bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Bonding and Modeling for Wafer-Level and Chip-Scale Packaging of Micro-Electro-Mechanical Systems
Authors: Tao Yi , Malshe Ajay P. , Brown W. D.
Published: June 2008

In this work, low temperature selective solder (Pb37/Sn63) bonding of silicon chips or wafers for MEMS applications using a continuous wave (CW) carbon dioxide (CO2) laser at a wavelength of 10.6μm was examined. The low reflectivity, fair transmittance, and high absorptivity of silicon at the 10.6μm wavelength led to selective heating of the silicon and reflow of an electroplated or screen printed intermediate solder layer which produced silicon-solder-silicon joints. Finite element simulations were carried out to optimize the process parameters in order to achieve uniform heating and minimum induced thermal stress. The bonding process was performed on the fixtures in a vacuum chamber at an air pressure of one milliTorr to achieve fluxless soldering and vacuum encapsulation of silicon dies. The bonding temperature at the sealing ring was close to the reflow temperature of the eutectic lead tin solder, 183°C. Pull test results showed that the joint was sufficiently strong and could not be separated before the silicon die broke. Helium leak testing showed that the leak rate of the package was below 10−8 atm · cc/sec under optimized bonding conditions. The results of the Design of Experiment (DOE) method indicated that both laser incident power and scribe velocity significantly influenced bonding results. This novel method is especially suitable for vacuum bonding wafers containing MEMS and other micro devices with low temperature budgets where managing stress distribution is important. Further, sealed encapsulated and released wafers can be diced without damaging the MEMS devices at wafer scale.
Low Temperature Anodic Bonding for MEMS Applications
Authors: Wei J. , Wang Z. P. , Wang L. , Li G. Y. , Mo Z. Q.
Published: June 2008

In this paper, anodic bonding between silicon wafer and glass wafer (Pyrex 7740) has been successfully achieved at low temperature. The bonding strength is measured using a tensile testing machine. The interfaces are examined and analyzed by scanning acoustic microscopy (SAM), scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). Prior to bonding, the wafers are cleaned in RCA solutions, and the surfaces become hydrophilic. The effects of the bonding parameters, such as bonding temperature, voltage, bonding time and vacuum condition, on bonding quality are investigated using Taguchi method, and the feasibility of bonding silicon and glass wafers at low temperature is explored. The bonding temperature used ranges from 200 °C to 300 °C. The sensitivity of the bonding parameters is analyzed and it is found that the bonding temperature is the dominant factor for the bonding process. Therefore, the effects of bonding temperature are investigated in detail. High temperatures cause high ion mobility and bonding current density, resulting in the short transition period to the equilibrium state. Almost bubble-free interfaces have been obtained. The bonded area increases with increasing the bonding temperature. The unbonded area is less than 1.5% within the whole wafer for bonding temperature between 200 °C to 300 °C. The bonding strength is higher than 10 MPa, and increases with the bonding temperature. Fracture mainly occurs inside the glass wafer other than in the interface when the bonding temperature is higher than 225 °C. SIMS results show that the chemical bonds of Si-O form in the interface. Higher bonding temperature results in more oxygen migration to the interface and more Si-O bonds. The bonding mechanisms consist of hydrogen bonding and Si-O chemical reaction.
A Statistical Approach to Improve Wafer Fabrication Yield
Authors: Barakat Nael , Enshasy Hesham
Published: June 2008

In spite of the recent advancements in wafer fabrication techniques, devices are still being individually checked and modified. This is due to the fact that the general manufacturing processes involved in wafer production have their inherent inconsistencies. As a consequence, individual devices show differences in characteristics that would render a big group of them operating out of the range of the pre-set spec limits. Therefore they would require types of modifications specific to the individual device. Knowing that the resources spent on checking and eliminating out-of-spec devices before they reach the customer are very significant, the manufacturing operation becomes hardly profitable. These wafers normally carry devices in the range of a thousand or so, making a statistical approach very attractive. In this paper, an actual industrial problem in wafer fabrication to the desired specifications is presented. The problem shows in passive filters built using Surface Acoustic Wave (SAW) theory. A solution considering a statistical process control approach to the population of devices on the wafer is proposed. The results of applying this solution are realized in significant product yield increase, huge cost cutting, and automation promotion and application.
On the Mathematical Modeling of Heat Transfer Characteristics of Turbulent Flames in Industrial Furnaces
Authors: Khalil Essam E.
Published: June 2008

