• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.383-388
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• 2019

High purity SiC fine powder with metal impurity contents of less than 1 ppm was synthesized by improved carbothermal reduction process, and the synthesized powder was used for SiC single crystal growth in RF heating PVT device at temperature above 2,100℃. In-situ x-ray image analyzer was used to observe the sublimation of the powder and single crystal growth behavior during the growth process. SiC powder was used as a source of single crystal growth, exhausted from the outside of the graphite crucible at the growth temperature and left graphite residues. During the growth, the flow of raw materials was concentrated in the middle and influenced the growth behavior of SiC single crystals. This is due to the difference in temperature distribution inside the crucible due to the fine powder. After the single crystal growth was completed, the single crystal ingot was cut into a 1 mm thick single crystal substrate and finely polished using a diamond abrasive slurry. A dark yellow 4H-SiC was observed overall of single crystal substrate, and the polycrystals generated in the outer part may be caused by the incorporation of impurities such as the bubble layer mixed in the process of attaching the seed crystal to the seed holder.

• ETRI Journal
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• v.35 no.6
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• pp.1152-1155
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• 2013

A cost-effective and simple solder on pad (SoP) process is proposed for a fine-pitch microbump interconnection. A novel solder bump maker (SBM) material is applied to form a 60-${\mu}m$ pitch SoP. SBM, which is composed of ternary Sn3.0Ag0.5Cu (SAC305) solder powder and a polymer resin, is a paste material used to perform a fine-pitch SoP through a screen printing method. By optimizing the volumetric ratio of the resin, deoxidizing agent, and SAC305 solder powder, the oxide layers on the solder powder and Cu pads are successfully removed during the bumping process without additional treatment or equipment. Test vehicles with a daisy chain pattern are fabricated to develop the fine-pitch SoP process and evaluate the fine-pitch interconnection. The fabricated Si chip has 6,724 bumps with a 45-${\mu}m$ diameter and 60-${\mu}m$ pitch. The chip is flip chip bonded with a Si substrate using an underfill material with fluxing features. Using the fluxing underfill material is advantageous since it eliminates the flux cleaning process and capillary flow process of the underfill. The optimized bonding process is validated through an electrical characterization of the daisy chain pattern. This work is the first report on a successful operation of a fine-pitch SoP and microbump interconnection using a screen printing process.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.261-264
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• 2007

In this study, the consolidation and casting processes of fine Si powders, by-products of making high purity Poly-Si rods in the current method, were systematically investigated for use as economical solar-grade feedstock. Morphology, size, and contamination type of the poly-Si fine powders were inspected by combined analysis of SEM, particle size analyzer, and FT-IR. Poly-Si powder compacts were tried to fabricate by a consolidation process without a binding agent and then their density ratio and strength were evaluated. Finally, the electrical resistivity of the specimens prepared by an electromagnetic casting method was examined for purity assessment.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1121-1121
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• 2006

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.799-800
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• 2006

Wrought Si-steels are generally used for electromagnetic valves, which are needed good response. To date, Hitachi Powdered Metals Co., Ltd. have produced Fe-Si base sintered magnetic material, EU-52, which shows a magnetic flux density of more than 1.25T at 2000A/m and a maximum permeability of more than 3500. However these magnetic properties are lower than that of wrought Si-steels. Because EU-52 has a low density of $7.2Mg/m^3$. For improving the magnetic properties, it is necessary to increase the density of sintered cores. To increase density, a new mixing method of coating fine Si powders on atomized iron powders was developed, for avoiding the Kirkendall effect. As the result, developed P/M Fe-Si magnetic cores shows higher density of $7.38Mg/m^3$, higher magnetic flux density of 1.48T at 2000A/m and higher maximum permeability of 6800.

• Journal of Powder Materials
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• v.4 no.3
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• pp.179-187
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• 1997

Milling media of steel and zirconia were used to produce $MoSi_2$ by mechanical alloying (MA) of Mo and Si powders. The effect of milling media on MA of Mo-65.8at%Si powder mixture has been investigated by SEM, XRD, DTh and in-situ thermal analysis. The powders mechanically alloyed by milling medium of steel for 8 hours showed the structure of fine mixture of Mo and Si, and those mechanically alloyed by milling medium of zirconia for longer milling time showed the structure of fine mixture of Mo and Si. The tetragonal $\alpha$-$MoSi_2$ Phase and the tetragonal $Mo_5Si_3$ phase appeared with small Mo peaks in the powders milled by milling medium of steel for 4 and 8 hours. The $\alpha$-$MoSi_2$ phase and the hexagonal $\beta$-$MoSi_2$ phase were formed after longer milling time. The $\alpha$-$MoSi_2$ phase appeared with large Mo peaks in the powders milled by milling medium of zirconia for 4 hours. The phases, $\alpha$-$MoSi_2$ and $\beta$-$MoSi_2$. were formed in the powders milled for longer milling time. DTA and annealing results showed that Mo and Si were transformed into $\alpha$-$MoSi_2$ and $Mo_5Si_3$, while $\beta$-$MoSi_2$ into $\alpha$-$MoSi_2$. In-situ thermal analysis results demonstrated that there were a sudden temperature rise at 212 min and a gradual increase in temperature in case of milling media of steel and zirconia, respectively. The results indicate that MA can be influenced by materials of milling medium which can give either impact energy on powders or thermal energy accumulated in vial.

• Journal of Powder Materials
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• v.11 no.1
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• pp.34-42
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• 2004

The effect of extrusion temperature on the microstructure and mechanical properties were studied in He-gas atomized $Al_{81-(x＋y)}Si_{19}Ni_xCe_y$ alloy powders and their extruded bars using SEM, tensile testing and thermal expansion testing. The extruded bar of $Al_{73}Si_{19}Ni_7Ce_1$ alloy consists of a mixed structure in which fine Si particles with a particle size below 20∼500nm and very fine $Al_3Ni,\;Al_3Ce$ compounds with a particle size below 200nm are homogeneously dispersed in Al martix with a grain size below 500nm. With increasing extrusion temperature, the microstructural scale was decreased. The ultimate tensile strength of the alloy bars has incresed with decreasing extrusion temperature from 500 to 35$0^{\circ}C$ and $Al_{73}Si_{19}Ni_7Ce_1$ alloy extreded at 35$0^{\circ}C$ shows a highest tensile strength of 810 MPa due to the fine namostructure. The addition of Ni and Ce decreased the coefficients of thermal expansion and the effects of extression temperature on the thermal expansion were not significant.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.04a
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• pp.34-35
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• 2004

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.265-273
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• 1990

Fine Si-Al-OH-C coprecipitate powders were prepared from Si(OC2H5)4, Al(i-OC3H7)3, and carbon black by a hydrolysis method before fabrication of Sialon-SiC composite powder by carbothermal reduction at 1350$^{\circ}C$ for 10h under N2/H2 mixed atmosphere. The characterization of the synthesized Sialon-SiC composite powders was performed using XRD, BET, SEM, TEM and particle size analysis methods. The average particle size and specific surface area of the synthesized Sialon-SiC composite powder were 0.13$\mu\textrm{m}$ and 20.1㎡/g, respectively when Z=1 and N2 : H2=50 : 50.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.201-209
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• 1989

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. $\beta$-Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the $\beta$-Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of $\beta$-Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.