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1 – 10 of over 4000
Article
Publication date: 11 April 2008

Jeffery C.C. Lo, B.F. Jia, Z. Liu, J. Zhu and S.W. Ricky Lee

The purpose of this paper is to evaluate the lead‐free solder joint reliability of a variety of surface mount components assembled onto printed circuit boards (PCBs) under…

Abstract

Purpose

The purpose of this paper is to evaluate the lead‐free solder joint reliability of a variety of surface mount components assembled onto printed circuit boards (PCBs) under a number of different tests.

Design/methodology/approach

Lead‐free solder with a composition of Sn96.5‐Ag3.0‐Cu0.5 was used in a surface mount reflow process. Different types of surface mount dummy components with a daisy chain, such as CBGAs, BGAs, PLCCs, CSPs, and QFNs, were assembled onto PCBs. Both the mechanical and thermo‐mechanical reliability of the solder joints were evaluated by several tests. The experiments included package shear, package pull, three‐point bending and accelerated thermal cycling testing for 2,000 cycles. The packages were examined by X‐ray and C‐SAM before the reliability tests were carried out. The maximum load and the corresponding load‐displacement curve were recorded in the mechanical test.

Findings

The results from the mechanical tests show the major failure mode is on the copper pad. Weibull analysis shows that the characteristic lives of most packages are between 1,100 and 2,400 cycles. For the CBGA, the characteristic life of 96 cycles is relatively short, due to the serious CTE mismatch. Cross‐section inspection shows failures occur at the solder joint. Copper pad failure is also observed.

Originality/value

This paper provides both the mechanical and thermal‐mechanical reliability of lead‐free solder joints. The experimental data are very useful in the lead‐free SMT industries.

Details

Soldering & Surface Mount Technology, vol. 20 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 28 August 2020

Qingying Wang, Rongjun Cheng and Hongxia Ge

The purpose of this paper is to explore how curved road and lane-changing rates affect the stability of traffic flow.

150

Abstract

Purpose

The purpose of this paper is to explore how curved road and lane-changing rates affect the stability of traffic flow.

Design/methodology/approach

An extended two-lane lattice hydrodynamic model on a curved road accounting for the empirical lane-changing rate is presented. The linear analysis of the new model is discussed, the stability condition and the neutral stability condition are obtained. Also, the mKdV equation and its solution are proposed through nonlinear analysis, which discusses the stability of the extended model in the unstable region. Furthermore, the results of theoretical analysis are verified by numerical simulation.

Findings

The empirical lane-changing rate on a curved road is an important factor, which can alleviate traffic congestion.

Research limitations/implications

This paper does not take into account the factors such as slope, the drivers’ characters and so on in the actual traffic, which will have more or less influence on the stability of traffic flow, so there is still a certain gap with the real traffic environment.

Originality/value

The curved road and empirical lane-changing rate are researched simultaneously in a two-lane lattice hydrodynamic models in this paper. The improved model can better reflect the actual traffic, which can also provide a theoretical reference for the actual traffic governance.

Details

Engineering Computations, vol. 38 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 31 May 2022

Liang Xuan and Zheng Xu

Gradient coils designed by conventional target field methods usually have a complex physical structure and these methods are not convergent for complex routing area…

Abstract

Purpose

Gradient coils designed by conventional target field methods usually have a complex physical structure and these methods are not convergent for complex routing area problems. This study aims to design a multi-coil (MC) gradient system arranged on a complex routing area including two cylindrical surfaces with different radii for a head magnetic resonance imaging scanner.

Design/methodology/approach

A MC system model is established. In this model, the sub-coils are evenly distributed on two cylindrical wiring surfaces, and the radii of coils are the same on one cylindrical surface. With the target magnetic field set, the currents in every individual coil are solved by constrained least-squares fitting based on the Levenberg–Marquardt method.

Findings

The magnetic field nonlinearity generated by designed coils is validated as 4.50% and 3.57% for X-gradient coil and Z-gradient coil, respectively, which satisfy the mainstream nonlinearity standards. The analysis of the optimization results indicates that hardware requirements can be considerably reduced by connecting coils with the same currents in series.

Originality/value

High-linearity gradient magnetic fields are generated on complex routing areas by adopting the MC structure. In addition, the requirements for current sources and amplifiers are considerably reduced.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0332-1649

Keywords

Open Access
Article
Publication date: 2 August 2019

Yazhou Mao, Yang Jianxi, Xu Wenjing and Liu Yonggang

The purpose of this paper is to investigate the effect of round pits arrangement patterns on tribological properties of journal bearing. In this paper, the tribological…

Abstract

Purpose

The purpose of this paper is to investigate the effect of round pits arrangement patterns on tribological properties of journal bearing. In this paper, the tribological behaviors of journal bearing with different arrangement patterns under lubrication condition were studied based on M-2000 friction and wear tester.

