• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.7
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• pp.13-20
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• 2004

In order to set up the design of micro optical bench, optical coupling efficiencies of two sets of test benches are calculated. Simple linear connections of incoming and outgoing optical fibers with and without ball lenses are designed. Positional errors that are possible in actual fabrication processes we considered in the calculations and their tolerances are determined from -3 ㏈ conditions. For a simple fiber-to-fiber connection, the lateral misalignment should be limited to 2.7 um and tilt error 5.8o. In case of the fiber-to-fiber with ball lens, the working distance between fibers can be extended over 60 um. The optical coupling efficiency depends strongly on the positional errors of ball lenses along the optical axis, and it is also found that the lateral and vertical positional errors should be considered simultaneously in order to keep the high coupling efficiency.

• Korean Journal of Metals and Materials
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• v.47 no.4
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• pp.261-266
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• 2009

The mechanical and electrical properties of ball grid array (BGA) solder joints were measured, consisting of Sn-3.5Ag, with organic solderability preservative (OSP)-finished Cu pads and Electroless Nickel/Immersion Gold (ENIG) surface finishes. The mechanical properties were measured by die shear test. When ENIG PCB was upper joint and OSP PCB was lower joint, the highest shear force showed at the third reflow. When OSP PCB was upper joint and ENIG PCB was lower joint, the highest shear force showed at the forth reflow. For both joints, after the die shear results reached the highest shear force, shear force decreased as a function of increasing reflow number. Electrical property of the solder joint decreased with the function of increasing reflow number. The scanning electron microscope results show that the IMC thickness at the bonding interface gets thicker while the number of reflow increases.

• Tribology and Lubricants
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• v.7 no.1
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• pp.40-45
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• 1991

Wear performances for dibutyl 3,5-di-t-butyl 4-hydroxy benzyl phosphonate (DBP) were invesitigated using the four ball test machine under sliding and also rolling contact conditions, and compared with ZDDP. DBP showed excellent antiwear performace compared with ZDDP under severe sliding contact. Also, DBP achieved a longer fatigue life than ZDDP under rolling contact conditions. The surface of the worn balls was observed using an optical microscope, and the wear derbis generated was measured using the Particle Quantifier (PQ).

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.5
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• pp.597-606
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• 1999

This study was performed to evaluate the effect of aging and thermal cycling on the biaxial flexure strength of low commercially available veneering resin composites for crown(Dentacolor : DC, Artglass : AG, Esternia : ET and Targis : TG). Disc specimens were fabricated in a teflon mold giving 12mm in diameter and 1mm in thickness. All samples were divided into 4 groups. Group 1 was dried in a dessicator at $25^{\circ}C$ for 30 days. Group 2 was immersed in distilled water at $37^{\circ}C$ for 30 days. Group 3 was immersed in distilled water at $65^{\circ}C$ for 30 days. Group 4 was subjected to 10,000 thermal cycles between $5^{\circ}C\;and\;55^{\circ}C$, and the immersion time in each bath was 15 seconds per cycle. Biaxial flexure test was conducted using the ball-on-three-ball method at the cross head speed of 0.5mm/min and fracture surfaces were observed with scanning electoron microscope. The results obtained were summarized as follows; 1. Weibull modulus values, except for the AG group, decreased after thermal cycling treatment. 2. Biaxial flexure strength values of aging group at $37^{\circ}C$ were the lowest in all sample groups. Except for the DC group, strength values were significantly decreased for the drying group. 3. After thermal cycling test, the highest value of biaxial flexure strength of 188.8 MPa was observed in the ET group and the lowest value of 73.2 MPa was observed in the DC group. The strength values showed the significant differences in each group (p<0.05). 4. Observation of surfaces after thermal cycling test revealed the ditching in the part of surrounding large fillers.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.450-455
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• 2002

Cu-cored Sn-Ag solder balls were fabricated by coating pure Sn and Ag on Cu balls. The melting behavior and the solderability of the BGA joint with the Ni/Au coated Cu pad were investigated and were compared with those of the commercial Sn-Ag and Sn-Ag-Cu balls. DSC analyses clarified the melting of Cu-cored solders to start at a rather low temperature, the eutectic temperature of Sn-Ag-Cu. It was ascribed to the diffusion of Cu and Ag into Sn plating during the heating process. After reflow soldering the microstructures of the solder and of the interfacial layer between the solder and the Cu pad were analyzed with SEM and EPMA. By EDX analysis, formation of a eutectic microstructure composing of $\beta$-Sn, Ag$_3$Sn, ad Cu$_{6}$Sn$_{5}$ phases was confirmed in the solder, and the η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer was found to form at the interface between the solder and the Cu pad. By conducting shear tests, it was found that the BGA joint using Cu-cored solder ball could prevent the degradation of joint strength during aging at 423K because of the slower growth me of η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer formed at the solder, pad interface. Furthermore, Cu-cored multi-component Sn-Ag-Bi balls were fabricated by sequentially coating the binary Sn-Ag and Sn-Bi solders on Cu balls. The reflow property of these solder balls was investigated. Melting of these solder balls was clarified to start at the almost same temperature as that of Sn-2Ag-0.75Cu-3Bi solder. A microstructure composing of (Sn), Ag$_3$Sn, Bi and Cu$_{6}$Sn$_{5}$ phases was found to form in the solder ball, and a reaction layer containing primarily η'-(Au, Co, Cu, Ni)$_{6}$Sn$_{5}$ was found at the interface with Ni/Au coated Cu pad after reflow soldering. By conducting shear test, it was found that the BGA joints using this Cu-core solder balls hardly degraded their joint shear strength during aging at 423K due to the slower growth rate of the η'-(Au, Cu, Ni)$_{6}$Sn$_{5}$ reaction layer at the solder/pad interface.he solder/pad interface.

