Paul P. Conway

Thermal Interface Materials - A Review of the State of the Art

The past few decades have seen an escalation of power densities in electronic devices, and in particular in microprocessor chips. Together with the continuing trend of reduction in device dimensions this has led to dramatic increase in the thermal issues within electronic circuits. Thermal management is therefore becoming increasingly more critical and fundamental to ensuring that electronic devices operate within their specification. Although a thermal management system may make use of all modes of heat transfer to maintain temperatures within their appropriate limits and to ensure optimum performance and reliability, conductive heat transfer is typically used to spread the heat out from its point of generation and into the extended surface area of a heat sink. To minimise the contact resistance, thermal interface materials (TIMs) are introduced to the joint to fill the air gaps and are an essential part of an assembly when solid surfaces are attached together. This paper reviews the conventional interface materials and then goes on to present a comprehensive review of the emerging state-of-the-art research in the use of carbon nanotube based materials. The paper also outlines the advantages and disadvantages of each TIM category and the factors that need to be considered when selecting an interface material

Preservation in the Age of Google: Digitization, Digital Preservation, and Dilemmas.

The cultural heritage preservation community now functions largely within the environment of digital technologies. This article begins by juxtaposing definitions of the terms “digitization for preservation” and “digital preservation” within a sociotechnical environment for which Google serves as a relevant metaphor. It then reviews two reports published twelve years apart under the auspices of the Council on Library and Information Resources. Preserving Digital Information presented an insightful and visionary framework for digital preservation in 1996. Preservation in the Age of Large‐Scale Digitization explores the implications for preservation practice of the digitization of books and, by implication, our cultural heritage in general. These juxtapositions frame four dilemmas for preservation relating to the impact of environmental storage, new challenges to preservation quality, threats to audiovisual heritage, and an emerging expertise gap. The article concludes with recommendations and observations on making difficult choices.

Electroless nickel bumping of aluminum bondpads. I. Surface pretreatment and activation

Electroless nickel bumping of aluminum (Al) bond-pads followed by solder paste printing is seen as one of the lowest cost routes for the bumping of wafers prior to flip-chip assembly. However, the electroless nickel bumping of Al bondpads is not straightforward and a number of activation steps are necessary to enable the nickel deposit to form a strong, electrically conductive bond with the Al. For the electroless nickel coating of mechanical components made of aluminum, a zincate activation process has been used for many years; however, extension of these techniques to semiconductor wafers requires careful control over these pretreatments to avoid damage to the very thin bondpads. This paper reports a number of experiments designed to characterize the activation of Al bondpads to electroless nickel plating, focusing on the effects of solution exposure time and bondpad composition. In addition, the results are discussed in the context of other studies presented in the literature to provide an understanding of the mechanism of the zincate activation process applied to Al bondpads.

Manufacture of a human mesenchymal stem cell population using an automated cell culture platform.

Tissue engineering and regenerative medicine are rapidly developing fields that use cells or cell-based constructs as therapeutic products for a wide range of clinical applications. Efforts to commercialise these therapies are driving a need for capable, scaleable, manufacturing technologies to ensure therapies are able to meet regulatory requirements and are economically viable at industrial scale production. We report the first automated expansion of a human bone marrow derived mesenchymal stem cell population (hMSCs) using a fully automated cell culture platform. Differences in cell population growth profile, attributed to key methodological differences, were observed between the automated protocol and a benchmark manual protocol. However, qualitatively similar cell output, assessed by cell morphology and the expression of typical hMSC markers, was obtained from both systems. Furthermore, the critical importance of minor process variation, e.g. the effect of cell seeding density on characteristics such as population growth kinetics and cell phenotype, was observed irrespective of protocol type. This work highlights the importance of careful process design in therapeutic cell manufacture and demonstrates the potential of automated culture for future optimisation and scale up studies required for the translation of regenerative medicine products from the laboratory to the clinic.

Effective modeling of the reflow soldering process: basis, construction, and operation of a process model

Thermal history variation within printed circuit assemblies (PCAs) during reflow soldering is considered one of the main drivers for manufacturing defects. It is recognized that predictive tools could be used to identify the temperature variations that arise during the reflow process and, in conjunction with experimentally derived data, determine their impact on manufacturing quality. This paper describes the development of representative process models of the reflow soldering of PCAs and outlines some of the more important parameters to consider for accurate simulation of the reflow process. This first part also presents results which illustrate the variation with temperature of critical properties for electronic materials, such as for common substrate and epoxy based packaging materials.