The recent advances in numerical methods and the vast development of computers had directed the designers to better development and modifications to air flow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the combustor zones and to reduce the emitted pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The present work fosters mathematical modeling techniques to primarily predict what happens in three-dimensional combustion chambers simulating boiler furnaces, areo engines in terms of flow regimes and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance, wall heat transfer under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent pressure gradients, turbulence and viscous action. The physical and chemical characteristics of the air and fuel are obtained from tabulated data in the literature. The flow regimes and heat transfer play an important role in the efficiency and utilization of energy. The results are obtained in this work with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl with liquid or gaseous fuels. The present numerical grid arrangements cover the combustion chamber in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations is typically less than 0.001%. The obtained results include velocity vectors, turbulence intensities and wall heat transfer distributions in combusors. Examples of large industrial furnaces are shown and are in good agreement with available measurements in the open literature. One may conclude that flow patterns, turbulence and heat transfer in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry. Both micro and macro mixing levels are influential. The present modeling capabilities can adequately predict the local flow pattern and heat transfer characteristics in Complex combustors. Proper representation of the heat transfer and radiation flux is important in adequate predictions of large furnace performance.
The Application of a Two-Dimensional Zone Model to the Design and Control of a Continuously Operated, Gas-Fired Furnace
Authors: Correia Sara A. C. , Ward John
Published: June 2008

This paper describes the development of a two-dimensional zone model to predict the throughput and thermal performance of a continuously operated gas-fired furnace heating steel bars to a nominal discharge temperature of 1250°C. Ultimately the model is intended to be a tool which can be used for the design and control of industrial furnaces. Consequently relatively short computing times are necessary and this was achieved by employing an isothermal computational fluid dynamics simulation to estimate the relative mass flows, and hence enthalpy flows to or from adjacent volume zones in the overall model. This simplified approach, which utilises a single “once off” isothermal computation of the flows, was considered to be adequate since isothermal flow models have been used successfully in the past to study the flow related behaviour of combustion systems. The coupling of a multi-zone model with a single “once off” isothermal computation of the flows enables a wide range of furnace design modifications to be studied quickly and easily. To illustrate the potential use of the model in a furnace design application, it was then used to investigate the effects of inclining the burners downwards towards the load as well as those associated with increasing the length of the furnace.
A New Surface Modification Method to Alleviate Stiction of Microstructures
Authors: Lee Cheng-Chang , Hsu Wensyang
Published: June 2008

Modification on surface roughness has been shown effectively to alleviate both release and in-use stiction in the previous literatures. However, the modified materials in the previously reported methods were limited to polysilicon or single crystalline silicon with special properties. Here, the proposed modification method not only can apply to silicon without extra property requirements, but also has potential to modify other materials, such as oxide, nitride, and some metals. The process combined spin-on photoresist and reactive ion etching (RIE). The proposed low temperature process is simple, and no extra mask is needed. Consequently, there is more flexibility to add the roughness modification to the original fabrication process of micro devices. In this study, polysilicon and silicon nitride are demonstrated as the modified materials. Then the anti-stiction effect is characterized by calibrating the detachment lengths of released cantilevers and water contact angle on the modified surface. The experimental results show that the detachment length is almost twice longer than the cantilevers without modified substrate, where the interfacial surface energy between solids is reduced about fifteen times. Besides, polysilicon with a nearly hydrophobic surface is obtained after the modification process.
Mixing Field Analysis of a Gas Turbine Burner
Authors: Flohr Peter , Schmitt Patrick , Paschereit Christian Oliver
Published: June 2008

An analytical and numerical study has been carried out with the view on the understanding of the physical mechanisms of the mixing process in a gas turbine burner. To this end, three methods at various levels of approximation have been used: At the simplest level an analytical model of the burner flow and the mixing process has been developed. It is demonstrated how this approach can be used to understand basic issues of the fuel-air mixing and how it can be applied as a design tool which guides the optimisation of a fuel injector device. At an intermediate level of approximation, steady-state CFD simulations, based on the k–ε- and RSM-turbulence models are used to describe the mixing process. All steady simulations fail to either predict the recirculation zone or the turbulence level correctly, and can therefore not be expected to capture the mixing correctly. At the most involved level of modelling time-accurate CFD based on unsteady RSM and LES-turbulence models are performed. The simulations show good agreement with experiments (and in the case of LES excellent agreement) for both, velocity and turbulence fields. Mixing predictions close to the fuel injectors suffer from a simplification used in the numerical setup, but the mixing field is predicted very well towards the exit of the burner. The contribution of the asymmetric coherent flow structure (which is associated with the internal recirculation zone) to the mixing process is quantified through a triple decomposition technique.
Plasma Sheath Modeling in the Presence of Collisions
Authors: Roy Subrata , Poggie Jonathan , Gaitonde Datta V.
Published: June 2008

The present work develops a finite element discretized one-dimensional formulation for plasma-sheath dynamics, using multi-fluid equations. The applications include dc and rf sheath inside a glow discharge tube and a partially ionized plasma sheath inside a electric propulsion thruster channel. Based on the experimental data for multiple ionization of a noble gas, a third order polynomial has been used as a fit to describe ionization processes. Such a polynomial has been used to self-consistently calculate the rate of ionization in the plasma dynamic equations. The electron and ion number densities of the numerical solution decrease in the plasma-sheath region as expected. The ion velocity, sheath potential and electron temperature profiles also exhibit the expected behavior. The computed sheath potential compares well with the available experimental data. The model needs to be generalized in the near future for potential application to the high-speed air vehicles.
Analysis of the Possibility to Simulate a 3D Single-Roll Burnishing Process Using FEA
Authors: Neagu-Ventzel Sorin , Luca Liviu C. , Cioc Sorin , Marinescu Ioan
Published: June 2008

