Numerical simulation of the mass loss process in pyrolizing char materials

We present here a decoupling technique to tackle the entanglement of the nonlinear boundary condition and the movement of the char/virgin front for a thermal pyrolysis model for charring materials. Standard numerical techniques to solve moving front problems — often referred to as Stefan problems — encounter difficulties when dealing with nonlinear boundaries. While special integral methods have been developed to solve this problem, they suffer from several limitations which the technique described here overcomes. The newly developed technique is compared with the exact analytical solutions for some simple ideal situations which demonstrate that the numerical method is capable of producing accurate numerical solutions. The pyrolysis model is also used to simulate the mass loss process from a white pine sample exposed to a constant radiative flux in a nitrogen atmosphere. Comparison with experimental results demonstrates that the predictions of mass loss rates and temperature profile within the solid material are in good agreement with the experiment.

Modelling technology to predict flip-chip assembly

This paper describes modelling technology and its use in providing data governing the assembly of flip-chip components. Details are given on the reflow and curing stages as well as the prediction of solder joint shapes. The reflow process involves the attachment of a die to a board via solder joints. After a reflow process, underfill material is placed between the die and the substrate where it is heated and cured. Upon cooling the thermal mismatch between the die, underfill, solder bumps, and substrate will result in a nonuniform deformation profile across the assembly and hence stress. Shape predictions then thermal solidification and stress prediction are undertaken on solder joints during the reflow process. Both thermal and stress calculations are undertaken to predict phenomena occurring during the curing of the underfill material. These stresses may result in delamination between the underfill and its surrounding materials leading to a subsequent reduction in component performance and lifetime. Comparisons between simulations and experiments for die curvature will be given for the reflow and curing process

Computational modelling-a key component in materials processing

Computational analysis software is now widely accepted as a key industrial tool for plant design and process analysis. This is due in part to increased accuracy in the models, larger and faster computer systems and better graphical interfaces that allow easy use of the technology by engineers. The use of computational modelling to test new ideas and analyse current processes helps to take the guesswork out of industrial process design and offers attractive cost savings. An overview of computer-based modelling techniques as applied to the materials processing industry is presented and examples of their application are provided in the contexts of the mixing and refining of lead bullion and the manufacture of lead ingots.

Heat and mass transfer in two-phase porous materials under intensive microwave heating

Computational results for the intensive microwave heating of porous materials are presented in this work. A multi-phase porous media model has been developed to predict the heating mechanism. Combined finite difference time-domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent both on temperature and moisture content. The model was able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change.

A new computational approach to microwave heating of two-phase porous materials

Computational results for the microwave heating of a porous material are presented in this paper. Combined finite difference time domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent on both temperature and moisture content. The model was able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change.

Powering the virtual university with standard portal technology

This article describes ongoing research on developing a portal framework based on the OASIS Web Services for Remote Portlets (WSRP) standard for integration of Web-based education contents and services made available through a model for a European Networked University. We first identify the requirements for such a framework that supports integration at the presentation level and collaboration in developing and updating study programmes and course materials. We then outline the architecture design, and report on the initial implementation and preliminary evaluation.

Comparison between weight loss of bends in a pneumatic conveyor and erosion rate obtained in a centrifugal erosion tester for the same materials

In order to find a link between results obtained from a laboratory erosion tester and tests carried out on a pneumatic conveyor, a comparison has been made between weight loss from bends on an industrial-scale pneumatic conveyor and erosion rates obtained in a small centrifugal erosion tester, for the same materials. Identical test conditions have been applied to both experiments so that comparable test results have been obtained. The erosion rate of mild steel commonly used as the wall material of conveyor pipes and pipe bends was determined individually on both test rigs. A relationship between weight loss from the bends and erosion rate determined from the tester has been developed. A discussion based on the results and their applicability to the prediction of wear in pneumatic conveyors concludes the paper.

Review of the technology and reliability issues arising as optical interconnects migrate onto the circuit board

Light has the greatest information carrying potential of all the perceivable interconnect mediums; consequently, optical fiber interconnects rapidly replaced copper in telecommunications networks, providing bandwidth capacity far in excess of its predecessors. As a result the modern telecommunications infrastructure has evolved into a global mesh of optical networks with VCSEL’s (Vertical Cavity Surface Emitting Lasers) dominating the short-link markets, predominately due to their low-cost. This cost benefit of VCSELs has allowed optical interconnects to again replace bandwidth limited copper as bottlenecks appear on VSR (Very Short Reach) interconnects between co-located equipment inside the CO (Central-Office). Spurred by the successful deployment in the VSR domain and in response to both intra-board backplane applications and inter-board requirements to extend the bandwidth between IC’s (Integrated Circuits), current research is migrating optical links toward board level USR (Ultra Short Reach) interconnects. Whilst reconfigurable Free Space Optical Interconnect (FSOI) are an option, they are complicated by precise line-of-sight alignment conditions hence benefits exist in developing guided wave technologies, which have been classified into three generations. First and second generation technologies are based upon optical fibers and are both capable of providing a suitable platform for intra-board applications. However, to allow component assembly, an integral requirement for inter-board applications, 3rd generation Opto-Electrical Circuit Boards (OECB’s) containing embedded waveguides are desirable. Currently, the greatest challenge preventing the deployment of OECB’s is achieving the out-of-plane coupling to SMT devices. With the most suitable low-cost platform being to integrate the optics into the OECB manufacturing process, several research avenues are being explored although none to date have demonstrated sufficient coupling performance. Once in place, the OECB assemblies will generate new reliability issues such as assembly configurations, manufacturing tolerances, and hermetic requirements that will also require development before total off-chip photonic interconnection can truly be achieved

