Search results

In the electronic assembly industry, low-temperature soldering holds great potential to be used in surface mounting technology. Tin–bismuth (Sn–Bi) eutectic alloys are lead-free solders applied in consumer electronics because of their low melting point, high strength and low cost. This paper aims to investigate how to address the problem of hot tear crack formation during Sn–Bi low-temperature solder (LTS) in the mass production of consumer electronics.

This paper explored the development of hot tear cracks during Sn–Bi soldering in the fabrication of flip chip ball grid arrays. Experiments were designed to simulate various conditions encountered in Sn–Bi soldering. Quantitative analysis was conducted on the number of hot tear cracks observed in different alloy compositions and solder volumes to explore the primary cause of hot tear cracks and possible methods to suppress crack formation.

Hot tear cracks existed in Sn–Bi solders with different bismuth (Bi) contents, but increasing the solder volume reduced the number of hot tear cracks. Experiments were designed to test the degree of chip transient thermal warpage with temperature change, and, according to the results, glue was dispensed in specific areas to reduce chip warpage deformation. Finally, the results of combined process experiments pointed to an effective method of low-temperature soldering to suppress hot tear cracks.

The study focuses on Sn–Bi solders only without other solder pastes such as SAC305 or Sn–Zn series.

With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles electronics, solar photovoltaic and other field, there will be more and more demand for low- temperature, energy-saving, lead-free solders. Therefore, this study will help the industry to roll out LTS (Sn–Bi) solutions rapidly.

In the long term, lean and green manufacturing is expected to be essential for maintaining an advanced manufacturing industry across the world. Developing new LTSs and soldering processes is the most effective, direct solution for energy conservation and emission mitigation. With the growing popularity of smart electronics, especially in intelligent terminals, new energy vehicles and solar photovoltaics, there would be an increased demand for low-temperature, energy-saving, lead-free techniques.

Although there are many methods that can be used to suppress hot tear cracks, there is little research on how to control the hot tear cracks caused by the low-temperature soldering of Sn–Bi in laptop applications. The authors studied the hot tear cracks that developed during the world’s first mass production of 50 million personal laptops based on low-temperature Sn–Bi alloy solder pastes. By controlling the Bi content, redesigning the solder paste printing process (e.g. through a printer’s stencil) and adding dispensing processes, the authors obtained reliable and stable experimental data and conclusions.

This study explores the characteristics of high-speed rail (HSR) and air transportation networks in China based on the weighted complex network approach. Previous related studies have largely implemented unweighted (binary) network analysis, or have constructed a weighted network, limited by unweighted centrality measures. This study applies weighted centrality measures (mean association [MA], triangle betweenness centrality [TBC], and weighted harmonic centrality [WHC]) to represent traffic dynamics in HSR and air transportation weighted networks, where nodes represent cities and links represent passenger traffic. The spatial distribution of centrality results is visualized by using ArcGIS 10.2. Moreover, we analyze the network robustness of HSR, air transportation, and multimodal networks by measuring weighted efficiency (WE) subjected to the highest weighted centrality node attacks. In the HSR network, centrality results show that cities with a higher MA are concentrated in the Yangtze River Delta and the Pearl River Delta; cities with a higher TBC are mostly provincial capitals or regional centers; and cities with a higher WHC are grouped in eastern and central regions. Furthermore, spatial differentiation of centrality results is found between HSR and air transportation networks. There is a little bit of difference in eastern cities; cities in the central region have complementary roles in HSR and air transportation networks, but air transport is still dominant in western cities. The robustness analysis results show that the multimodal network, which includes both airports and high-speed rail stations, has the best connectivity and shows robustness.

The quality and quantity of data are vital for the effectiveness of problem solving. Nowadays, big data analytics, which require managing an immense amount of data rapidly, has attracted more and more attention. It is a new research area in the field of information processing techniques. It faces the big challenges and difficulties of a large amount of data, high dimensionality, and dynamical change of data. However, such issues might be addressed with the help from other research fields, e.g., swarm intelligence (SI), which is a collection of nature-inspired searching techniques. The paper aims to discuss these issues.

In this paper, the potential application of SI in big data analytics is analyzed. The correspondence and association between big data analytics and SI techniques are discussed. As an example of the application of the SI algorithms in the big data processing, a commodity routing system in a port in China is introduced. Another example is the economic load dispatch problem in the planning of a modern power system.

