Thermal and mechanical stability of soldering QFP with Sn-Bi-Ag lead-free alloy

Thermal stability of the circuit boards with a quad flat package (QFP) soldered with Sn-58wt%Bi-(0, 0.5 and 1.0) wt% Ag and their microstructural features were evaluated. The addition of 1.0 wt% Ag causes the formation of large primary Ag/sub 3/Sn precipitates in the solder while no primary Ag/sub 3/Sn is found in Sn-57Bi-0.5Ag. Thermo-Calc calculation indicates that the lowest limit content for the formation of primary Ag/sub 3/Sn is about 0.8 wt%. Heat-exposure below 100/spl deg/C has no serious degradation on the joint structure for all solders. Heat-exposure at 125/spl deg/C caused serious degradation in joint strength for all alloys. The contamination of Pb from Sn-Pb surface plating on the components reduces the interface tolerance by forming ternary Sn-Pb-Bi phase melting at low temperature. Thermal fatigue between -20 and 80/spl deg/C does not have any significant influence on joint structure.     

Mechanical properties of amorphous alloy compacts prepared by different consolidation techniques

Amorphous alloy compacts of Fe₇₈B₁₃Si₉ prepared by three different techniques (explosive consolidation, high hydrostatic pressure consolidation and warm extrusion) were deformed in compression between 573 and 723 K at a strain rate ranging from 8.3×10^–5–4.2×10^–4s^–1. Explosively consolidated compacts had high strength ranging from 1.9–2.5 GPa below 623 K and could be plastically deformed to a strain of more than 50% at 673 K while preserving the amorphous state. Amorphous alloy compacts prepared by high hydrostatic pressure consolidation showed lower compressive strength. Those produced by warm extrusion were anisotropic in strength, the highest strength being as high as 2.74 GPa. It was also found that the geometry of the starting powders had a profound effect on the strength of the product compacts. Compacts prepared from flaky powders were stronger than those prepared from spherical ones. It is concluded that the mechanical properties of the amorphous alloy compacts depend on the consolidation technique, powder geometry and surface conditions of the powders, especially existence of oxide films.     

Transparent Hydroxyapatite Prepared by Hot Isostatic Pressing of Filter Cake

Hydroxyapatite powder was synthesized and formed into a compact in an aqueous medium using a filter-cake method. The compact was hot isostatically pressed at 700° to 1000°C and 100 MPa for 2 h. Fully dense, transparent materials were obtained above 800°C. Both forming and densification methods were found to be important in obtaining transparent materials.     

GaAs lateral bipolar transistor with field-separated carriers

A new type of GaAs lateral bipolar transistor has been developed by introducing an n-i-p-i-n structure where the electric field is applied perpendicular to the direction of carrier injection in order for the carriers to be separated. The diffusion length is increased owing to the increase of lifetime due to the spatial separation of injected carriers, resulting in the increase of current gain.     

Reduction of irreversible capacities of amorphous carbon materials for lithium ion battery anodes by Li2CO3 addition

Amorphous carbon materials for lithium ion battery anodes which contain a small amount of Li₂CO₃ were prepared by three methods. The obtained materials were characterized using X-ray diffraction (XRD) analysis, Raman spectroscopy and CO₂ adsorption experiments. Although the XRD profiles and Raman spectra of these materials were similar to those of carbon materials synthesized with no addition, the amount of CO₂ adsorbed was largely decreased by Li₂CO₃ addition. These results suggest that the micropores in these materials were plugged and/or filled with Li₂ CO₃. Galvanostatic lithium charging and discharging experiments showed that the irreversible capacity of the material can be significantly decreased by Li₂CO₃ addition, which is thought to be due to the plugging of the pore inlets by Li₂CO₃. Moreover, it was also found that the reversible capacities of the materials can be increased by adjusting both the amount of Li₂CO₃ addition and carbonization temperature.     

Principal decomposition by-products generated at variousabnormalities in gas-insulated transformers

Gas analysis provides a promising means for a diagnosis of gas-insulated equipment. Although many studies have been concentrated on SF₆ gas decomposition, they were mostly related to the faults in GIS systems and not directly applicable to gas-insulated transformers, which have much more complicated material structure. An experimental survey on decomposition by-products at various abnormal conditions was carried out by use of simulation models to develop a diagnostic method for gas-insulated transformers based on gas and ion chromatograph analyses. Major components characteristic in each abnormality, such as SO₂ on metal overheat, SO₂F ₂ on partial discharges, etc. were identified by the experiments     

Stereospecific analysis of triacyl-sn-glycerols by chiral high-performance liquid chromatography

A method for the stereospecific analysis of triacyl-sn-glycerols by high-performance liquid chromatography (HPLC) on a chiral column is described. Triacyl-sn-glycerols were partially degraded with ethyl magnesium bromide, and the monoacylglycerols produced were separated as 1- and 2-monoacylglycerol fractions by thin-layer chromatography on boric acid-impregnated silica gel plates. The 1-monoacylglycerols were resolved intosn-1 andsn-3 monoacylglycerol fractions by HPLC on a chiral column (Sumichiral OA-4100) after derivatization with 3,5-dinitrophenyl isocyanate. Fatty acid methyl esters obtained from the original triacyl-sn-glycerols, 1- and 2-monoacylglycerol fractions, andsn-1 andsn-3 monoacylglycerol fractions were analyzed by gas chromatography on open-tubular columns. Stereospecific acyl distributions in triacyl-sn-glycerols were calculated from the data. The acyl distributions of several oils were obtained. The method is rapid, simple and gave reproducible results.     

A new high-density fiber organizer for optical-fiber cable joints

A new slack fiber organizer structure composed of individual box-shaped plastic sheets is presented. It is capable of accommodating 800 fiber splices with the same size as the existing metallic cable joints. The conditions to accommodate reinforced mass-splices and slack fibers into the organizer are clarified by considering optical loss increase and reliability evaluation for bent fiber ribbons, and also a computer-aided dimension simulation. The new organizer with 800 fiber splices experimentally exhibits good transmission characteristics with an average slack fiber accommodation loss of 0.04 dB and a good workability of 1.2 min/ribbon.