• ETRI Journal
• /
• v.35 no.2
• /
• pp.340-343
• /
• 2013

A novel bumping process using solder bump maker is developed for the maskless low-volume solder on pad (SoP) technology of fine-pitch flip chip bonding. The process includes two main steps: one is the aggregation of powdered solder on the metal pads on a substrate via an increase in temperature, and the other is the reflow of the deposited powder to form a low-volume SoP. Since the surface tension that exists when the solder is below its melting point is the major driving force of the solder deposit, only a small quantity of powdered solder adjacent to the pads can join the aggregation process to obtain a uniform, low-volume SoP array on the substrate, regardless of the pad configurations. Through this process, an SoP array on an organic substrate with a pitch of $130{\mu}m$ is successfully formed.

• Journal of the Microelectronics and Packaging Society
• /
• v.28 no.3
• /
• pp.17-24
• /
• 2021

Perovskite solar cells (PSCs) can be fabricated through solution process economically with variable bandgap that is controlled by composition of precursor solution. Tandem cells in which PSCs combined with silicon solar cells have potential to reach high power conversion efficiency over 30%, however, lack of long-term stability of PSCs is an obstacle to commercialization. Degradation of PSCs is mainly attributed to the mass transport of halide and metal electrode materials. In order to ensure the long-term stability, the mass transport should be inhibited. In this study, we confirmed degradation behaviors due to the mass transport in PSCs and designed buffer layers with LiF and/or SnO₂ to improve the long-term stability by suppressing the mass transport. Under high-temperature storage test at 85℃, PSCs without the buffer layers were degraded by forming PbI₂, AgI, and the delta phase of the perovskite material, while PSCs with the buffer layers showed improved stability with keeping the original phase of the perovskite. When the LiF buffer and encapsulation were applied to PSCs, superior long-term stability on 85℃-85% RH dump heat test was achieved; efficiency drop was not observed after 200 h. It was also confirmed that 90.6% of the initial efficiency was maintained after 200 hours of maximum power tracking test under AM 1.5G-1SUN illumination. Here, we have demonstrated that the buffer layer is essential to achieve long-term stability of PSCs.

• Korean Journal of Materials Research
• /
• v.26 no.5
• /
• pp.258-265
• /
• 2016

Fluorine-doped tin oxide (FTO) nanoparticles have been successfully synthesized using ultrasonic spray pyrolysis. The morphologies, crystal structures, chemical bonding states, and electrochemical properties of the nanoparticles are investigated. The FTO nanoparticles show uniform morphology and size distribution in the range of 6-10 nm. The FTO nanoparticles exhibit excellent electrochemical performance with high discharge specific capacity and good cycling stability ($620mAhg^{-1}$ capacity retention up to 50 cycles), as well as excellent high-rate performance ($250mAhg^{-1}$ at $700mAg^{-1}$) compared to that of commercial $SnO_2$. The improved electrochemical performance can be explained by two main effects. First, the excellent cycling stability with high discharge capacity is attributed to the nano-sized FTO particles, which are related to the increased electrochemical active area between the electrode and electrolyte. Second, the superb high-rate performance and the excellent cycling stability are ascribed to the increased electrical conductivity, which results from the introduction of fluorine doping in $SnO_2$. This noble electrode structure can provide powerful potential anode materials for high-performance lithiumion batteries.

• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.3
• /
• pp.43-49
• /
• 2019

In this study, a new approach using graphene oxide (GO) powder-composited Sn-3.0Ag-0.5Cu(in wt.%) solder paste for improving the bending reliability of solder joints between a flexible substrate and small outline package (SOP) was suggested. The GO addition slightly affected the melting temperature, however, the change in the melting temperature was not significant. Meanwhile, we observed the addition of GO could suppress IMC growth and IMC thickness of solder joint during the reflow process. Moreover, the cyclic bending test was also performed for evaluation of reliability in solder joint and we could improve the cyclic bending reliability of solder joint by adding GO powders. For 0.2 wt.% of GO added to the solder joint, the bending lifetime was increased to 20% greater than that without GO. Pull strength and ductility of the solder joint with GO were also higher than those of the joint without GO and it was assumed that this effect by adding GO could contribute to improve cyclic bending reliability of solder joint.