This simulation follows research conducted at The University of Toledo on single roll burnishing. A couple of FEM models using a commercial software have been developed for investigating stress and strain distribution within the workpiece material. Based on the data collected and analyzed from both a simulated and experimental indentation, adjustment of the initial surface of roll was performed, so that to correspond to the final shape of the real roll when the nominal load is reached. Finally, the burnishing process is simulated and some results are shown. The model developed in this paper could be used to predict stress and strain distribution in the workpiece material.
Predictions of the Transport and Dispersion of a Power Plant Plume for Hilly Terrain Computed With AEROMOD and Measured in a Wind Tunnel
Authors: Stock David E. , Lamb Brian , Hoffman Mark
Published: June 2008

Wind tunnel simulations and computations with AERMOD were used to investigate the impact of the emission from a proposed gas-turbine heat-recovery plant. The plant will be located near a university and has 80 m hills to the south and east. Seasonal meteorological conditions required by AERMOD were obtained from a regional airport 80 miles from the site. AERMOD was best suited for obtaining 3-hour, 24-hour, and yearly averaged worst conditions and for determining the drainage flow into a small river valley in the general vicinity of the plant. The wind tunnel was well suited for studying the impact of the plume on buildings and the hills surrounding the plant. In general the wind tunnel-measured impact was higher that predicted by AERMOD, but both data sets followed the same trends with higher concentration at sites near the plant when the wind speed increased and as the stack height was shortened. A one-to-one comparison of the predictions was not possible.
Stress and Deflection Analysis of a Glass Window (Circular Plate) Elastically Restrained Along Its Edge in a Photonic Device
Authors: Lau John H. , Erasmus Steve , Zou Yida
Published: June 2008

An exact analysis is presented for the stresses and deflections of circular plates (glass windows) elastically restrained along its edge in a photonic device’s housing subjected to the pressure and temperature loadings. Dimensionless curves and charts are also provided for engineering practice convenience. These charts show the interactions of the deflection, stress, temperature, pressure, linear spring constant, rotational spring constant, geometry of the glass windows, and the Young’s modulus, Poisson’s ratio, thermal coefficient of expansion, geometry, stress-optical coefficient, and birefringence of glass materials. The results presented herein should be useful for designing glass windows for shipping, storing, handling, functioning, and reliability.
Analytic Characterization of Area Array Interconnect Shear Force Behavior
Authors: Barker Donald B. , Mager Brent M. , Osterman Michael D.
Published: June 2008

Shear forces in the interconnects of electronic devices can cause electrical opens, which result in device failure. The shear forces are often caused by the thermal expansion (CTE) mismatch between a component and the printed wiring board (PWB). In this paper, an elastic strength of materials analytic model, which is demonstrated by Vandevelde [21], is used to characterize the interconnect shear force behavior in area array packages. The benefit of modeling the shear forces is that they can be related to the device life, a relationship obtained by converting shear to average stress, which can be converted to strain and used as input in a failure model equation. The most significant characterization that will be presented is that the maximum shear force behavior in the outermost interconnects can be characterized by three distinct regions of maximum shear force behavior.
Opportunities and Challenges in Micropump Technology
Authors: Darabi J. , Wang H.
Published: June 2008

The rapidly growing applications in micro fluidic systems, biotechnology, micro chemical analysis systems, drug delivery systems, and chip-integrated cooling systems has introduced new opportunities and challenges in developing micropumps. Micropumps are one of the crucial components for moving liquids in these miniaturized systems. In this article, the focus is placed on both fundamental scientific and application specific issues. First, a brief review of the growing need for micropumps and the state of the art materials and fabrication technologies is presented. Next, the various pumping techniques, their working principle and their potential applicability to the future development of cost-effective miniature systems are discussed. Finally, selected results of an electrohydrodynamic micropump are presented.
Numerical and Experimental Study of Impeller Diffuser Interaction
Authors: Mekhail Tarek , Du Zhaohui , Jansen Willem , Chen Hanping
Published: June 2008

