• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.1-13
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• 2014

The paper gives an overview of the concepts, basic requirements, and trends regarding packaging technologies of power modules in hybrid (HEV) and electric vehicles (EV). Power electronics is gaining more and more importance in the automotive sector due to the slow but steady progress of introducing partially or even fully electric powered vehicles. The demands for power electronic devices and systems are manifold, and concerns besides aspects such as energy efficiency, cooling and costs especially robustness and lifetime issues. Higher operation temperatures and the current density increase of new IGBT (Insulated Gate Bipolar Transistor) generations make it more and more complicated to meet the quality requirements for power electronic modules. Especially the increasing heat dissipation inside the silicon (Si) leads to maximum operation temperatures of nearly $200^{\circ}C$. As a result new packaging technologies are needed to face the demands of power modules in the future. Wide-band gap (WBG) semiconductors such as silicon carbide (SiC) or gallium nitride (GaN) have the potential to considerably enhance the energy efficiency and to reduce the weight of power electronic systems in EVs due to their improved electrical and thermal properties in comparison to Si based solutions. In this paper, we will introduce various package materials, advanced packaging technologies, heat dissipation and thermal management of advanced power modules with extended reliability for EV applications. In addition, SiC and GaN based WBG power modules will be introduced.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.4
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• pp.239-245
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• 2000

A copper-tungsten sintered alloy(WCu) has been friction-welded to a tough pitch copper (Cu) in order to investigate friction weldability. The maximum tensile strength of the SWu-Cu friction welded joints had cp to 96% of those of the Cu base metal under the condition of friction time 0.6sec, friction pressure 45MPa, upset pressure 125MPa and upset time 5.0sec. And it is confirmed that the tensile strength of friction welded joints are influenced highly by upset pressure rather than friction time. And it is considered that mixed layer was formed in the Cu adjacent side to the weld interface, W particles included in mixed layer induced fracture in the Cu adjacent side to the weld interface and also, thickness of mixed layer was reduced as upset pressure increase.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.85-87
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• 2008

DMWs are common feature of the PWR in the welded connections between carbon steel and stainless steel piping. The nickel-based weld metal, Alloy 82/182, is used for welding the dissimilar metals and is known to be susceptible to PWSCC. A round-robin program has been implemented to benchmark the numerical simulation of the transient temperature and weld residual stresses in the DMWs. To solve the round-robin problem related to Pressurizer Safety & Relief nozzle, the thermal elasto-plastic analysis is performed in the DMW by using the FEM. The welding includes both the DMW of the nozzle to safe-end and the SMW of the safe-end and piping. Major results of the analyses are discussed: The axial and circumferential residual stresses are found to be -88MPa(225MPa) and -38MPa(293MPa) on the inner surface of the DMW; where the values in parenthesis are the residual stresses after the DMW. Thermo-mechanical interaction by the SMW has a significant effect on the residual stress fields in the DMW.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.633-644
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• 2008

The structural framework design uses high-strength bolts and welding in column splices. However, for the column under high compression, the number of the required high-strength bolts can be excessive and the increase of welding results in difficulty of quality inspection, the transformation of the structural steels, and the increase of erection time. According to the AISC criteria, when columns have bearing plates, or they are finished to bear at splices, there shall be sufficient connections to hold all parts securely in place. The Korean standard sets the maximum 25% of the load as criteria. Using direct contact makes it possible to transfer all compressive force through it. The objective of this study is to examine the generally applied stress path mechanism of welded or bolted columns and to verify the bending moment and compression transfer mechanism of the column splice according to metal touch precision. For this study,22 specimens of various geometric shapes were constructed according to the change in the variables for each column splice type, which includes the splice method, gap width, gap axis, presence or absence of splice material, and connector type. The results show that the application of each splice can be improved through the examination of the stress path mechanism upon metal contact. Moreover, the revision of the relative local code on direct contact needs to be reviewed properly for the economics and efficiency of the splices.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.4
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• pp.440-450
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• 2003

Statement of problem : The joints of removable partial denture alloys have failed frequently after routine usage. Purpose : The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. Material and method : For this study 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. Results : The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically significant differences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. Conclusion : The tensile strengths of the as-cast joints were higher than those for the laser welded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.140-146
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• 2012

A variety of dyes are commercially available today, there is an ongoing need for new chromophoric systems and low-band-gap materials. For example, near-infrared (NIR) emission has received increased attention for applications in bioassays and medicine while NIR absorption is demanded for laser-welding of plastics or efficient blocking of heat rays. Most of the commercially available NIR materials are not suitable for such purposes owing to their insufficient stability. We have developed a novel NIR-absorbing polyaromatic dye. By extending the system of perylenebis(dicarboximide)s along the molecular long axis, we have obtained the higher homologue pentarylenebis(dicarboximide). We have tried to introduce imide functional group to pentarylene in order to increase chemical and thermal stability.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.117-122
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• 1999

An objective of this study is that when the steel sheet for automobiles would be sheared by using shearing machine, it is to design the forms of pad for obtaining the precision shearing surface to satisfy the conditions required to laser beam butt welding for processed sheared surface and to establish the appropriate condition against the size of gap between strength of pressure and location and clearance between punch and die. For doing so, we will attempt to make a precision of the most possibility of shearing machine by the shearing machine in analyzing the characteristics of the shearing working upon analyzing and clarifying the interrelation among these.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.66-66
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• 2010