• Microbiology and Biotechnology Letters
• /
• v.20 no.2
• /
• pp.150-155
• /
• 1992

- Some properties of an extracellular cytosine deaminase excreted from an isolate from soil samples were examined after 20~80%' ammonium sulfate fractionation. The enzyme catalyzed the conversion of cytosine and 5-fluorocytosine into uracil and 5-fluorouracil by substrate specificity, respectively. The optimum temperature and storage time on the stability of the enzvme preparation were below $50^{\circ}C$ keeping above 90% of the residual activity and near 4 days keeping above 80% of the residual one in Tris-HCI buffer. The maximum activity was also obtained at 8.0 in pH and 37'C in temperature. The pHs and temperatures for enzyme activity ranged from 8.0~8.5 and from 37~$45^{\circ}C$. respectively. The presence of $Ag^-,Hg^{2-}, Zn^{2-}, Cu^{2-}, Sn^{2-}, \; or\; Pb^{2-}$ in the reaction mixture resulted in the marked inhibition in enzyme activity, but 1 mM of $K^+, Fe^[3+}, Mg^{2+}, \; or \; Na^+$. slightly increased the activity. The enzyme preparation was heavily affected by most of inhibitors tested such as 1 mM of EIITA, NaCN and pentachlorophenol, and completely inactivated by p-CMB and TCA of 1 mM, or 10 mM.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.16 no.5
• /
• pp.134-139
• /
• 2007

This paper presents a computer-based analysis on the thermal shock characteristics of Pb-free solder joints and UBM in flip chip assemblies. Among four types of popular UBM systems, TiW/Cu system with 95.5Sn-3.9Ag-0.6Cu solder joints was chosen for simulation. A simple 3D finite element model was first created only including silicon die, mixture between underfill and solder joints, and substrate. The displacements due to CTE mismatch between silicon die and substrate was then obtained through FE analysis. Finally, the obtained displacements were applied as mechanical loads to the whole 2D FE model and the characteristics of flip chip assemblies were analyzed. In addition, based on the hyperbolic sine law, the accumulated creep strain of Pb-free solder joints was calculated to predict the fatigue life of flip chip assemblies under thermal shock environments. The proposed method for fatigue life prediction will be evaluated through the cross check of the test results in the future work.

• Applied Biological Chemistry
• /
• v.39 no.5
• /
• pp.349-354
• /
• 1996

The Polyvinyl alcohol(PVA) oxidase involved in PVA degradation by microorganism has been purified to homogeneity from culture broth of Xanthomonas campestris J2Y grown in a minimal medium containing PVA as a sole carbon source. The enzyme was purified by DEAE-cellulose chromatograpy and Sephadex G-150 gel filtration. The purified PVA oxidase was electrophoretically homogeneous both in the absence and presence of SDS. The molecular weight of the enzyme was estimated to be about 55,000 daltons by SDS-polyacrylamide gel electrophoresis and Sephadex G-150 gel filtration. The native enzyme existed as a monomer. The optimal pH and temperature was shown to be pH 7 and $37^{\circ}C$ respectively. The activity of enzyme was stable below $55^{\circ}C$ and between pH range of $5{\sim}11$. The enzyme activity was significantly inhibited by metal compounds such as $Ag^{2+},\;Hg^{2+}$. While, metal ions such as $Mn^{2+},\;and\;Cu^{2+}$ stimulated the reaction. Km value of the enzyme for PVA was $7.04{\times}10^{-2}mmol/{\ell}$.

