Al surface morphology effect on flip-chip solder bump shear strength

This paper reports the result of a study on the effect of aluminum pad surface morphology on the flip-chip solder bump reliability. The influence of the Al surface morphology on the electroless zinc/nickel/gold UBM is presented. The reliability of the solder bump as measured by ball shear force is reported. Al pad were produced using two RF sputtering systems: CVC-601 and Varian-3180. The Al targets used in CVC and Varian system were 99%Al–1%Si and 98.95%Al–1%Si–0.05%Ti respectively. The surface of the CVC sputtered Al samples were smooth while the surface of the Varian sputtered Al samples were rough. All the samples were subjected to the electroless zinc/nickel/gold plating. The results suggest that after plating, the smooth Al surface resulted in a fine nickel UBM surface while the rough Al surface formed a coarse nickel UBM surface. Ball shear test was conducted after the solder balls were bumped on the UBM. Result shows that the fine UBM surface samples have twice the shear strength compared to the samples with coarse UBM surface samples. The analysis of the results indicates that shear surface occurred at the UBM and the solder interface for samples with rough UBM surface leading to the lower shear strength. Nickel bump shear test result shows that pretreatment of Al pad surface by sodium hydroxide and nitric acid created more zinc seeds this led to better electroless nickel plating. Nickel bump shear tests also shows that double zincated bumps had higher shear strength than single zincated bumps. To obtain reliable flip-chip solder bumps, it is essential to maintain good Al pad surface morphology, pretreatment of the Al pad and undergo second zincation.     

Facile Generation of L10‐FePt Nanodot Arrays from a Nanopatterned Metallopolymer Blend of Iron and Platinum Homopolymers

Hard ferromagnetic (L1₀ phase) FePt alloy nanoparticles (NPs) with extremely high magnetocrystalline anisotropy are considered to be one of the most promising candidates for the next generation of ultrahigh‐density data storage system. The question of how to generate ordered patterns of L1₀‐FePt NPs and how to transform the technology for practical applications represents a key current challenge. Here the direct synthesis of L1₀ phase FePt NPs by pyrolysis of Fe‐containing and Pt‐containing metallopolymer blend without post‐annealing treatment is reported. Rapid single‐step fabrication of large‐area nanodot arrays (periodicity of 500 nm) of L1₀‐ordered FePt NPs can also be achieved by employing the metallopolymer blend, which possesses excellent solubility in most organic solvents and good solution processability, as the precursor through nanoimprint lithography (NIL). Magnetic force microscopy (MFM) imaging of the nanodot pattern indicates that the patterned L1₀ phase FePt NPs are capable of exhibiting decent magnetic response, which suggests a great potential to be utilized directly in the fabrication of bit patterned media (BPM) for the next generation of magnetic recording technology.     

A tight upper bound on discrete entropy

The standard upper bound on discrete entropy was derived based on the differential entropy bound for continuous random variables. A tighter discrete entropy bound is derived using the transformation formula of Jacobi theta function. The new bound is applicable only when the probability mass function of the discrete random variable satisfies certain conditions. Its application to the class of binomial random variables is presented as an example     

Gordon-Haus timing jitter reduction in dispersion-managed solitoncommunications

An analytic theory is presented which demonstrates that the noise induced Gordon-Haus timing jitter in arbitrary dispersion-managed transmission systems is reduced by the power-enhancement factor required to support a dispersion-managed solitons provided the path-average soliton period is much greater than the dispersion-map period. The analysis further predicts the behaviour of the amplitude, width, and quadratic chirp fluctuations due to the amplified spontaneous emission (ASE) noise     

Ideal amplifier spacing for reduction of Gordon-Haus jitter indispersion-managed soliton communications

Based on a variational analysis, the authors demonstrate that the noise-induced Gordon-Haus timing jitter in a dispersion-managed soliton transmission system can be substantially reduced by appropriate placement of the amplifiers     

Microclimatic modeling of the urban thermal environment of Singapore to mitigate urban heat island

