[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

Damascene copper electroplating for chip interconnections

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201700464

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Hybrid supercapacitors with their improved performance in energy density without altering their power density have been in trend since recent years. The hybrid supercapacitor delivers higher specific capacitance in comparison to the existing electric double layer capacitor (EDLC) and pseudocapacitors. Generally, the asymmetric behavior of hybrid supercapacitors which is the combination of EDLC and pseudocapacitor acts as an enhancer in its respective capacitance values. This asymmetric approach marks a new beginning towards the much-needed pollution free, long lasting and proficient energy-storing performance. Corresponding to their utilization in hybrid electric vehicles and similar sort of power necessity based devices; the research in developing new advanced storage devices finds an enormous and vast future ahead. The most significant factor for the energy efficient applications demands a considerably higher ratio of surface to the volume by incorporation of new materials. This review article gives an overview of recent advances in the development of hybrid supercapacitors, storage mechanism, criteria of formation, components, different electrode and electrolyte materials, electrochemical profile assessment, design fabrication and their applications.

A review on recent advances in hybrid supercapacitors: Design, fabrication and applications

Unit warpage in Ball Grid Array (BGA) packages with different substrates due to coefficient of thermal expansion (CTE) and Young's Modulus mismatch was investigated. The effect of substrate materials on BGA packages warpage was analyzed. Thermal Mechanical Analyzer (TMA) and Dynamic Mechanical Analyzer (DMA) were used to measure Glass Transition Temperature (Tg) and CTE and Young's Modulus of the substrates and the properties of these substrates were analyzed. Shadow Moire was used to measure the unit warpage at room temperature (25°C) and during reflow. A Finite Element Analysis (FEA) method was used to simulate the warpage results to compare with results from the experiment and to verify the results. From this work, Cu, core materials, and solder mask (SM) have a combined effect on Tg, CTE and Young's Modulus of the substrate. Higher CTE of substrate than that of moldcap results in units presenting Cry, and compared with CTE, the modulus plays a dominate role in the strip compress and decreasing modulus of substrate helps to lower unit warpage. The Shadow moire test results and the simulation results state that the two results are credible.

Impact of substrate materials on packages warpage

This paper has explored the using of Cr micro-alloying method to enhance the corrosion resistance of Sn-Zn-Bi alloy. In addition, the influence of long-term aging on solder corrosion resistance has been studied. The electrochemical corrosion behaviour of Sn-8Zn-3Bi-XCr solder in 3.5% NaCl solution was investigated by using potentiodynamic polarization methods, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray an X-RAY diffractometer (XRD) analysis. The results obtained from polarization study show that: adding a small amount of Cr can improve the corrosion resistance of Sn-Zn-Bi alloy. It shifted the corrosion potential towards more noble values. This change was also reflected in the current density of solder alloy in passivation, corrosion rate, respectively. The oxides of zinc were responsible for the formation of passive film. Presence of Cr atoms in the oxide layer also improved the passivation behaviour of solders to a certain extent and the Sn-9Zn-3Bi-0.5Cr has the best resistance property. We can see from the SEM that it has proportional passive film. Long-term aging decreases the corrosion resistance property and it became poorer with prolonging the aging time. However, it is also more difficult to form passive film.

Electrochemical corrosion behaviour of Sn-8Zn-3Bi-XCr solder in 3.5% NaCl

Through Glass Vias (TGV) interconnection has important application and development in 2.5D package, especially for interposers. Compared with through silicon vias (TSV), the coefficient of thermal expansion is well matched to wafer. Also, TGV interposer has less dielectric loss when transmitting high-frequency signals. The electrodeposition of through-holes (THs) is a key step, especially at a fast speed. In this research, typical tapered THs with double-sided seed layers were filled by copper electroplating, which has an aspect ratio of 3: 1 and diameter of 50 μm. Double anode plating method is used to achieve void-free filling under different current densities. The test results of scanning electron microscopy confirm the surface and cross section quality of electroplating. With the synergistic effect of particular inhibitor A, accelerator B and leveler C which ratio is 60:1:1, we can fill the THs without voids at a current density of 1.5ASD in 1.5 hours, along with smoother coating surfaces and uniformity of two coating surfaces.

Synergistic Effect of Additives on Filling of Tapered TGV Vias by Copper Electroplating

In this paper, Traces of Cr were added into Sn-8Zn-3Bi solder alloys to study the influences of Cr on mechanical properties and high temperature reliability of solder alloys by room temperature tensile test and high-temperature aging treatment. With observation of microstructure and fracture surface analysis, the strengthening mechanisms of Cr in solder alloys were discussed. Experiments show that: the microstructure was refined after traces of Cr added and two kinds of intermetallic compound (IMC) formed. Therefore the addition of Cr improved the plasticity of Sn-8Zn-3Bi alloy. The elongation reached up to 50.96% after 0.1% Cr added; and the fracture mechanism converted from quasi-cleavage fracture into ductile fracture. But after more than 0.3% Cr added, the brittleness of the alloy increased. During 0, 4, 9, 16 days aging, the mechanical properties of Sn-8Zn-3Bi-0.3Cr alloy were improving slightly with aging time. Through the microstructure analysis it was found that the Sn-Zn-Cr phase was transited after aging and Zn in alloy was consumed, so that primary Zn phase was reduced and microstructure was improved.

Studies on microstructure and mechanical properties of Sn-Zn-Bi-Cr lead-free solder

Via filling by copper electrodeposition is of great interest for industry to realize 3D packaging and reduce cost. To achieve “bottom-up” filling with no voids and seams, numerous studies on additives mechanism have been conducted. The organic sulful-containing accelerator, bis(3-sulfopropyl) disulfide (SPS) and the inhibitor (e.g., poly(ethylene glycol) (PEG) ), are common additives in “bottom-up” filling of vias. This work investigates a straightforward method for “bottom-up” filling simulation of SPS-PEG additive system. In this method, the potential dependence of additives adsorption behavior was summarized and employed in further simulation. A model estimation method was applied to estimate the precision. This model was then utilized in Finite Element Method (FEM) simulation, and the results gave a glimpse of the defect formation in via filling.

Ming Li

Papers

Impact of substrate materials on packages warpage

Electrochemical corrosion behaviour of Sn-8Zn-3Bi-XCr solder in 3.5% NaCl

Synergistic Effect of Additives on Filling of Tapered TGV Vias by Copper Electroplating

Studies on microstructure and mechanical properties of Sn-Zn-Bi-Cr lead-free solder

Potential-dependence of additives distribution in copper electrodeposition via filling