• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.55-61
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• 2022

In this study, properties of Pb-free solder joints which were combined using Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder with a mid-temperature type of melting temperature and Sn-57Bi-1Ag Pb-free solder with a low-temperature type of melting temperature were reported. Combined Pb-free solder joints were formed by reflow soldering processes with ball grid array (BGA) packages which have SAC305 solder balls and flame retardant-4 (FR-4) printed circuit boards (PCBs) which printed Sn-57Bi-1Ag solder paste. The reflow soldering processes were performed with two types of temperature profiles and interfacial properties of combined Pb-free solder joints such as interfacial reactions, formations of intermetallic compounds (IMCs), diffusion mechanisms of Bi, and so on were analyzed with the reflow process conditions. In order to compare reliability characteristics of combined Pb-free solder joints, we also conducted thermal shock test and analyzed changes of mechanical properties for joints from a shear test during the thermal shock test.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.215-220
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• 2011

A 0.5 t/h class non-furnace boiler has been developed with the aim of achieving a high efficiency and compactness. A metal fiber burner has been adopted so that a stable flame can be obtained. The tube banks are installed downstream of the burner. Bare tubes are used upstream, while finned tubes are installed downstream. The heat-transfer characteristics of the non-furnace boiler have been studies on the basis of the results of the numerical simulation as well as those of the experiment. Important design parameters such as the bulk temperature along the streamwise direction and the temperature of the fin tips have been evaluated using the CFD results and compared with the experimental data and the empirical correlations typically used for the design of the boiler.

• Resources Recycling
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• v.17 no.5
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• pp.19-27
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• 2008

In this study, the porosity and electrical resistivity of the formed coke produced by sintering the mixture of domestic anthracite and phenolic resin were mainly investigated, when the effect of the amount of binder, the hydration temperature and time, the hardening temperature and time, sintering temperature and time, the particle size of anthracite, the grade of anthracite, and the mixing ratio of phenolic resin on the physical properties of the coke were studied. As a result, It was found that the electrical resistivity and porosity of the formed coke are varied in the range of $0.3\sim1.2\Omega{\cdot}cm$ of $10\sim30%$, respectively, in accordance with the variation of factors.

• Resources Recycling
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• v.2 no.2
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• pp.39-44
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• 1993

This study was carried out to remove the water from low grade anthracite slurry produced at Eoryong coal mine by the oil agglomeration process. 80% of Anthracite as a coal oil mixture (COM) was separated from water by the difference of specific gravity. Then, the amount of kerosene, diesel oil, and heavy oil forming COM was 10% of the amount of sample, respectively. The recovery rate of combustibles and ash content of agglomerated anthracite were affected largely by the amount of added oil, pulp density, particle size, mixing time, and impeller speed. The recovery rate of combustibles was increased to 95% and ash content was decrea-sed from 30% to 13.5% under the optimum conditions.

• Plant Journal
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• v.11 no.3
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• pp.46-52
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• 2015

200MWe 순환유동층보일러인 A화력발전소는 정부정책에 의해 국내 무연탄만을 연료로 배정받아 운영되었다. 하지만 무연탄에 대한 민간수요 증가에 따른 정부의 정책변경에 따라 유 무연탄 혼탄을 2000년대 후반부터 시행하고 있다. 하지만 기동시 석탄 투입온도는 여전히 무연탄 전소시의 기준온도인 $600^{\circ}C$에 석탄을 투입하고 있는 실정이라 기동시간 지연의 한 원인으로 작용하고 있고 기동 중 소요되는 경유의 과다소비라는 고질적인 문제점을 안고 있다. 이에 본 연구에서는 A화력에서 사용되는 석탄에 대한 공업분석과 원소분석을 통하여 비교적 휘발분이 많고 반응성이 좋은 러시아산 유연탄(Suek) 연소에 따른 경유에서 석탄으로의 연료교체시 경제적인 시점을 예측하였다. 실험결과 러시아산 유연탄 (Suek) 연소시 투입가능온도는 연소전환율이 90%이상이 되는 연소최대온도($426^{\circ}C$)가 기술적, 경제적으로 가장 적합한 것으로 예상하였다.

• Resources Recycling
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• v.17 no.6
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• pp.57-61
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• 2008

The aim of this study is to produce the coke which can be used for the production of ferroalloy, by mixing phenolic resin and anthracite and sintering it. The influence of factors on the strength of coke were investigated. The results of this study are as follows: It is found that the anthracite coke of $100{\sim}150\;kgf/cm^2$ strength for ferroalloy can be made by a series of process as follows; Mixing homogeneously 6% liquefied phenolic resin and 6% water with $35{\sim}325$ mesh anthracite of low ash content. Making pellet by press the mixture in $10-50\;kgf/cm^2$ pressure. Dehydrating the pellet for 6 hrs at $50^{\circ}C$, and hardening it for 180 min at $200^{\circ}C$. Sinter the mixture for 6 hrs at $1,200^{\circ}C$.

