Abstract: The experimental investigation and non-linear finite element analysis using elastic-viscoplastic constitutive model were conducted to study the effect of ball shear speed on shear force of BGA solder joints. The Ag3Sn intermetallic compound (IMC) particles were found inside the Sn-3.5Ag solder, while the fine intermixed structure of lead-rich phases and tin-rich phases was investigated inside the eutectic Sn-37Pb solder. The shear force linearly increased with shear speed and reached to the maximum value at the highest shear speed in both experimental and computational results. All of the test specimens were fractured like ductile mode, and the plastic strain energy density distributions were deeply related to the failure mechanism.
Abstract: Specimens of aluminum (Al), austenitic stainless steel (SUS304L), pure iron (Fe) and Oxygen-free high conductivity copper (Cu) were treated by argon ion bombardment, and then were bonded by diffusion bonding method. The effects of argon ion bombardment on diffusion-bonded joints of four kinds of metallic materials were compared from the tensile strength at real bonded area and the fractographs. The results showed that bonding temperature was lowered by argon ion bombardment treatment for four kinds of materials. The effect of argon ion bombardment on diffusion-bonded joint depended strongly on the chemistry of the surface to be bonded, and increased in Al, SUS304L, Fe, and Cu in turn.
Abstract: The n-type thermoelectric materials of Bi2Te2.7Se0.3 doped with SbI3 were prepared by spark plasma sintering technique. The powders were ball-milled in an argon and air atmosphere. Then, powders were reduced in H2 atmosphere. Effects of oxygen content on the thermoelectric properties of Bi2Te2.7Se0.3 compounds have been investigated. Seebeck coefficient, electrical resistivity and thermal conductivity of the sintered compound were measured at room temperature. It was found that the effect of atmosphere during the powder production was remarkable and thermoelectric properties of sintered compound were remarkably improved by H2 reduction of starting powder. The obtained maximum figure of merit was 2.4 x 10-3/K.
Abstract: While the Heusler-type Fe2VAl compound exhibits a semiconductor-like behavior in
electrical resistivity, doping of quaternary elements causes a sharp decrease in the low-temperature resistivity ρ and a large enhancement in the Seebeck coefficient S. Substantial enhancement in S can be explained on the basis of the electronic structure where the Fermi level shifts slightly from the center of a pseudogap either up- or downward depending on doping. In particular, a slight substitution of Si for Al leads to a large power factor (P = S2/ρ) of 5.5×10-3 W/m K2 at around room temperature.
Abstract: In this study, we attempted to fabricate dendrimer Langmuir-Blodgett (LB) films
functionalized with azobenzene groups in their periphery. It is well known that azoenzene-type compounds undergo an efficient and fully reversible photo-isomerization reaction. We investigated monolayer behavior and its characteristics at air-water interface by LB method. Then the molecular behavior shift of the monolayer by 365[nm] light irradiation was also measured because of the isomerization of azobenzene group in periphery. The electrical properties of G4-48Azo dendrimer were compared with between trans form and cis form using metal/dendrimer LB film/metal (MIM)structure and using STM system.
Abstract: CoSb3 compounds were prepared by the arc melting and their thermoelectric properties were investigated at 300K-600K. Annealing effects were examined and they were correlated to phase transformation and homogenization. Undoped CoSb3 showed p-type conduction and intrinsic semiconducting behavior at all temperatures examined. Thermoelectric properties were changed with constituent phases because α-CoSb2, β-CoSb and Sb are metallic or semimetallic phases while δ-CoSb3 is semiconducting phase. Thermoelectric properties were remarkably improved by annealing in vacuum and they were closely related to phase transitions. Single phase δ-CoSb3 was successfully obtained by annealing at 400°C for 24hrs.
Abstract: Pd/Ge/Ti/Pt and Pd/Si/Ti/Pt ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In both ohmic contacts, low-resistance and non-spiking planar interfaces were obtained by rapid thermal annealing. RF performance of the AlGaAs/GaAs HBT was also examined by employing these contact systems.
Abstract: New method for characterization of coating microstructures and for evaluation of coating property by means of surface morphology has been proposed. In this paper, the distribution of shape and dimensions of splat was examined using quantitative analysis of scanning electron microscope images from the surface of spray pattern as well as the surface of coating. Results obtained in this study indicate that it is necessary to analyze the spray pattern as well as the surface morphology in order to estimate the coating property by means of the distribution of splat which composes the coating. Moreover, the splats, which are in the interface between the substrate and the coating, should have the same morphology as those of the coating surface. The relationship between splat morphology and the property of coatings was discussed.
Abstract: This study was conducted to observe the influence of oxygen to fuel ratio[O2/H2 ratio] of HVOF(High Velocity Oxygen Fuel) process on the amorphous formation and coating properties of NiTiZrSiSn bulk amorphous alloy. The bulk amorphous feedstock was prepared by inert gas atomization. Amorphous contents were followed by differential scanning calorimetry(DSC). Microstructural characterization was done by scanning electron microscope(SEM) and x-ray diffraction(XRD). Mechanical properties were obtained by Vickers microhardness testing and pin on disk wear testing. A maximum 72% amorphous phase could be obtained with an optimum O2/H2 ratio. High amorphous content resulted in a low friction coefficient and weight loss than high oxide content coating and fully crystallized coating.
Abstract: Isothermal crystallization of Zr55Al10Ni5Cu30 bulk amorphous alloy near the glass
transition temperature has been investigated. The microstructures and thermal stability of the annealed amorphous alloy were examined by HRTEM, XRD and DSC. The amorphous phase in the Zr55Al10Ni5Cu30 bulk amorphous alloy crystallized at 420°C through the following processes of amorphous →amorphous with clusters + metastable phases→metastable phases.