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Article

J.W. Morris, D. Grivas, D. Tribula, T. Summers and D. Frear

This paper discusses the microstructures of solder joints and the mechanism of thermal fatigue, which is an important source of failure in electronic devices. The solder…

Abstract

This paper discusses the microstructures of solder joints and the mechanism of thermal fatigue, which is an important source of failure in electronic devices. The solder joints studied were near‐eutectic Pb‐Sn solder contacts on copper. The microstructure of the joints is described. While the fatigue life of near‐eutectic solder joints is strongly dependent on the operating conditions and on the microstructure of the joint, the metallurgical mechanisms of failure are surprisingly constant. When the cyclic load is in shear at temperatures above room temperature the shear strain is inhomogeneous, and induces a rapid coarsening of the eutectic microstructure that concentrates the deformation in well‐defined bands parallel to the joint interface. Fatigue cracks propagate along the Sn‐Sn grain boundaries and join across the Pb‐rich regions to cause ultimate failure. The failure occurs through the bulk solder unless the joint is so thin that the intermetallic layer at the interface is a significant fraction of the joint thickness, in which case failure may be accelerated by cracking through the intermetallic layer. The coarsening and subsequent failure are influenced more strongly by the number of thermal cycles than by the time of exposure to high temperature, at least for hold times up to one hour. Thermal fatigue in tension does not cause well‐defined coarsened bands, but often leads to rapid failure through cracking of the brittle intermetallic layer. Implications are drawn for the design of accelerated fatigue tests and the development of new solders with exceptional fatigue resistance.

Details

Soldering & Surface Mount Technology, vol. 1 no. 3
Type: Research Article
ISSN: 0954-0911

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Book part

Md. Nazmul Ahsan and Jean-Marie Dufour

Statistical inference (estimation and testing) for the stochastic volatility (SV) model Taylor (1982, 1986) is challenging, especially likelihood-based methods which are…

Abstract

Statistical inference (estimation and testing) for the stochastic volatility (SV) model Taylor (1982, 1986) is challenging, especially likelihood-based methods which are difficult to apply due to the presence of latent variables. The existing methods are either computationally costly and/or inefficient. In this paper, we propose computationally simple estimators for the SV model, which are at the same time highly efficient. The proposed class of estimators uses a small number of moment equations derived from an ARMA representation associated with the SV model, along with the possibility of using “winsorization” to improve stability and efficiency. We call these ARMA-SV estimators. Closed-form expressions for ARMA-SV estimators are obtained, and no numerical optimization procedure or choice of initial parameter values is required. The asymptotic distributional theory of the proposed estimators is studied. Due to their computational simplicity, the ARMA-SV estimators allow one to make reliable – even exact – simulation-based inference, through the application of Monte Carlo (MC) test or bootstrap methods. We compare them in a simulation experiment with a wide array of alternative estimation methods, in terms of bias, root mean square error and computation time. In addition to confirming the enormous computational advantage of the proposed estimators, the results show that ARMA-SV estimators match (or exceed) alternative estimators in terms of precision, including the widely used Bayesian estimator. The proposed methods are applied to daily observations on the returns for three major stock prices (Coca-Cola, Walmart, Ford) and the S&P Composite Price Index (2000–2017). The results confirm the presence of stochastic volatility with strong persistence.

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Topics in Identification, Limited Dependent Variables, Partial Observability, Experimentation, and Flexible Modeling: Part A
Type: Book
ISBN: 978-1-78973-241-2

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Project Management
Type: Book
ISBN: 978-1-78714-830-7

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Article

J. Seyyedi

An empirical study was conducted to determine the thermal fatigue behaviour of 1.27 mm pitch, J‐bend and gullwing surface mount solder joints, manufactured with four…

