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Transient liquid phase (TLP) bonding is a promising electronic packaging technology to satisfy the needs of operating at high temperatures due to the increasing power density of power electronic devices. More and more power chips are finished with Ni/Ag metallization, while the top metal is Cu in direct bonded copper. However, interfacial reactions in Cu/Sn/Ag system were rarely studied. In order to explore the intermetallic reaction kinetics between solder and substrate in Cu/Sn/Ag system, this study investigated the effect of different reflow temperatures (250–350 °C) and time (30–960 s) on the microstructure evolution of the interfaces of three different TLP systems (Cu/Sn, Ag/Sn and Cu/Sn/Ag), and the growth kinetics of two intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. The results indicate that the activation energy of Cu6Sn5 in Cu/Sn/Ag TLP increases by 42.8% compared to Cu/Sn TLP, and the activation energy of Ag3Sn increases by 34.1% compared to Ag/Sn TLP. During the solid–liquid process of Ag/Sn/Cu TLP, Ag atoms from the Ag substrate side will cross through the molten Sn layer to form Ag3Sn on the surface of Cu6Sn5 IMCs on the Cu substrate side. Meanwhile, Cu atoms from the Cu substrate side will reach Ag substrate side to form Cu6Sn5 on the surface of Ag3Sn IMCs. Heterogeneous IMCs at the interface hinder the grain boundary/melting channel for the diffusion of substrate atoms, increasing the activation energy and inhibiting their growth. [ABSTRACT FROM AUTHOR]

Human perturbations such as dam regulation have led to significant changes in nutrient flux, structure, and spatiotemporal distribution through rivers and have greatly influenced coastal and estuarine ecological environments. Based on the data from 2001–2019, the impacts of the water-sediment regulation scheme (WSRS) in the Huanghe (Yellow) River on nutrient concentrations, forms, fluxes, and potential ecological effects on the Huanghe River estuary and Bohai Sea were analyzed. Nutrient concentrations and forms were significantly influenced by the different regulatory modes and were associated with hydrological and biogeochemical processes. The concentrations and forms of nutrients were strongly influenced by the riparian floodplains and scouring process of the downstream riverbed at the water draining stage, while they were influenced mainly by the mixing process in the Xiaolangdi Reservoir at the sediment desilting stage. Compared with those in non-WSRS years, the seasonal distributions of water discharge and nutrient fluxes in WSRS years significantly changed, with peaks occurring at least one month earlier than those in non-WSRS years. Nitrate (NO3-N), phosphate (PO4-P), and silicate (SiO3-Si) fluxes during the WSRS, which were strongly controlled by water discharge at Lijin (the nearest hydrological station to the river mouth), accounted for more than 20% of the annual fluxes; these fluxes were more than 5–9 times greater than those during the same period in non-WSRS years. WSRS exacerbated nutrient imbalances and increased Pyrrophyta/Bacillariophyta ratios by 231% in the Huanghe River estuary, resulting in chlorophyll-a peaks in the Bohai Sea shifting from spring to autumn in the 20th century to spring-summer in the 21st century. [ABSTRACT FROM AUTHOR]

In this paper, we study the lower and upper bounds for Stokes eigenvalues by finite element schemes. For the schemes studied here, roughly speaking, the loss of the local approximation property of the discrete velocity and pressure spaces may lead to different computed bounds of the eigenvalues. Formally theoretical analysis is constructed based on certain mathematical hypotheses, and numerical experiments are given to illustrate the validity of the theory. [ABSTRACT FROM AUTHOR]

The final processing techniques for ultra-high strength steel typically involve turning and grinding. The selection of processing parameters is crucial in determining the surface integrity and fatigue behavior of the resulting parts. This study investigates the surface integrity of 45CrNiMoVA steel, including surface roughness, residual stress, and microhardness, as well as its low cycle torsional fatigue behavior, such as fatigue life and fatigue fracture morphology. The effects of different turning and grinding allowance conditions on surface integrity parameters and fatigue behavior are examined. In addition, this text analyzes the differences between the surfaces produced by turning and grinding. It examines the microscopic factors that affect surface quality and fatigue life by considering crystallographic characteristic parameters. The results show that the specimens that subjected to fine turning exhibit poor surface morphology, high compressive residual stress, high microhardness, and the longest fatigue life. Among the various grinding allowance distributions, RFGF1 is considered relatively optimal. It consists of a rough grinding allowance of 0.45 mm and a fine grinding allowance of 0.15 mm, with the use of cutting fluid. [ABSTRACT FROM AUTHOR]

