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Article
Publication date: 1 April 1998

Paul Conway, David Whalley, Michelle Wilkinson and S.M. Hyslop

This paper describes a technique for the monitoring and control of the reflow soldering process. The technique combines state‐of‐the‐art infra‐red (IR) sensor technology, coupled…

290

Abstract

This paper describes a technique for the monitoring and control of the reflow soldering process. The technique combines state‐of‐the‐art infra‐red (IR) sensor technology, coupled with application‐specific process monitoring and control software, providing a unique capability both to monitor product temperatures during processing and to modify the process settings. The development of techniques to allow variation of the heat transfer from the oven to the in‐process printed circuit assemblies (PCAs) provides the means to adjust the soldering oven’s process settings for each individual PCA. This automatic profiling ensures consistent thermal histories and optimises oven energy consumption. Archiving of the reflow profiles along with temperatures recorded for each PCA provides full traceability to the reflow process settings for each individual PCA. The incorporation of IR sensing technology also provides a means to monitor the performance of the process.

Details

Soldering & Surface Mount Technology, vol. 10 no. 1
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 1 September 2005

S.M. Hyslop, P.J. Palmer and D.C. Whalley

Routing efficiency provides an estimate of the compactness of a specific PCB layout in comparison with the theoretical minimum size for the circuit design. This work describes a…

342

Abstract

Purpose

Routing efficiency provides an estimate of the compactness of a specific PCB layout in comparison with the theoretical minimum size for the circuit design. This work describes a methodology for estimating the routing efficiency of existing PCB layouts from scanned images of either a manufactured PCB or the relevant PCB artwork. Measuring and maximising routing efficiency offers a powerful tool in the drive to minimise the size and cost of a PCB, as it provides a quantitative measure of the need to include costly features such as multiple signal layers and blind (or partial) vias.

Design/methodology/approach

The methodology was proven as a manual method, before implementation as a software tool. This work describes the image processing techniques used to recognise traces and vias and describes how this information is processed to derive substrate utilisation statistics.

Findings

An initial survey suggests that trace routing efficiency has declined through time, indicating that many layouts are larger than necessary, or use more signal layers than are required by routing constraints alone.

Research limitations/implications

This work finds that digital logic circuits follow a more coherent trend than analogue or mixed technology circuits. The results are therefore much more applicable in the digital domain.

Practical implications

As the methodology is implemented using images of PCB layouts, it offers the potential to investigate the performance of routing capability for current and legacy applications where CAD data are not available.

Originality/value

Where CAD drawings exist, routing efficiency can easily be calculated from the data. However, the methodology for estimating routing efficiency retrospectively from circuit images is believed to be unique, and sidesteps the problems of gaining access to this information.

Details

Circuit World, vol. 31 no. 3
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 15 January 2020

Daniel Straubinger, István Bozsóki, David Bušek, Balázs Illés and Attila Géczy

In this paper, analytical modelling of heat distribution along the thickness of different printed circuit board (PCB) substrates is presented according to the 1 D heat transient…

346

Abstract

Purpose

In this paper, analytical modelling of heat distribution along the thickness of different printed circuit board (PCB) substrates is presented according to the 1 D heat transient conduction problem. This paper aims to reveal differences between the substrates and the geometry configurations and elaborate on further application of explicit modelling.

Design/methodology/approach

Different substrates were considered: classic FR4 and polyimide, ceramics (BeO, Al2O3) and novel biodegradables (polylactic-acid [PLA] and cellulose acetate [CA]). The board thicknesses were given in 0.25 mm steps. Results are calculated for heat transfer coefficients of convection and vapour phase (condensation) soldering. Even heat transfer is assumed on both PCB sides.

Findings

It was found that temperature distributions along PCB thicknesses are mostly negligible from solder joint formation aspects, and most of the materials can be used in explicit reflow profile modelling. However PLA shows significant temperature differences, pointing to possible modelling imprecisions. It was also shown, that while the difference between midplane and surface temperatures mainly depend on thermal diffusivity, the time to reach solder alloy melting point on the surface depends on volumetric heat capacity.

Originality/value

Results validate the applicability of explicit heat transfer modelling of PCBs during reflow for different heat transfer methods. The results can be incorporated into more complex simulations and profile predicting algorithms for industrial ovens controlled in the wake of Industry 4.0 directives for better temperature control and ultimately higher soldering quality.