The Evolution of Pd ∕ Sn Catalytic Surfaces in Electroless Copper Deposition

This paper describes the different catalytic surfaces of Pd/Sn formed before electroless copper deposition onto a glass substrate. In this study, silanization of the glass surfaces with (3-aminopropyl) trimethoxysilane was used to provide a surface-coupled layer of functional molecules to assist in the adsorption of Pd/Sn catalyst and the subsequent copper deposition. The composition and microstructure of the modified glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. These showed that catalytic Pd/Sn structures on the surface changed with increasing immersion time in the catalyst bath. The core-level XPS spectrum of Pd indicated that metallic Pd(0) became more significant in the catalyst layer than Pd(II) with the increasing immersion time. A model of the adsorption process is proposed to explain these changes. It was observed that too high a quantity of Pd(0) does not always improve the adhesion of the Cu deposits in the electroless process.

Microstructure and shear strength evolution of Sn-Ag-Cu solder bumps during aging at different temperatures

Flip-chip devices with Sn-3.8Ag-0.7Cu solder on electroless Ni (EN) without immersion Au were studied after aging at different temperatures. The (Cu,Ni)6Sn5 intermetallics (IMCs) growth was volume diffusion controlled and Kirkendall voids were found in the Ni3P layer even at the initial stage of high-temperature aging due to the faster diffusion of Ni in the Ni3P layer via its column structure boundaries. The Ag3Sn IMCs were distributed in the bulk solder, existing as plate- or lamella-like phases or as small particles around the β-Sn dendrites, and the (Cu,Ni)6Sn5 IMCs existed as facet-like phases. The plate- and lamella-like Ag3Sn phases break up into small parts and these broken parts, together with small Ag3Sn particles, coarsen into pebble-like phases during high-temperature aging. Shear tests showed that all the solder bumps fractured in the bulk solder. The shear strength of solder bumps decreases at the initial stage of aging at 150°C and 175°C, and the strength degradation during aging may be caused by the coarsening of small Ag3Sn particles.

Design and Implementation of an Integrated Performance Monitoring Tool for Swimming to Extract Stroke Information at Real Time

Current methods used to monitor performance for swimming do not offer real-time feedback to coaches and significantly increase post session analysis times. The aim of the research outlined in this paper is to design and implement a novel performance analysis tool to measure swimmer performance using wireless technology previously developed at Loughborough University. The Computer Integrated Manufacturing Open System Architecture (CIMOSA) has been coupled with a software architecture based on object-oriented techniques to formalize and structure the development of a computer integrated real-time monitoring system. Filtering and signal-processing algorithms are applied to extract performance indicators in real time, hence allowing faster access of feedback that can be used to enhance the swimming performance during each training session.

Accelerometer Profile Recognition of Swimming Strokes (P17)

The use of technology in sports performance analysis is a rapidly increasing practise. Tools for analysis aim to provide useful information to supplement coach knowledge and improve feedback in the development of athletes. In swimming the use of subjective video analysis is wide-spread, however, unlike some other sports, there are few quantitative measures of performance. Quantitative measures, such as intra cyclic variations of stroke characteristics, have the potential to provide more specific performance metrics from which to make improvements. Such measures are currently not widely available to coaches, support staff and swimmers, due to the infancy or lack of sufficiently developed technologies.

Modeling the digital content landscape in universities

Purpose – Digital content is a common denominator that underlies all discussions on scholarly communication, digital preservation, and asset management. This past decade has seen a distinctive evolution in thinking among stakeholders on how to assemble, care for, deliver, and ultimately preserve digital resources in a college and university environment. At first, institutional repositories promised both a technical infrastructure and a policy framework for the active management of scholarly publications. Now other approaches that take a broader view of digital content hold sway, the result being confusion rather than clarity about where digital content originates, who the stakeholders are, and how to establish and adjust asset management priorities. This article seeks to present a model for plotting the range of digital content that might be amenable to management as digital assets in higher education.Design/methodology/approach – The article reviews differing perspectives on digital content, outlines a g...