Background: Glioblastoma (GBM) with distant extension is rarely reported. We retrieved the data of GBM patients from the SEER database to identify the prognostic factors of GBM with distant extension and constructed a nomogram to predict the overall survival (OS) of these patients. Methods: The data of GBM patients between 2003 and 2018 were retrieved from the SEER Database. 181 GBM patients with distant extension were randomly divided into the training cohort (n = 129) and the validation cohort (n = 52) at a ratio of 7:3. The prognostic factors associated with the OS of the GBM patients were identified through univariate and multivariate cox analyses. A nomogram was constructed based on the training cohort to predict OS, and its clinical value was verified using the validation cohort data. Results: Kaplan–Meier curves showed that the prognosis was significantly worse for GBM patients with distant extension than GBM patients without distant extension. Stage (GBM patients with distant extension) was independent prognostic factor of survival. Multivariate Cox analyses demonstrated that age, surgery, radiotherapy and chemotherapy were independent risk factors for OS of GBM patients presenting with distant extension. The C-indexes of the nomogram for predicting OS were 0.755 (95% CI 0.713–0.797) and 0.757 (95% CI 0.703–0.811) for the training and validation cohorts, respectively. The calibration curves of both cohorts showed good consistency. The area under the curve (AUC) for predicting 0.25-year, 0.5-year and 1-year OS in the training cohort were 0.793, 0.864 and 0.867, respectively, and that in the validation cohort were 0.845, 0.828 and 0.803, respectively. The decision curve analysis (DCA) curves showed that the model to predict the 0.25-year, 0.5-year and 1-year OS probabilities was good. Conclusion: Stage (GBM patients with distant extension) is independent prognostic factor for GBM patients. Age, surgery, radiotherapy and chemotherapy are independent prognostic factors for GBM patients presenting with distant extension, and the nomogram based on these factors can accurately predict the 0.25-year, 0.5-year and 1-year OS of these patients. [ABSTRACT FROM AUTHOR]

Plating Sn3Ag on copper substrates represents a crucial electronic packaging technique. In this study, we propose a novel composite plating approach, wherein CoSn3 nanocrystals are deposited within the Sn3Ag coating. The resulting reflowed Sn3Ag joints exhibit a range of distinctive properties. Notably, CoSn3 nanocrystals dissolve in Sn during the reflow process, thereby lowering the supercooling required for Sn nucleation. Consequently, Sn crystals grow in six-fold cyclic twins. Additionally, the dissolution of Co atoms in Sn leads to a reduced solubility of Cu atoms in Sn, consequently lowering the supercooling required for the nucleation of Cu6Sn5. Simultaneously, this phenomenon promotes the nucleation of Cu6Sn5, resulting in a considerable precipitation of Cu6Sn5 nanoparticles within the joints. Therefore, the mechanical properties of the joints are significantly enhanced, leading to a notable 20% increase in shear strength. Furthermore, the presence and distribution of Co elements within Sn induce changes in the growth pattern of interfacial Cu6Sn5. The growth process of Cu6Sn5 is dominated by the interfacial reaction, leading to its growth in a faceted shape. During the aging process, the dissolution of Co elements in Sn impedes the continuous growth of Cu6Sn5 at the interface, causing Cu6Sn5 to be distributed in the form of islands inside the joint. Remarkably, elemental Co acts as an inhibitor for the development of Cu3Sn and reduces the occurrence of Kirkendall voids. [ABSTRACT FROM AUTHOR]

In this paper, we construct two new linear, decoupled, unconditionally energy stable finite element schemes for electrohydrodynamic model of charge transport with variable density dielectric fluid. The fully-decoupled schemes are achieved by the property of two nonlocal auxiliary variables and applying the operator Strang-splitting method. At each time step, all variables can be computed independently by solving a sequence of linear finite element schemes and algebraic equations. The solvability and unconditionally energy stability of the two schemes are rigorously demonstrated. Numerical experiments verify the effectiveness and stability of the proposed schemes. [ABSTRACT FROM AUTHOR]

The increasing packaging density and power density have led to a drastic increase in the electric field strength between solder joints, and the accelerated movement of ions significantly rises the potential for failure of solder joints caused by electrochemical migration (ECM). To improve the anti-electrochemical migration ability of Sn3Ag0.5Cu solder (SAC305), we doped Cu6Sn5 nanoparticles (NPs) into SAC305 solder paste and studied its mechanism for inhibiting ECM. In this experiment, Cu6Sn5 NPs were prepared by ultrasound-assisted chemical reduction, and composite solder pastes were prepared by mechanically mixing Cu6Sn5 NPs with SAC305. In situ observation of the ECM between electrodes was carried out under different operating conditions. The addition of Cu6Sn5 NPs within 0.6 wt% could effectively inhibit the ECM by prolonging the incubation period. However, when the amount of Cu6Sn5 NPs exceeded 0.6 wt%, the catalytic effect of Cu6Sn5 NPs on the hydrogen evolution reaction would create vigorous convection within the droplet, which accelerated the failure by ECM. Apart from that, it was found that the addition of Cu6Sn5 NPs could increase the threshold for instantaneous failure of solder joints under high voltage. [ABSTRACT FROM AUTHOR]

The ever-increasing packaging density of electronic products has led to a dramatic reduction in the dimensions of solder joints, which further results in a surge in current density and harsher operating environments. The reliability of lead-free solders is facing more and more challenges during service. In this study, Cu6Sn5 nanoparticles (NPs) were added to Sn3.0Ag0.5Cu (SAC305) solder paste to improve its mechanical strength and service reliability. We designed an ultrasound-assisted method to prepare Cu6Sn5 NPs and studied the effect of energy input on the crystallinity and size of Cu6Sn5 NPs. Cu6Sn5 NPs with an average diameter of 19.1 nm were prepared in ultrasonic bath for 15 min. The addition of Cu6Sn5 NPs could improve the solderability of the composite solder paste while having little effect on the melting point. Since the adsorption of Cu6Sn5 NPs at the interface reduced the interfacial energy, the addition of Cu6Sn5 NPs could also inhibit the growth of the interfacial IMC layer. When the mass fraction of Cu6Sn5 NPs was 0.6 wt%, the shear strengths of the solder joints increased by 13.5% to 53.8 MPa. In general, the composite solder joints prepared by adding Cu6Sn5 NPs have better solderability and shear strength, which can improve the reliability of SAC305 in harsh operating environments. [ABSTRACT FROM AUTHOR]