국내 화력발전의 $CO_2$배출량을 크게 줄이고, 친환경, 그린 화력발전시스템을 위한 가장 효과적인 수단은 발전효율을 획기적으로 증대시키는 것이기 때문에 이를 목표로 한 기술개발은 경제적으로나 산업적으로 파급효과가 매우 크다. 발전효율 증대를 위한 핵심기술은 증기터빈의 성능향상이다. 현재 일본, 미국, EU 등 각국이 가장 관심을 가지고 기술개발에 심혈을 쏟고 있는 초내열, 내식 합금소재는 $700^{\circ}C$이상에서 기계적 성능을 보장할 수 있는 Ni기 합금개발이고, 현재까지 상당한 기술수준에 이르고 있는 것으로 파악되고 있다. 국내의 경우는 관련기술개발을 위해 연구가 진행되고 있으나, 기술적으로 아직 미흡한 수준이다. Ni기 초내열, 내식합금을 개발해서 그것을 화력발전용 증기터빈 부품, 특히 초내열합금 용접형 터빈로터 소재로 이용하기 위해서는 체계적이고 실용적인 연구를 통하여 용접형로타의 내구성과 신뢰성이 보장되는 최적 수준의 접합기술 개발이 선행되어야 한다. 따라서 본 연구는 선행연구로 $700^{\circ}C$이상 초내열/내식 Ni기 합금소재의 용접기술 개발을 위한 후보 소재 Alloy 617의 동종재료 용접 기술 개발을 목표로 한다. 본 연구는 Alloy617 12.6t 맞대기 이음으로 U그루브 내로갭 TIG용접을 하였다. 1pass 1layer 방식으로 총 8pass 8layer로 용접하였다. 전류 및 용접속도는 동일하게 두고 실드가스를 Ar 또는 Ar-$H_2$ 가스로 변경하여 시험하였다. Ar가스 TIG용접은 비드표면에 산화스케일이 생기고, 비드면이 거칠며 전체적으로 산화되었다. 반면에 Ar-$H_2$가스 TIG용접은 비드표면에 산화스케일이 없으며 표면이 미려하고 산화되지 않았다. 실드가스에 수소가스 첨가시 환원성가스로 역할을 하게 되고 이에 따라 용융지 표면에 산화피막을 제거하여 용접비드를 청정하게 하는 효과를 가진다.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.1-7
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• 2017

When implementing butt joint welding of two plates, it is useful to attach end-tabs made of a metal with high heat conductivity (e.g., copper) at the front and back sides of the welded plates to prevent the bead from rolling down and prevent defects that may occur at the tips of the weld zone. In this study, the fin shape, which is known to have good heat discharging characteristics by natural convection, has been applied to enhance the cooling performance of the end-tab. From both experiment and numerical analysis, it was confirmed that end-tabs with fin-shaped holes have better heat discharging performance than end-tabs without holes. Through thermal and fluid flow analysis, the cooling rates of end-tabs with different hole shapes were estimated in order to figure out characteristics of shape factor that are important for the heat discharging performance. As a result, we found that the structure including vertical fins with optimal fin gap was the best-performing shape.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.20-20
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• 2010

GTA (Gas Tungsten Arc)용접은 불활성 분위기에서 용접이 이루어지기 때문에 타 아크용접법에 비해 용접부 품질이 우수하여 고품질이 요구되는 산업분야에 널리 이용되고 있다. 하지만 스테인리스강으로 pipe를 제조하기 위해 GTA 용접을 적용할 경우, Laser 및 고주파 용접 (HFIW)에 비해 용접부 품질 및 용접속도가 낮기 때문에 pipe를 제조하는 산업에서 적용에 제한을 받고 있다. 하지만, GTA는 laser 혹은 HFIW에 비해 가격이 1/10수준으로 낮고, 용접부 gap tolerance 및 용접면 관리범위가 넓은 장점이 있기 때문에 GTA의 용접속도 및 용접품질을 향상시키기 위한 연구가 꾸준히 진행되고 있다. 일반적으로 스테인리스강 GTA용접 시 용접속도를 향상시키기 위해, 모재의 성분 제어 (합금성분 최적화-Al, S, Se, O등), Flux 도포 기술 (산화물을 용접전에 도포하여 용접속도 향상) 및 혼합보호가스 적용 등이 있다. 스테인리스강 용접 시 보호가스로는 용접부 품질을 확보하기 위해 Ar을 주로 사용하고 있다. 하지만 용입 특성을 향상시키기 위해 아크의 온도를 높일 수 있는 He, 혹은 $H_2$ gas를 단독 혹은 혼합하여 사용하고 있다. 오스테나이트계 스테인리스의 경우 용입특성을 향상시키기 위해 Ar에 $H_2$를 2~10%정도 혼합하여 사용하고 있다. 페라이트계 스테인리스강은 수소에 대한 고용도가 상대적으로 작아 용접부 수소 취화를 일으킬 수 있기 때문에 적용에 제한을 받고 있어 그 대안으로 산소를 극히 소량을 혼합하여 용입성 향상에 대한 연구가 보고 되고 있다. 따라서 본 연구에서는 페라이트계 스테인리스강의 용입특성을 향상시킬 목적으로 Ar에 산소를 미량 첨가 (1%미만) 하여 용접전류 및 산소 함량에 따른 용입특성의 변화에 대해 연구하였다. 또한 기계적인 물성 및 부식특성을 평가하였고, 최종적으로 실용화 가능성을 파악하기 위해 용접전극의 수명 테스트를 실시하였다. 실시한 결과, 산소가 첨가량 증가 할수록 용입특성은 상승하였으며, 기계적인 물성 또한 산소를 첨가하지 않은 경우에 비해 거의 유사한 값을 얻을 수 있었다, 하지만 산소함량이 증가 할수록 전극의 수명은 감소하여 교체주기가 증가함을 알 수 있다. 본 연구를 통해 얻어진 기술을 상용화시키기에는 극복해야할 문제가 있지만, 소재 합금성분 설계 시 용접생산성 향상위한 산소성분 범위를 제시할 수 있으리라 판단된다.