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김덕후,김효곤,조국,강민성,박상덕,손웅희 한국공작기계학회 2008 한국공작기계학회 추계학술대회논문집 Vol.2008 No.-
The purpose of maintaining of bridges was to secure of them and expend its life. They wereneeded to have a regular safety check. But, most parts of a bridge were not able to access easily for people so it was difficult to maintain. To improve it, the flight mechanism and mobile mechanism were combined to examine with moving when they were attaching to bridges up and down. The flight mechanism is a co-axial-rotor-helicopter shape that cut the body down and can be done hovering. The mobile mechanism was shaped to move every direction with holding the position of a robot. These robot platforms showed possibilities to use them not only for observation and patrol but they could be used for a new usage with transformation of flying robots. This paper was focused on location maintaining when a robot was examined a bridge. The flight mechanism would only have thrust and adhesive force, the mobile mechanism would be used for moving. Therefore, defining the mechanistic model of the mobile mechanism has proved the validity of the model through simulations and experiments.
閔雄基,張珍成,全正壹,金輝,崔道烈,金承昆 서울대학교 수목원 2001 서울大學校 樹木園 硏究報告 Vol.- No.21
This study was carried out to investigate the flora of Mt. Undal (alt. 1,097.2m) located on the northwestern side of province Gyeongsangbuk-do, near Myngyeong-si city, from April 2000 to Sept. 2000. Total number of vascular plants discovered in Mt. Undal were 70 families, 154 genera, and 243 taxa(including species, subspecies, varieties and forma). Major vegetation was Acer pictum var. mono - Quercus mongolica - Carpinus laxiflora community. The overall forest stand age of this area was 40 to 50 years, and occasionally ca 70 years old Abies holophylla trees were found. Although, there were no rare and endangered speices, we found two species of level IV by the Ministry of Environment - Anemone koraiensis Nakai, Anemone reflexa. Steph. et Willd.
Effect of high-speed loading conditions on the fracture mode of the BGA solder joint
Kim, Jong-Woong,Jang, Jin-Kyu,Ha, Sang-Ok,Ha, Sang-Su,Kim, Dae-Gon,Jung, Seung-Boo Elsevier 2008 Microelectronics reliability Vol.48 No.11
<P><B>Abstract</B></P><P>High-speed ball shear test was investigated in terms of the effects of two test parameters, shear speed and shear height, with an experimental and computational simulation utilizing 3-dimensional non-linear finite element modeling for evaluating the solder joint integrity of ball grid array (BGA) packages. A representative Pb-free solder alloy, Sn–0.7Cu, was employed in this study. Far greater shear forces were measured by high-speed shear test than by low-speed shear test. The shear force further increased with shear speed mainly due to the high strain-rate sensitivity of the solder alloy. Brittle interfacial fractures can be more easily achieved by high-speed shear test, especially in higher shear speed. These were discussed with the strengthening mechanism of the solder materials by density and mobility of dislocations. Shear force decreased with shear height, and it could be found that excessively high shear heights unfavorably affected the test results leading to unexpectedly high standard deviation values or shear tip sliding from the solder ball surface.</P>
Characteristic analysis of electroless Ni plating layer for electronic packaging
Kim, Dae-Gon,Kim, Jong-Woong,Yoon, Jeong-Won,Lee, Won-Bae,Jung, Seung-Boo Heyden & Son 2006 Surface and interface analysis Vol.38 No.4
<P>The crystallization behavior of electroless Ni–P film was investigated using X-ray diffractometry (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). XRD analyses revealed that the amorphous state of the as-plated Ni–P film was crystallized by heat treatment at 573 K for 1 h. Two peaks were observed simultaneously, indicating Ni and Ni<SUB>3</SUB>P compounds. Convergent beam electron diffraction (CBED) pattern analyses confirmed a size of the Ni<SUB>3</SUB>P in the crystallized Ni–P layer of 50–70 nm. The contact resistance decreased with a heat treatment, which is mainly due to the crystallized Ni–P layer and the grain growth. The activation energy calculated from DSC analyses using the Kissinger equation was 195.2 kJ/mol. Copyright © 2006 John Wiley & Sons, Ltd.</P>
