Electrical Resistance and Microstructural Changes of Silver–Epoxy Isotropic Conductive Adhesive Joints Under High Humidity and Heat

In this study, the degradation mechanism of chip resistors mounted with Ag–epoxy isotropic conductive adhesive (ICA) under two different environmental conditions, i.e., humidity exposure (85°C/85% relative humidity) and thermal cycling (TC, –40°C to 125°C), was examined by monitoring the change in electrical resistance and by transmission electron microscopy. The effect of the terminal finishes (Sn/Ni or Au/Ni) of the chip components on joint stability during those two tests was also examined. The electrical resistance of the Sn/Ni-plated chip component joined with Ag–epoxy ICA during both environmental tests increased with exposure time. On the other hand, the electrical resistance of the Au/Ni-plated chip component joined with Ag–epoxy ICA remained unchanged during both tests. In the case of the Sn/Ni-plated chip joint, Sn oxides such as SnO, SnO₂, and Sn-Cl-O were formed inhomogeneously on the surface of the Sn plating during the humidity exposure test. Under the TC test, microcracks were also observed at the Sn/epoxy and the Ag filler/epoxy interfaces. A Ni₃Sn intermetallic compound (IMC) was formed at the interface between Sn and Ni, and the Ni₃Sn₄ IMC was also formed at the Sn surface. In contrast, no oxide was found in the Au/Ni-plated chip joint during the humidity exposure test. Also, no IMC was found in that joint during the TC test. It is suggested that oxides, microcracks, and IMCs cause the electrical degradation of Sn/Ni-plated chip components joined with Ag–epoxy ICA.     

Altered Induction of Reactive Oxygen Species by X-rays in Hematopoietic Cells of C57BL/6-Tg (CAG-EGFP) Mice

Previous work pointed to a critical role of excessive production of reactive oxygen species (ROS) in increased radiation hematopoietic death in GFP mice. Meanwhile, enhanced antioxidant capability was not demonstrated in the mouse model of radio-induced adaptive response (RAR) using rescue of radiation hematopoietic death as the endpoint. ROS induction by ex vivo X-irradiation at a dose ranging from 0.1 to 7.5 Gy in the nucleated bone marrow cells was comparatively studied using GFP and wild type (WT) mice. ROS induction was also investigated in the cells collected from mice receiving a priming dose (0.5 Gy) efficient for RAR induction in WT mice. Significantly elevated background and increased induction of ROS in the cells from GFP mice were observed compared to those from WT mice. Markedly lower background and decreased induction of ROS were observed in the cells collected from WT mice but not GFP mice, both receiving the priming dose. GFP overexpression could alter background and induction of ROS by X-irradiation in hematopoietic cells. The results provide a reasonable explanation to the previous study on the fate of cells and mice after X-irradiation and confirm enhanced antioxidant capability in RAR. Investigations involving GFP overexpression should be carefully interpreted.     

旋转光栅调制傅里叶变换频谱仪

提出了一种基于圆盘旋转光栅调制的傅里叶变换光谱仪 (FTS) ,光栅同时实现了分束和外差调制的功能。分析了三种实现分光的方案 ,通过对三个波长分别为 670nm ,63 3nm和 5 3 2nm的激光进行了频谱测量实验 ,结果表明该光谱仪具有良好的稳定性和抗干扰能力 ,经调制后测量灵敏度倍增 2 0倍 ,尤其适用于微弱信号测量和近红外领域。     

High-Rate Diamond Deposition by Combustion Flame Method Using Twin Acetylene/Oxygen Gas Welding Torch

To develop a high-rate diamond deposition process using combustion flame method, diamond deposition equipment with twin acetylene/oxygen welding torch was manufactured, and diamond deposition by using this equipment was carried out. 304 Stainless steel plates and molybdenum plates were used as substrates. The diamond deposition was conducted under the following conditions: oxygen flow rate: 1.25 SLM, acetylene/oxygen flow ratio: 1.15, and diamond deposition temperature: around 1473 K. Consequently, diamonds could be deposited even on the stainless steel substrate, and diamond deposition rate was promoted by using twin torch equipment. Besides, the diamond/molybdenum hybrid coating using diamonds deposited by twin torch equipment have the same wear-resistant property as that using diamonds by the single torch equipment. From these results, this technique was thought to have high potential for high-rate diamond deposition in combustion flame method.     