• Journal of Energy Engineering
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• v.17 no.3
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• pp.153-160
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• 2008

The combustion behaviors of the blends of Korean anthracite, bituminous coal and their blends were studied with a thermogravimetric analyzer. Concerning the burning profiles of the anthracite-bituminous coal blends in TGA, it has been observed the independent burning of two coals without any interaction between two coals. With the blends of 50% anthracite with 50% bituminous coal in weight basis, the combustion tests in a utility boiler have been carried out for the analysis of the combustion and operational characteristics by increasing the power output from 134 MW to 197 MW. The stable combustion has been observed in a boiler. With the increase of power output, the exhaust gas temperature was exceeded the design value of $430^{\circ}C$, so the combustion air was taken from atmosphere instead of the boiler penthouse.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.94-94
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• 2009

전기 에너지를 기계적 에너지 변환하고 또한, 기계적 에너지를 전기 에너지로 변환할 수 있는 압전 세라믹스는 압전 변압기 (piezoelectric transformer), 초음파모터, 센서등과 같은 응용분야에 넓게 사용되고 있다. 특히, 압전 변압기의 설계와 제조방법에 대해서는 이미 상당히 많은 연구가 수행되어 왔다. 특히, 전원장치에 있어서는 현재 주요부품으로 사용되고 있는 권선형 변압기와 같은 전자 변환기의 대체품으로서 누설손실이 없는 압전세라믹스 소재의 특성을 이용한 압전변압기의 개발과 응용연구가 국내외적으로 활발히 진행 중이다. 하지만 지금 까지 널리 사용된 PZT계 압전 세라믹스는 환경문제에 있어서 문제점을 가지고 있다. $1200^{\circ}C$ 이상에서 소결되는 PZT계열의 압전세라믹스 소재를 사용한 전자부품의 60~70%이상이 PbO로 구성되어 있기 때문에 $1000^{\circ}C$ 부근에서 급격한 휘발특성을 보이는 PbO로 인한 환경오염문제가 대두되고 있다. 압전변압기, 초음파모터등에 사용될 수 있는 무연계 압전재료 중에 PZT 압전소자의 기능을 대체할 만한 물질로는 높은 큐리온도와 우수한 압전특성을 보이는 $(Na,K)NbO_3$세라믹스가 가장 유력한 것으로 알려져 있다. 즉, 압전변압기용 조성 세라믹스는 높은 에너지 변환효율을 위해서 전기기계 결합계수($k_p$)가 커야 되며, 발열에 의한 온도 상승을 억제하기 위하여 기계적 품질계수($Q_m$)가 큰 것이 바람직하다. 또한, 높은 전류를 발생하기 위해서는 유전상수가 커, 압전변압기의 출력측 정전용량을 크게 하여야 한다. 본 연구에서는 무연계 압전세라믹스를 개발하고, 이를 이용한 전력밀도(power density)가 높은 무연계 압전변압기를 제작하여 그에 대한 전기적 특성을 조사하였다. 따라서 본 연구에서는 무연 압전변압기용 압전 세라믹스를 개발하기 위해 뛰어난 압전 및 유전특성을 가진 무연$(Na,K)NbO_3$계 세라믹스를 기본조성으로 하였고, KCN을 복합 첨가하여 볼 변화에 따른 미세구조, 압전 및 유전특성을 조사하고. 가장 우수한 조성으로 비납 압전변압기를 제작하여 전기적특성을 조사하였다.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.11-17
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• 2010

The electromigration phenomenon in lead-free flip-chip solder joint has been one of the serious problems. To understand the mechanism of this phenomenon, the crystallographic orientation of Sn grain in the Sn-Ag-Cu solder bump has been analyzed. Different time to failure and different microstructural changes were observed in the all test vehicle and bumps, respectively. Fast failure and serious dissolution of Cu electrode was observed when the c-axis of Sn grain parallel to electron flow. On the contrary of this, slight microstructural changes were observed when the c-axis of Sn perpendicular to electron flow. In addition, underfill could enhance the electromigration reliability to prevent the deformation of solder bump during EM test.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.2 s.43
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• pp.23-33
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• 2007

The growing environmental regulation governs the use of lead by RoHS, WEEE, and then. The electronic industry is moving to replace Pb-bearing solder with Pb-free solder. To use the Pb-free solder, microelectronic industry needs consequently the new reliability appraisal such as the packaging for high temperature process, various mechanical change caused by new solder, and the development of Pb-free sloder for long life of product. The evaluation of solder bar and mechanical properties of joint were performed compared with international standard, and new appraisal standard was established. The solderability and spread ability of Sn-0.7Cu solder material showed up to the standard. Shear test of solder joint using by the solder resulted that the shear strengths after thermal shock or after aging were not much lower than the shear strength of as-soldered and that they were also up to the standard.