bending fatigue tester and was investigated under the environments of various specific resistance and air. The specific resistance, as a corrosion environment, was changed 15, 20, 25 and 5000$\Omega$.cm. The corrosion fatigue crack initiation sensitivity was quantitatively inspected for 5086 Al-Alloy in the various specific resistance. The experimental constants of Paris rule were examined in the various specific resistances, and the influences of load and corrosion with affect the crack growth rate were compared with. Main results obtained are as follows: (1) Number of stress cycles to corrosion fatigue crack initiation delaies and corrosion fatigue crack initiation sensitivity decreases with the increasing for the specific resistance. (2) The experimental constant m of Paris rule decreases with the decreasing for specific resistance. Hence the effect of corrosion is more susceptible than that of stress intensity factor. (3) The corrosion fatigue crack of 5086 Aluminium Alloy appears intergranular fracture. (4) Corrosion sensitivity is decreased with the increasing stress intensity factor and is nearly uniform when stress intensity factor is over 40kg.mm super(-3/2)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.1010-1015
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• 2012

In this study, a thin-film thermo-electrochemical cell that directly converts waste thermal energy into electrical energy was fabricated. Electrical conductivity of conducting carbon fiber, which was used as flexible electrode, was increased through coating of carbon nanotube, and resistance of the CNT-coated fiber electrode was not changed even after bending test with various curvatures. Maximum output power of the thermocell was increased quadratically with the temperature difference, and showed a value of about 2.5 mW/kg at temperature difference of $3.4^{\circ}C$. As a result of discharge test for 12 hours, it is confirmed that the cell can operates continuously. And thin-film thermocell wrapped around a pipe with hot liquid flowing within was demonstrated. Internal resistance of the cell was decreased with various curvature of heat pipe, and maximum output power was increased by 30 %. Therefore, the cell can be applied to various heat source.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.190-195
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• 2021

Typical Mn-SnO₂/Ag/Mn-SnO₂ tri-layer films were prepared on a PET substrate by RF/DC magnetron sputtering method at room temperature. Based on EMP simulation, the thicknesses of the top and bottom Mn-doped SnO₂ layers were kept at 40 nm and the Ag layer was maintained at 13 nm for continuous electrical conduction. The experimentally measured optical transmittances at 550 nm wavelength were ranged from 82.9 to 88.1 % and sheet resistances were varied from 5.9 to 6.9 Ω/☐. The highest value of figure of merit, ϕ_TC was 48.1 × 10^-3 Ω^-1. Based on bending test under 4 and 5 mm of inner and outer curvature radius condition, tri-layer film resistance varies only by approximately 1.5 % after 10,000 bending cycles, showing excellent mechanical flexibility.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.273-273
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• 2009

고체산화물 연료전지 (Solid Oxide Fuel Cell, 이하 SOFC)는 제조형태에 따라 크게 평판형과 원통형으로 구분할 수 있다. 단위면적당 출력 효율이 높은 평판형의 장점과 원통형의 밀봉이 용이한 장점을 동시에 가지는 평관형 형태로 지지체를 제작하였으며, 셀의 배치를 평면상 직렬로 연결하는 다전지식으로 구성함으로 전극의 길이나, 셀 간격을 기존 평판형이나 원통형에 비해 대폭 감소시켜 단위면적당 전압 및 출력효율을 높이고자 하였다. Segmented 평관형 지지체의 소재로는 연료전지의 성능 특성에 관여하지 않으며 열사이클 저항성과 기계적 강도가 우수한 spinel구조를 가지는 $MgAl_2O_4$를 선정하였다. 연료가스의 원활한 공급이 가능하도록 carbon을 기공 전구체로 사용하여 압출성형하였으며 건조과정에서 crack이 생기지 않는 공정을 확립한 후 $1400^{\circ}C$ 에서 소결하였다. 제조된 지지체는 수은침투법과 3점 굽힘 강도법으로 기공율과 기계적 강도를 각각 측정하였다. Anode를 스크린 프린팅법으로 지지체 위에 적층한 후 미세구조를 확인하였고 이를 바탕으로 다공성이며 기계적 강도를 가지고 음극과의 반응이 없는 우수한 지지체를 제조할 수 있었다.

• Journal of the Ergonomics Society of Korea
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• v.28 no.4
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• pp.17-23
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• 2009

The purpose of this study was to assess activation and contribution of muscles of the elderly according to increased loading during the arm flexion extension resistance exercise. Surface electromyographic signals were acquired from biceps brachii, triceps brachii, deltoid posterior, pectoralis major and latissimmus dorsi to determine the difference of the activation of specific muscles between the elderly and young. Five elderly and five young males with no musculoskeletal disease volunteered for the study. Electromyographic activities in the muscles were measured during resistance exercise and normalized to the maximum EMG activity recorded in the maximal voluntary static contraction (MVC). Against the increased loading during arm flexion/extension resistance exercises, the young uses muscles evenly but the elderly uses one specific muscle frequently. Contribution of triceps brachii during extension and deltoid posterior during flexion was principal in the elderly.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.472-478
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• 1989

Using the SMC(sheet moulding compound) composite material consisting of E-glass chopped strand mat and unsaturated polyester resin, three-point bending tests are carried out to evaluate the elasto-plastic fracture toughness by means of R curve. The crack extension is experimentally observed with the ink staining method. The point of stable crack growth is discussed in consideration of the load-load point displacement curve, the damage behavior of the notch vicinity, and the R-curves. The damage zone of the notch vicinity was composed of the initiation and growth of subcracks as well as those of the main crack. The point of stable crack growth can be defined as the inflection point in the R curves and its point also concurrs with the proportional limit on the load-load point displacement curve.

• Korean Journal of Materials Research
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• v.31 no.2
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• pp.108-114
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• 2021

In the manufacturing of bulk graphite, pores produced by vaporization and discharge of volatile materials in binders during carbonization reduce the density of bulk graphite, which adversely affects the electrical conductivity, strength and mechanical properties. Therefore, an impregnation process is introduced to fill the pores and increase the density of bulk graphite. In this study, bulk graphite is prepared by varying the viscosity of the impregnant. The microstructure of bulk graphite is observed. The flexural strength and electrical resistivity are measured. As the viscosity of the impregnants decreases and the number of impregnations increases, it is shown that the number of pores decreases. The density before impregnation is 1.62 g/㎤. The density increases to 1.67 g/㎤ and porosity decreases by 18.6 % after three impregnations using 5.1 cP impregnant, resulting in the best pore-filling effect. After three times of impregnation with a viscosity of 5.1 cP, the flexural strength increases by 55.2 % and the electrical resistivity decreases by 86.76 %. This shows that a slight increase in density due to the pore-filling effect improves the properties of bulk graphite.