The unsteadiness of the flow at the leading edge of a vaned diffuser represents a source of low efficiency and instability in a centrifugal turbomachine. Furthermore, the internal flow of the impeller can be affected by asymmetric downstream conditions, which results in extra flow unsteadiness and instabilities. Numerical and experimental data are obtained. The simulation of impeller diffuser interaction is performed using CFX-Tascflow. A frozen rotor simulation is used for the steady calculation and a rotor-stator simulation is used for the unsteady calculation using the steady results as an initial guess. The unsteady simulation is done not only for one impeller and diffuser blades, but also for the whole impeller and diffuser blades using Unix workstation. For the experimental work, a transparent fan is design and tested at The Turbomachinery Laboratory of SJTU. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A particle image velocimeter (PIV) is used to measure the 2-D instantaneous velocity in the interaction region between impeller, vaned. A series of performance measurements were carried out at different speeds. The first trial of measuring the instantaneous flow field in a part of the impeller and vaned diffuser together at different relative locations between them is presented in this work at different flow rates. Obtaining detailed measurements in the interaction region between the impeller and diffuser can help in understanding the complex flow phenomena and improving centrifugal fan and compressor performance. Finally, the comparison between the unsteady measurements and unsteady calculations showed that the Rotor/Stator Model can predict the basic characteristics of unsteady flow in centrifugal fan but still need improvement to satisfy the true transient simulation for unsteady impeller diffuser interaction.
The Challenge of Design and Optimisation of Centrifugal Compressors for the UK’s Largest Producing Offshore Gas Field
Authors: Akhtar M. S. , Clark Simon
Published: June 2008

The South Morecambe Field, owned and operated by Hydrocarbon Resources Ltd (a wholly owned subsidiary of Centrica PLC), has proved and probable reserves of 5.3 tcf and is located offshore in the East Irish Sea. With a plateau production rate of 1800mmscfd, the field delivered up to 20% of the UK peak gas demand.
Mixing and Combustion Improvement Using Jet Injection Into Swirling Flowfields
Authors: Lilley David G.
Published: June 2008

The aerodynamics benefits of lateral jet injection into swirling crossflow have long been recognized and used by combustion engineers. Studies are reported here on experimental and theoretical research on lateral jet injection into typical combustor flowfields for low-speed turbulent swirling flow conditions in the absence of combustion. The main flow is air in a round cross-sectioned plexiglass tube. The degree of swirl can be varied by varying the angles of the blades of an annular swirler, located upstream of the test section. Lateral jet injection is normal to the main airflow, from round-sectioned nozzles. Either a single lateral jet or two diametrically opposed jets are used for this secondary injection of air into the main airflow. The principal aim is to investigate the trajectory, penetration and mixing efficiency of the lateral injection. Flow visualization with helium-filled soap bubbles and multi-spark ionized path techniques, five-hole pitot probe time-mean velocity measurements, and single-wire time-mean velocity and turbulence data (normal and shear stress) have been obtained in the experimental research program. A fully three-dimensional computer code with two-equation turbulence model has been developed and used in the theoretical research program.
Thermal Crack Development and Wheel Useful Life
Authors: Sarunac Radovan
Published: June 2008

The impact of thermal crack development on the wheel useful life was investigated. The actual data from the “Railroad” has been actively and intensely reviewed. Initial efforts were concentrated on the wheel metallurgy, thermal crack development mechanism and maximum allowable operating speeds on each line. Recent efforts have concentrated on the braking control and associated equipment configuration. The effect of worn wheel and repetitive braking was also investigated. However, it is difficult to postulate alternative approaches to managing wheel useful life without completely identifying existing operating policies and maintenance procedures, and without establishing measurable results of such policies/procedures. It is also crucial to understand the physical process involved. This process will be repeated with every brake application in combination with the residual compressive stress (due to rolling and battering of the wheel on the rail and by rim-quenching) causing the cyclic stressing of the material due to thermal expansion, i.e., “thermal fatigue”. Higher brake rate and higher tread to disc brake ratio lead to higher temperature gradient and higher compression stresses (higher portion of stress in plastic range). In addition, the microstructure change in the surface zone material involves additional uncertainty, i.e., the existence of material of unknown physical properties (perlite transformation in to spheroidite). The presence of spheroidite is a good indication that a wheel tread has been subjected to direct thermal damage. It is a common conclusion based on two completely independent research projects that the combination of heat and compression increases hardness and yield strength. The maximum wheel temperature has a major impact on microstructure changes of the wheel surface layer. Also a smaller wheel diameter yields to higher maximum tread temperature. Various studies relating new and worn wheel clearly show the impact.
Scaled Room Three-Dimensional Computational Fluid Dynamics Simulations
Authors: O’Halloran Steven P. , Hosni Mohammad H. , Beck B. Terry , Gielda Thomas P.
Published: June 2008

Computational fluid dynamics (CFD) simulations were used to predict three-dimensional flow within a one-tenth-scale room. The dimensions of the scaled room were 732 × 488 × 274 mm (28.8 × 19.2 × 10.8 in.) and symmetry was utilized so that only half of the room was modeled. Corresponding measurements were made under isothermal conditions and water was used as the working fluid instead of air. The commercially available software Fluent was used to perform the simulations. Two turbulence models were used: the renormalization group (RNG) k-ε model and the Reynolds-stress model. The CFD setup is presented in this paper, along with the velocity and turbulent kinetic energy results. The simulation results are compared to previously obtained three-dimensional particle image velocimetry (PIV) measurements made within the same scaled room under similar conditions.
Performance Analysis of Brayton and Rankine Cycle Microsystems for Portable Power Generation
Authors: Mu¨ller Norbert , Fre´chette Luc G.
Published: June 2008