Low‐resistive and transparent AZO films prepared by PLD in magnetic field

Al₂O₃‐doped ZnO (AZO) thin films have been deposited onto glass substrates using a split target consisting of AZO (1 wt%) and AZO (2 wt%) by pulsed laser deposition with an ArF excimer laser (λ = 193 nm, 15 mJ, 10 Hz, 0.75 J/cm²). By applying a magnetic field perpendicular to the plume, the lowest resistivity of 8.54 × 10^?5Ω·cm and an average transmittance exceeding 91% over the visible range were obtained at a target‐to‐substrate distance of 25 mm for approximately 279‐nm‐thick AZO film (1.8 wt%) grown at a substrate temperature of 230 °C in vacuum. From cross‐sectional TEM observations and the XRD spectrum, a reason why the low resistivity (54 × 10^?5Ω·cm) was reproducibly obtained was considered to be due to the fact that a disorder of crystal growth originating in the vicinity of the interface between the substrate and the film was suppressed by application of the magnetic field and the c‐axis orientation took preference, giving rise to the increase of mobility. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 40–45, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20026     

Determination of the π-Charge Distribution of the DMe-DCNQI Molecule in (DMe-DCNQI) 2 M, M=Li, Ag, and Cu

Solid state high-resolution NMR of ¹H and ¹³C along with ¹⁵N is analyzed to investigate the electronic states of the charge transfer salts (DMe-DCNQI)₂M, (M=Li, Ag, and Cu). We determined the spin/charge distribution in a DMe-DCNQI molecule of the Li-salt from the Knight shifts at each atom on the molecule. It is found that the obtained charge distribution is similar to the theoretical prediction. The charge density on the DCNQI molecules of the Ag-salt is found to be smaller by 20% than the Li-salt, which could be an origin of differences from the Li-salt. This result is consistent with the first principle calculations (Miyazaki and Terakura, Phys. Rev. B 54, 10452, 1996).     

Combustion behavior of a falling sodium droplet: Burning rate‐constant and drag coefficient

The combustion behavior of a single sodium droplet has been studied experimentally, by use of a falling droplet. It was found that D²‐law can hold for the sodium droplet combustion after the ignition, which can be observed to occur through an increase in the droplet temperature under a condition without a gaseous flame, suggesting that a surface reaction plays an important role in the ignition of sodium. It was also found that the burning rate‐constant without forced convection has nearly the same value as those for conventional hydrocarbon droplets, although it is considered that the sodium combustion proceeds in an oxidizer‐rich environment even in the air. This can be judged by comparing a temporal variation of the flame/droplet diameter ratio for the sodium droplet with that for the hydrocarbon droplet. A micro‐explosion of the burning droplet is also observed when oxygen concentration in the ambience exceeds 0.33 in mass fraction. As for the falling velocity and/or distance of the burning droplet, it turned out that the use of the drag coefficient for solid sphere under isothermal condition is inappropriate in obtaining accurate values. It was also found in another experiment that when Re > 500, the drag coefficient of the falling droplet undergoing combustion is as high as 2 depending on combustion situation and/or droplet temperature, while that of the solid sphere under an isothermal condition is 0.44. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 481–495, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20084     

Determination of the pre-exponential factor and the activation energy for the low-temperature dislocation relaxation in aluminum

The ultrasonic attenuation and the sound velocity at 10 MHz were measured in deformed Al single crystals in the temperature range between 1.5 and 50 K. In the high purity specimen (RRR=20 000) the change in sound velocity due to deformation shows a step in temperature dependence at 17 K, which corresponds to the 11 K relaxation peak at 50 kHz found by Kosugi and Kino [J. Phys. Soc. Jpn. 58 (1989) 4269], although the change in attenuation due to deformation was masked by the large background attenuation due to phonon–electron interaction. From the present experiment and that of Kosugi and Kino, the activation energy and the attack frequency of the relaxation process are estimated to be 14 meV and 1.0×10¹²/s, respectively. If the kink pair formation process of dislocations on the Peierls potential is responsible for this relaxation, the Peierls stress is 5.4×10⁻⁵G, where G is the shear modulus, and this value does not conflict with the flow stress at low temperatures.     

Thickness distribution of high-speed free-surface lithium flow simulating IFMIF target

International Fusion Materials Irradiation Facility (IFMIF) employs liquid lithium as D⁺ beams target. The liquid Li target is formed as flat plane free-surface flow by a nozzle and flows at high speed around 15 m/s. This paper focuses on flatness of the liquid Li target. The Li flow experiment was conducted in Osaka University Li Loop with a test section which was 1/2.5 scaled model of IFMIF. The thickness of the Li flow was measured and obtained by a contact method which was developed for the measurement. Analytical study on Kelvin wake and numerical calculation on the wake near the side wall of the flow channel were also conducted and compared with the experimental results. As a result, the positions of the wake crest obtained from both of the experiment and numerical calculation assuming contact angle 140° agreed well with the iso-phase line of the analytical model. The generation of the wake likely depends on wettability between Li and the structural material which is 304SS in the present study.