• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.9-12
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• 2004

The effect of x wt% CuO-y wt% $V_2O_5$ content on the microwave properties of $(Pb_{0.45}Ca_{0.55})[(Fe_{0.5}Nb_{0.5})_{0.9}Sn_{0.1}]O_3$ (PCFNS) ceramics was investigated. In order to decrease the sintering temperature and use as a Low Temperature co-firing Ceramics (LTCC), CuO-$V_2O_5$ are added in the PCFNS. The bulk density, dielectric constant (${\varepsilon}_r$) and quality factor(Q${\cdot}f_0$) increased with increase in CuO content within a limited value. The microwave properties were degraded with increases in $V_2O_5$ content. The temperature coefficient of the resonant frequency (${\tau}_f$) of PCFNS was shifted to positive value abruptly with increasing the $V_2O_5$ content, while the ${\tau}_f$ was slightly shifted to positive value with increasing the CuO content. The optimized microwave properties, ${\varepsilon}_r$ = 88, Q${\cdot}f_0$ = 6100 (GHz), and ${\tau}_f$ = 18 ppm/$^{\circ}C$, were obtained in $(Pb_{0.45}Ca_{0.55})[(Fe_{0.5}Nb_{0.5})_{0.9}Sn_{0.1}]O_3$ with 0.2wt% CuO 0.05 wt% $V_2O_5$ and sintered at $1000^{\circ}C$ for 3 h. The relationship between the microstructure and microwave dielectric properties of ceramics was studied by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1856-1863
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• 2004

In the last 50 years, lead-contained solder materials have been the most popular interconnect materials used in the electronics industry. Recently, lead-free solders are about to replace lead-contained solders for preventing environmental pollutions. However, the reliability of lead-free solders is not yet satisfactory. Several researchers reported that lead-contained solders have a good fatigue property. The others published that the lead-free solders have a longer thermal fatigue life. In this paper, the reason for the contradictory results published on the estimation of fatigue life of lead-free solder is investigated. In the present study, fatigue behavior of 63Sn37Pb, and two types of lead-free solder joints were compared using pseudo-power cycling testing method, which provides more realistic load cycling than chamber cycling method does. Pseudo-power cycling test was performed in various temperature ranges to evaluating the shear strain effect. A nonlinear finite element model was used to simulate the thermally induced visco-plastic deformation of solder ball joint in BGA packages. It was found that lead-free solder joints have a good fatigue property in the small temperature range condition. That condition induce small strain amplitude. However in the large temperature range condition, lead-contained solder joints have a longer fatigue life.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.6
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• pp.265-271
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• 2021

In this study, anti-tarnishing and corrosion characteristics of a single 𝛽1' and Bangjja Yugi alloy in the Cl^- ion environment before and after potentiostatic electrolysis treatment were compared. Stable and uniform SnO₂ oxide film with several nanometer thickness is formed after potentiostatic electrolysis treatment. In the case of Bangjja Yugi prior to potentiostatic electrolysis (PE) treatment for exposure in Cl^- environment, tarnishing occurs rapidly within 0.5hr, whereas PE treated Bangjja Yugi indicates stable surface without tarnishing up to 3hr. Especially, it is noticeable that anti-tarnishing and corrosion characteristic of PE treated single 𝛽1', which were significantly improved by 3 times and 15 times, respectively, compared to conventional Bangja Yugi.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.73-79
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• 2022

In this study, a reaction study between Ga, which has recently been spotlighted as a low-temperature bonding material, and Cu, a representative electrode material, was conducted to investigate information necessary for low-temperature soldering applications. Interfacial reaction and intermetallic compound (IMC) growth were observed and analyzed by reacting Ga and Cu/Au substrates in the temperature range of 80-200℃. The main IMC growing at the reaction interface was CuGa₂ phase, and AuGa₂ IMC with small particle sizes was formed on the upper part and Cu₉Ga₄ IMC with a thin band shape on the lower part of the CuGa₂ layer. CuGa₂ particles showed a scallop shape, and the particle size increased without significant shape change as the reaction time increased, similar to the case of Cu₆Sn₅ growth. As a result of analyzing the CuGa₂ growth mechanism, the time exponent was calculated to be ~3.0 in the temperature range of 120-200℃, and the activation energy was measured to be 17.7 kJ/mol.

