T. Y. Lee

Hanbat National University, Daiden, Daejeon, South Korea

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Publications (52)42.81 Total impact

  • Source
    Y.H. Xia, Y.K. Jee, J. Yu, T.Y. Lee
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    ABSTRACT: Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag-xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations. Four different Sn-3.0Ag-xAl solders (x=0wt.%, 0.1wt.%, 0.5wt.%, and 1.0wt.%) were used for comparison. It was found that the composition, morphology, and thickness of interfacial reaction products were strongly dependent on aluminum concentration. At low aluminum concentration (0.1wt.%), the typical Cu6Sn5 layer was formed at the interface. When the aluminum concentration was 0.5wt.%, a continuous CuAl2 layer spalled off from the interfacial Cu-Sn intermetallic compound (IMC) layer. Only a planar CuAl2 layer was observed at the interface when the aluminum concentration was increased to 1.0wt.%. In Sn-Ag-Al/ENIG reactions, Ni3Sn4 was formed and spallation occurred near the interface in the Sn-3.0Ag and Sn-3.0Ag-0.1Al solder joints. When the aluminum concentration was higher than 0.1wt.%, a thin planar AuAl compound formed at the interface. There was no P-rich phase formation that retarded the spalling phenomenon. The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints.
    Journal of Electronic Materials 11/2008; 37(12):1858-1862. · 1.64 Impact Factor
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    ABSTRACT: Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al2O3, Al/SiO2, Al2O3/SiO2 were prepared onto a n-type Si (100) substrate. The thickness of SiO2 was ∼ 550 nm, where as, Al2O3 and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al2O3/SiO2 barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.
    Thin Solid Films 04/2008; 516(11):3646–3650. · 1.87 Impact Factor
  • Y. H. Xia, Y. K. Jee, J. Yu, T. Y. Lee
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    ABSTRACT: Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag- xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations. Four different Sn-3.0Ag- xAl solders ( x = 0 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) were used for comparison. It was found that the composition, morphology, and thickness of interfacial reaction products were strongly dependent on aluminum concentration. At low aluminum concentration (0.1 wt.%), the typical Cu6Sn5 layer was formed at the interface. When the aluminum concentration was 0.5 wt.%, a continuous CuAl2 layer spalled off from the interfacial Cu-Sn intermetallic compound (IMC) layer. Only a planar CuAl2 layer was observed at the interface when the aluminum concentration was increased to 1.0 wt.%. In Sn-Ag-Al/ENIG reactions, Ni3Sn4 was formed and spallation occurred near the interface in the Sn-3.0Ag and Sn-3.0Ag-0.1Al solder joints. When the aluminum concentration was higher than 0.1 wt.%, a thin planar AuAl compound formed at the interface. There was no P-rich phase formation that retarded the spalling phenomenon. The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints.
    Journal of Electronic Materials 01/2008; 37:1858-1862. · 1.64 Impact Factor
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    ABSTRACT: Highly aligned, 2-3 wall carbon nanotube (CNT) arrays were used to examine the kinetics of CNT growth. A growth interruption method was used to determine the in situ growth rate. The growth interruption method with a water vapor treatment or acetylene treatment during the interruption enabled the production of CNT stacks with different morphologies. The catalytic activity was also monitored using this method. The lifetime of the catalyst was predicted and verified using the catalyst decay model. High temperature metal oxidation behavior using parabolic curve fitting is assigned to the decay process. Details of the analysis are presented.
    Applied Physics Letters 01/2008; 93(11):114101-114101-3. · 3.52 Impact Factor
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    ABSTRACT: The performance of drop reliability was measured with Sn-3.5Ag-xZn solder joint on Cu and electroless Ni(P)/Au metallization after reflow and thermal aging (150degC, 500 hr). The content of Zn was 0, 1, 3 and 7 wt%. And interfacial reactions were investigated. The presence of Zn affected the type and morphology of IMC and showed the benefits on the drop reliability. In the case of Cu pad, Zn addition of more than 3 wt% suppressed growth of Cu<sub>6</sub>Sn<sub>5</sub> and introduced Ag<sub>5</sub>Zn<sub>8</sub>/Cu<sub>5</sub>Zn<sub>8</sub> layer, which increased drop resistance by about two times. During thermal aging, Cu<sub>6</sub>Sn<sub>5</sub> and Ag<sub>3</sub>Sn precipitated and grew in the interfacial IMC layer, which decreased the beneficial effect of Zn. In the case of Ni(P)/Au, Zn addition of 1 and 3 wt% transformed IMC from Ni<sub>3</sub>Sn<sub>4</sub> to Ni<sub>3</sub>Sn<sub>4</sub>/Ni<sub>5</sub>Zn<sub>21</sub>. Only Ni<sub>5</sub>Zn<sub>21</sub> were found for 7Zn specimen. The solder of 1 wt% Zn showed drop resistance about six times than that of Sn-3.5Ag. The improvement of drop resistance resulted from suppression of Ni<sub>3</sub>P and Ni<sub>3</sub>SnP growth. As the growth of Ni<sub>3</sub>P and Ni<sub>3</sub>SnP layer was effectively suppressed by zinc, the drop resistance increased substantially.