Details

Circuit World, vol. 46 no. 2
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 1 February 1992

O. Pedersen, B.‐E. Flaten and T. Gleditsch

A new model for the power system, covering resistance, self‐inductance, mutual inductance, and capacitive coupling between planes is presented. The model parameters are calculated…

35

Abstract

A new model for the power system, covering resistance, self‐inductance, mutual inductance, and capacitive coupling between planes is presented. The model parameters are calculated from the geometry of the actual board. No measurements are necessary to set up a model for a new board. The model has been verified against detailed computer simulations and measured data.

Details

Circuit World, vol. 18 no. 3
Type: Research Article
ISSN: 0305-6120

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Book part
Publication date: 6 August 2014

Kenneth Y. Chay and Dean R. Hyslop

We examine the roles of sample initial conditions and unobserved individual effects in consistent estimation of the dynamic binary response panel data model. Different…

Abstract

We examine the roles of sample initial conditions and unobserved individual effects in consistent estimation of the dynamic binary response panel data model. Different specifications of the model are estimated using female welfare and labor force participation data from the Survey of Income and Program Participation. These include alternative random effects (RE) models, in which the conditional distributions of both the unobserved heterogeneity and the initial conditions are specified, and fixed effects (FE) conditional logit models that make no assumptions on either distribution. There are several findings. First, the hypothesis that the sample initial conditions are exogenous is rejected by both samples. Misspecification of the initial conditions results in drastically overstated estimates of the state dependence and understated estimates of the short- and long-run effects of children on labor force participation. The FE conditional logit estimates are similar to the estimates from the RE model that is flexible with respect to both the initial conditions and the correlation between the unobserved heterogeneity and the covariates. For female labor force participation, there is evidence that fertility choices are correlated with both unobserved heterogeneity and pre-sample participation histories.

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Book part
Publication date: 9 October 2019

Linda Chisholm

Abstract

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Teacher Preparation in South Africa
Type: Book
ISBN: 978-1-78743-694-7

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Book part
Publication date: 6 August 2014

Lorenzo Cappellari and Stephen P. Jenkins

We analyse the dynamics of social assistance benefit (SA) receipt among working-age adults in Britain between 1991 and 2005. The decline in the annual SA receipt rate was driven…

Abstract

We analyse the dynamics of social assistance benefit (SA) receipt among working-age adults in Britain between 1991 and 2005. The decline in the annual SA receipt rate was driven by a decline in the SA entry rate rather than by the SA exit rate (which also declined). We examine the determinants of these trends using a multivariate dynamic random effects probit model of SA receipt probabilities applied to British Household Panel Survey data. We show how the model may be used to derive year-by-year predictions of aggregate SA entry, exit and receipt rates. The analysis highlights the importance of the decline in the unemployment rate over the period and other changes in the socio-economic environment including two reforms to the income maintenance system in the 1990s and also illustrates the effects of self-selection (‘creaming’) on observed and unobserved characteristics.

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Book part
Publication date: 9 October 2019

Linda Chisholm

Abstract

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Teacher Preparation in South Africa
Type: Book
ISBN: 978-1-78743-694-7

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Book part
Publication date: 26 November 2020

Alessio Fusco and Nizamul Islam

This paper investigates the effect of household size, and in particular of the number of children of different age groups, on poverty, defined as being in a situation of low…

Abstract

This paper investigates the effect of household size, and in particular of the number of children of different age groups, on poverty, defined as being in a situation of low income. We apply various static and dynamic probit models to control for the endogeneity of the variables of interest and to account for unobserved heterogeneity, state dependence, and serially correlated error components. Using Luxembourg longitudinal data, we show that the number of children of different age groups significantly affects the probability of being poor. However, the magnitude of the effect varies across different specifications. In addition, we find strong evidence of true poverty persistency due to past experience, spurious poverty persistency due to individual heterogeneity, and transitory random shocks.

Details

Inequality, Redistribution and Mobility
Type: Book
ISBN: 978-1-80043-040-2

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Book part
Publication date: 18 October 2019

Mohammad Arshad Rahman and Angela Vossmeyer

This chapter develops a framework for quantile regression in binary longitudinal data settings. A novel Markov chain Monte Carlo (MCMC) method is designed to fit the model and its…

Abstract

This chapter develops a framework for quantile regression in binary longitudinal data settings. A novel Markov chain Monte Carlo (MCMC) method is designed to fit the model and its computational efficiency is demonstrated in a simulation study. The proposed approach is flexible in that it can account for common and individual-specific parameters, as well as multivariate heterogeneity associated with several covariates. The methodology is applied to study female labor force participation and home ownership in the United States. The results offer new insights at the various quantiles, which are of interest to policymakers and researchers alike.

Details

Topics in Identification, Limited Dependent Variables, Partial Observability, Experimentation, and Flexible Modeling: Part B
Type: Book
ISBN: 978-1-83867-419-9

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