The characteristics of big data include volume, variety, velocity, veracity, and value. In the SI algorithms, these features can be, respectively, represented as large scale, high dimensions, dynamical, noise/surrogates, and fitness/objective problems, which have been effectively solved.

In current research, the example problem of the port is formulated but not solved yet given the ongoing nature of the project. The example could be understood as advanced IT or data processing technology, however, its underlying mechanism could be the SI algorithms. This paper is the first step in the research to utilize the SI algorithm to a big data analytics problem. The future research will compare the performance of the method and fit it in a dynamic real system.

Based on the combination of SI and data mining techniques, the authors can have a better understanding of the big data analytics problems, and design more effective algorithms to solve real-world big data analytical problems.

China after 1949, especially since entering the 21st century, significant progress has been made in leadership research under Chinese context. However, so far there has been no systematic review and prospect of China's leadership research in the past 70 years. Therefore, with the help of scientific visualization software Citespace, this paper analyzes the research papers on leadership in the context of China from the top international journals of management science and applied psychology (1949–2018), supplemented and verified the previous research conclusions based on qualitative review, and quantitatively demonstrated the research evolution of leadership field.

Using a scientific visualization tool CiteSpace and 145 international leadership works, which were published in 64 top international journals and collected from the Web of Science database, and 852 domestic works which were published in 28 top domestic journals and collected from the CNKI database from 1949 to 2018, we draws keyword co-occurrence knowledge graph and keyword strategy map to visualize the landscape and evolution of leadership research and analyze the hot topics and research trends in the field of leadership.

The research found that: (1) Before 2002, there were only 7 articles published in 64 international top journal, mainly focusing on Western leadership theories such as transformational, cross-cultural comparison and the adaptability in Chinese context; (2) From 2003 to 2012, scholars had begun to introduce mainstream quantitative research paradigm in international academic community; (3) From 2013 to 2018, researches tended to be synchronized, with 461 and 99 papers published respectively. How emerging leaderships (such as ethical leadership) affect on various emerging outcome variables (such as creativity, voice behavior, unethical pro-organizational behavior etc.) is hot topic for future research.

Different from the previous qualitative reviews on organizational culture research, this paper, for the first time, uses bibliometric research methods to systematically analyze the evolution path of leadership research during the 70 years of China(1949–2018, and puts forward the future research prospects.

This paper aims to study the synergistic effect of graphene sponge on the thermal properties and shape stability of composite phase change material (PCM).

Graphene oxide sponge is first prepared from an aqueous solution of graphene oxide by freeze-drying method. The oxidized graphene sponge is reduced by hydrazine hydrate. Finally, use vacuum impregnation method to introduce paraffin into graphene sponge to prepare composite PCM.

Graphene sponge is used to improve the shape stability of paraffin wax and improves the thermal conductivity and latent heat of the composite PCM. The thermal conductivity increases by 200 per cent and the composite PCM has excellent reliability in 100 melt-freezing cycles.

A simple way for fabricating composite PCM with high thermal conductivity and latent heat which has the potential to be used as thermal storage materials without container encapsulation has been developed by using graphene sponge and paraffin.

The materials and preparation methods with special structure and properties in this paper provide a new idea for the research of PCM, which can be widely used in the fields of energy conversion and storage.

Combined defects in ball bearings may be caused during the use or manufacturing process, which can significantly affect their vibration characteristics. The previous defect models in the literature can only describe single defects such as the surface waviness and localized defect. This paper aims to propose an in-depth understanding of radial vibrations of a ball bearing with the combined defect.

A dynamic model for a ball bearing with the combined defect including the surface waviness and localized defect on its races is proposed. The effects of the combined defect sizes on the radial bearing vibrations are investigated. The results from the proposed model considering the combined defect are compared with the available results from the previous methods considering the single defects.

The acceleration amplitude is significantly affected by the surface waviness, localized defect and the combined defect on its races. The effect of the combined defect on the acceleration amplitude is larger than that of the single defect. The amplitude and peak frequency of the spectrum of acceleration for the combined defect increases with the defect sizes. The RMS value of the accelerations for the combined defect increases with the combined defect sizes.

Consequently, the proposed model can predict more accurate and in-depth understanding of the radial vibrations caused by the combined defect in the ball bearing.

This study pinpoints the critical factors influencing the acceptance of blockchain technology in supply chain management in the light of the extended unified theory of acceptance and use of technology (UTAUT2) with additional factors personal innovativeness in technology and user's self-efficacy.

The questionnaire-based data was obtained from SC professionals in China (Beijing). The essential factors influencing it are evaluated through structural equation modeling (SEM), using AMOS software.

