1,721,024 research outputs found
Detection of Solder Joint Cracking of High Power LEDs on Al-IMS During Temperature Shock Test by Transient Thermal Analysis
No full textAn innovative sensitive test method is developed to detect solder joint cracking for high power LED packages. The method is
based on transient thermal analysis and can replace the dominating Light-On test. Test groups of LED packages were
soldered with two different lead free solders (SnAgCu 305 and Innolot FL-640) on Aluminum Insulated Metal Substrate and
exposed to temperature cycles. Transient thermal measurements were performed directly after assembly and after specific
cycle numbers. After data processing the increase of the relative thermal resistance between the initial signal at ‘0’ cycles and
‘n’ cycles is obtained and correlated with cracks in the solder joint by cross sections. The transient curves are reproduced by
time resolved finite element analysis. Based on the simulation, a failure criterium is defined representing a crack length of
30% of the solder joint area. A higher creep resistance for the test group soldered with Innolot FL-640 compared to the test
group soldered with SAC 305 is observed
Thermomechanical local stress in assembled GaN LEDs investigated by Raman optical spectroscopy
No full textIntegrated circuits constitute a complex mosaic, where materials with different characteristics, grown or deposited in different ways and at different temperatures, are linked together in various geometries. It is well known that during and after processing of these devices, mechanical stresses develop in the layers. These stresses may be due to thermal steps, intrinsic stresses, which are inherent in the formation process of the film, or due to the geometry of the material. For example, high stresses are present in the substrate at film edges. The presence of local residual stress has an important effect on the electrical properties of electronic devices, in particular on the reliability and the lifetime of the semiconductor components. The present work focuses on the optical investigation of the thermomechanical stress of semiconductor materials used to realize new LED modules for front lighting application. Blue LEDs, based on gallium nitride (GaN) on sapphire, are bonded to a silicon carrier using gold silicon. Afterwards the sapphire is removed. The GaN on silicon devices are soldered by eutectic AuSn soldered on copper substrates, with different thicknesses. In the solder process different AuSn solder layer are achieved by varying the bond force. Raman spectroscopy is used to investigate the influence of the assembly process and assembly material on the local stress in the semiconductor. By that the physical, mechanical and chemical properties of the interconnect material can be analyzed. A model is developed to simulate the thermomechanical stress in the GaN LED assemblies. The Raman results validate the computational model. The phenomena are evaluated at room temperature, at -50°C and at 180°C
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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