• The Korean Journal of Ceramics
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• v.3 no.3
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• pp.169-172
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• 1997

Sintered diamond/(WC-Co) composites were prepared by spark plasma sintering technique. Tribological properties were measured at temperatures from RT to $500^{\circ}C$ in sliding tests with alumina ball. They show coefficient of friction of 0.1 and below at RT and wear of the diamond composites is hardly detected. Effects of diamond grit size, diamond content and test temperature on the coefficient of friction and the wear are discussed. The wear scars were analyzed.

• Elastomers and Composites
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• v.49 no.3
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• pp.245-252
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• 2014

FT-IR measurement and the physical properties of polyurethane adhesive prepared from the polyol, isocyanate, 2-HEMA and other acrylate monomers were examined. The softening point, viscosity, adhesion strength and mechanical properties of the PU adhesives were reviewed by Ring and Ball method, Brookfield viscometer and universal test machine, respectively. Results revealed that increment of both PPG amount and butyl acrylate content decreased softening point, adhesion strength, tensile strength and 100% modulus. However as 2-HEMA and MDI content increased the mechanical properties including tensile strength, 100% modulus increased, and also the viscosity and NCO content increased.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.27-36
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• 1997

This paper evaluates the static and fatigue bending strengths of CFRP (carbon fiber reinforced plastic) laminates subjected to hygrothermals. The specimens which had different stacking composition, orthotropic and quasi-isotropic laminated plates, were prepared for this experiment. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages, and the 3-point fatigue bending test is carried out by using the impacted laminates to investigate the influence of hygrothermals on the effect on the residual bending fatigue strength of CFRP laminates.

• Journal of Dental Rehabilitation and Applied Science
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• v.23 no.4
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• pp.269-281
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• 2007

Fluoric acid etching is an essential procedure in cementation of reinforced ceramics to tooth surface. But there have been few studies about the changes of surface structure and flexural strength of IPS $Empress^{(R)}$ 2 ceramic according to the etching time. The objectives of this study were to examine the surface structure changes and the difference in biaxial flexural strength of IPS $Empress^{(R)}$ 2 ceramic according to various etching times. Sixty one disk-shaped specimens of IPS $Empress^{(R)}$ 2 ceramic($14mm{\times}1.2mm$) were fabricated for the biaxial flexural strength test and SEM analysis according to the manufacturer's recommendations. Sixty specimens were divided into 6 groups(n=10) according to the time of HF acid etching(0, 20, 180 and 300s)and silane/resin cement application. Each disk was loaded using a piston-on-3 ball biaxial configuration in a universal testing machine. The failure loads(N) were recorded, and the biaxial flexural strength for each disk was calculated. A one-way analysis of variance and independent t-test on transformed fracture strength data were used to determine significant differences between groups. The groups of no cementation showed a trend toward progressive weakening with increasing the etching time. However, this was not statistically significant at p=0.05 level. The groups of resin cementation exhibited no apparent trend in their mean strength values. SEM photomicrographs showed very different results of etching. Within the conditions of this study, alteration of surface topography by acid etching does not have a deleterious effect on the biaxial flexural strength of IPS $Empress^{(R)}$ 2 ceramic.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.237-242
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• 2011

The effect of shearing speed on the shear force and energy of Sn-0Ag-0.5Cu solder ball was investigated. Various UBM (under bump metallurgy)'s on Cu pads were used such as ENEPIG (Electroless Nickel, Electroless Palladium, Immersion Gold; Ni/Pd/Au), ENIG (Electroless Nickel, Immersion Gold; Ni/Au), OSP (Organic Solderability Preservative). To fabricate a shear test specimen, a solder ball, $300{\mu}m$ in diameter, was soldered on a pad of FR4 PCB (printed circuit board) by a reflow soldering machine at $245^{\circ}C$. The solder bump on the PCB was shear tested by changing the shearing speed from 0.01 m/s to 3.0 m/s. As experimental results, the shear force increased with a shearing speed of up to 0.6 m/s for the ENIG and the OSP pads, and up to 0 m/s for the ENEPIG pad. The shear energy increased with a shearing speed up to 0.3 m/s for the ENIG and the OSP pads, and up to 0.6 m/s for the ENEPIG pad. With a high shear speed of over 0 m/s, the ENEPIG showed a higher shear force and energy than those of the ENIG and OSP. The fracture surfaces of the shear tested specimens were analyzed, and the fracture modes were found to have closer relationship with the shear energy than the shear force.