    Electronic Components and Technology Conference, 2007. ECTC '07. Proceedings. 57th; 07/2007
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    ABSTRACT: PAL-XFEL is the 4-th generation light source based on Self Amplified Spontaneous Emission (SASE) that Pohang Accelerator Laboratory is going to build. For the purpose, the linear accelerator, which is used for the injection to the PLS storage ring, will be upgraded and expanded to 3.7 GeV. In this paper, the overview of PAL-XFEL will be introduced including the physics design.
    01/2007;
  • Journal- Korean Physical Society 01/2007; 50(95). · 0.51 Impact Factor
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    ABSTRACT: The Pohang Accelerator Laboratory (PAL) is going to build a 4th generation light source, an X-ray free electron laser (XFEL) based on self-amplified spontaneous emission. For the purpose, the existing 2.5-GeV linear accelerator will be upgraded to 3.7 GeV and will include new features such as photo-cathode electron gun and bunch compressors. The other important parts of the PAL-XFEL are the long undulator and photon beamlines. In this paper, the design philosophy and the details of the PAL-XFEL will be presented along with the key physics issues.
    Journal- Korean Physical Society 05/2006; 4860(52). · 0.51 Impact Factor
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    ABSTRACT: We report the fabrication, characterization, and field emission properties of silicon oxide SiO x coated thin-multiwalled carbon nanotubes t-MWNTs. The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs diameter 5–8 nm were functionalized by acid treatment. Using spin on glass as a Si precursor, SiO x was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy HRTEM, Fourier transform infrared FTIR spectroscopy, and thermogravimetric analysis TGA techniques. The HRTEM results show that the local thickness of the coating varies from 1 to 2 nm. The FTIR investigations show the formation of nanophases, such as Si–C, Si–O–C, and intercalated Si–O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on fields and current density are improved for the coated nanotubes. This improvement was attributed to the lowering of the work function and dielectric constant of the C / SiO x interface layer and the localization of the density of states close to the Fermi energy for the coated nanotubes. The analysis of the emission stability spectra shows that the coated nanotubes have a more favorable lifetime. The observed enhancement was attributed to the protection of the nanotubes from the reactive sputter etching during the field emission process. The details of the analysis are presented. © 2006 American Institute of Physics.
    Journal of Applied Physics 01/2006; 100. · 2.21 Impact Factor
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    ABSTRACT: Pohang Accelerator Laboratory has a plan to build an X-ray FEL machine. This new machine will utilize the exist-ing 2.5 GeV injection linac to the storage ring by upgrading its energy up to 3.7 GeV or more. The target wavelength will be 3-4. A and its third harmonic 1-1. A will also be used. The project will proceed in two stages: In the first stage, a VUV SASE machine with 320 MeV will be constructed and tested for the proof-of-principle. The full X-ray machine will be constructed in the next stage.
    01/2006;
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    ABSTRACT: MWNT/nylon 6, 6 composite nanofibers were fabricated using an electrospinning method, and the electrical properties were examined as a function of the filler concentration. Initially, the pristine, purified MWNTs were treated with a 3:1 mixture of concentrated H2SO4/HNO3 to introduce carboxyl groups onto the MWNT surface. The carboxylated MWNTs were then treated with thionyl chloride and an ethylenediamine solution for amide functionalization. FT-IR spectroscopy was used to examine the functionalization of the MWNTs. Nylon 6, 6 is readily soluble in formic acid. Therefore, the amide functionalized MWNTs were dispersed in formic acid. The solution remained stable and uniform for more than 40 h. –NH2 termination of the MWNTs improved the dispersion stability of the MWNTs in formic acid. The MWNTs-suspended in a solution of nylon 6, 6 in formic acid was electrospun to obtain the nanofibers. The electrical properties of the nanofibers were examined as a function of the filler concentration. The results showed that the I–V properties of the nanofiber sheet improved with increasing filler concentration.
    Diamond and Related Materials - DIAM RELAT MATER. 01/2006; 15(11):1839-1843.