• Korean Journal of Materials Research
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• v.34 no.10
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• pp.515-521
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• 2024

Solar energy has been recognized as an alternative energy source that can help address fuel depletion and climate change issues. As a renewable energy alternative to fossil fuels, it is an eco-friendly and unlimited energy source. Among solar cells, thin film Cu₂ZnSn(S,Se)₄ (CZTSSe) is currently being actively studied as an alternative to heavily commercialized Cu(In,Ga)Se₂ (CIGS) thin film solar cells, which rely upon costly and scarce indium and gallium. Currently, the highest efficiency achieved by CZTSSe cells is 14.9 %, lower than the CIGS record of 23.35 %. When applied to devices, CZTSSe thin films perform poorly compared to other materials due to problems including lattice defects, conduction band offset, secondary phase information, and narrow stable phase regions, so improving their performance is essential. Research into ways of improving performance by doping with Germanium and Cadmium is underway. Specifically, Ge can be doped into CZTSSe, replacing Sn to reduce pinholes and bulk recombination. Additionally, partially replacing Zn with Cd can facilitate grain growth and suppress secondary phase formation. In this study, we analyzed the device's performance after doping Ge into CZTSSe thin film using evaporation, and doping Cd using chemical bath deposition. The Ge doped thin film showed a larger bandgap than the undoped reference thin film, achieving the highest Voc of 494 mV in the device. The Cd doped thin film showed a smaller bandgap than the undoped reference thin film, with the highest J_sc of 36.9 mA/cm². As a result, the thin film solar cells achieved a power conversion efficiency of 10.84 %, representing a 20 % improvement in power conversion efficiency compared to the undoped reference device.

• Progress in Superconductivity
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• v.2 no.1
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• pp.6-10
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• 2000

New cuprates with the nominal composition $(Pb_{0.75}Sn_{0.25})Sr_2(Ca_{1-x}Lu_x)Cu_2O_z(x=0.4{\sim}1.0)$ have been synthesized. These materials exhibit superconducting properties for 0.4 $\leq$ x $\leq$ 0.7. It is also observed that the superconductivity of the as-prepared sample is enhanced by post-annealing at high temperature followed by quenching. X-ray diffraction analysis reveals that the c lattice parameter decreases as x increases whereas the a lattice parameter is nearly independent of the value of x for both the as-prepared and the post-treated samples. The thermoelectric power measurements indicate that the post-heat-treatments result in an increase in the hole carrier density which account for the observed increase of $T_c$. Bulk superconductivity with a $T_c$ value of 60 K is observed in this system.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.19-21
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• 2005

The ball shea. tests for ball grid array (BGA) and flip chip packages were carried out with different displacement rates to find out the optimum condition of the displacement rate for this test. The BGA packages consisted of two different kinds of solder balls (eutectic Sn-37wt.%Pb and Sn-3.5wt.%Ag) and electroplated Au/Ni/Cu substrate, whereas the flip chip package consisted of electroplated Sn-37Pb solder and Cu UBM. The packages were reflowed up to 10 times, or aged at 443 K up to 21 days. The variation of the displacement rate resulted in the variations of the shear properties such as shear force, displacement rate at break, fracture mode and strain rate sensitivity. The increase in the displacement rate led to the increase of the shear force and brittleness of solder joints.

• Journal of Korea Foundry Society
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• v.19 no.6
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• pp.484-492
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• 1999

The microstructures and mechanical properties of high strength yellow brass, Al bronze and Sn bronze alloys fabricated by gravity die casting and squeeze casting were investigated. A rapid cooling of casting was enhanced by pressure applied during solidification of Cu alloys, the cooling rate of casting was more great for high strength yellow brass alloy than other Cu alloys. Grain size and phases of the squeeze cast products become refined to 1/2 level compared to gravity die castings. Squeeze cast Al bronze and high strength yellow brass has about 10-20% higher yield and tensile strength and slighter decreased or nearly same elongation, compared to gravity die cast ones. Sn bronze has nearly same strength and hardness, but shows increased in elongation, compared to gravity die cast ones.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.97-103
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• 2014

Among various lead-free solders, the Sn-58Bi solders have been considered as a highly promising lead-free solders because of its low melting temperature and high tensile strength. However, Sn-58Bi solder has the poor ductility. To enhance the mechanical property of Sn-58Bi solder, epoxy-enhanced Sn-58Bi solders have been studied. This study compared the microstructures and the mechanical properties of Sn-58Bi solder and Sn-58Bi epoxy solder with aging treatment. The solders ball were formed on the printed circuit board (PCB) with organic solderability preservative (OSP) surface finish, and then the joints were aged at 85, 95, 105 and $115^{\circ}C$ for up to 100, 300, 500 and 1000 hours. The shear test was conducted to evaluate the mechanical property of the solder joints. $Cu_6Sn_5$ intermetallic compound (IMC) layer grew with increasing aging time and temperature. The IMC layer for the Sn-58Bi epoxy solder was thicker than that for the Sn-58Bi solder. According to result of shear test, the shear strength of Sn-58Bi epoxy solder was higher than that of Sn-58Bi solder and the shear strength decreased with increasing aging time.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.526-532
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• 2015

Solar cells with other alternative energies are being importantly recognized related with post-2020 climate change regime formation. In a point of view of materials, solar cells are classified to organic and inorganic solar cells which can provide a plant-scale electricity. In particular, recent studies about compound semiconductor solar cells, such as III-V tandem solar cells, chalcopyrite-series CIGSSe solar cells, and kesterite-series CZTSSe solar cells were rapidly accelerated. In this report, we introduce a research trend and technical issues for the compound semiconductor solar cells.