Abstract

An empirical study was conducted to determine the thermal fatigue behaviour of 1.27 mm pitch, J‐bend and gullwing surface mount solder joints, manufactured with four low‐temperature solders. Selected solder alloys were: 58Bi‐42Sn (wt %), 43Sn‐43Pb‐14Bi, 52ln‐48Sn and 40ln‐40Sn‐20Pb. Accelerated thermal cycling was used in conjunction with metallographic analysis and mechanical (pull) strength measurement to test their behaviour. The relative merit of each solder composition was determined by comparing it with 63Sn‐37Pb solder, subjected to identical testing conditions. The strength decreased linearly with increased number of thermal cycles for gullwing solder joints of all four solder alloys. The fatigue lifetime was relatively longer for 58Bi‐42Sn and 40ln‐40Sn‐20Pb than for other alloys, but significantly lower than that obtained with 63Sn‐37Pb solder. No discernible degradation of strength was observed with the J‐bend solder joints of any solder alloy, even after the completion of 6000 thermal cycles. Thermal fatigue resistance of the latter joints was attributed to a more favourable coefficient of thermal expansion (CTE) mismatch. Solder joint cracking occurred only in gullwing components soldered with 52ln‐48Sn, 40ln‐40Sn‐20Pb and 43Sn‐43Pb‐14Bi alloys, after 1000 or 2000 thermal cycles. The crack initiated on the outside surface of the solder fillet, and appeared to propagate through both phases of the microstructure. The stress‐induced heterogeneous coarsening of the microstructure was evident only with 43Sn‐43Pb‐14Bi solder, although not as prevalent as that usually observed with eutectic Sn‐Pb solder. Fatigue cracks were absent from solder joints of 58Bi‐42Sn and 63Sn‐37Pb alloys.

Details

Soldering & Surface Mount Technology, vol. 5 no. 1
Type: Research Article
ISSN: 0954-0911

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Article

J.W. Head

THE orthodox solution of Lagrangian frequency equations involves the expansion into polynomial form of the characteristic determinantal equation in the latent roots, but…

Abstract

THE orthodox solution of Lagrangian frequency equations involves the expansion into polynomial form of the characteristic determinantal equation in the latent roots, but this method becomes exceedingly laborious if a large number of frequencies and their associated modes are required accurately for any system of equations of high order, say above the sixth. We define a system of Lagrangian frequency equations to be of the nth order if it consists of n equations for n homogeneous unknowns, which we call modes. A useful contribution to the problem was made by the iteration solution of Duncan and Collar, which is especially valuable when only the highest one or two latent roots are required. But when an aircraft propeller vibration problem required the first seven frequencies and their associated modes for a 12th‐order equation whose coefficients involved a variable pitch angle, the labour of calculation by this method appeared at that time (1941) to be prohibitive. The ‘Escalator’ method was therefore devised jointly by the author and Captain J. Morris of the Royal Aircraft Establishment as an alternative. In the propeller problem all the latent roots involved were necessarily real. Dr L. Fox, using relaxation methods, has recently solved a similar problem in a remarkably short time. Unfortunately, relaxation methods cannot easily be extended to the case of complex latent roots, which can occur in connexion with flutter, radio circuits and other problems. In this paper it is shown how the Escalator method can be adapted without essential change to cases in which complex quantities occur.

Details

Aircraft Engineering and Aerospace Technology, vol. 22 no. 4
Type: Research Article
ISSN: 0002-2667

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Article

Chi‐nien Chung

In this paper, I demonstrate an alternative explanation to the development of the American electricity industry. I propose a social embeddedness approach (Granovetter…

Abstract

In this paper, I demonstrate an alternative explanation to the development of the American electricity industry. I propose a social embeddedness approach (Granovetter, 1985, 1992) to interpret why the American electricity industry appears the way it does today, and start by addressing the following questions: Why is the generating dynamo located in well‐connected central stations rather than in isolated stations? Why does not every manufacturing firm, hospital, school, or even household operate its own generating equipment? Why do we use incandescent lamps rather than arc lamps or gas lamps for lighting? At the end of the nineteenth century, the first era of the electricity industry, all these technical as well as organizational forms were indeed possible alternatives. The centralized systems we see today comprise integrated, urban, central station firms which produce and sell electricity to users within a monopolized territory. Yet there were visions of a more decentralized electricity industry. For instance, a geographically decentralized system might have dispersed small systems based around an isolated or neighborhood generating dynamo; or a functionally decentralized system which included firms solely generating and transmitting the power, and selling the power to locally‐owned distribution firms (McGuire, Granovetter, and Schwartz, forthcoming). Similarly, the incandescent lamp was not the only illuminating device available at that time. The arc lamp was more suitable for large‐space lighting than incandescent lamps; and the second‐generation gas lamp ‐ Welsbach mantle lamp ‐ was much cheaper than the incandescent electric light and nearly as good in quality (Passer, 1953:196–197).

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International Journal of Sociology and Social Policy, vol. 17 no. 7/8
Type: Research Article
ISSN: 0144-333X

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Book part

Jenny Morris and Ray Kinnear

Purpose — This chapter considers how transport policy and planning has been developing in Victoria in tandem with the research program described elsewhere in this book…

Abstract

Purpose — This chapter considers how transport policy and planning has been developing in Victoria in tandem with the research program described elsewhere in this book. Developments in policy and planning are discussed with particular regard to transport disadvantage and social inclusion.

