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Zhigang Suo's picture

International Journal of Solids and Structures (IJSS) will be freely accessible

At a meeting of the Editorial Board of IJSS, on Sunday, 3 June 2007, in Austin, Texas, the representatives from Elsevier, the publisher of IJSS, told the members of the Board that all articles published in IJSS will be freely accessible 24 months after publication.  The first of these articles will become available in October 2007.  That is, all IJSS articles published after October 2005 will become freely accessible after a delay of 24 months.

Jie-Hua Zhao's picture

Research Position at Texas Instruments (Dallas, Texas)

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This is a stress modeling position in TI's research organization Silicon Technology Development (SiTD). The opening is immediate and the position is filling very fast. Minimum requirement: MS degree in the following fields: Mechanical Engineering, Physics, Materials Science or Engineering Mechanics. PhD degree is preferred.  Please email your resume to Jie-Hua (Jeff) Zhao at jhzhao@ti.com or Darvin Edwards at rvin@ti.com. Call Jeff at 972-995-8851 for detail. Job description is listed below:

aitang's picture

Metal cutting

I am in the industry of Metal cutting, about Truning, milling, drilling... Mainly on solid carbide now. But new CBN, cermetal, ceramic are also great complementarities.

Hope I can join you and discuss about new tec in this field

Xiao Hu Liu's picture

IBM Airgap Microprocessor

From IBM Press Room announcement on May 3, 2007: IBM Airgap Microprocessor -- This microprocessor cross section shows empty space in between the chip's wiring. Wires are usually insulated with a glass-like material.

Taxonomy upgrade extras: 

Chip-package interaction and interfacial delamination

In flip-chip package, the mismatch of thermal expansion coefficients between the silicon die and packaging substrate induces concentrated stress field around the edges and corners of silicon die during assembly, testing and services. The concentrated stresses result in delamination on many interfaces on several levels of structures, in various length scales from tens of nanometers to hundreds of micrometers. A major challenge to model flip-chip packages is the huge variation of length scales, the complexity of microstructures, and diverse materials properties. In this paper, we simplify the structure to be silicon/substrate with wedge configuration, and neglect the small local features of integrated circuits. This macroscopic analysis on package level is generic with whatever small local features, as long as the physical processes of interest occur in the region where the concentrated stress field due to chip-packaging interaction dominates. Because it is the same driving force that motivates all of the flaws. Therefore, the different interface cracks with same size and same orientation but on different interfaces should have similar energy release rates provided that the cracks are much smaller than the macroscopic length. We calculate the energy release rate and the mode angle of crack on the chip-package interface based on the asymptotic linear elastic stress field. In a large range of crack length, the asymptotic solution agrees with finite element calculation very well. We discuss the simplified model and results in context of real applications. In addition, we find that the relation of energy release rate G and crack length a is not power-law since local mode mixity is dependent of crack length a. Therefore, the curve of G~a can be wavy and hardly goes to zero even if crack length a goes to atomically small. The local mode mixity plays an important role in crack behavior.

Xuejun Fan's picture

Fracture at corners or edges in bi-material systems

Dr. Suo's group is recently studying the sharp features such as corners or edges. It becomes important to characterize fracture behaviors at corners and edges in microelectronics.

I have two questions,

The Industry First Compact Reverse Pulse Plating Controller for R&D Applications in MEMS and Nanotechnology

Laguna Beach, CA March 31, 2007 -- Kebaili Corporation a leading California based high-tech company announced today the release of the CPG-500 Series, the industry first compact current pulse generator, specifically designed for electrodeposition applications, such as (direct current) DC plating, pulse plating, and periodic reverse pulse plating for a variety of applications in MEMS and nanotechnology.

Liu's picture

Motion of precision linear bearings on nanometre scale

A systematic characterization of the motion and friction of a linear bearing with rolling elements used for nanopositioning reveals an explicit distinction of static and rolling friction. The effects

Flowrate in Gravity Discharge Pipe

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I would like to know the average velocity and friction loss in a gravity discharge line. I am pumping water (it is actually a chemical feed that is mostly water so let's just analyze the problem as if it were water) at constant (the pump is positive displacement type with sufficient head to overcome moderate discharge pressures) flow rates (anywhere from 1 to 5 gpm) to a vertical line that runs straight down (vertically) 200 feet into a water reservoir. The vertical pipe is PVC and 1 inch nominal inside diameter (during design it may range for 0.5 inch to 1.0 inch with the exact ID dependent on wall thickness/schedule). The pipe is immersed (i.e., submerged) in the water reservoir 50 feet down (so PVC pipe is actually 250 vertical feet long). There is a backpressure valve at the top of the vertical pipe that will keep the feed line full for immediate discharge to the top of the vertical pipe when the pump is turned on. It is very important in this process application to know how long it will take for the feed to travel the vertical 200 feet distance as immediate (or as near as practical) feed to the reservoir is desired when the process logic turns on the feed.

Simpleware signs up reseller in China

Simpleware Ltd., the world leader in image-based meshing software, has signed an agreement with Gaitech International Ltd. to resell the Simpleware suite of software products in China, Hong Kong, Taiwan and Macao.

