The binary skutterudite CoSb3 is a narrow bandgap semiconductor thermoelectric (TE) material with a relatively flat band structure and excellent electrical performance. However, thermal conductivity is very high because of the covalent bond between Co and Sb, resulting in a very low ZT value. Therefore, researchers have been trying to reduce its thermal conductivity by the different optimization methods. In addition, the synergistic optimization of the electrical and thermal transport parameters is also a key to improve the ZT value of CoSb3 material because the electrical and thermal transport parameters of TE materials are closely related to each other by the band structure and scattering mechanism. This review summarizes the main research progress in recent years to reduce the thermal conductivity of CoSb3-based materials at atomic-molecular scale and nano-mesoscopic scale. We also provide a simple summary of achievements made in recent studies on the non-equilibrium preparation technologies of CoSb3-based materials and synergistic optimization of the electrical and thermal transport parameters. In addition, the research progress of CoSb3-based TE devices in recent years is also briefly discussed.

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A review of CoSb3-based skutterudite thermoelectric materials

The corrosion behavior and passive film properties of CrMnFeCoNi and CrFeCoNi coatings in 0.5 mol/L H2SO4 solution were investigated by potentiodynamic and potentiostatic measurements, electrochemical impedance spectroscopy and Mott-Schottky tests. The chemical compositions of passive film were characterized by X-ray photoelectron spectroscopy (XPS). Results indicated that CrFeCoNi coating possessed lower passive current density, higher polarization resistance, lower donor and acceptor density compared with CrMnFeCoNi coating, which determined CrFeCoNi coating has higher corrosion resistance than CrMnFeCoNi coating. The excellent resistance to corrosion could be attributed to the structure and chemical compositions of passive film

Comparison of the corrosion and passivity behavior between CrMnFeCoNi and CrFeCoNi coatings prepared by argon arc cladding

The purpose of this article is the effect of doping minor Ni on the microstructure evolution of a Sn-xNi (x = 0, 0.05 and 0.1 wt.%)/Ni (Poly-crystal/Single-crystal abbreviated as PC Ni/SC Ni) solder joint during reflow and aging treatment. Results showed that the intermetallic compounds (IMCs) of the interfacial layer of Sn-xNi/PC Ni joints were Ni3Sn4 phase, while the IMCs of Sn-xNi/SC Ni joints were NiSn4 phase. After the reflow process and thermal aging of different joints, the growth behavior of interfacial layer was different due to the different mechanism of element diffusion of the two substrates. The PC Ni substrate mainly provided Ni atoms through grain boundary diffusion. The Ni3Sn4 phase of the Sn0.05Ni/PC Ni joint was finer, and the diffusion flux of Sn and Ni elements increased, so the Ni3Sn4 layer of this joint was the thickest. The SC Ni substrate mainly provided Ni atoms through the lattice diffusion. The Sn0.1Ni/SC Ni joint increases the number of Ni atoms at the interface due to the doping of 0.1Ni (wt.%) elements, so the joint had the thickest NiSn4 layer.,The effects of doping minor Ni on the microstructure evolution of an Sn-xNi (x = 0, 0.05 and 0.1 Wt.%)/Ni (Poly-crystal/Single-crystal abbreviated as PC Ni/SC Ni) solder joint during reflow and aging treatment was investigated in this study.,Results showed that the intermetallic compounds (IMCs) of the interfacial layer of Sn-xNi/PC Ni joints were Ni3Sn4 phase, while the IMCs of Sn-xNi/SC Ni joints were NiSn4 phase. After the reflow process and thermal aging of different joints, the growth behavior of the interfacial layer was different due to the different mechanisms of element diffusion of the two substrates.,In this study, the effect of doping Ni on the growth and formation mechanism of IMCs of the Sn-xNi/Ni (single-crystal) solder joints (x = 0, 0.05 and 0.1 Wt.%) was investigated.

Effects of doping trace Ni element on interfacial behavior of Sn/Ni (polycrystal/single-crystal) joints

The influence of Nb doping on the structure evolution, hardness and wear behaviors of laser-cladded (Fe0.25Co0.25Ni0.25(B0.7Si0.3)0.25)100-xNbx (denoted as Nbx hereafter, x = 0, 1, 2, 3 and 4 at.%) high entropy alloy coatings were analyzed. Detailed characterization indicated that the microstructures evolve from face-centered cubic (FCC) and (Fe, Co, Ni)2B phases of the Nb-free coating to FCC, (Fe, Co, Ni)2B and amorphous phases of the Nb-containing coating (1 ≤ x ≤ 2). Notably, the glass formation ability of the coating is enhanced with the addition of Nb. As the Nb content further increases (3 ≤ x ≤ 4), it promotes the fully crystalline structures of body-centered-cubic (BCC), Laves, FCC and (Fe, Co, Ni)2B phases. The average crystalline size of the coating is refined from 3.5 to 1.3 μm as a function of Nb content. The wear resistance of the coatings improves firstly and then aggravates with increasing of Nb content, which corresponds to the variation trend of microhardness and microstrain. The Nb2 coating shows a maximum hardness value of 11.9 Gpa and excellent wear resistance due to the formation of amorphous structure and good elastic properties. The phase prediction in the coating was calculated by thermodynamic parameters. The relationships between the structure and properties of the present coating were elucidated. The new metal-metalloid high entropy metallic glassy coating and superior properties give its good promise for engineering applications.