In recent years, porous metals have been used for transient liquid phase bonding because of their high specific surface areas. However, current studies have mainly focused on the preparation of porous metal joints and lack awareness of their reliability issues. Therefore, we prepared a porous Cu joint for high-temperature-resistant packaging and investigated its aging and thermal shock resistance. Porous Cu joints were prepared using commercial porous Cu and pure Sn foils. After soldering at 250 °C for 10 min, the shear strength of the porous Cu joints was 83 MPa and 61 MPa at 25 and 300 °C of shear temperatures, respectively. The electrical resistivity and thermal conductivity of the porous Cu joints were 8.65 µΩ·cm and 58.9 W/(m·K), respectively. The room-temperature shear strength of the joints aged at 300 °C for 1000 h could still reach 60 MPa. Reticular Cu2O/Cu3Sn was discovered for the first time in aged porous Cu joints. After 1000 cycles, the room-temperature shear strength of the joints could still reach 73 MPa, which was only 14.5% lower than that of the joints without the thermal shock test. In conclusion, porous Cu joints exhibited good aging resistance and excellent thermal shock resistance. [ABSTRACT FROM AUTHOR]

With the development of high-integration and high-power electronics, the lack of matching chip connecting materials that can withstand high temperatures has been a challenge. In this manuscript, a Cu@Cu6Sn5 core–shell bimetallic particles (approx. 1 μm in diameter) are successfully prepared and introduced as a new solder material for the packaging of power devices to obtain a Cu3Sn all-IMC solder joint. The joint consisted mainly of equiaxed Cu3Sn grains, and a small portion of columnar Cu3Sn grains. In columnar-type growth, Sn is the dominant diffusing species, which comes from the depletion of Sn in Cu6Sn5. The depleted Cu6Sn5 is transformed into columnar Cu3Sn. In equiaxed-type growth, Cu is the dominant diffusing species. Cu reacts with Cu6Sn5 to grow a Cu3Sn layer. This conclusion was confirmed by the orientation relationship. The equiaxed Cu3Sn grain nucleates at the Cu/Cu3Sn interface have an orientation relationship with the Cu substrate. Columnar Cu3Sn grains at the Cu6Sn5/Cu3Sn interface have an orientation relationship with Cu6Sn5. [ABSTRACT FROM AUTHOR]

Copper foam can be used as an interlayer to relieve high residual stresses and enhance the mechanical properties of the solder joints. However, the residual low-melting-point phase in microporous copper foam limits its ability to sustain at high temperatures as the transient liquid phase does. To form solder joints with high melting point, the Cu-foam/Sn composite preform with nanoporous structures was prepared. The nanoporous structures increased the reaction area, and speeded up the consumption of the low-melting-point phase. It was demonstrated that the solder could be completely consumed by reflowing at 250 °C for 15 min under a pressure of 3 MPa, raising the melting point of the solder joints to 415 °C. The novel solder joints also had excellent mechanical properties, with shear strengths of 27.6 MPa at 30 °C and 17.1 MPa at 300 °C, respectively. Different fracture modes were observed at room temperature and high temperature. The results show that the preform is a promising die attach material for high-power devices. [ABSTRACT FROM AUTHOR]

We proposed Zn@Sn particles to improve the mechanical properties of the Sn–58 wt% Bi (Sn58Bi) solder. The effects of 3, 6, and 9 wt% Zn@Sn particles on the microstructure and mechanical properties of Sn58Bi were investigated. The addition of Zn@Sn to Sn58Bi solder inhibited microstructural coarsening, which mitigated the brittleness of Sn58Bi solder joints during aging. The zinc-rich phases dispersively distributed in the solder joints effectively inhibited the coarsening of the Bi-riched phase. At the same time, Cu5Zn8 instead of Cu6Sn5 formed at the composite solder/Cu interface. After 21 days of aging, the shear strengths of solder joints doped with 6 wt% Zn@Sn decreased from 54.06 to 36.41 MPa. Compared with the undoped solder joints before and after aging, the shear strengths increased by 34% and 173.1%, respectively. Thus, the composite solder paste has great potential to be used as a low-temperature lead-free solder in the electronic packaging industry. [ABSTRACT FROM AUTHOR]

