[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

The superfilling of through silicon vias (TSVs) is a technical challenge for the fabrication of modern 3D Electronic packaging. In order to achieve void-free-filling for TSVs with different aspect ratios, various organic additives need to be added into the plating bath. Since TSV filling is a complex electrochemical and physical process, it is difficult and very time-consuming to get an optimal additive ratio through experiments. So, numerical simulation will play an important role in the optimization of vias filling. To explain the mechanism of void-free filling, different models have been developed recently. In this paper, a numerical model was built to simulate the electroplating process in different conditions. The arbitrary Lagrange-Eulerian (ALE) method for solving moving boundaries in Finite Element Method (FEM) was used for the simulation. Since the working mechanism of the additives is still not totally clear, the results in this study try to explain the roles of different additives qualitatively. The tool used in this experiment is Comsol Multiphysics, a commercial FEM software. The parameters used in this study are based on the experimental results or published literatures.

Modeling the bottom-up filling of through silicon vias with different additives

The performance and degradation process of a greenly synthesized transient heterojunction diode

Three-dimensional (3D) integration sets improved requirements on the structure and performance of the Ni deposits. Pulse reverse current (PRC) electroplating is regarded as a promising technique to obtain Ni plating fulfilling such requirements. This work investigated the influence of two PRC parameters, average current density and pulse frequency, on surface morphology and grain size of the Ni deposits. Ni deposits were prepared by first direct current (DC) pre-plating and then PRC electroplating process of given average current density and pulse frequency. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to characterize the deposits. It was found that the surface morphology and grain size of the Ni deposits were significantly influenced by average current density and pulse frequency. Such results are instructive in the electroplating obtainment of Ni for packaging applications.

Influence of Average Current Density and Pulse Frequency on Morphology and Structure of Pulse-reverse Current Electroplated Ni Plating

The microstructual stability of Sn-8Zn-3Bi/Cu and Sn-8Zn-3Bi-0.3Cr/Cu joints has been investigated under 85 °C temperature and 85% humidity conditions as a function of exposure time. The evolution of interface and near surface cross-sectional microstructures during exposure has been examined. A continuous single layer of intermetallic compound (IMC, hereafter) appears in both of the two kinds of solders. The IMCs grows during exposure at 85°C/85%RH, and the thickness of the Sn-8Zn-3Bi-0.3Cr solder joint is much thinner than that of Sn-8Zn-3Bi solder joint under the same condition. The better oxidation resistance of the Cr content solder is attributed to the Cr-rich phase which restrains the diffusion of Zn atom to the grain boundaries of Sn matrix. Near the surface and the interface of the joint, there is also Zn-depleted layer. The invalidation of the Sn-8Zn-3Bi solder is worse.

Microstructural evolution of Sn-9Zn-3Bi and Sn-9Zn-3Bi-0.3Cr solder under high-temperature and high-humidity conditions

High I/O density, short interconnect lines, self-aligned mounting, good heat dissipation, and small assembly area make flip chip packaging become one of the most attractive technologies for contemporary electronic packaging. As the chip size increases, the gap between the chip and the substrate and the pitch of the solder connection point decrease, non-uniform voids will be produced in the conventional flip chip underfilling process. In this study, the problem of high-density flip-chip underfilling is studied. NCP thermocompression bonding is used to solve the void problem that occurs in the traditional under-filling process. Voids in the underfilling process can be effectively eliminated by optimizing the process condition for NCP thermocompression bonding.

Ming Li

Papers

Modeling the bottom-up filling of through silicon vias with different additives

The performance and degradation process of a greenly synthesized transient heterojunction diode

Influence of Average Current Density and Pulse Frequency on Morphology and Structure of Pulse-reverse Current Electroplated Ni Plating

Microstructural evolution of Sn-9Zn-3Bi and Sn-9Zn-3Bi-0.3Cr solder under high-temperature and high-humidity conditions

An effective way to solve the void problem of traditional underfill based on NCP technology