Nb doping in laser-cladded Fe25Co25Ni25(B0.7Si0.3)25 high entropy alloy coatings: Microstructure evolution and wear behavior

Unveiling the Correlation between the Crystalline Structure of M‐Filled CoSb 3 (M = Y, K, Sr) Skutterudites and Their Thermoelectric Transport Properties

Characterization of multiple-filled skutterudites with high thermoelectric performance

ZnS has been widely used as a material for windows in optical systems. This is because it has a good transmittance in both mid-infrared and far-infrared bands, a stable chemical performance, a moderate linear thermal expansion coefficient and an adequate mechanical strength. ZnS windows need the so-called splice technology implementation to satisfy the integrity of large size applications or special surface structures. Traditional ZnS light windows are mechanically assembled with metal frames. However, the strength of the large-size ZnS formed by mechanical assembly is low. Consequently, an adequate joining technology is needed to overcome the low splice strength and improve the mechanical strength of the assembly. In this paper, we proposed a pre-metallization method by using an electroless plating of Ni on ZnS surface. Subsequently, a low temperature joining by using a Sn63Pb37 solder was completed. By a study of the process and the corresponding mechanism of the electroless nickel plating, a Ni–P layer with a controllable P content and thickness has been formed, and a smooth surface and a good combination with ZnS has been obtained. The microstructure of the Sn63Pb37 and Ni–P/ZnS was analyzed, and the phase composition and element distribution within the joint were determined. The influences of process parameters on the microstructures of the joints have been explored, including the brazing temperature, the time of thermal energy preservation and the thickness of the coating. Finally, the shear strengths of joints under different imposed parameters were optimized leading to the peak soldering temperature of 250 °C and the dwell at the peak of 1 min. The fractures were along Ni–P/ZnS ceramic interface, therefore, a successfully low temperature joining process on ZnS ceramics using Ni–P plating and Sn63Pb37 solder had been performed.

Effects of electroless nickel plating method for low temperature joining ZnS ceramics

As the packaging density in wafer-level packaging increases, there is an increasing need for packaging processes for fan-out packaged devices; thus, the soldering reliability of board-level devices is particularly important. Fan-out wafer-level packaging (FOWLP) is typically packaged using flip-chip methods on Cu electrodes and printed circuit board (PCB) substrates. Therefore, in this study, we designed new PCBs based on a 6 × 4 mm2 FOWLP test vehicle with an electroless electroless nickel gold (ENIG) surface finish. After optimizing 21 bonding parameters (temperature, holding time, and shear strength), the ideal bonding parameter was achieved at 260°C for 10 s. We also found that the ENIG pads were dissolved in solder joints at conditions above 270°C for 10 s, causing the pads to break away from the PCB and the solder joint failure. As a result, the mechanical properties of the joints declined. Under long high-temperature durations, the molten Sn bypassed the Ni layer, flowed into the bottom of the pad, and reacted with Cu, causing volume shrinkage of the solder joints and the pads to break away from the PCB.

Shear performance and accelerated reliability of solder interconnects for fan-out wafer-level package

The invention discloses a clamp facilitating PDMS (Polydimethylsiloxane) die releasing and a method for preparing a PDMS layer thereby, and belongs to the technical field of polymer films. The clamp facilitating the PDMS die releasing comprises a bottom plate, an intermediate plate and a permanent magnet, wherein the bottom plate is manufactured through a paramagnetic metal; a groove is formed inthe upper surface of the bottom plate, and the depth of the groove is more than the thickness of the intermediate plate; a plurality of die releasing holes which are uniformly distributed around the groove extend from the groove to the inner wall of the bottom plate; the shape of the intermediate plate fits that of the groove in the bottom plate; the intermediate plate is positioned into the groove in the bottom plate, and the intermediate plate can cover the bottom surface of the groove and can also be moved out from the groove; the intermediate plate is manufactured through a ferromagnetic substance; and the permanent magnet is positioned at the rear part of the bottom plate and is used for attracting the intermediate plate to cling to the bottom surface of the groove in the bottom platethrough the surface. The invention also provides a method for preparing the PDMS layer through the clamp. The clamp is good in forming effect, and hard to break during die releasing; and the clamp isapplicable to PDMS layer manufacturing.

Sunwu Xu

Papers

Characterization of multiple-filled skutterudites with high thermoelectric performance

Effects of electroless nickel plating method for low temperature joining ZnS ceramics

Shear performance and accelerated reliability of solder interconnects for fan-out wafer-level package

Clamp facilitating PDMS (Polydimethylsiloxane) die releasing and method for preparing PDMS layer thereby