Design/methodology/approach

The friction and wear of journal bearing contact surface were simulated by ANSYS. The wear mechanism of bearing contact surfaces was investigated by the means of energy dispersive spectrum analysis on the surface morphology and friction and wear status of the journal bearing specimens by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). Besides, the wearing capacity of the textured bearing was predicted by using the GM (1,1) and Grey–Markov model.

Findings

As the loads increase, the friction coefficient of journal bearing specimens decrease first and then increase slowly. The higher rotation speed, the lower friction coefficient and the faster temperature build-up. The main friction method of the bearing sample is three-body friction. The existence of texture can effectively reduce friction and wear. In many arrangement patterns, the best is 4# bearing with round pits cross-arrangement pattern. Its texturing diameters are 60 µm and 125 µm, and the spacing and depth are 200 µm and 25 µm, respectively. In addition, the Grey–Markov model prediction result is more accurate and fit the experimental value better.

Originality/value

The friction and wear mechanism is helpful for scientific research and engineers to understand the tribological behaviors and engineering applications of textured bearing. The wear capacity of textured bearing is predicted by using the Grey–Markov model, which provides technical help and theoretical guidance for the service life and reliability of textured bearing.

Article
Publication date: 3 July 2020

Ruben B.O. Acevedo, Klaudia Kantarowska, Edson Costa Santos and Marcio C. Fredel

This paper aims to generate a review of available techniques to measure Residual Stress (RS) in Ti6Al4V components made by Ti6Al4V.

Abstract

Purpose

This paper aims to generate a review of available techniques to measure Residual Stress (RS) in Ti6Al4V components made by Ti6Al4V.

Design/methodology/approach

State of the art; literature review in the field of Residual Stress measurement of Ti6Al4V parts made by selective laser melting (SLM).

Findings

Different Residual Stress measurement techniques were detailed, regarding its concept, advantages and limitations. Regarding all researched references, hole drilling (semi destructive) and X-ray diffraction (nondestructive) were the most cited techniques for Residual Stress measurement of Ti6Al4V parts made by SLM.

Originality/value

An extensive analysis of RS measurement techniques for Ti6Al4V parts made by SLM.

Details

Rapid Prototyping Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 30 August 2022

Bo Chen, Tao Wang, Xin Xi, Caiwang Tan and Xiaoguo Song

Ti-Al composite plates have been used in aerospace and other important fields for specific purposes in recent years. However, relatively few studies have concentrated on…

Abstract

Purpose

Ti-Al composite plates have been used in aerospace and other important fields for specific purposes in recent years. However, relatively few studies have concentrated on Ti-Al additive manufacturing because during additive manufacturing process the local fusion and mixing of Ti/Al are inevitable. These areas where Ti and Al are mixed locally, especially interface, could easily generate high residual stresses and cracks. This study aims to manufacture Ti-Al functionally graded material and investigate the interaction of interface.

Design/methodology/approach

In this study, Ti6Al4V/AlSi10Mg functionally graded materials were fabricated by laser based directed energy deposition (L-DED) and a strategy using V interlayer to relieve interfacial stress was investigated.

Findings

The area between the two materials was divided into transition zone (TZ) and remelting zone (RZ). The phase distribution, microstructure and micro-Vickers hardness of the TZ and RZ were investigated. Typical intermetallic compounds (IMCs) such as TiAl3, Ti3Al and Ti5Si3 were found in both composites. The addition of V interlayer promoted the homogenization of IMCs near interface and led to the formation of new phases like V5Si3 and Al3V.

Originality/value

The solidification process near the interface of Ti-Al functionally graded material and the possible generation of different phases were described. The result of this paper proved the feasibility of manufacturing Ti-Al functionally graded material by L-DED.

Details

Rapid Prototyping Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1355-2546

Keywords

Article
Publication date: 16 August 2013

Yuanming Chen, Wei He, Guoyun Zhou, Zhihua Tao, Yang Wang and Daojun Luo

Pb‐free soldering challenged printed circuit board (PCB) assembly with high temperature. The purpose of this paper is to explain the failure mechanism of printed circuit…

Abstract

Purpose

Pb‐free soldering challenged printed circuit board (PCB) assembly with high temperature. The purpose of this paper is to explain the failure mechanism of printed circuit board (PCB) assembly with solder bubbles of vias to avoid the problems of via‐drilling defects and solder joint failure.

Design/methodology/approach

The failure of PCB vias with solder bubbles was investigated through cross sections and SEM microstructure inspection, TMA measurement, moisture absorption analysis and DSC measurement. The moisture absorption and CTE of FR4 laminate matched with manufacturing requirement to avoid the effects of solder bubbles. The effects of via drilling with a dull drill bit were compared to that with a new drill bit.