Simpleware software offers an advanced solution to problems that were previously intractable due to the complexity in geometry reconstruction. Simpleware's technology has opened up numerical analysis (CFD and FEA) to a variety of applications, including biomedical engineering, material characterisation and industrial reverse engineering.

CAD/CAM/CAE Outsourcing India

Outsourcing of Engineering Design projects to “Sphinx Worldbiz Ltd” can greatly Reduce Cost and Produce Faster Turnaround while giving you excellent Technical Expertise.
We are based in New Delhi - India and have expertise in following Engineering Services - CAD/CAM/CAE :

Xiao-Yan Gong's picture

Role of Mechanics in Medical Implant Industry

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I believe that questions Zhigang raised today worth discussing as a topic within this forum.  I will start and please comment.

The traditional roles of mechanics in the medical implant industry is to ensure safety through reliability assessment and to prove functionality through in-vitro testing.

Things are changing, in mid-90s, Charley Taylor and his colleagues pioneered "predictive medicine" and "simulation-based medical planning" in which they uses CFD to help making surgical decisions.  Professor Taylor's research in "predictive medicine" and "simulation-based medical planning" has been featured on several television and radio programs including Quantum, Beyond 2000, New Media News, and The Osgood Files and has appeared in Discover, Mechanical Engineering, Technology Review and The Scientist magazines. (statement directly from his web site).  Mechanics goes into the prediction of medicine performances.

Mechanics of Materials Research Impacts US Aluminum Industry, Energy, and Environment

Initially posted on Applied Mechanics News on 28 April 2007.

Hot rolling from ingot is the dominant fabrication method of producing plate, sheet, and foil aluminum products. It is a striking fact that the total rolling-plant recovery of aluminum process from ingot to final products is typically about 50%. This recovery loss causes enormous amount of energy waste both as remelt energy and energy to process material that is just recycled. Assuming the annual US domestic net shipments of sheet and plate products being 10,500 million lb, 10% improvement of the hot rolling recovery will result annual savings of $126 million per year for the US domestic aluminum industry. The annual domestic energy savings would be 2.54 trillion Btu. The environmental benefits include annual reduction of 2.32 million lb SOx , 1.01 million lb NOx, 303.2 million lb CO2, 0.67 million lb of particulate, and 11000 lb VOCsd .

The fundamental inability to reduce or eliminate these recovery losses is “lack of the integrated models that relate structural properties to manufacturing processes”. Currently, processing parameters are determined by trial and error and largely based on experience. This makes it difficult to optimize the process even on the macroscale level, and almost impossible from microstructure level. Research in the following areas are desirable:

Henry Tan's picture

Mitigating the threat of terrorist attacks

The following are links to the FEMA (Federal Emergency Management Agency) documents:

Mitigating the threat of terrorist attacks against high occupancy buildings is a challenging task.

Chapter 1: ASSET VALUE, THREAT/HAZARD, VULNERABILITY, AND RISK
This chapter presents several methodologies for architects and engineers to quantify risk and to identify the most effective mitigation measures to achieve a desired level of protection against terrorist attacks at an acceptable cost.

Xiao-Yan Gong's picture

Nitinol, stent fracture and related issues

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Stent and Nitinol have revolutionized the medicine.  In past decades, guidewires, stents, filters and many minimumly invasive devices and implants are made of Nitinol and they proved to be very successful.

However, the fatigue behavior of Nitinol has not been well understood.  As a consequences, many stent fractures have been observed in-vivo.  Below is a list of misconcepts that may contribute to the widely observed in-vivo fractures on Nitinol stents:

Zhigang Suo's picture

Texas Instruments will extend outsourcing model. Will more people lose jobs?

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News of Texas Instruments are intriguing. The world's largest maker of chips for mobile phones has just posted good fourth-quarter earnings. Despite the gains, the company said it will further increase efficiency and profitability by extending the model of outsourcing. This time it will include development of certain chips. The news on the Internet is rather terse. Will the company drastically reduce its research and development activities? Will many people lose jobs?

Nicolas Cordero's picture

Channel cracks in a hermetic coating consisting of organic and inorganic layers

Abstract: Flexible electronic devices often require hermetic coatings that can withstand applied strains. This paper calculates the critical strains for various configurations of channel cracks in a coating consisting of organic and inorganic layers. We show that the coating can sustain the largest strain when the organic layer is of some intermediate thicknesses.

Flexible electronics are promising for diverse applications, such as rollable displays, conformal sensors, and printable solar cells. These systems are thin, rugged, and lightweight. They can be manufactured at low costs, for example, by roll-to-roll printing. The development of flexible electronics has raised many issues concerning the mechanical behavior of materials. This paper examines a particular issue: channel cracks in hermetic coatings.

Electronic devices (e.g., organic light-emitting devices, OLEDs) often degrade when exposed to air. Developing hermetic coatings has been a significant challenge. Organic films are permeable to gases, and inorganic films inevitably contain processing flaws, so that neither by themselves are effective gas barriers. These considerations have led to the development of multilayer coatings consisting of alternating organic and inorganic films. To be used in flexible electronics, these coatings must also withstand applied strains without forming channel cracks...

