1,721,163 research outputs found
Thermogravimetric investigation on the interaction of formic acid with solder joint materials
No full textSoldering is a dominating process for semiconductor packaging. For electronic manufacturing tin based solders play a key role. The surface of most solder alloys is oxidized under an oxygen containing atmosphere. Usually reducing chemicals, called fluxing agents, are used to enable the formation of solder contacts. However, standard liquid flux leaves aggressive residues on the electronic devices. Clean processes were developed using gaseous flux, i.e. formic acid vapor. Despite the competitiveness of the reducing effect of formic acid vapour on many solder alloys, only little is known about the corresponding reaction mechanism, especially at the surface. An oxidized copper powder and a tin silver copper alloy were investigated using thermogravimetric and mass spectra analysis under formic acid flow. Details on the adsorbed and desorbed species and the formation of intermediates and decomposition products are presented. Activation temperatures are estimated and correlated with heating processes
Formic acid and formate salts for chemical vapor deposition of copper on glass substrates at atmospheric pressure
No full textChemical vapor deposition (CVD) typically occurs at pressures below 100 kPa because the quality of the produced film usually degrades at higher pressures. Two different approaches of CVD are presented in this study to successfully deposit thin films of copper on glass substrates at atmospheric pressure. The CVD processes occurred as a result of sublimation and thermal decomposition of Cu formate salts. The chemical composition and morphology of the deposited layers were investigated using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. The thickness of the layers was increased with a series of deposition cycles and was analysed using X-ray fluorescence spectroscopy and profilometry. The best results were obtained using Cu formate powder as the starting material and operating under a N2 atmosphere at 240 °C and 1 atm. A thickness of 600 nm was obtained after 10 deposition cycles. The resistivity values of Cu films were 2.6 × 10-7 and 8 × 10-8 Ω m after 5 and 10 cycles of deposition, respectively
Thermomechanical Stress in GaN LED Soldered on Copper Substrate Evaluated by Raman Measurements and Computer Modelling
No full textThermomechanical stress due to tensile and compressive strain is a critical aspect in packaging technology. Residual
thermomechanical stress due to large difference in coefficients of thermal expansion between materials generates reliability
problems not only at the bonded interfaces but also for the lifetime of the active regions of high power semiconductors. Raman
spectroscopy is a non-destructive method to investigate the residual stress in semiconductors. Blue LEDs based on gallium
nitride bonded to a silicon carrier by a gold layer were soldered with eutectic gold-tin solder on a copper substrate. The bond
line thickness was varied by application of a bond force between 0 and 21 N and the thickness of the copper substrate was
chosen between 1 and 0.2 mm. The Raman shift of the E2
H phonon mode in the GaN layer was measured between -50° and
180°C. The temperature and assembly depending Raman shifts were analysed using literature data to access the residual
thermomechanical stress. The stress was mapped through the surface to measure its homogeneity. Finite analysis simulation
were performed for further analysi
Novel approach to copper sintering using surface enhanced brass micro flakes for microelectronics packaging
Full text linkCopper pastes suitable for low temperature and low pressure die-attach bonding were developed to enable sintering at 275 °C under N2 atmosphere. First, brass flakes were treated with HCl to selectively etch Zn and to realize enhanced surface modifications on the flakes. Then, polyethylene glycol was added as binder to the modified flakes due to its reducing effects on copper oxides and its property to prevent agglomeration. Shear strength of ca. 50 MPa was achieved while sintering with 10 MPa bonding pressure thereby providing suitable, easy and low-cost sintering pastes for microelectronics packaging applications
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
Evaluation of silver and copper sintering of first level interconnects for high power LEDs
No full textSilver sintering, well known in power electronic applications, is migrating into optoelectronic assembly, to replace other interconnect materials like the eutectic Au80Sn20 or SnAgCu solder. Sintering offers an interconnect that can be formed at low temperature while at the same time can operate at high temperature. The goal of the research of this paper is to develop a sintered interconnect which can replace traditional AuSn or SnAgCu (SAC) solder, offering low thermal resistance, sufficient shear strength and thermo-mechanical fatigue resistance. Silver offers excellent thermal properties and can be an effective replacement in case of low mechanical stress applications. But copper is in case of applications with high thermo-mechanical stress the material of choice due to its higher yield strength and in general due to lower material cost.
Process conditions in case of silver sintering under pressure and pressureless silver sintering have been established. A stable interconnect matching the reference SAC305 solder in terms of mechanical and thermal performance has been realized returning shear strength values averaging 59MPa for silver sintering under pressure and 42MPa for pressureless sintering as against the reference SAC305 solder averaging 56MPa. The thermal performance, measured by transient thermal analysis (TTA) reveal the lower thermal resistance of 0,8K/W and 0,5K/W for silver sintering under pressure and pressureless silver sintering respectively, as against the reference SAC305 solder as expected based on the thermal conductivity of the material. Particles size, binding material, bonding force and bonding atmosphere are shown to have a major impact on the quality of the silver sintered interconnect. Pastes consisting sub-micron and nanoscale silver particles provide less porous interconnect compared to paste containing solely micron sized particles in case of pressureless sintering.
A major challenge with regards to copper nano-powder based sintering is to ensure sufficient penetration of the reducing gas during the sintering process. This is observed also in terms of the mechanical (4MPa) as well as the thermal performance. The paste used in the experiments has not sufficient reducing agents. Based on the results strategies to improve the activation need to be developed for the binder chemistry
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
A multi-pronged approach to low-pressure Cu sintering using surface-modified particles, substrate and chip metallization
No full textHigh temperature power electronics based on wide-bandgap semiconductors have prominent applications, such as automotive, aircrafts, space exploration, oil/gas extraction, and electricity distribution. Die-attach bonding process is an essential process in the realization of high temperature power devices. Transient liquid phase (TLP) bonding and Ag sintering has been on the forefront of research over the past decade as suitable replacements to high-Pb solders. However, brittle intermetallics in the case of TLP bonded interconnects and high cost of Ag coupled with challenges of high electromigration in Ag, warrant the development of reliable substitutes. Cu offers to be a promising alternative to Ag, especially because of thermal and mechanical properties on par with Ag and a cost advantage by being a factor 100 cheaper than Ag. However, high tendency of Cu to be oxidized poses a major challenge in realizing stable interconnects. For this purpose, in this contribution, we present the use of poly-ethylene-glycol 600 as reducing binder in the formulation of the Cu sintering paste. Moreover, with the aim to achieve a low-pressure Cu sintering process, a low cost wet chemical etching process is developed to selectively etch Zn from brass to create nano-porous surface modifications to enhance sinterability, enabling sintering with low bonding pressure of 1MPa and at temperatures below 300°C. Finally, we propose a multi-pronged approach based on three crucial factors: surface-modified substrates, nanostructured surface modifications on micro-scale Cu particles and use of a reducing binder in the Cu particle paste. Results of sintering experiments under N2 atmosphere are discussed and compared with sintering results using non modified materials
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