Search results

The purpose of this paper is to determine: how much the residual curvature could be formed in sintered nano‐silver assembly when it is cooled to room temperature from the sintering temperature (normally 275°C); how the cyclic temperature load affects the residual curvature or stresses in sintered joint. Then the stress level and the reliability of sintered nano‐silver for high‐temperature applications can be understood.

5 mm * 2.5 mm silicon chip was bonded with 96 per cent Al₂O₃ substrate by sintering nanosilver paste. An optical system was developed to measure the curvature of the sintered assemblies. Reliability of the sintered assemblies was evaluated by temperature cycling of −40∼125°C. Finite element analysis was employed to simulate the behavior of the joint subjected to the temperature cycling from −40°C to 125°C by ANSYS. SEM images were taken to investigate the impact of temperature cycling on the reliability of sintered silver attachment.

This residual bending at room temperature was found concave towards the substrate (alumina) side. Also, with the bondline thickness increasing, the residual curvature decreases obviously. The severity of the residual bending in all the structures was mitigated to some extent with increasing number of cycles. There is no crack in the joint with the thickness of 25 μm. The drop of the residual curvature of the samples with bondline of 25 μm is caused mainly by stress relaxation in sintered silver before 300 cycles. Sample with thicker bondline is more susceptible to thermal cycling for the structure bonded with nanosilver than that with thinner bondline. The poor quality of bonding is due to the thicker sintered joint, which means that sintered nanosilver is not suitable for die‐attachment requiring thick bondline.

The paper describes: how a precise optical system was developed to measure the residual curvature of the sintered assemblies; how the evolution of the residual curvature of the sintered assembly with the temperature cycling was obtained by both experiment and simulation; and how microstructures of the sintered silver joint were analyzed for as‐sintered assembly and the sintered assembly after temperature cycling.

The purpose of this paper is to evaluate the mechanical properties of nano‐silver paste sintered lap shear structures and to discuss the effects of loading rate and ambient temperature on shear strength and fracture mechanism.

Single lap shear joints with an area of 2 mm² and thickness of 50 μm were fabricated by joining two copper substrates with nano‐silver paste. The lap shear tests were carried out under strain control mode on a micro uniaxial fatigue testing system with four loading rates and temperatures. The fracture sections were analyzed by SEM observation to determine the effect of temperature on the fracture mechanism.

Results from the study highlighted that the shear strain rate and temperature can have a significant impact on the shear behaviour of nano‐silver paste sintered lap shear joints. The shear strength increased with shear strain rate, but decreased with increasing ambient temperature. The lap shear joints displayed excellent ductility at higher temperatures due to the grain plastic flow.

So far, the investigation of the mechanical behaviour of low‐temperature sintered nano‐silver paste was restricted to a film form. No work had been done on nano‐silver paste connected structures. The findings presented in this paper give a basic understanding of the mechanical properties of nano‐silver sintered joints when sheared under different loading rates and temperatures.

Traditional chip‐level interconnection materials show many weaknesses given the development trend of microelectronic packaging technology. In order to meet the needs of high‐temperature packaging for wide‐bandgap semiconductors, low‐temperature sintered nano‐silver as a novel semiconductor device‐metallized substrate interconnection material is being developed. One phenomenon that larger interconnection area would cause poor interconnection quality had been found in the industry butut the mechanisms were never previously studied. This paper aims to address these issues.

The changes in the shear strengths and microstructures of nano‐silver joints induced by the changes of interconnection areas were investigated by shear tests and scanning electron microscopy.

The increased interconnection area blocks the organic components to be burnout and causes a higher pore ratio. Thus, it reduces the bonding quality. To ensure a good and steady sintering quality, the interconnection area should be limited to 3 × 3 mm².

A sintering technology or paste with oxygen agent will be studied in the future.

A relationship of shear strength and interconnection area of sintering joints with nano‐silver paste was observed.

Direct‐bond‐copper (DBC) substrates crack after about 15 thermal cycles from −55 to 250°C. The purpose of this paper is to study the phenomenology of thermal‐cracking to determine the suitability of DBC for high‐temperature packaging.

The thermal plastic strain distribution at the edge of the DBC substrate was analyzed by using a finite element method with the Chaboche model for copper. The parameters of the Chaboche model were verified by comparing with the three‐point bending test results of DBC substrate. The thermal analyses involving different edge tail lengths indicated that susceptibility to cracking was influenced by the edge geometry of the DBC substrate.

Interface cracking was observed to initiate at the short edge of the bonded copper and propagated into the ceramic layer. The interface crack was caused by the accumulation of thermal plastic strain near the short edge. The edge tail can decrease the thermal strain along the short edge of the DBC substrate. Thermal cycling lifetime was improved greatly for the DBC substrate with 0.5 mm edge tail length compared with that without edge tail.

The thermal cracking of DBC substrates should be studied at the microstructure level in the future.