A 3–5 μm Cu@Sn core–shell powder was prepared by chemical plating. Based on the mixture of this Cu@Sn and SAC305 powder, a solder material for third-generation semiconductors was prepared. The joints prepared with this solder material have a shear strength of over 40 MPa at 25 °C. Shear strength of the joint at 300 °C exceeds 60 Mpa. And the strength of the joint is still above 60 MPa when it is aged for 800 h at 300 °C. The organization of the joint is mainly composed of Cu6Sn5 and Cu3Sn. The small size of Cu@Sn particles provides many reaction interfaces so that IMC (intermetallic compound) can be generated rapidly, while the Sn atoms provided by SAC305 inhibit the nucleation and growth of Cu3Sn. The Kirkendall voids in the joint are distributed in the spherical interface between Cu6Sn5 and Cu3Sn, a feature that gives the joints excellent resistance to shear damage. [ABSTRACT FROM AUTHOR]

Green credit plays a crucial role in reducing energy consumption and environmental degradation in China. Using data on China's new energy listed companies from 2007 to 2018, this study explores the impact of green credit on new energy firms' value, as well as the mediating effects of financing constraints and external supervision on the relationship between green credit and new energy companies' economic benefits. Our results suggest that green credit significantly improved new energy firms' value, and this positive impact can last over the long term. The above result is robust to using alternative measures, replacement of fixed effects, exclusion of abnormal samples, and placebo test. Additional tests reveal that green credit improves new energy companies' value by alleviating financing constraints and strengthening external supervision. Finally, green credit's value-enhancement effect is heterogeneous, depending on corporate property rights, business life cycle, implementation of Green Credit Guideline policy, and the firms' geographical location. Our conclusions suggest that government should not only pay attention to the continuity of green credit commitment but also the mitigation of financing constraints and improvement of external supervision for new energy companies. Moreover, heterogeneous factors should be considered to formulate and calibrate related policy rather than a one-size-fits-all policy. [ABSTRACT FROM AUTHOR]

This paper presents a high-temperature-resistant preform based on Cu@In@Ag particles that can be used as a die attach material for high-power devices, using an electroless method to achieve the preparation of core–shell structure particles. Indium has a lower melting point of 156.6 °C and can be completely consumed to form intermetallic compounds of Cu2In, Ag9In4, and Ag3In, which will raise the melting point of the solder joint to over 400 °C. The silver coating is intended to enhance the oxidation resistance of the Cu@In particles and to improve the service reliability of the solder joint. It was demonstrated that high-temperature-resistant solder joints could be obtained by reflowing at 200 °C for 15 min under a pressure of 10 MPa. The shear strengths of solder joints were 29.70 MPa and 21.85 MPa at 25 °C and 300 °C, respectively. The thermal and electrical properties of the solder joints after reflow composed of Cu@In@Ag core–shell particles were tested and the thermal conductivity was 79.02 W/m K and 58.64 W/m K at 30 °C and 250 °C, respectively. Great electrical and thermal conductivity and high shear strength at high temperatures result in high-temperature reliability. As a high-temperature-resistant die attachment material, it has the potential to be used in die attachment in high-power equipment modules. [ABSTRACT FROM AUTHOR]

In this review, the present status of nanosilver sintering is adapted in detail. This review shows the current scholarly exploration and achievements in this field through the two aspects of manufacturing and reliability. The preparation of nanosilver particles, organic coating and sintering methods, microstructure and failure modules of sintered nanosilver layers are described in detail. Finally, prospects and dilemmas of nanosilver sintering technology as a connection material for semiconductor devices and the directions of future extensions are discussed. [ABSTRACT FROM AUTHOR]

A low-temperature sintered silver paste was used for the metallization of tempered glass, which was used to prepare vacuum-tempered glass by soldering with Sn96.5Ag3Cu0.5 paste (SAC305). The effects of the glass content and the sintering temperature on the microstructures, shear strengths, and fracture mechanisms of the bondlines were investigated in detail. The microstructure of the thick silver film and its interface with the tempered glass was characterized. The dissolution and precipitation behaviors of silver in Bi–B–Zn glass were also analyzed. Bi4B2O9 crystals were detected in the microstructure of the thick silver film when the joining temperature was increased above 450 °C, which can strengthen the silver film and the interface with the tempered glass. After soldering at 450 °C for 10 min, an excellent bondline was formed using the low-temperature sintered paste, which had a shear strength of 42.3 ± 2.4 MPa and a leak rate of 7.2 ± 0.4 × 10–3 Pa.cm3/s. The sintered paste had a composition of 80 wt.% silver and 20 wt.% glass powder. Furthermore, heat transfer tests revealed that the vacuum tempered glass had excellent thermal insulation properties. The results showed that the low-temperature sintered silver paste combined with soldering was an effective method to prepare vacuum-tempered glass. [ABSTRACT FROM AUTHOR]