The presented work analyses the design space and performance potential of microfabricated Brayton cycle and Rankine cycle devices, accounting for lower component efficiencies, temperatures limited by the material properties and system implementation—constraints imposed by silicon microfabrication and miniaturization. By exploring the design space of such microsystems, their potential thermal efficiency and power density are defined. Results for both types of devices are shown graphically and design challenges and guidelines are determined and found to be different from their large-scale counterparts. Similar analysis was performed for Brayton and Rankine cycle devices, with more complete assessment of the latter by including, windage, generator, conductive and heat sink losses. In contrast to the Brayton cycle, the compression work of the Rankine cycle is minimal and the pump efficiency is not critical. The investigation suggests a higher potential for Rankine cycle devices than for Brayton cycle devices.
Thermal Sensation Under Unsteady Thermal Environments
Authors: Masuoka Takashi , Takatsu Yasuyuki , Kohri Itsuhei
Published: June 2008

As the absolute level of thermal sensation is vague for human beings, one cannot correctly select the absolute level of the multi-point thermal sensation scale with any kinds of precise classification. To achieve a breakthrough in such a situation, we propose a new voting method based on the relative change of thermal sensation, and investigate the thermal sensation under the unsteady thermal environments. It is shown that the new voting method is essential for the evaluation of thermal sensation under the unsteady environments and brings some aspects of the thermal sensation under the unsteady environments. Furthermore, we discuss the standardization of the thermal sensation in detail, and propose a new parameter for the standardization.
Analytical Expressions for Shear and Axial Joint Deformations in Area-Array Assemblies Due to Global CTE Mismatch
Authors: Heinrich S. M. , Shakya S. , Lee P. S. , Liang J.
Published: June 2008

In a previous study the authors derived an analytical expression for calculating the maximum shear deformation, (Δu)max, in an area array of solder joints under global CTE mismatch loading. The result was expressed in the form (Δu)max = βsh(Δu)0, where βsh fish is the “shear correction factor” and (Δu)0 is the commonly used and easily calculated estimate of shear deformation, which is based on the free thermal expansion of component and substrate. A key assumption in the previous model was that warping of the assembly was neglected. In the present work the companion problem of assembly warpage is treated, the results of which are analytical expressions for the maximum axial deformation in the array, (Δw)max. The present results are cast in the form of an “axial correction factor,” βax, to be applied to the same convenient reference deformation: (Δw)max = βax(Δu)0. Exact solutions are presented for several cases of practical interest: (1) an assembly in which the component and substrate have the same plan dimensions, (2) a rigid-substrate assembly, and (3) a rigid-component assembly. In addition, approximate expressions are presented in simple analytical form for the case in which the array is relatively flexible in comparison with the component and substrate. When combined with the previous solution for array shear deformation, the present results may be viewed as furnishing the complete solution to the thermal deformation problem for area-array assemblies of the types considered. The analytical results clearly indicate the relationship between the correction factors and the physical parameters of the problem: (a) the dimensions and material properties (elastic and thermal) of the component and substrate; (b) the material properties of the interconnect material (effective Young’s modulus and Poisson’s ratio); (c) the array size and population; and (d) the geometric parameters of the individual joints. An interesting and potentially useful conclusion is that the sign of the maximum axial deformation (tension or compression) in the corner joints can be related to the sign of a very simple expression that depends on the assembly dimensions and the material properties of the component and substrate. This result could be used to design more reliable assemblies, as it enables one to minimize the amount of axial deformation in the corner joints or, for a given thermal loading condition, to create a desirable compression in the corner joints to inhibit shear-driven fatigue cracking. The solution is based on a theoretical model of two circular elastic disks connected by an elastic layer whose distributed axial and shear stiffnesses are related to the joint/array characteristics by means of the authors’ previously derived stiffnesses for a single joint.
Accelerated Reliability Methodologies for Electronic Components: A Case Study
Authors: Strifas Nick , Fraysse John , Ruzzene Massimo
Published: June 2008

The procedures of estimating the time to failure from accelerated test data are reviewed in this study. An accelerated life test approach which provides the desired reliability results for a fiber optic sensor in shorter times than would be possible with a test performed under normal stress conditions is presented. Utilizing ReliaSoft ALTA software the statistical and life distribution that describe the time to failure of the sensor is determined and the desired reliability results are calculated using the level probability density function.
Characterization of Mechanical Properties of Thin Films by Nanoindentation Technique and Finite Element Simulation
Authors: Shan Zhaohui , Sitaraman Suresh K.
Published: June 2008