Findings

The moisture absorbed inside holes of via plating layers could be exposed to induce solder bubbles during Pb‐free soldering assembly and dull drill bits should be prevented during the drilling process to avoid the no‐bearing drilling effects.

Originality/value

The failure of PCB vias is not only involved in the voiding in solder joints but manufacturing processes of PCB. The paper designs an approach to analyse the properties of PCB materials and the drilling effects of vias to find out the mechanism resulting in solder bubbles of vias. The problem of drill bits should be considered to prevent the moisture absorbed in drilling vias with defects.

Details

Circuit World, vol. 39 no. 3
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 14 August 2021

Huayi Li, Qingxian Jia, Rui Ma and Xueqin Chen

The purpose of this paper is to accomplish robust actuator fault isolation and identification for microsatellite attitude control systems (ACSs) subject to a series of…

Abstract

Purpose

The purpose of this paper is to accomplish robust actuator fault isolation and identification for microsatellite attitude control systems (ACSs) subject to a series of space disturbance torques and gyro drifts.

Design/methodology/approach

For the satellite attitude dynamics with Lipschitz constraint, a multi-objective nonlinear unknown input observer (NUIO) is explored to accomplish robust actuator fault isolation based on a synthesis of Hinf techniques and regional pole assignment technique. Subsequently, a novel disturbance-decoupling learning observer (D2LO) is proposed to identify the isolated actuator fault accurately. Additionally, the design of the NUIO and the D2LO are reformulated into convex optimization problems involving linear matrix inequalities (LMIs), which can be readily solved using standard LMI tools.

Findings

The simulation studies on a microsatellite example are performed to prove the effectiveness and applicability of the proposed robust actuator fault isolation and identification methodologies.

Practical implications

This research includes implications for the enhancement of reliability and safety of on-orbit microsatellites.

Originality/value

This study proposes novel NUIO-based robust fault isolation and D2LO-based robust fault identification methodologies for spacecraft ACSs subject to a series of space disturbance torques and gyro drifts.

Details

Aircraft Engineering and Aerospace Technology, vol. 93 no. 7
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 1 December 2011

Jia Beisi and Jiang Yingying

Although an important facet of modernist architecture in which function plays a prominent role, building flexibility is not entirely a new concept. Its relevance…

Abstract

Although an important facet of modernist architecture in which function plays a prominent role, building flexibility is not entirely a new concept. Its relevance transcends generations, allowing space and structure to evolve through time. This paper investigates the relationship among main building structures, infill elements, and space by studying examples in ancient Chinese architecture. It reveals the role of building owners, users, and craftsmen from a survey of historical documentation. In studying these examples, it is concluded that craftsmen in ancient China were involved not only during the construction phase but throughout the period of use as well. Thus, in select cases, the relationship between craftsmen and owners or users had been preserved for generations. Finally, this paper suggests potential strategies for the building industry and technology in the move towards sustainable development.

Details

Open House International, vol. 36 no. 4
Type: Research Article
ISSN: 0168-2601

Keywords

Article
Publication date: 5 April 2013

Chien‐Yi Huang and Yueh‐Hsun Lin

The purpose of this paper is to employ data mining as a new diagnosing scheme for investigating void formation to the thermal pad in quad flat non‐lead (QFN) assembly…

Abstract

Purpose

The purpose of this paper is to employ data mining as a new diagnosing scheme for investigating void formation to the thermal pad in quad flat non‐lead (QFN) assembly. Occurrences of voiding in various scenarios of component design, materials selection and manufacturing process are analyzed.

Design/methodology/approach

This research investigates the process yield of a PCB assembly for a handheld device in the electronics manufacturing industry using the chi‐square automatic interaction detection (CHAID) algorithm and chi‐square test. Practical data generated by an X‐ray apparatus from the shop floor are collected. The critical attributes to the void formation (in the solder joint) of the QFN component are identified.

Findings

Stocking the PCB material beyond ten days may increase the level of voiding by 1%. Using PCB provided by vendor U helps decrease the level of voiding by 1.6%. Stocking the component material above 43 days may increase the level of voiding by 1.9%. In addition, reflow soldering profile with time above liquid (TAL) less than or equal to 62 sec and with peak temperature higher than or equal to 241°C generate less voids. Finally, the via‐in‐pad design causes a concave geometry on the surface of thermal pad which contributes to the voiding formation. The amount of voiding can be further diminished by plugging the via with plated copper.

Originality/value

This research implements CHAID that extracts useful knowledge from a huge amount of manufacturing data in order to realize the complex interaction effects through automated analysis. The extent of voiding in the samples using the optimal process suggested through CHAID algorithm can be reduced from 16% to 10.2%.

Details

Soldering & Surface Mount Technology, vol. 25 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

1 – 10 of over 4000