Variable frequency microwave curing of polymer materials in microelectronics packaging applications

The use of variable frequency microwave technology in curing of polymer materials used in microelectronics applications is discussed. A revolutionary open-ended microwave curing system is outlined and assessed using experimental and numerical approaches. Experimental and numerical results are presented, demonstrating the feasibility of the system

Impact of assembly process technologies on electronic packaging materials

Assembly processes used to bond components to printed circuit boards can have a significant impact on these boards and the final packaged component. Traditional approaches to bonding components to printed circuit boards results in heat being applied across the whole board assembly. This can lead to board warpage and possibly high residual stresses. Another approach discussed in this paper is to use Variable Frequency Microwave (VFM) heating to cure adhesives and underfills and bond components to printed circuit boards. In terms of energy considerations the use of VFM technology is much more cost effective compared to convection/radiation heating. This paper will discuss the impact of traditional reflow based processes on flexible substrates and it will demonstrate the possible advantages of using localised variable frequency microwave heating to cure materials in an electronic package.

On the application of variable frequency microwave technology for processing of individual surface mount components

Dual-section variable frequency microwave systems enable rapid, controllable heating of materials within an individual surface mount component in a chip-on=board assembly. The ability to process devices individually allows components with disparate processing requirements to be mounted on the same assembly. The temperature profile induced by the microwave system can be specifically tailored to the needs of the component, allowing optimisation and degree of cure whilst minimising thermomechanical stresses. This paper presents a review of dual-section microwave technology and its application to curing of thermosetting polymer materials in microelectronics applications. Curing processes using both conventional and microwave technologies are assessed and compared. Results indicate that dual-section microwave systems are able to cure individual surface mount packages in a significantly shorter time, at the expense of an increase in thermomechanical stresses and a greater variation in degree of cure.

Prospect for EPM application to environmental technology

EPM seems to have good prospects for the future not only in the materials processing but also in environmental technologies by the help of superior features like contactless processing, clean heating and melting, and good controllability. In the present paper, the authors commentate on the possibility of EPM to avoid environmental issues of energy, resources and hazardous wastes by the use of the functions of Lorentz force and Joule heating. Firstly, the present situation and future trend of electric power generation is outlined, and then some examples of the application of EPM to environmental technologies are introduced, which have been performed by the author’s group. Examples are as follows: production of spherical solar cell from a liquid jet by using intermittent electromagnetic force; fabrication of semi-solid Al-Si slurry for die-casting of vehicle-parts to reduce the weight of vehicle; electromagnetic separation of nonmetallic inclusions from liquid Al scrap and its application to the fabrication of partially particle-reinforced aluminum alloy; electromagnetic melting of hazardous wastes from power plants to stabilize wastes in glass state.

Microwave curing of thermosetting polymer materials in microelectronics applications

Thermosetting polymer materials are widely utilised in modern microelectronics packaging technology. These materials are used for a number of functions, such as for device bonding, for structural support applications and for physical protection of semiconductor dies. Typically, convection heating systems are used to raise the temperature of the materials to expedite the polymerisation process. The convection cure process has a number of drawbacks including process durations generally in excess of 1 hour and the requirement to heat the entire printed circuit board assembly, inducing thermomechanical stresses which effect device reliability. Microwave energy is able to raise the temperature of materials in a rapid, controlled manner. As the microwave energy penetrates into the polymer materials, the heating can be considered volumetric – i.e. the rate of heating is approximately constant throughout the material. This enables a maximal heating rate far greater than is available with convection oven systems which only raise the surface temperature of the polymer material and rely on thermal conductivity to transfer heat energy into the bulk. The high heating rate, combined with the ability to vary the operating power of the microwave system, enables the extremely rapid cure processes. Microwave curing of a commercially available encapsulation material has been studied experimentally and through use of numerical modelling techniques. The material assessed is Henkel EO-1080, a single component thermosetting epoxy. The producer has suggested three typical convection oven cure options for EO1080: 20 min at 150C or 90 min at 140C or 120 min at 110C. Rapid curing of materials of this type using advanced microwave systems, such as the FAMOBS system [1], is of great interest to microelectronics system manufacturers as it has the potential to reduce manufacturing costs, increase device reliability and enables new device designs. Experimental analysis has demonstrated that, in a realistic chip-on-board encapsulation scenario, the polymer material can be fully cured in approximately one minute. This corresponds to a reduction in cure time of approximately 95 percent relative to the convection oven process. Numerical assessment of the process [2] also suggests that cure times of approximately 70 seconds are feasible whilst indicating that the decrease in process duration comes at the expense of variation in degree of cure within the polymer.

Can the use of supplementary video and audio materials support student understanding of 3D animation? Some results, analysis and conclusions

A project within a computing department at the University of Greenwich, has been carried out to identify whether podcasting can be used to help understanding and learning of a subject (3D Animation). We know that the benefits of podcasting in education (HE) can be justified, [1]; [2]; [3]; [4]; [5]; [6] and that some success has been proven, but this paper aims to report the results of a term-long project that provided podcast materials for students to help support their learning using Xserve and Podcast Producer technology. Findings in a previous study [6] identified podcasting as a way to diversify learning and provde a more personalised learning experience for students, as well as being able to provide access to a greater mix of learning styles [7]. Finally this paper aims to present the method of capture and distribution, the methodologies of the study, analysis of results, and conclusions that relate to podcasting and enhanced supported learning.