This paper presents a novel die attach material for power device packaging based on transient liquid phase (TLP) bonding. Through two-step electroless plating, the Cu@Sn@Ag particles were prepared, and realize interconnection with Cu Substrates after being compressed into preform. Due to the large specific surface area of the core–shell particles, the reflow time can be reduced to 15 min at a low temperature of 250 °C under a pressure of 3 MPa to form high-remelting-point intermetallic compounds (IMCs), which can withstand a high temperature of at least 475 °C. Due to the protection of the Ag coating, the Cu@Sn@Ag particles exhibited excellent oxidation resistance, and the bonding process can be carried out in the atmosphere. Then, the service reliability of the bondlines was evaluated in harsh environments, such as high temperature and humidity, high temperature storing, and thermal shock. The average resistivity of the bondlines was increased from 4.6 ± 1.4 to 8.5 ± 3.8 µΩ cm after being stored at high temperature (85 °C) and high humidity (85% RH) environment for 14 days. After storing at 300 °C for 15 days, the porosity of bondline increased from 6.8 to 10.8%, and the average shear strength decreased from 30.5 ± 6.3 to 22.3 ± 5.6 MPa. After thermal shock between − 40 and 125 °C for 500 cycles, the bonding rate decreased from 99.9 to 84.2%. Moreover, the short-circuit time of electrochemical migration under 60 V voltage was extended to 145 s. The bondline based on the novel core–shell particles exhibited excellent performance as a die attach material under harsh environments. [ABSTRACT FROM AUTHOR]

This paper develops a new recovery-based linear C0 finite element method for approximating the weak solution of a fourth-order singularly perturbed Monge-Ampère equation, which is known as the vanishing moment approximation of the Monge-Ampère equation. The proposed method uses a gradient recovery technique to define a discrete Laplacian for a given linear C0 finite element function (offline), the discrete Laplacian is then employed to discretize the biharmonic operator appeared in the equation. It is proved that the proposed C0 linear finite element method has a unique solution using a fixed point argument and the corresponding error estimates are derived in various norms. Numerical experiments are also provided to verify the theoretical error estimates and to demonstrate the efficiency of the proposed recovery-based linear C0 finite element method. [ABSTRACT FROM AUTHOR]

To assist physicians identify COVID-19 and its manifestations through the automatic COVID-19 recognition and classification in chest CT images with deep transfer learning. In this retrospective study, the used chest CT image dataset covered 422 subjects, including 72 confirmed COVID-19 subjects (260 studies, 30,171 images), 252 other pneumonia subjects (252 studies, 26,534 images) that contained 158 viral pneumonia subjects and 94 pulmonary tuberculosis subjects, and 98 normal subjects (98 studies, 29,838 images). In the experiment, subjects were split into training (70%), validation (15%) and testing (15%) sets. We utilized the convolutional blocks of ResNets pretrained on the public social image collections and modified the top fully connected layer to suit our task (the COVID-19 recognition). In addition, we tested the proposed method on a finegrained classification task; that is, the images of COVID-19 were further split into 3 main manifestations (ground-glass opacity with 12,924 images, consolidation with 7418 images and fibrotic streaks with 7338 images). Similarly, the data partitioning strategy of 70%-15%-15% was adopted. The best performance obtained by the pretrained ResNet50 model is 94.87% sensitivity, 88.46% specificity, 91.21% accuracy for COVID-19 versus all other groups, and an overall accuracy of 89.01% for the three-category classification in the testing set. Consistent performance was observed from the COVID-19 manifestation classification task on images basis, where the best overall accuracy of 94.08% and AUC of 0.993 were obtained by the pretrained ResNet18 (P < 0.05). All the proposed models have achieved much satisfying performance and were thus very promising in both the practical application and statistics. Transfer learning is worth for exploring to be applied in recognition and classification of COVID-19 on CT images with limited training data. It not only achieved higher sensitivity (COVID-19 vs the rest) but also took far less time than radiologists, which is expected to give the auxiliary diagnosis and reduce the workload for the radiologists. [ABSTRACT FROM AUTHOR]

Cu-to-Cu interconnection has drawn increasing attention as the bump pitch is decreasing continuously. Cu-to-Cu interconnections exhibit excellent mechanical, electrical, and thermal properties without forming IMCs, which usually degrade the interconnect reliability due to their brittle nature. In this paper, Cu-to-Cu interconnection can be realized at 150 °C for 10 min under a pressure of 3 MPa. The microstructure of the nanoporous Cu coarsened significantly and the interfaces of the bondline can not be distinguished clearly after bonding at 250 °C for 30 min under a pressure of 3 MPa. The microstructure was more densified along the bonding interface than the rest part, and the degree of densification was increased with the increasing bonding temperature and pressure. The average resistivity, thermal conductivity, and shear strength of the bondlines were determined to be 4.12 μΩ cm, 176.49 W m−1 K−1, and 18.78 MPa, respectively. After aging at 200 °C for 300 h, the shear strength was increased by 44.5% due to the increased densification rate brought by the diffusion of Cu atoms, which confirmed the Cu–Cu interconnection reliability during long-term service. [ABSTRACT FROM AUTHOR]