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    W. S. Lee, Jin Yu, T. Y. Lee
    Journal of Materials Science 10/2005; · 2.31 Impact Factor
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    ABSTRACT: Single-walled nanotubes (SWNTs), thin multiwalled carbon nanotubes (t-MWNTs) and multiwalled carbon nanotubes (MWNTs) were treated with H2SO4–HNO3 acid solution, under different chemical conditions. The acid-treated CNTs were dispersed in DI water and in poly (3,4-ethylenedioxythiophene) (PEDOT) solution. Furthermore, the finely dispersed CNTs/PEDOT solutions were employed to a simple method of bar coating to obtain the transparent conductive films on the glass and polyethylene terephthalate (PET) film. A sheet resistance of 247 Ω/sq and a transmission of 84.7% were obtained at a concentration of the acid-treated CNTs of 0.01 wt.%.
    Diamond and Related Materials 09/2005; · 1.71 Impact Factor
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    J.S. Oh, T.Y. Lee, I.S. Ko, W. Namkung
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    ABSTRACT: The PAL XFEL will supply coherent radiations from VUV to X-rays. X-ray FEL for 0.3 nm lasing requires a minimum 3-GeV driver linac and a 60-m long in-vacuum undulator with a narrow variable gap. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a lower energy spread less than 0.03%. The beam quality is degraded along the undulator trajectory due to the energy loss, the wake field, and the magnetic field errors, etc. Especially the wake field effect is most sensitive parameter due to the narrow gap of the undulator. The preliminary design details of undulators for PAL-XFEL are presented with parametric analysis. The SASE performance is analyzed using simulation tool SIMPLEX [1].
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    ABSTRACT: The thermal characteristics of thermally conductive underfill in flip chip package was studied. To enhance the thermal conductivity of underfill, the epoxy was mixed with thermally conductive fillers, such as silica (1.5W/mK), alumina (36W/mK), or diamond (2000W/mK). Coefficient of thermal expansion (CTE) was changed by filler and its content, and CTE was 28 ppm for 60 wt% silica, 39 ppm for 60 wt% alumina and 24 ppm for 60 wt% diamond. Thermal conductivity was calculated from the measurement of thermal diffusivity, density and specific heat capacity under the various temperature conditions with the various fillers. To investigate thermal characteristics of different underfill, diode temperature sensor array (DTSA) was fabricated, which consists of 32 by 32 array of diodes (1,024 diodes) for temperature measurement and 8 heaters for heat source on a 8mm by 8mm of silicon surface. The DTSA was packaged by flip chip packaging method and applied with the same power (0.84W) for different underfilled packages. Finally, the thermal simulations with ICEPAK matched very well with the measurement
    Electronics Packaging Technology Conference, 2004. EPTC 2004. Proceedings of 6th; 01/2005
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    ABSTRACT: A slow global orbit feedback (SOFB) is routinely operating in the usual user service operation at PLS. The orbit feedback uses 22 correctors in each plane which have 20-bit capability for the vertical plane and 16-bit capability for the horizontal plane, and the feedback speed is 4 seconds. The orbit stability in RMS was maintained below 1 µ m in both planes for one hour and 3 µ m for a 12-hour operation. The BPM chamber movement due to the change of synchrotron radiation heat load mainly limits the SOFB performance. The intensity dependence of BPM electronics is well compensated by a look-up table of BPM.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 01/2005
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    ABSTRACT: The growth of carbon nanotubes (CNTs) were evidently observed, at the channel ends of the mesoporous SAPO4-5 zeolites. The Fe-catalyst SAPO4-5 crystallites prepared by the sol–gel method were employed to the thermal CVD process, at a temperature ∼650 °C for 30 min, using the mixture of acetylene and ammonia gases. The recorded SEM images show the formation of well aligned MWNTs at the channel ends of the crystallites. The analysis of HRTEM shows that, the outer diameter of CNTs varies in the range of 25–27 nm, whereas, the inner diameter varies in the range of 14–17 nm. The diameter of the CNTs was found to be varied marginally as compared to that of the channel diameter of the SAPO4-5 crystallite. Furthermore, the observed formation of CNTs, along the ab-plane, could either be originated at a depth from the channels or at the channel ends of the crystallites. Although the former is attributed to the precipitation of the Fe-catalyst in the channels, the later is thought to be due to the out diffusion and clustering of Fe-atoms near the channel ends of the crystallites. The recorded micro-Raman spectrum showed the small ratio of, I(D)/I(G), which suggest that, the synthesized tubes are of high quality with less amount of defects.