Titanium thin films have been widely used in microelectronics due to their good adhesion to substrates, such as Silicon wafer and Quartz. However, mechanical behavior of Titanium thin films has not been well characterized. This paper presents a methodology that combines the nanoindentation technique and finite element modeling to characterize the mechanical (elastic and plastic) properties of thin film with its application on Titanium thin film deposited on silicon substrate. The results show that the elastic properties (Young’s modulus) of the Titanium thin film does not change much from the bulk Titanium, and the plastic properties (yield stress and strain hardening exponent) of the Titanium thin film are higher than those of bulk Titanium. This method is also applicable for the study of mechanical properties of other thin films and small volume materials.
Enhanced Reliability of High Density Wiring (HDW) Substrates Through New Dielectric and Base Substrate Materials
Authors: Hegde Shashikant , Pucha Raghuram V. , Sitaraman Suresh K.
Published: June 2008

FR4 has been extensively used as a board material due to its cost effectiveness and overall performance. For high-density wiring (HDW) substrates with microvias and with embedded capacitors, inductors, resistors, RF and optoelectronic waveguides in a single board, there is a need for alternative base substrates to meet the stringent warpage requirements during fabrication. Typically, these base substrate materials should have high modulus, good planarity, in addition to having a CTE that is close to that of silicon so that the flip-chips can be directly attached to the substrate, eliminating the need for an underfill. Although low-CTE, high modulus base substrate materials can eliminate the need for underfill as well as can result in less warpage during fabrication, they can potentially cause delamination and cracking in the interlayer dielectric. This is due to the high CTE mismatch between the base substrate and typical polymer dielectric. This paper aims to explore a combination of base substrate materials and interlayer dielectric materials such that warpage is minimal, dielectric will not crack or delaminate, and flip-chip solder joints, assembled without an underfill, will not crack prematurely during qualification regimes and operating conditions. A non-liner finite element model with Design-of-Simulations approach is used in arriving at optimized thermo-mechanical properties for the base-substrate and dielectric materials to enhance the overall reliability of the integrated substrate with flip chip assembly. The results from the models have been compared with experimental data and a discussion is presented on the various failure modes.
High Cycle Vibration Testing of BGA Packages
Authors: Sooklal Valmiki K. , Larson Michael C. , Liu Xia
Published: June 2008

The objective of this work is to develop an experimental apparatus, which will facilitate visual monitoring of the solder joint interconnects in a plastic ball grid array (PBGA) package during cyclic testing. The apparatus has been used to determine crack initiation, crack propagation speed, and joint failure. The experiments are complemented by nonlinear finite element modeling and static strain measurements using moire´ interferometry. A representative test is described and the result compared to two model descriptions found in the literature.
Study on the Choice of Constitutive and Fatigue Models in Solder Joint Life Prediction
Authors: Tunga Krishna , Pyland James , Pucha Raghuram V. , Sitaraman Suresh K.
Published: June 2008

Various constitutive and fatigue-life predictive models for lead-tin solders in SBGA (Super Ball Grid Array) packages are studied and compared with the results from experimental data. Two solder compositions, 62Sn/36Pb/2Ag and 63Sn/37Pb are studied in this work. The fatigue life of 62Sn/36Pb/2Ag solder is studied using different constitutive models that take into consideration both the time-independent and time-dependent behavior of the solder. The fatigue life of 62Sn/36Pb/2Ag solder is predicted using an energy-based predictive model and compared with the experimental data. The choice of various predictive models on the solder joint life is studied using 63Sn/37Pb solder. Various predictive models, available in the literature, for eutectic and near eutectic solder compositions are studied to predict the fatigue life. Guidelines are provided for selecting constitutive and predictive models with appropriate damage metrics.
ACHIEVING SUPERIOR INTERNATIONAL NEW VENTURE (INV) PERFORMANCE: EXPLOITING SHORT-TERM DURATION OF TIES
Authors: HAN MARY
Published: June 2008

Network ties help international new ventures (INVs) achieve success. However, researchers have paid little attention to the duration of network ties and the impact of duration on performance. I draw on network analysis and the resources-based view to examine this area and propose a conceptual model that depicts the variables and mediating factors for INV performance. The model explains how INVs acquire, manage and exploit ties to achieve superior performance. I argue that resource-constrained INVs can minimize their investment of time and capital, and maximize the economic effect of ties, by using briefer time periods and short-term projects. I also propose that INVs adopt a 'hedging' or portfolio approach to managing ties, by collecting larger number of prospects to reduce uncertainty. The model and propositions contribute to the body of literature in network analysis and INVs. The paper highlights implications for research and practice.
UNDERSTANDING THE SELECTION AND DEVELOPMENT OF LIFE GOALS OF FAMILY BUSINESS OWNERS
Authors: MOYER STEVEN K. , CHALOFSKY NEAL E.
Published: June 2008

