High Voltage Pulsed Power Supply Using IGBT Stacks

High voltage pulsed power supply using IGBT (insulated gate bipolar transistor) stacks and pulse transformer for plasma source ion implantation is proposed. To increase voltage rating, twelve IGBTs are used in series at each IGBT stack and a step-up pulse transformer is utilized. To increase the current rating, the proposed system makes use of synchronized three pulse generator modules composed of diodes, capacitors and IGBT stacks. The proposed pulsed power supply uses semiconductor switches as main switches. Hence, the system is compact, and has semi-infinite lifetime. In addition, it has high flexibility in parameters such as voltage magnitude (10-60 kV), pulse repetition rate (PRR) (10-2000 pps), and pulse width (2-5 muS).     

Dissolution of Cu into Sn-based solders during reflow soldering

Cu contents in pure Sn and Sn-37Pb solders were measured as a function of reflowing time. The results indicated that the contents are significantly higher than that of the Cu solubility limit in each solder. Several plausible causes for the excess dissolution of Cu into the solders were explored with experimental observations.     

Design and fabrication of a microlens on the sidewall of an optical fiber with a metallized 45 degrees end face

We propose a method for designing a self-aligned microlens. We have improved its fabrication by employing metallization on a 45 degrees angled surface of the optical fiber. We designed the focal length of the microlens to be 14.0 microm, considering the dimensions of a scanning near-field optical microscopy (SNOM) probe, and we calculated possible dimensions of diameter and height by the ray-tracing method. The modeling of lens formation was also carried out with two assumptions: no volume change and no movement of peripheral parts of the photoresist (PR) on the substrate during reflow. To fabricate a microlens of diameter 16.0 microm and height 5.0 microm we exposed a coated PR to UV light guided into the optical fiber, followed by optimized reflow of 150 degrees C for 2 min. For this microlens the focal length and the beam waist were 14.0 and 1.4 microm, respectively. This lens can be used for compact optical data storage.     

Optical characteristics of a refractive optical attenuator with respect to the wedge angles of a silicon optical leaker

We design, fabricate, and characterize the micromachined refractive variable optical attenuator (VOA) with a wedge-shaped silicon optical leaker (SOL). The vertical structures of the VOA device can be simply fabricated by deep reactive ion etching with no sidewall metallization, and the 8 degrees angled fibers are employed for a high return loss even in air-ambient conditions. The SOL successively transmits and refracts part of the incident light far outside the acceptance angle of the output fiber, showing an effective optical attenuation. The fabricated VOA gives high optical performances, such as a response time of 6 ms, a return loss of 39 dB, an insertion loss of 0.6 dB, an attenuation range of 43 dB, and a polarization-dependent loss (PDL) of a 10% attenuation level, including a wavelength-dependent loss. The optical characteristics of the VOA are also theoretically investigated with respect to the wedge angles of the SOL. The experimental characteristics are in good agreement with the theoretical values calculated, considering light scattered from the endface of an optical fiber and sidewall of the SOL. The PDL estimation was confirmed especially to sufficiently explain the fundamental characteristic of the PDL for the refractive VOA.     

Fatigue crack growth and fracture toughness properties of 304 stainless steel pipe for LNG transmission

The fatigue crack growth rate and fracture toughness tests of type 304 stainless steel were studied over a temperature range of −162°C to room temperature. Girth weld metal specimens were fabricated using a combination of gas-tungsten-arc-welding and shielded-metal-arc-welding. The seam weld metal was made with submerged arc welding. Fatigue crack growth rate tests were conducted using compact tension specimens in accordance with ASTM E647. Fracture toughness was evaluated through CTOD tests with three point bend specimens. The CTOD values were affected by crack orientation with respect to the rolling direction, but orientation had no influence on fatigue crack growth rates. The fatigue crack growth rates and the CTOD values decreased with decreasing test temperature.     