The empirical findings specify that performance expectancy, facilitating conditions, price value, hedonic motivation, user self-efficacy, and personal innovativeness are positively influencing user satisfaction. User satisfaction has a substantial progressive effect on habit. Furthermore, facilitating conditions, price value, habit, user self-efficacy, personal innovativeness, and user satisfaction have a progressive impact on continued intention to use blockchain technology in supply chain management.

Although numerous studies investigated the influencing factors of blockchain technology adoption in supply chain management, no study examined the determinants of UTAUT2. However, this study not only empirically studied the UTAUT2 model but also extended it with the most influencing elements such as personal innovativeness in technology and user's self-efficacy. Furthermore, this study contributes to the BT-enabled SCM literature by studying the continued use and acceptance, rather than testing behavioral intention and initial adoption which is common in previous studies of BT-enabled SCM. Finally, this study discusses the limitations, future directions, and managerial implications of the results so that supply chain professionals can deliver what supply chain stakeholders require.

The construction industry accounts for a large proportion of the economy of developing countries, but the connotation and influencing factors of high-quality development (HQD) are still unclear. This study aims to gain a more comprehensive insight into the current development status of the regional construction industry under China's HQD orientation and the obstructive factors affecting its development and to provide informative suggestions for its HQD prospects.

In this study, the construction industry of 16 cities in the Chengdu-Chongqing economic circle (CCEC), a new region in southwest China, was used as the research object to collect data from the 2006–2019 yearbooks, construct an evaluation index system for HQD of the construction industry, derive the development level of the construction industry using the entropy value method and spatial autocorrelation method and then apply the barrier Diagnostic model was used to compare and analyze the impact level of each index.

In terms of the time dimension, the development of the construction industry in CCEC is characterized by “high in the twin core and low in the surrounding area”, with unbalanced and insufficient development; in terms of spatial correlation, some factors have positive aggregation in spatial distribution, but the peripheral linkage decreases; through barrier analysis, the impact of different barrier factors is different.

This paper will help governments and enterprises in developing countries to make urban planning and management policies to fundamentally improve the development of the construction industry in underdeveloped regions.

The authors examined the impact of environmental concerns, knowledge of organic/novel food, food neophobia, food neophilia, health consciousness and social norms on satisfaction toward organic food leading to the intention to purchase organic food (IPOF). Moreover, perceived barriers are used as a moderator between satisfaction toward organic food and IPOF.

PLS-SEM followed and multiple regression analysis followed for hypotheses testing. Convenience sampling is used and 497 questionnaires were used for the final analysis.

Environmental concerns, knowledge of organic food, food neophilia, health consciousness, and social norms are positively related to satisfaction toward organic food leading to the IPOF. Food neophobia decreases satisfaction toward organic food. Moreover, perceived barriers are significantly moderate between satisfaction toward organic food and IPOF.

Organic food organizations can use the findings to increase their IPOF. Moreover, academicians and practitioners can get an advantage from study outcomes.

This is a pioneer study that incorporates environmental concerns, knowledge of organic food, food neophobia, food neophilia, health consciousness, social norms, satisfaction toward organic food and perceived barriers to examine IPOF in light of the theory of planned behavior (TPB).

The purpose of this paper is to reveal the influence of dimples on the tribological properties of the “washers-cage-rollers” system of rolling element bearing (REB) under starved lubrication.

A fiber laser marking system was used to prepare dimples patterns on the raceways of the shaft washers of cylindrical roller thrust bearings (CRTBs). The friction and wear properties of dimples textured CRTBs with different diameter of dimples (200 µm, 250 µm, 300 µm) and depth of dimples (4 µm, 8 µm, 12 µm) were researched through a vertical universal wear test rig using a customized tribo-pair under starved lubrication. The surface stresses and the influence mechanism of dimple units on the tribological behavior of REBs were also compared and discussed.

Although the surface stresses on the raceways of dimples textured bearings are significantly higher than that of the smooth group, the coefficients of friction and wear losses of them are all reduced under starved lubrication. When the effective volume of dimples is between 1.13 and 2.25 and the depth of dimples is smaller than 12 µm, the tribological properties of dimples textured CRTBs are significantly improved. In this work, when the diameter of dimples is 250 µm, and the depth of dimples is 8 µm, the textured bearings can provide the excellent friction-reduction ability and outstanding wear resistance.

This work is a valuable reference for the raceway design and optimization of REBs.