    Diamond and Related Materials 01/2005; 14(11):1876-1881. · 1.71 Impact Factor
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    ABSTRACT: Recent success in SASE-FEL experiments provides high confidence in achieving FEL radiation wavelengths as short as 0.1 nm.The SASE-XFEL requires multi-GeV electron beams with extremely low-emittance, short bunches, and long undulator systems. PAL is operating a 2.5-GeV electron linac as a full-energy injector to the PLS storage ring. With a proposed energy upgrade to 3.0 GeV and an in-vacuum undulator, PAL will be able to produce coherent X-ray radiation at wavelengths as short as 0.3 nm.This paper presents the preliminary design details for the proposed PAL-XFEL. The required undulator period is 12.5 mm with a 3-mm gap. The third harmonic enhancement technique can be used to obtain radiation wavelengths of 0.1 nm.The technical parameters related to these goals are reviewed.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2004; · 1.14 Impact Factor
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    S. -H. Kim, J. -Y. Kim, J. Yu, T. Y. Lee
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    ABSTRACT: Pure Ni, the Ni-Cu alloy, and pure Cu layers as the under bump metallurgy (UBM) for a flip-chip solder joint were deposited by electrolytic plating. For the pure Ni layer, residual stress can be controlled by adding a wetting agent and decreasing current density, and it is always under tensile stress. The Ni-Cu alloys of different Cu compositions from ∼20wt.%Cu to 100wt.%Cu were deposited with varying current density in a single bath. The residual stress was a strong function of current density and Cu composition. Decreasing current density and increasing Cu content simultaneously causes the residual stress of the metal layers to sharply decrease. For the pure Cu layer, the stress is compressive. The Cu layer acts as a cushion layer for the UBM. The residual stress of the UBM strongly depends on the fraction of the Cu cushion layer. Interfacial reaction of the UBM with Sn-3.5 wt.% Ag was studied. As the Cu contents of Ni-Cu alloys increased, the dissolution rate increased. Several different intermetallic compounds (IMCs) were found. The lattice constants of alloys and the IMC increase with increasing Cu contents because the larger Cu atoms substitute for the smaller Ni atoms in the crystallites. The Cu content of the IMC are strongly dependent on the composition of the alloys. Ball shear tests were done with different metal-layer schemes. The failure occurs through the IMC and solder.
    Journal of Electronic Materials 01/2004; 33(9):948-957. · 1.64 Impact Factor
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    ABSTRACT: Intermetallic compound (IMC) spalling from electroless Ni-P film was investigated with lead-free solders in terms of solder-deposition methods (electroplating, solder paste, and thin foil), P content in the Ni-P film (4.6, 9, and 13 wt% P), and solder thickness (120 versus .200 μm). The reaction of Ni-P with Sn3.5Ag paste easily led to IMC spalling after 2-min reflow at 250 °C while IMCs adhered to the Ni-P layer after 10-min reflow with electroplated Sn or Sn3.5Ag. It has been shown that not only the solder composition but also the deposition method is important for IMC spalling from the Ni-P layer. The spalling increased with P content as well as with solder volume. Ni3Sn4 intermetallics formed as a needle-shaped morphology at an early stage and changed into a chunk-shape. Needle-shaped compounds exhibited a higher propensity for spalling than chunk-shaped compounds because many channels among the needle-shaped IMCs facilitated Sn penetration. A reaction between the penetrated Sn and the Ni3P layer formed a Ni3SnP layer and Ni3Sn4 IMCs spalled off the Ni3SnP surface. Dewetting of solder from the Ni3SnP layer, however, did not occur even after spalling of most IMCs.
    Journal of Materials Research 01/2004; 19(8):2428-2436. · 1.82 Impact Factor

Publication Stats

207 Citations
42.81 Total Impact Points

Institutions

  • 2004–2008
    • Hanbat National University
      • Department of Material Sciences and Engineering
      Daiden, Daejeon, South Korea
    • Korea Institute of Machinery and Materials
      Sŏul, Seoul, South Korea
  • 2002–2008
    • Sungkyunkwan University
      • School of Advanced Materials Science and Engineering (AMSE)
      Sŏul, Seoul, South Korea
  • 2006
    • Duke University
      Durham, North Carolina, United States
  • 2001–2006
    • Pohang University of Science and Technology
      • Pohang Accelerator Laboratory
      Andong, North Gyeongsang, South Korea
    • University of Suwon
      Tse-tsiu, Jeju, South Korea
  • 2005
    • Korea Advanced Institute of Science and Technology
      • Department of Materials Science and Engineering
      Seoul, Seoul, South Korea
  • 1998–2001
    • Pohang Accelerator Laboratory
      Urusan, Ulsan, South Korea