This study investigates the urban heat island effect in Singapore and examines the key factors causing this effect. The possibilities of improving heat extraction rate by optimizing air flow in selected hot spots were explored. The effect of building geometry, façade materials and the location of air-conditioning condensers on the outdoor air temperature was explored using computational fluid dynamics (CFD) simulations. It was found that at very low wind speeds, the effect of façade materials and their colours was very significant and the temperature at the middle of a narrow canyon increased up to 2.5 °C with the façade material having lower albedo. It was also found that strategically placing a few high-rise towers will enhance the air flow inside the canyon thereby reducing the air temperature. Adopting an optimum H/W ratio for the canyons increased the velocity by up to 35% and reduced the corresponding temperature by up to 0.7 °C.     

Efficient routing for IP subnet VLAN over Ethernet

Existing IP routing algorithms have been developed mainly for non‐VLAN networks. For these routing algorithms to work, an end station must be attached to its associated network. The introduction of VLAN has, however, allowed the physical location of the end station to be changed from time to time. Therefore, some extra mechanism is required to support routing in VLAN environment. Existing approaches have some drawbacks in terms of inefficiency in traffic forwarding and switch software complexity. In this paper, a simple and efficient method for routing over IP subnet VLAN in Ethernet is proposed. This method has been implemented in hardware and found to work correctly. Various measurements and analyses have been performed to verify the efficiency of this protocol. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of Oligothienyl Chain Length on Tuning the Solar Cell Performance in Fluorene‐Based Polyplatinynes

A series of solution‐processable and strongly visible‐light absorbing polyplatinynes containing oligothienyl–fluorene ring hybrids were synthesized and characterized. These rigid‐rod organometallic materials are soluble in polar organic solvents and show intense absorptions in the visible spectral region, rendering them excellent candidates for bulk heterojunction polymer solar cells. The photovoltaic behavior depends significantly on the number of thienyl rings along the polymer chain, and some of these polymer solar cells show high power conversion efficiencies (PCEs) of up to 2.9% and a peak external quantum efficiency to 83% under AM1.5 simulated solar illumination. The effect of oligothienyl chain length on improving the polymer solar cell efficiency and on their optical and charge transport properties is elucidated in detail. At the same blend ratio of 1:5, the light‐harvesting capability and PCE increase markedly with increasing number of thienyl rings. The power dependencies of the solar cell parameters (including the short‐circuit current density, open‐circuit voltage, fill‐factor, and PCE) were also examined. The present work opens up an attractive avenue to developing conjugated metallopolymers with broad and strong solar energy absorptions and tunable solar cell efficiency and supports the potential of metalated conjugated polymers for efficient power generation.     

Ultrawide-band La-codoped Bi/sub 2/O/sub 3/-based EDFA for L-band DWDM systems

The demonstration of a 253-cm-long lanthanum-codoped Bi/sub 2/O/sub 3/-based erbium-doped fiber which provides gain of greater than 20 dB and noise figure less than 6.7 dB to 142 dense wavelength-division-multiplexing channels simultaneously over an extended wavelength range of 58 nm from 1554 to 1612 nm is reported. The 3-dB (gain of 17-20 dB) bandwidth of the erbium-doped fiber amplifier is 54 nm when it is pumped with 350 mW of 1480-nm light. The power conversion efficiency of the fiber is about 54%.     

Haptic information in Internet-based teleoperation

Many tasks can be done easily by humans turn out to be very difficult to accomplish with a teleoperated robot. The main reason for this is the lack of tactile sensing, which cannot be replaced by visual feedback alone. Once haptic devices are developed, their potential in many fields is obvious. Especially, in teleoperation systems, where haptic feedback can increase the efficiency and even render some tasks feasible. This paper studies Internet-based teleoperation systems that include haptic feedback, concentrating on the control of such systems and their performance. The potential of this technology and its advantages are explored. In addition, key issues, such as stability, synchronization, and transparency are analyzed and studied. Specifically, an event-based planning and control of Internet-based teleoperation systems is presented with experimental results of several implemented system scenarios in micro- and macro-scales