Thermal cycling induced failure of DBC was analyzed. A method of alleviating the thermal plastic strain distribution on the weakest site and improving the thermal fatigue lifetime of DBC substrates under thermal cycling was proposed.

The purpose of this paper is to propose a novel method to analyze Table of Contents (TOC) in Chinese books automatically based on the hierarchy organization rules which gained by investigation.

This paper analyzed the main literature in this field first, then hierarchy organization rules of Chinese book TOC were generated and the method parsing TOC automatically based on these rules was proposed. A prototype system implementing the method was also developed. The method was evaluated through processing a corpus on the prototype system, and the results were checked with calculation of precision and recall.

The experiment result illustrated the superiority (extensive application, recall is 95.34 percent and precision is 94.44 percent) of the method.

The result can help Chinese libraries deal with electronic texts from four aspects. First, it can be used to complement or enhance current digitization and optical character recognition methods and cut the financial and labor cost of Chinese libraries. Second, it can help libraries to keep information on indexing words as well as chapters, sections and subsections in Chinese book databases, which ensures easy retrieval and extract any intended portion as demanded by user. Third, it helps to enrich the services and then enhances the user experiences in Chinese libraries. Fourth, it improves the specification and policy of digitalizing Chinese books.

The paper provided insight into the hierarchy organization of TOCs in Chinese books, the method based on the rules has extensive application than other methods. This method for Chinese book TOC automatic analysis is also as reference for English book TOC automatic analysis.

The purpose of this paper is to propose a novel approach to integrate portable document format (PDF) interface into Java-based digital library application. It bridges the gap between conducting content operation and viewing on PDF document asynchronously.

In this paper, the authors first review some related research and discuss PDF and its drawbacks. Next, the authors propose the design steps and implementation of three modes of displaying PDF document: PDF display, image display and extensible markup language (XML) display. A comparison of these three modes has been carried out.

The authors find that the PDF display is able to completely present the original PDF document contents and thus obviously superior to the other two displays. In addition, the format specification of PDF-based e-book does not perform well; lack of standardization and complex structure is exposed to the publication.

The proposed approach makes viewing the PDF documents more convenient and effective, and can be used to retrieve and visualize the PDF documents and to support the personalized function customization of PDF in the digital library applications.

This paper proposes a novel approach to solve the problem between content operation and the view of PDF synchronously, providing users a new tool to retrieve and reuse the PDF documents. It contributes to improve the service specification and policy of viewing the PDF for digital library. Besides, the personalized interface and public index make further development and application more feasible.

In this paper, some strategies taken to improve the reliability of solder joints on power devices in single device and multi‐chip packages are presented. A strategy for improving solder joint reliability by adjusting solder joint geometry, underfilling and utilization of flexible substrates is discussed with emphasis on triple‐stacked solder joints that resemble the shape of an hourglass. The hourglass shape relocates the highest inelastic strain away from the weaker interface with the chip to the bulk region of the joint, while the underfill provides a load transfer from the joints. Thermal cycling data show significant improvements in reliability when these techniques are used. The design, testing and finite‐element analyses of an interconnection structure, termed the Dimple‐Array Interconnect, for improving the solder joint reliability is also presented.

Internet + and Electronic Business in China is a comprehensive resource that provides insight and analysis into E-commerce in China and how it has revolutionized and continues to revolutionize business and society. Split into four distinct sections, the book first lays out the theoretical foundations and fundamental concepts of E-Business before moving on to look at internet+ innovation models and their applications in different industries such as agriculture, finance and commerce. The book then provides a comprehensive analysis of E-business platforms and their applications in China before finishing with four comprehensive case studies of major E-business projects, providing readers with successful examples of implementing E-Business entrepreneurship projects.

Internet + and Electronic Business in China is a comprehensive resource that provides insights and analysis into how E-commerce has revolutionized and continues to revolutionize business and society in China.

The purpose of this paper is to propose a novel within-document analysis tool (DAT) topic hierarchy and context-based document analysis tool (THC-DAT) which enables users to interactively analyze any multi-topic document based on fine-grained and hierarchical topics automatically extracted from it. THC-DAT used hierarchical latent Dirichlet allocation method and took the context information into account so that it can reveal the relationships between latent topics and related texts in a document.

The methodology is a case study. The authors reviewed the related literature first, then utilized a general “build and test” research model. After explaining the model, interface and functions of THC-DAT, a case study was presented using a scholarly paper that was analyzed with the tool.

THC-DAT can organize and serve document topics and texts hierarchically and context based, which overcomes the drawbacks of traditional DATs. The navigation, browse, search and comparison functions of THC-DAT enable users to read, search and analyze multi-topic document efficiently and effectively.

It can improve the document organization and services in digital libraries or e-readers, by helping users to interactively read, search and analyze documents efficiently and effectively, exploringly learn about unfamiliar topics with little cognitive burden, or deepen their understanding of a document.

This paper designs a tool THC-DAT to analyze document in a THC way. It contributes to overcoming the coarse-analysis drawbacks of existing within-DATs.