With the rapid development of the third-generation semiconductor materials, an appropriate high-temperature-resistant die attach material has become one of the bottlenecks to fully exploit the excellent properties of the third-generation semiconductor power devices. At the same time, a low-bonding temperature is always the pursuit goal of packaging engineers to reduce the thermal residual stress in electronic devices. In this paper, a low-temperature bonding method was proposed to address the above-mentioned issue based on In infiltrating the nanoporous Cu. In, as a low melting point metal, can significantly reduce the bonding temperature, and the nanoporous Cu structure can provide a very large specific surface area, which greatly increases the consumption rate of In. Furthermore, the formed Cu-In IMCs with high-remelting temperature can withstand the high operating temperature. The microstructures of the bondlines before and after bonding were studied in detail. The results show that the bondline can completely consume the low melting point In, within 10 min at 165 °C under a pressure of 0.75 MPa. When the bonding temperature was further increased to 310 °C, the bondline was composed of η-Cu2In and δ-Cu7In3 phases, whose melting points were more than 600 °C. The average electrical resistivity was determined to be 5.53 ± 0.65 μΩ cm, and the thermal conductivities were 144.33 W m−1 K−1, 139.24 W m−1 K−1 and 129.79 W m−1 K−1 at 30 °C, 150 °C and 300 °C, respectively. The average shear strength were 19.09 ± 3.4 MPa, 20.47 ± 4.6 MPa and 30.73 ± 5.2 MPa at 30 °C, 250 °C, 310 °C, respectively. These results indicate that the nanoporous Cu infiltrated with In could meet the requirements of electrical, thermal conduction, and mechanical support as a die attachment for high-power devices. [ABSTRACT FROM AUTHOR]

An electrochemical sensor that can sensitively detect levodopa without fragile and expensive antibodies has been prepared on the basis of indium sulfide and graphene. The indium sulfide nanospheres synthesized by a hydrothermal method were grown on the surface of three-dimensional graphene prepared by chemical vapor deposition. The graphene maintains a good 3D structure and the indium sulfide nanospheres increases the specific surface area of graphene. The composite possesses a low detection limit of 87 nM (S/N = 3) and the sensitivity of it reaches 1.98 μA μM−1 cm−1. Also, good electrochemical performance, selectivity, and stability make it available to be used for detecting real biomolecules. [ABSTRACT FROM AUTHOR]

We carry out in this paper a rigorous error analysis for a finite element discretization of the scalar auxiliary variable (SAV) schemes. The finite-element method we study is a Galerkin method with standard Lagrange elements based on a mixed variational formulation. We derive optimal error estimates for both the first- and second-order SAV schemes with the finite-element method in space. [ABSTRACT FROM AUTHOR]

A nonenzymatic voltammetric assay for dopamine (DA) was developed based on the combination of three-dimensional graphene (3D Gr) and indium oxide nanosheet arrays (In2O3 NSAs). 3D Gr was prepared by chemical vapor deposition (CVD), and In2O3 NSAs were grown on its surface by hydrothermal synthesis. The results show that 3D Gr maintains a good porous structure (200 μm), and the pore size of In2O3 NSAs is 0.50 μm. Differential pulse voltammetry (DPV) is mainly used to determine the electrochemical properties of In2O3 NSAs/3D Gr. It possesses a sensitivity of 2.69 μA·μM−1·cm−2 towards DA (5–60 μM) at 0.14 V, and the detection limit (LOD) is 0.10 μM (S/N = 3). The recoveries obtained for spiked samples in the real sample detection is 105 (± 8)%. [ABSTRACT FROM AUTHOR]

Metal sulfide-graphene hybrid materials have attracted increased attention as promising supercapacitor electrode materials. Herein, three-dimensional multi-layered graphene (3D GR) is prepared by chemical vapor deposition using nickel nanowires (Ni NWs) as the template and then, indium sulfide nanosheet arrays (In2S3 NSAs) were grown on the 3D GR by hydrothermal synthesis to obtain In2S3 NSA/3D GR composite. The hybrid is characterized by scanning and transmission electron microscopy, X-ray diffraction, and Raman scattering. The electrode exhibits a high specific capacitance of 530.7 F g−1 at 1 A g−1. Moreover, the electrode possesses an excellent cycle life with 84% capacitance retention after 20,000 cycles at 1 A g−1. [ABSTRACT FROM AUTHOR]

A novel hybrid of polyaniline nanowire array/three-dimensional hollow graphene balls-graphene oxide (PANI NWA/3D HGBs-GO) is prepared. 3D HGBs are first fabricated by template-oriented carbon segregation, and then PANI NWAs are grown on their surface by in situ polymerization to obtain PANI NWA/3D HGBs. Finally, the surface of PANI NWA/3D HGBs is modified by hexadecyl trimethyl ammonium Bromide (CTAB), and PANI NWA/3D HGBs and GO are combined by electrostatic self-assembly method to obtain PANI NWA/3D HGBs-GO composite. Due to the unique structure, the hybrid exhibits a high specific capacitance of 690.0 F·g−1 at 1 A·g−1. When it is assembled into a symmetric supercapacitor, it exhibits an energy density of 30.9 Wh·kg−1 at a power density of 690.1 W·kg−1 and maintains a good cycle stability of 90% after 10,000 cycles at 1.0 A·g−1. [ABSTRACT FROM AUTHOR]

In this paper, a simple and efficient electrochemical sensor based on indium sulfide nanosheet arrays (In2S3 NSAs) grown on 3D graphene (3D Gr) has been developed. 3D Gr was obtained by chemical vapor deposition (CVD) and In2S3 NSAs were prepared by a hydrothermal method. The composite (In2S3 NSAs-3D Gr) has a large accommodation space to contact with biological molecules. The current generated by the redox reaction of epinephrine (EP) on the surface of the In2S3 NSAs-3D Gr becomes an important indicator of the sensor value. The sensitivity of the sensor for the detection of EP in the range of 0–60 µm is 2.46 µA µM− 1 with a detection limit of 0.12 µM (S/N = 3). Meanwhile, the novel sensor has a good stability and selectivity. It also has potential for real detection of EP in human serum. [ABSTRACT FROM AUTHOR]