Laser soldering for chip-on-glass mounting in flat panel display application

Chip-on-glass (COG) mounting of area array electronic packages was attempted by heating the rear surfrace of a contact pad film deposited on a glass substrate. The pads consisted of an adhesion (i.e., Cr or Ti) and a top coating layer (i.e., Ni or Cu) was heated by an UV laser beam transmitted through the glass substrate. The laser energy absorbed on the pad raised the temperature of a solder ball which was in physical contact with the pad, forming a reflowed solder bump. The effects of the adhesion and top coating layer on the laser reflow soldering were studied by measuring the temperature profile of the ball during the laser heating process. The results were discussed based on the measurement of reflectivity of the adhesion layers. In addition, the microsctructures of solder bumps and their mechanical properties were examined.     

Copper lead frame: an ultimate solution to the reliability of BLPpackage

Copper lead frame was chosen as an on-board reliability enhancement for the BLP (bottom leaded plastic) package. Adopting the copper lead frame needed a verification process for the package reliability because of its high affinity with oxygen that degrades package reliability. A series of tests were performed to select the best copper material and to determine the adhesion index parameter. The experimental results showed that the adhesion strength between the copper lead frame and EMC (epoxy molding compound) was affected by alloy composition, oxide layer thickness, and cupric/cuprous oxide ratio, Among them, the adhesion index parameter proved to be the cupric/cuprous oxide ratio. When it falls between 0.2-0.3, the highest adhesion strength was obtained regardless of alloy composition and oxide thickness. From the adhesion test results, the Cr-Zr-Cu copper alloy was employed as the lead frame for the 54-pin BLP package. The package reliability and on-board reliability tests including surface mountability, mechanical robustness, and solder joint reliability were carried out to compare the 54-pin BLP package, with Cr-Zr copper alloy and alloy 42 lead frame     

Stretchable calix[4]arene-based gels by induction of water

This study focused on controlling the stretching property of gels. This resilience is dependent on the water content in the calix[4]arene-based gel solvent system, where the stretching property of gels could be controlled upon the addition of water. The storage (G′) and loss (G″) moduli of the calix[4]arene-based gels prepared in solvent systems with different water contents were investigated via rheological measurements. By the strain sweeps, the values of G′ decreased, while tan-delta increased with water content in the solvent system. In addition, a significant changes in the G′ and G″ values were observed upon the addition of water by frequency sweeps. In particular, the decrease in the G″ value of the gel prepared from the 1,3-alternated calix[4]arene derivative ( HC4 ) and diisocyanate linker ( HDI ) in DMSO/H₂O mixed solvent (8:2 v/v) was approximately 5-fold larger than that of the gel prepared in 100% DMSO. Thus, this novel approach would useful for the development of new soft materials with finely controllable mechanical properties.     

Acid tolerance and morphological characteristics of five Weissella cibaria bacteriophages isolated from kimchi

Food Science and Biotechnology - Five bacteriophages were isolated from kimchi with the hosts of two Weissella cibaria and acid-producing bacteria, and characterized for understanding Weissella...     

Development of new assay for sucrose phosphorylase and its application to the characterization of Bifidobacterium longum SJ32 sucrose phosphorylase

Sucrose phosphorylase, a hexosyltransferase, that is an important enzyme in starch and sucrose metabolisms, reversibly catalyzes the conversion of sucrose and orthophosphate to fructose and α-d-glucose-1-phosphate. A simple assay method for sucrose phosphorylase using 3,5-dinitrosalicylic acid (DNS) was developed. Its effectiveness was compared with that of a previously used NAD method. The results establish that the DNS method is comparable to the NAD method for the assay of sucrose phosphorylase. In particular, analysis of the enzyme activity level of sucrose phosphorylase (SPase) from Bifidobacterium longum SJ32 revealed that the DNS method is not only simple and accurate, but it also is a time-saving method for assaying sucrose phosphorylase activity. Most importantly, the DNS method is stable in broad pH ranges (pH 4–10), whereas the NAD method showed inaccurate profiles in the alkaline pH ranges (pH 8–10). Kinetic studies on SPase from B. longum SJ32 were performed using the simple DNS method developed in this study.