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Article
Publication date: 18 February 2019

Fen Peng, Wensheng Liu, Yufeng Huang, Siwei Tang, Chaoping Liang and Yunzhu Ma

The purpose of this study is to develop a monolayer surface coating of stearic acid on Sn-Ag-Cu solder powder to limit oxidation.

Abstract

Purpose

The purpose of this study is to develop a monolayer surface coating of stearic acid on Sn-Ag-Cu solder powder to limit oxidation.

Design/methodology/approach

Stearic acid was adsorbed onto Sn-Ag-Cu solder powder through liquid-phase adsorption. The isotherm of adsorption was measured and then the microstructure of coated powder was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy.

Findings

The adsorption isotherm of stearic acid on the powder was “H” type, which revealed the layer-by-layer adsorption on non-porous surface. When the concentration of solution was in the range of 0.001-0.006 mol/L, with an adsorption amount of 0.12 ± 0.1 mg/g, monolayer stearic acid covered the solder powder completely. Uniform and integrated self-assembled monolayer coating was formed through hydrogen bonds between the oxygen ions in surface lattice of Sn3.0Ag0.5Cu solder powder and the —O—H hydroxyl group of stearic acid. The maximum angle of stability of coated powder also reduced by 2.87° compared with that of non-coated powder. The increase rate of oxygen content of coated powder was much slower than that of non-coated powder when they were exposed to humid air.

Originality/value

As a result, oxidation of fine solder powder was effectively limited. Essentially, this method can also be applied to the coating of other types of solder powder and has reference significance to other coating by liquid-phase method.

Details

Soldering & Surface Mount Technology, vol. 31 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

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Article
Publication date: 18 February 2019

Fen Peng, Wensheng Liu, Yunzhu Ma, Chaoping Liang, Yufeng Huang and Siwei Tang

To explore substitutes for traditional Sn-Pb solder, Sn-20In-2.8Ag was considered because of its appropriate melting temperature, good reliability and high ductility at…

Abstract

Purpose

To explore substitutes for traditional Sn-Pb solder, Sn-20In-2.8Ag was considered because of its appropriate melting temperature, good reliability and high ductility at less than 100°C. However, the mechanical properties of Sn-20In-2.8Ag were not satisfactory. The reason for the poor mechanical properties of the Sn-20In-2.8Ag/Cu joint was revealed, and a way to solve the problem was found.

Design/methodology/approach

The microstructure evolution, characteristics of melting and solidification and joining performance with Cu were investigated using scanning electron microscopy (SEM), electron probe microanalysis, differential scanning calorimetry (DSC) and mechanical testing.

Findings

SEM results showed that the microstructure of Sn-20In-2.8Ag was composed of coarse dendritic Ag2In and γ phases, with Ag2In distributed at the grain boundaries. DSC measurements revealed that small amount of low temperature eutectic reaction, L → Ag2In + β + γ, occurred at 112.9°C. This reaction was caused by the segregation of indium, which is a process that has a strong driving force. In the lap-shear testing, a crack propagated along the grain boundary of the solder, and failure showed an intergranular fracture. This failure was connected with the three-phase eutectic and coarse Ag2In. Thus, to improve the mechanical properties, segregation of indium should be reduced and coarsening of Ag2In should be prevented.

Originality/value

The reason for the unsatisfactory mechanical properties of Sn-20In-2.8Ag was revealed via microstructural observations and solidification analysis, and the way to solve this problem was found.

Details

Soldering & Surface Mount Technology, vol. 31 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

Content available
Article
Publication date: 24 June 2020

Shenggen Fan, Wei Si and Yumei Zhang

The purposes of this paper are to review the impact on food and nutrition security of several pandemic emergencies and the 2018 food price crisis from a global…

Abstract

Purpose

The purposes of this paper are to review the impact on food and nutrition security of several pandemic emergencies and the 2018 food price crisis from a global perspective, examine the Chinese experiences and lessons in ensuring food and nutrition security for its citizen and propose policy actions to prevent a global food and nutrition security crisis.

Design/methodology/approach

The authors utilize a noncomprehensive review of peer-reviewed and nonpeer-reviewed literature, as well as a case study approach.

Findings

Under the ongoing COVID-19, China's food and nutrition are relatively secure in short run largely due to governmental proactive policies but may face uncertainties in livestock production and imports of soybean in the medium and long terms. Given that the disease has spread to almost all countries in the world, global cooperation and coordination are needed to prevent systemic risks to global food and nutrition security.

Practical implications

The review and analysis of this paper will help policymakers in China and other countries to design strategies and actions to prevent food and nutrition security crisis under the ongoing COVID-19 emergency and other similar threats in the future.

Originality/value

This paper provides recommendations to prevent food and nutrition security crisis based on data, evidence and case studies.

Details

China Agricultural Economic Review, vol. 12 no. 3
Type: Research Article
ISSN: 1756-137X

Keywords

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Article
Publication date: 11 May 2010

Wei Cai

The paper aims to explore how the undue state control leads to the weak stock market in China. It analyzes how the undue state control is exerted in some key areas in the…

Abstract

Purpose

The paper aims to explore how the undue state control leads to the weak stock market in China. It analyzes how the undue state control is exerted in some key areas in the Chinese stock market. This paper intends to expand the existing literature in the relationships among law, politics, and economy.

Design/methodology/approach

This paper mainly adopts the exploratory method to analyze the undue state influences. Under some circumstances, comparative study and historical explanation are also adopted.

Findings

The paper suggests that to create a strong stock market and facilitate the development of the listed companies and the whole economy, the state should first release its control on the stock market.

Research limitations/implications

Various fields are contained in a stock market, in most of which the undue state control can be observed. In this paper, only some key ones are explored. Further research on other fields and if possible more first‐hand data are necessary.

Practical implications

This paper not only offers an answer to concerns on the various misconducts in the inefficient Chinese stock market and helps to realize the possible ways out of such dilemma, but also it offers implications for other emerging economies.

Originality/value

The on‐going debate on the role of common‐law versus civil‐law system in the capital market may have ignored the state involvement. This paper indicates that it is the undue state control rather than the legal system that leads to the weak stock market in China.

Details

Journal of Financial Crime, vol. 17 no. 2
Type: Research Article
ISSN: 1359-0790

Keywords

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