The effect of Zn addition on the evolution of IMC at near-eutectic 50In-50Sn/Cu interfaces was investigated at 210°C. In 50In-(50-x)Sn-xZn/Cu(x = 0, 6) diffusion couples, two types of intermetallic compound layers were observed: ε-Cu3(In,Sn) adjacent to the Cu substrate and η-Cu2(In,Sn) adjacent to the solder, which were formed though a solid–solid diffusion reaction and solid–liquid reaction, respectively. The growth of ε-Cu3(In,Sn) was at the expense of η-Cu2(In,Sn). In 50In-44Sn-6Zn/Cu diffusion couple, the growth of ε-Cu3(In,Sn) was grain-boundary diffusion controlled and n (the time constant) was 0.31. But in the 50In-50Sn/Cu diffusion couple, due to the slow growth of η-Cu2(In,Sn), the time constant of ε-Cu3(In,Sn) was down to 0.19. With the addition of Zn in the 50In-50Sn/Cu couple, the diffusion of Cu was alleviated. Zn exhibited high activity and moderated the dissipation of the main atoms (In/Sn) in the solder. So the growth of Cu3(In,Sn) was suppressed significantly. [ABSTRACT FROM AUTHOR]

This paper presents a novel die attach material based on Cu@Sn@Ag particles, in which the outermost Ag layer prevents the oxidation of the Sn layer and expedites the consumption of the low-melting point Sn phase. The die attach material can be reflowed at 250 °C for 15 min under a pressure of 3 MPa in the atmosphere, subsequently, the bondline can sustain a much higher temperature up to 480 °C. The results show that the Sn phase was totally transformed into Cu3Sn and Ag3Sn intermetallic compounds (IMCs) after reflow. Moreover, the Cu particles were evenly distributed in the Cu3Sn and Ag3Sn IMCs. After Cu@Sn@Ag particles were heated at 250 °C for 6 h, the average mass increased only by 2.8%, which indicates that the oxidation resistance property of Cu@Sn@Ag particles is excellent. The average electrical resistivity of the bondline was 4.6 µΩ cm, and the thermal conductivities were 159.97 W m−1 K−1, 142.71 W m−1 K−1, 137.28 W m−1 K−1 at 30 °C, 150 °C, 300 °C, respectively. The average shear strengths of the bondline were 25.8 MPa and 19.7 MPa at 30 °C and 400 °C, respectively. The coefficient of thermal expansion of the bondline was measured to be 15.77 × 10–6/°C. This novel paste shows great potential in die attachment in power device packaging. [ABSTRACT FROM AUTHOR]

Urbanization is an important direction for China's future social development and an important focus of its carbon emission reduction path. China's current administrative management is a vertical nested structure, and the characteristics of high-scale regions have a non-negligible impact on low-scale areas. Taking the county scale of the basic unit of economic and social development as the research scale, according to the panel data of the Yangtze River Delta from 2008 to 2016, a two-level hierarchical linear model (HLM) for carbon emission intensity is constructed, especially considering the characteristics of high-scale regions (i.e., low-carbon pilot cities) at the second level, and is combined with the mediating effect test method to analyze the impact path of urban development on carbon emissions intensity. The results show that (1) there is a spatial nesting relationship between regions of different scales, and the city scale can explain 85.21% of the carbon emissions intensity, which is much higher than the county scale. (2) There is an N-shaped curve relationship between urban development and carbon emissions intensity. After considering the high-scale factor (low-carbon pilot cities) at the city scale (the second level of the HLM), if a high-scale city is a low-carbon pilot city, then improvement in the level of urbanization in the county can promote a reduction in carbon intensity. (3) The impact path of urban development ⇄ per capita gross domestic product (the proportion of secondary industry, patent application volume) → carbon emissions intensity and urban development → the proportion of tertiary industry → carbon emissions intensity is significant. However, the path of the proportion of tertiary industry → urban development → carbon emissions intensity is not significant. [ABSTRACT FROM AUTHOR]

In-Sn alloys have great potential in high-power semiconductor packaging, but their applications are constrained by electromigration. The electromigration mechanism of a In-44Sn-6Zn alloy was studied with the current density at a direct current of 1.0 × 103A/cm2. The results indicated that the alloy exhibited an obvious phase separation under the influence of electron wind force. The β phase (In3Sn) was enriched at the cathode side and the γ phase (InSn4) was enriched at the anode side, while the zinc (Zn) phase had no obvious migration tendency. The migration of indium (In) and tin (Sn) atoms caused lattice distortion and the change rate of unit cell volume at the anode side was about twice as high as that of the cathode side. The primary Zn phase tended to migrate along the phase boundary and its size decreased with the process of diffusion. The mutual transformation between γ and β phases was carried out in a manner similar to the spinodal decomposition and the process of transformation accompanied by the solid solution or precipitation of Zn. After electromigration, the structure of the alloy was more uniform. The average area of the β phase at the cathode side was about 64% of the original size and that at the anode side was about 31% from the initial size. The resistance of the alloy increased 4% and the microhardness of the two poles were both increased by about 30%. [ABSTRACT FROM AUTHOR]

