Characteristics of the Sn-Pb eutectic solder bump formed via fluxless laser reflow soldering

In an attempt to develop a fluxless reflow solder bumping process, the effects of processing variables, which include energy input rate and time, and the shape of solder disk on the microstructure of the solder/Cu pad interface and the shear strength of the joints were investigated. It was demonstrated that a proper combination of the variables could lead to the formation of a spherical solder bump with shear strength comparable to that formed via the conventional reflow soldering process. In addition, the kinetics of Cu pad dissolution into the solder during laser heating was modeled numerically to elucidate intermetallic formation mechanism at the solder/Cu pad interface. Jointly appointed by CAAM at POSTECH     

Room-temperature continuous-wave quantum cascade lasers grown by MOCVD without lateral regrowth

We report on room-temperature continuous-wave (CW) operation of /spl lambda//spl sim/8.2 /spl mu/m quantum cascade lasers grown by metal-organic chemical vapor deposition without lateral regrowth. The lasers have been processed as double-channel ridge waveguides with thick electroplated gold. CW output power of 5.3 mW is measured at 300 K with a threshold current density of 2.63 kA/cm/sup 2/. The measured gain at room temperature is close to the theoretical design, which enables the lasers to overcome the relatively high waveguide loss.     

Effect of Hot-Pressing Temperature on Densification and Mechanical Properties of Titanium Diboride with Silicon Nitride as a Sintering Aid

The effect of hot-pressing temperature on the densification behavior and mechanical properties of titanium diboride (TiB₂) was investigated. TiB₂ specimens were hot-pressed for 1 h at temperatures in the range of 1500°–1800°C, with an addition of 2.5 wt% of silicon nitride (Si₃N₄) as a sintering aid. The density increased markedly at temperatures in the range of 1500°–1600°C and remained constant thereafter. The formation of a eutectic liquid at 1550°C was attributed to the steep increase in density. The hot-pressing temperature also improved the mechanical properties, such as the flexural strength, Vickers hardness, and fracture toughness of the specimens. Similar to the density, the mechanical properties improved remarkably at ∼1550°C, so that optimum properties were obtainable at temperatures as low as 1600°C.     

Underground cavern development in the Jurong sedimentary rock formation

The Jurong Formation forms the west and southwest of the Singapore Island. The formation consists of sedimentary rocks of late Triassic to early Jurassic age. The rocks include various types of mudstone, sandstone, shale, conglomerate, phyllite, slate and limestone. They have been intensely folded with their structural strike generally oriented NW-SE and faulted with the faults generally aligned parallel with or perpendicular to the fold strike. The Jurong Formation has been studied for the potential development of rock caverns. Extensive investigations including geological mapping, seismic reflection surveys, and deep coring have been conducted. This paper presents some of the results from the investigations and discusses the potential of cavern development in the Jurong Formation.     

Formation of Barrier Ribs for Plasma Display Panels via a Powder-Blasting Process: Part I, Effects of Binder Content and Baking Treatment

The powder-blasting characteristics of a thick film prepared using a tape-casting process have been investigated. The powder-blasting process is commonly used in the manufacturing of barrier ribs of plasma display panels. The effects of binder content and baking temperature on the powder-blasting rate of the thick film have been studied. The rates observed are discussed based on the volume fraction of the pores and the degradation of binder during the baking treatment. In addition, the effect of powder-blasting resistance of thick film on the morphology of barrier ribs formed is examined.     

Kinetics of Au-containing ternary intermetallic redeposition at solder/UBM interface

In this study, the effects of the under bump metallurgy (UBM) structure and Cu content in solders on the redeposition rate of Au-containing ternary intermetallics at the solder/UBM interface were investigated. A UBM structure with a Ni diffusion barrier, Au/Ni/Cu, appeared to promote the redeposition of ternary Au-containing intermetallics at the solder/UBM interface of the ternary during the solid-state aging treatment and the Au-embrittlement of the solder interconnections. Copper added to the eutectic Sn-Pb and Sn-Ag solders was observed to be very effective in retarding the redeposition by forming the ternary intermetallics in solder matrices and preventing the Au-embrittlement. These phenomena were discussed with the microstructures observed. Jointly appointed by CAAM at POSTECH     

Zinc-doping of InP during chemical beam epitaxy using diethylzinc

Diethylzinc was used as ap-type dopant source during InP growth by chemical beam epitaxy. In InP, electrically activated Zn saturated at a concentration of ∼2.0 × 10¹⁸ cm⁻³ for epilayers grown at 540‡ C. Higher role concentrations were obtained by lowering the growth temperature. However, measurements with SIMS indicated that very serious Zn diffusion occurred when the Zn concentration appeared to reduce the pyrolysis efficiency of trimethylindium. This caused a reduction in the InP growth rate and InAs mole fraction in InGaAs epilayers. No Zn “memory effect≓ was detected in our system. Undoped InP epilayers maintained an n-type background of ∼5 × 10¹⁵ cm⁻³.     

High-speed modulation of vertical-cavity surface-emitting lasers

The IM (intensity modulation) and FM (frequency modulation) characteristics of vertical-cavity surface-emitting lasers are studied. The laser has high FM efficiency and broad IM bandwidth (near 8 GHz) at a very low bias (4.5 mA). Five Gb/s pseudorandom direct intensity modulation of this laser with open eyes is demonstrated.<>     

ppb-Level ethanol gas sensor of porous anodic aluminum oxide at room temperature

Excessive ethanol in breath can be an indicator of alcoholism and a biomarker of liver disease. Herein, we present a novel porous aluminum anodic oxide (AAO)-based chemi-capacitive sensor that can detect ppb-levels of ethanol gas at room temperature. The oxalic acid-based porous AAO is an amorphous material contaminated with Al(OH)₃ and C₂O₄²⁻ ions (anion-contamination), which react with adsorbed ethanol gas. The optimal resonance frequency of ethanol was determined to be 500 Hz, and the response to 200 ppm ethanol at this frequency was 1.56%. Especially, the limit of detection of ppb-level (16.49 ppb) was obtained. The detection range, reliability, and selectivity of the sensor, as well as its surface properties were comprehensively investigated. The proposed sensor is promising for the detection of liver disease as well as for commercial breath ethanol analyzers.