Liu's picture

Positioning on nanometer scale: fighting friction

Most friction models for automatic control are targeted for the macro world, and are of questionable value for the motion control of the high precision positioing stages. We published a paper recently in Technishes Messen (TM) on a study of the friction behavior in the moving range of micrometers. It provides info for the development of friction models targeted for the motion control in high precision engineering.

The following is the abstract, and the full paper can be downloaded from http://www.atypon-link.com/OLD/doi/abs/10.1524/teme.2006.73.9.500

ABSTRACT Most friction models for automatic control are targeted for the macro world, and are of questionable value for the motion control of the nanopositioning and nanomeasuring machine (NPM) system. We present the frictional behaviour of some selected materials, coatings, lubricants, and bearings tested under running conditions similar to a NPM system. Continuous change of surface properties results in various friction characteristics, which substantiate the further development of tribological coatings, particularly for vacuum applications. We emphasize the system engineering approach in developing friction models, which combines fundamental knowledge of surface science, materials science, and its applications in design, construction and automatic control.

A method to analyze dislocation injection from sharp features in strained silicon structures

Stresses inevitably arise in a microelectronic device due to mismatch in coefficients of thermal expansion, mismatch in lattice constants, and growth of materials. Moreover, in the technology of strained silicon devices, stresses have been deliberately introduced to increase carrier mobility. A device usually contains sharp features like edges and corners, which may intensify stresses, inject dislocations into silicon, and fail the device.

Xiao Hu Liu's picture

Delamination in Patterned Films

When the dielectric constant of an insulator in an interconnect is reduced, mechanical properties are often compromised, giving rise to significant challenges in interconnect integration and reliability. Due to low adhesion of the dielectric an interfacial crack may occur during fabrication and testing. To understand the effect of interconnect structure, an interfacial fracture mechanics model has been analyzed for patterned films undergoing a typical thermal excursion during the integration process.

Zhigang Suo's picture

Saturated voids in interconnect lines due to thermal strains and electromigration

Zhen Zhang and Zhigang Suo (Harvard), Jun He (Intel)

Attached is a set of slides presented at ASME Congress, 10 November 2006. Thermal strains and electromigration can cause voids to grow in conductor lines on semiconductor chips. This long-standing failure mode is exacerbated by the recent introduction of low-permittivity dielectrics. We describe a method to calculate the volume of a saturated void (VSV), attained in a steady state when each point in a conductor line is in a state of hydrostatic pressure, and the gradient of the pressure along the conductor line balances the electron wind. We show that the VSV will either increase or decrease when the coefficient of thermal expansion of the dielectric increases, and will increase when the elastic modulus of the dielectric decreases. The VSV will also increase when porous dielectrics and ultrathin liners are used. At operation conditions, both thermal strains and electromigration make significant contributions to the VSV. We discuss these results in the context of interconnect design.

Jun He's picture

Statistics of Electromigration Lifetime Analyzed Using a Deterministic Transient Model

void due to electromitationThe electromigration lifetime is measured for a large number of copper lines encapsulated in an organosilicate glass low-permittivity dielectric. Three testing variables are used: the line length, the electric current density, and the temperature. A copper line fails if a void near the upstream via grows to a critical volume that blocks the electric current. The critical volume varies from line to line, depending on line-end designs and chance variations in the microstructure. However, the statistical distribution of the critical volume (DCV) is expected to be independent of the testing variables. By contrast, the distribution of the lifetime (DLT) strongly depends on the testing variables. For a void to grow a substantial volume, the diffusion process averages over many grains along the line. Consequently, the void volume as a function of time, V(t), is insensitive to chance variations in the microstructure. As a simplification, we assume that the function V(t) is deterministic, and calculate this function using a transient model. We use the function V(t) to convert the experimentally measured DLT to the DCV. The same DCV predicts the DLT under untested conditions.

Jeannette Jacques's picture

Environmental Effects on Crack Characteristics for OSG Interconnect Materials

Jeannette M. Jacques, Ting Y. Tsui, Andrew J. McKerrow, and Robert Kraft

To improve capacitance delay performance of the advanced back-end-of-line (BEOL) structures, low dielectric constant organosilicate glass (OSG) has emerged as the predominant choice for intermetal insulator. The material has a characteristic tensile residual stress and low fracture toughness. A potential failure mechanism for this class of low-k dielectric films is catastrophic fracture due to channel cracking. During fabrication, channel cracks can also form in a time-dependent manner due to exposure to a particular environmental condition, commonly known as stress-corrosion cracking. Within this work, the environmental impacts of pressure, ambient, temperature, solution pH, and solvents upon the channel cracking of OSG thin films are characterized. Storage under high vacuum conditions and exposure to flowing dry nitrogen gas can significantly lower crack propagation rates. Cracking rates experience little fluctuation as a function of solution pH; however, exposure to aqueous solutions can increase the growth rate by three orders of magnitude.

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