A Dynamic Queue Management for Network Coding in Mobile Ad-hoc Network
Kim, Byun-Gon,Kim, Kwan-Woong,Huang, Wei,Yu, C.,Kim, Yong K. The Institute of Internet 2013 International journal of advanced smart convergenc Vol.2 No.1
Network Coding (NC) is a new paradigm for network communication. In network coding, intermediate nodes create new packets by algebraically combining ingress packets and send it to its neighbor node by broadcast manner. NC has rapidly emerged as a major research area in information theory due to its wide applicability to communication through real networks. Network coding is expected to improve throughput and channel efficiency in the wireless multi-hop network. Many researches have been carried out to employ network coding to wireless ad-hoc network. In this paper, we proposed a dynamic queue management to improve coding opportunistic to enhance efficiency of NC. In our design, intermediate nodes are buffering incoming packets to encode queue. We expect that the proposed algorithm shall improve encoding rate of network coded packet and also reduce end to end latency. From the simulation, the proposed algorithm achieved better performance in terms of coding gain and packet delivery rate than static queue management scheme.
Characterization of Failure Behaviors in Anisotropic Conductive Interconnection
Kim, Jong-Woong,Kim, Dae-Gon,Koo, Ja-Myeong,Yoon, Jeong-Won,Choi, Sunglak,Kim, Kyung-Sik,Nam, Jae-Do,Lee, Hoo-Jeong,Joo, Jinho,Jung, Seung-Boo The Japan Institute of Metals 2007 MATERIALS TRANSACTIONS Vol.48 No.5
<P>The effects of bonding forces and reflow process on the failure behaviors of anisotropic conductive film (ACF) interconnections were analyzed. Conventional reflow process was employed with peak temperatures of 220°C for soldering of Sn-37Pb and 260°C for soldering of Pb-free Sn-Ag or Sn-Ag-Cu. Two kinds of main failure mode were detected after double reflows at 220°C: formation of a conduction gap between conductive particles and Ni/Au-plated Cu pad, and delamination of the adhesive matrix from the plated Cu pad on the flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. The main failure mode of the reflowed ACF joints was conduction gap for the joints with lower bonding forces and adhesive matrix delamination for the joints with higher bonding forces. However, only adhesive matrix delamination was observed after reflows at 260°C. A theoretical calculation was also conducted to predict the connection resistance of the ACF joint before and after reflows. The calculation showed that the optimum bonding forces are between 65 and 70 N.</P>
Kim, Jong-Woong,Kim, Dae-Gon,Jung, Seung-Boo Elsevier 2006 Microelectronics reliability Vol.46 No.2
<P><B>Abstract</B></P><P>An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of flip chip solder bumps. A solder composition used in this study was Sn–3mass%Ag–0.5mass%Cu. A low cost bumping process has been employed using electroless Ni and immersion Au followed by solder paste stencil printing. A thin layer of intermetallic compound, (Ni<SUB>1−<I>x</I></SUB>Cu<SUB><I>x</I></SUB>)<SUB>3</SUB>Sn<SUB>4</SUB>, was formed by the reaction between the solder and electroless Ni with a thickness of about 1.4μm, while some discontinuous (Cu<SUB>1−<I>y</I></SUB>Ni<SUB><I>y</I></SUB>)<SUB>6</SUB>Sn<SUB>5</SUB> particles were also formed at the interface. The compositions of the resulting compounds were identified using energy dispersive spectrometer (EDS) and electron microprobe analysis (EPMA). Shear tests were carried out over a shear speed range from 20 to 400μm/s at a shear ram height of 20μm. The shear force was observed to linearly increase with shear speed and reach the maximum value at the fastest shear speed in both experimental and computational results. The optimum shear speeds for the shear test of solder bumped flip chip were recommended to be not exceeding 200μm/s. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions.</P>