Methodology — The chapter commences by providing a policy and planning context in terms of the geography and demography of travel needs, the relevant jurisdictional responsibilities in Australia and the policy history. It then describes the evolution of transport policy in the past decade and outlines the way in which the findings of this research are being incorporated into the development of programs and projects to support social inclusion. Additionally, some key policy challenges are outlined, at least some of which may provide fruitful areas for undertaking further research to support the development of future policies and programs.

Findings — The results show that applied research can be a highly successful endeavour, particularly when policy and planning perspectives are integrated into the development of the research design and strong collaboration is an ongoing feature of the research program.

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New Perspectives and Methods in Transport and Social Exclusion Research
Type: Book
ISBN: 978-1-78-052200-5

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Book part

Michael Polgar

Sociology promotes and describes public health, helping to explain macro-social dynamics of mental health care through studies of organizations, networks, and systems of care.

Abstract

Purpose

Sociology promotes and describes public health, helping to explain macro-social dynamics of mental health care through studies of organizations, networks, and systems of care.

Methodology/approach

This chapter summarizes sociological research on mental health care organizations and systems, illustrating a macro-social perspective by examining the problem of transitions in care for young adults. Summary findings from a regional mental health services research project describe a system of care that includes 100 organizations. This system helps young adults with mental health needs.

Findings

The scope and management of care involves a focus on modes of treatment supported by research evidence and delivered effectively by people with cultural competencies. Care and continuity of care are delivered through coordinated systems of inter-organizational networks, linking organizations and providers. Active inter-organizational linkages are needed to support mental health for young adults during challenging and sometimes difficult transitions.

Originality/value

This research summarizes original and regional data on mental health care organizations within a regional system of care. Practical implications include support for the importance of coordination, transition planning, and cultural competence within and among organizations. Sociological and original research on organizations and systems should continue to elaborate the needs and values of mental health services for regional planning and public health.

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Education, Social Factors, and Health Beliefs in Health and Health Care Services
Type: Book
ISBN: 978-1-78560-367-9

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Book part

Erdoğan Koç, Çağatan Taşkın and Hakan Boz

Consumers are faced with many new products. In almost every product category it is seen that there are more alternatives than provided in previous years. This situation…

Abstract

Consumers are faced with many new products. In almost every product category it is seen that there are more alternatives than provided in previous years. This situation may cause consumers to feel uncomfortable/uncertain, especially about new products. Therefore, since they perceive this uncertainty, customers want to be in control. Control is one of the ways to help customers to decide on perceived risky situations.

The main purpose of the study is to explain the effects of the risk and control drive on consumer behavior and determine how businesses reduce the risk that consumers feel.

It is critical for enterprises to increase their brand awareness in order to reduce consumers’ risk perceptions and increase their controls (cognitive, behavioral, and decision) during purchasing decisions. Also, it will be useful for them to focus on activities increasing brand loyalty. They can especially carry out marketing activities allowing consumers to try new products or providing money back guarantees. Moreover, in order to reduce the risk perception and increase control by the customers, making the promotional contents of the product understandable and simple without hidden factors will contribute in a positive way.

Details

Contemporary Issues in Behavioral Finance
Type: Book
ISBN: 978-1-78769-881-9

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Article

J. Morris and W.J. Evans

OWING to vibration troubles which occasionally arise in engine crankshaft propeller systems, it has become necessary to investigate such possibilities in the design stage…

Abstract

OWING to vibration troubles which occasionally arise in engine crankshaft propeller systems, it has become necessary to investigate such possibilities in the design stage. In this paper we are concerned with the torsional vibration of an engine crankshaft coupled with flexural vibration of the propeller. The engine crankshaft will have a number of throws, which it has become customary to replace by “equivalent” pulleys which have the same moments of inertia as the complete crankthrows and are usually designated as engine “masses”. Assuming that there is a node in the propeller shaft, we may represent the torsional stiffness of the propeller shaft between the gears and the node by ca / (l−γ) where ca is the torsional stiffness of the propeller shaft; the torsional stiffness of the other portion of the propeller shaft will then be ca/γ. The frequencies of torsional vibrations of the engine crankshaft system about the assumed node are found for various values of γ. The corresponding frequencies of flexural vibrations of the propeller arc also found for the same values of γ. The two sets of frequencies may then be plotted against γ, giving engine crankshaft and propeller frequency curves respectively.

Details

Aircraft Engineering and Aerospace Technology, vol. 15 no. 6
Type: Research Article
ISSN: 0002-2667

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