The purpose of this qualitative, phenomenological study was to understand how owners of family businesses select and develop life goals. Findings indicate life goals are substantially influenced and impacted by parents, mentors and influential "others". The selection and development of life goals required a high level of self-confidence in their own knowledge, skills, and abilities with the attitude to make things happen. A faith in a higher being contributed to the belief and feeling that they were at the right place at the right time and possessed the correct knowledge, skills, abilities, and attitude to take advantage of the opportunities placed before them. A strong desire for personal independence influenced the selection and development of the family business as a life goal.
CHANGING CULTURES: AN INTERNATIONAL STUDY OF MIGRANT ENTREPRENEURS
Authors: HAMILTON ROBERT , DANA LEO-PAUL , BENFELL CAMILLA
Published: June 2008

This is a comparative study about the assimilation and integration of migrant entrepreneurs of Chinese and Indian origins. The research is based on surveys of 320 entrepreneurs who migrated to Manchester and 885 entrepreneurs whose ancestors moved to Singapore. With the dramatic change in national cultures associated with such migration, the study sought to identify the emergence of differences over time in the business behaviour and adherence to traditional family values. The main finding of the study is that these migrant communities are willing to adapt in terms of their traditional family values and that their lack of integration into mainstream society should not be ascribed to their strict adherence to such values.
Prolonged Exposure to NMDAR Antagonist Suppresses Inhibitory Synaptic Transmission in Prefrontal Cortex
Authors: Zhang Yuchun , Behrens M. Margarita , Lisman John E.
Published: June 2008

Postmortem studies have shown that schizophrenia produces a reduction in the 67-kilodalton isoform of glutamic acid decarboxylase (GAD67), a key enzyme for γ-aminobutyric acid (GABA) synthesis. N-methyl-d-aspartate receptor (NMDAR) antagonists have been extensively used to study schizophrenia because they can induce many aspects of the disease, including the decrease in GAD67. It is generally thought that this reduction in GAD implies a reduction in functional inhibition, but direct evidence had been lacking. We have therefore performed physiological studies in slices of prefrontal cortex taken from rats treated with the NMDAR antagonist ketamine. Both frequency and amplitude of miniature inhibitory postsynaptic currents were reduced. Consistent with a reduction of inhibition, we observed an increase in postsynaptic excitability. The increased excitability is likely to result from disinhibition because miniature excitatory postsynaptic current properties and intrinsic excitability were not changed. Ketamine did not affect inhibition or GAD levels in young rats, indicating a developmental regulation that may be related to the developmental increase in ketamine sensitivity that occurs in humans. Our results show that NMDAR antagonist produces biochemical changes in the GABA system that lead to a functional disinhibition. Such disinhibition would be expected to decrease gamma oscillations, which are reduced in schizophrenia.
Recommendations for Reporting Independent Variables in Outcome Studies of Early and Intensive Behavioral Intervention for Autism
Authors: Lechago Sarah A. , Carr James E.
Published: June 2008

Early and intensive behavioral intervention (EIBI) has been established as an effective treatment for autism. However, the complexity and intensity of EIBI programs make it difficult to fully report all critical aspects of the independent variable. Consequently, scientific reports of EIBI outcomes have been criticized for providing less than comprehensive treatment descriptions. In an effort to address this problem, the present article provides a template to aid outcome researchers in (a) clearly reporting each participant's curricular targets and (b) describing critical aspects of treatment.
Conflict Transformation
Authors: Greer Lindred L. , Jehn Karen A. , Mannix Elizabeth A.
Published: June 2008

In this longitudinal study, the authors examine the relationships between task, relationship, and process conflict over time. They also look at the role of conflict resolution in determining whether certain forms of intragroup conflict are related to the appearance of other forms of conflict over time. Their findings indicate a negative and long-lasting impact of process conflict occurring early in the team's interaction. Specifically, they find that process conflict, but not task or relationship conflict, occurring early in a team's interaction leads to higher levels of all other conflict types for the remaining interactions of the team. In addition, the authors find that the effect of process conflict on the other types of conflict over time may be limited when members are able to resolve their process conflicts at the start of their time together.
Aberrant CpG island methylation in acute myeloid leukemia is accentuated at relapse
Authors: Kroeger Heike , Jelinek Jaroslav , Estécio Marcos R. H. , He Rong , Kondo Kimie , Chung Woonbok , Zhang Li , Shen Lanlan , Kantarjian Hagop M. , Bueso-Ramos Carlos E. , Issa Jean-Pierre J.
Published: June 2008

DNA methylation of CpG islands around gene transcription start sites results in gene silencing and plays a role in leukemia pathophysiology. Its impact in leukemia progression is not fully understood. We performed genomewide screening for methylated CpG islands and identified 8 genes frequently methylated in leukemia cell lines and in patients with acute myeloid leukemia (AML): NOR1, CDH13, p15, NPM2, OLIG2, PGR, HIN1, and SLC26A4. We assessed the methylation status of these genes and of the repetitive element LINE-1 in 30 patients with AML, both at diagnosis and relapse. Abnormal methylation was found in 23% to 83% of patients at diagnosis and in 47% to 93% at relapse, with CDH13 being the most frequently methylated. We observed concordance in methylation of several genes, confirming the presence of a hypermethylator pathway in AML. DNA methylation levels increased at relapse in 25 of 30 (83%) patients with AML. These changes represent much larger epigenetic dysregulation, since methylation microarray analysis of 9008 autosomal genes in 4 patients showed hypermethylation ranging from 5.9% to 13.6% (median 8.3%) genes at diagnosis and 8.0% to 15.2% (median 10.6%) genes in relapse (P < .001). Our data suggest that DNA methylation is involved in AML progression and provide a rationale for the use of epigenetic agents in remission maintenance.
Unique motifs identify PIG-A proteins from glycosyltransferases of the GT4 family
Authors: Oswal Nupur , Sahni Narinder Singh , Bhattacharya Alok , Komath Sneha Sudha , Muthuswami Rohini
Published: June 2008