• Korean Journal of Metals and Materials
• /
• v.46 no.2
• /
• pp.80-87
• /
• 2008

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than $1,000{\Omega}$. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

• Korean Journal of Heritage: History & Science
• /
• v.51 no.4
• /
• pp.224-233
• /
• 2018

Thirty-three Early Iron Age bronzes at the sites of Hoam-dong in Chungju and Cheongsong-ri in Buyeo were investigated in order to study the manufacturing technique and the provenance of lead. Chemical analysis using X-ray fluorescence showed that 33 bronzes consist of copper(Cu), tin(Sn) and lead(Pb) served as major elements. Major and minor elemental analyses by EPMA were performed on two mirrors and 2 weapons of the bronzes investigated. The results shows that bronze mirrors from Chungju and Buyeo were high-tin bronzes(> 30 wt%). And 20% of tin and 5% of lead were founded in bronze weapons. Iron, zinc, arsenic, silver, nickel, sulfur and cobalt detected in four bronzes as minor and trace elements. The four bronzes were alloyed considering their function and were not heat treated after casting due to their high tin content. Lead isotope analysis using TIMS indicates that thirty-three bronzes were distributed southern Korea peninsula except Zone 1. As a result, lead raw materials came from various regions in Korean Peninsula not from Gyeongsang-do regions. The manufacturing techniques of bronze ware generalized at this age, and bronze was produced in various sites using raw materials from various sources.

• Restorative Dentistry and Endodontics
• /
• v.21 no.1
• /
• pp.87-105
• /
• 1996

The purpose of this study is to investigate the characteristics of the compositions and phases of amalgam alloys and amalgams by using EMPA and X-ray diffractometer. Each specimen was made from Caulk Fine Cut Clow copper lathe cut amalgam), Caulk Spherical (low copper spherical amalgam), Tytin (high copper unicorn position amalgam), Dispersally (high copper admixed amalgam) and Valiant (Palladium enriched amalgam). For preparing amalgam alloys, Tytin and Valiant were used as powder forms and the others were used as tablet forms after being polished with polishing machine. For preparing amalgams, each amalgam alloy and Hg were measured, and triturated by mechanical amalgamater according to user's instructions. After triturating, the triturated mass was inserted to cylindrical metal mold and simultaneously adapted by cylindrical condenser with same diameter and condensed by Instron universal testing machine with 80kg pressure & 1mm/min speed. Each specimen was removed from the metal mold and stored at room temperature for a week. The specimen was polished with the same polishing machine for amalgam alloy. For observation of microstructure and analysis of composition of amalgam alloys and amalgams, EMPA was used to get secondary electron images, backscattered images and characteristic X-ray images of Ag, Sn, Cu, Zn, Hg. To analyze compositions of amalgam alloys and amalgams, X-ray diffractometer was used. Amalgam alloys were scanned at the range of 2${\theta}$ of 30-$85^{\circ}$ and the speed of $4^{\circ}$/min with Cuka line and amalgams were scanned at the range of 2${\theta}$ of 28-$44^{\circ}$ and the speed of $4^{\circ}$/min with Cuka line. By comparing obtained d(distance between surfaces) and d of expected phases and atoms in amalgam alloys and amalgams in ASTM card, phases and atoms were identified. The results were as follows, 1. In Caulk Fine Cut amalgam alloy typical ${\gamma}$ phase was shown, and in amalgam, ${\gamma}$, ${\gamma}_1$ and ${\gamma}_2$ phases were observed. 2. In Caulk Spherical amalgam alloy ${\gamma}$, Ag, Cu and $\varepsilon$ phases were shown, and in amalgam ${\gamma}$, ${\gamma}_1$, ${\gamma}_2$ and $\eta$ phases were observed. 3. In Tytin amalgam alloy ${\gamma}$, Cu and $\varepsilon$ phases were shown, and in amalgam ${\gamma}$, ${\gamma}_1$, $\eta$ and $\varepsilon$ phases were observed. 4. In Dispersalloy ${\gamma}$, Ag, Cu and $\varepsilon$ phases were shown, and in amalgam ${\gamma}$, ${\gamma}_1$, $\eta$ and $\varepsilon$ phases were observed. 5. In Valiant alloy ${\gamma}$, Cu and e phases were shown, and in amalgam ${\gamma}$, ${\gamma}_1$, $\eta$ and $\varepsilon$ phases were observed.