Background

The first step of GPI anchor biosynthesis is catalyzed by PIG-A, an enzyme that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol. This protein is present in all eukaryotic organisms ranging from protozoa to higher mammals, as part of a larger complex of five to six 'accessory' proteins whose individual roles in the glycosyltransferase reaction are as yet unclear. The PIG-A gene has been shown to be an essential gene in various eukaryotes. In humans, mutations in the protein have been associated with paroxysomal noctural hemoglobuinuria. The corresponding PIG-A gene has also been recently identified in the genome of many archaeabacteria although genes of the accessory proteins have not been discovered in them. The present study explores the evolution of PIG-A and the phylogenetic relationship between this protein and other glycosyltransferases.

Results

In this paper we show that out of the twelve conserved motifs identified by us eleven are exclusively present in PIG-A and, therefore, can be used as markers to identify PIG-A from newly sequenced genomes. Three of these motifs are absent in the primitive eukaryote, G. lamblia. Sequence analyses show that seven of these conserved motifs are present in prokaryote and archaeal counterparts in rudimentary forms and can be used to differentiate PIG-A proteins from glycosyltransferases. Using partial least square regression analysis and data involving presence or absence of motifs in a range of PIG-A and glycosyltransferases we show that (i) PIG-A may have evolved from prokaryotic glycosyltransferases and lipopolysaccharide synthases, members of the GT4 family of glycosyltransferases and (ii) it is possible to uniquely classify PIG-A proteins versus glycosyltransferases.

Conclusion

Besides identifying unique motifs and showing that PIG-A protein from G. lamblia and some putative PIG-A proteins from archaebacteria are evolutionarily closer to glycosyltransferases, these studies provide a new method for identification and classification of PIG-A proteins.
The genome of the versatile nitrogen fixer Azorhizobium caulinodans ORS571
Authors: Lee Kyung-Bum , De Backer Philippe , Aono Toshihiro , Liu Chi-Te , Suzuki Shino , Suzuki Tadahiro , Kaneko Takakazu , Yamada Manabu , Tabata Satoshi , Kupfer Doris M , Najar Fares Z , Wiley Graham B , Roe Bruce , Binnewies Tim T , Ussery David W , D'Haeze Wim , Den Herder Jeroen , Gevers Dirk , Vereecke Danny , Holsters Marcelle , Oyaizu Hiroshi
Published: June 2008

Background

Biological nitrogen fixation is a prokaryotic process that plays an essential role in the global nitrogen cycle. Azorhizobium caulinodans ORS571 has the dual capacity to fix nitrogen both as free-living organism and in a symbiotic interaction with Sesbania rostrata. The host is a fast-growing, submergence-tolerant tropical legume on which A. caulinodans can efficiently induce nodule formation on the root system and on adventitious rootlets located on the stem.

Results

The 5.37-Mb genome consists of a single circular chromosome with an overall average GC of 67% and numerous islands with varying GC contents. Most nodulation functions as well as a putative type-IV secretion system are found in a distinct symbiosis region. The genome contains a plethora of regulatory and transporter genes and many functions possibly involved in contacting a host. It potentially encodes 4717 proteins of which 96.3% have homologs and 3.7% are unique for A. caulinodans. Phylogenetic analyses show that the diazotroph Xanthobacter autotrophicus is the closest relative among the sequenced genomes, but the synteny between both genomes is very poor.

Conclusion

The genome analysis reveals that A. caulinodans is a diazotroph that acquired the capacity to nodulate most probably through horizontal gene transfer of a complex symbiosis island. The genome contains numerous genes that reflect a strong adaptive and metabolic potential. These combined features and the availability of the annotated genome make A. caulinodans an attractive organism to explore symbiotic biological nitrogen fixation beyond leguminous plants.
TMJ metastasis: A unusual case report
Authors: Boniello Roberto , Gasparini Giulio , D'Amato Giuseppe , Di Petrillo Alessandro , Pelo Sandro
Published: June 2008

The metastases to the TMJ from a primary lung tumour is a very rare occurrence.

This case is unusual in several aspects, as the non-reducible dislocation of the TMJ was the first clinical manifestation of the tumour. CT staging showed that this secondary tumour in the condyle was the only bone metastasis.