A new die attach material prepared by pressing micro-sized Sn-coated Ag powders as a preform is proposed for high-temperature power device packaging. The Sn-coated Ag powders were completely transformed into Ag3Sn with a melting point of 480°C after bonding at 250°C for 10 min, subsequently producing a bondline which can sustain a much higher temperature than the processing temperature. The detailed microstructural analysis indicates that a fine-grained full Ag3Sn bondline with high-density twin boundaries can be formed in a short reflow time, which contributes to the improved performance of the full Ag3Sn bondline, with an average shear strength of 37.5 MPa at 400°C. Nano-indentation testing showed that the average hardness and elasticity modulus of the prepared full Ag3Sn bondline were 3.1 ± 0.26 GPa and 84.56 ± 6.13 GPa, respectively. The electrical resistivity was measured to be 11.42 μΩ cm. The shear strength at 400°C was kept above 20 MPa after aging at 200°C for 200 h due to the thermostability of Ag3Sn microstructure in the bondlines. [ABSTRACT FROM AUTHOR]

Phase separation mechanism and property changes in In–41Sn–9Zn solder was investigated with the current density of direct current 1.0 × 103 A/cm2. The results indicated that the phase separation was affected by the combination of electron wind force and back stress. The different degree of lattice distortion between different regions was one of the causes of the back stress. In the alloy, In-rich β phases and Sn-rich γ phases were segregated at the cathode side and anode side respectively, while Zn atoms didn't migrate to the two poles significantly. Sn was the main diffusing atom Z Sn ∗ > Z In ∗ in the alloy, so the volume change rates at the anode side was about four times higher than that of the cathode side. After 72 h electromigration, the cathode–anode difference in micro-hardness, melting point, thermal enthalpy and melting interval was about 0.3 Mpa, 2 °C, 4.18 J/g, and 0.9 °C, respectively. [ABSTRACT FROM AUTHOR]

A silver (Ag) composite paste was fabricated based on Ag nanoparticles (NPs) and Ag microflakes (MFs). Robust interconnections were achieved after sintering in the temperature range of 150-225 °C. The shear strengths of the Ag MF + NP joints before and after thermal shock from − 50 to 150 °C for 1000 cycles were 155.7 ± 14.5 MPa and 78.4 ± 20.8 Mpa, respectively. The results show that the Ag composite paste not only has similar sintering properties to the Ag NP pastes but also exhibited superior mechanical reliability due to the addition of the Ag MFs. In addition, the sintered properties of different Ag pastes were discussed in terms of the coating organics, thermal behaviour and microstructure. The fracture modes after the shearing tests were analysed in detail. The Ag composite paste provides a potential solution for high-temperature applications. [ABSTRACT FROM AUTHOR]

This paper presents a fabrication method for high-temperature-resistant bondlines based on Cu@Ag@Sn multilayer core-shell hybrid microspheres in which a Ag layer was adopted to accelerate the consumption of a Sn layer. The phase transformation and microstructural evolution during the bonding process were investigated in detail. After the microspheres were heated at 250 °C for 20 min under a pressure of 0.5 MPa, the bondline could withstand high operation temperatures of up to 480 °C. After reflowing at 250 °C for just 5 min, the outer low-melting-point Sn layer was completely consumed. After 20 min, the bondline was composed of Ag3Sn and Cu3Sn intermetallic compounds with a dispersion of Cu microspheres. The average shear strengths of the resulting bondlines were 39.9 and 31.9 MPa at room temperature and at 400 °C, respectively. [ABSTRACT FROM AUTHOR]

Ag nanoparticle (NP) paste is considered to be a next-generation thermal interface material. However, its sintered microstructure is at risk of volume shrinkage and mechanical property degradation under harsh environments. In this work, silicon carbide (SiC) NPs were mixed with Ag NP paste to improve the stability and reliability of sintered Ag joints. Robust joints were prepared by a rapid thermal compression method at 275 °C for 20 s. Although the addition of SiC NPs degraded the initial shear strengths of these joints, the SiC-containing joints exhibited excellent mechanical properties and microstructural stability during thermal shock tests from − 50 to 150 °C for up to 1000 cycles. When the added amount of SiC NPs was 2%, the joints achieved the highest shear strength of 87.1 MPa (after 1000 cycles). In addition, the shear strengths of the joints were investigated at 250 °C. The addition of SiC NPs is believed to enhance the reliability of joints at high temperature. [ABSTRACT FROM AUTHOR]

Existing studies have analyzed the effects of financial development on economic growth and environmental pollution respectively, but few studies have analyzed the effects of financial development on economic growth and environmental protection from a unified framework. This paper reports on a study which took the 28 provinces of China, for the years 2002-2014, as its research object. It used green efficiency to measure the win-win balance between economic growth and environmental protection. It divided green efficiency into economic efficiency and environmental efficiency and then studied the effects of financial development on economic growth and environmental protection within a unified framework. The primary findings indicate that (1) overall, financial development is conducive to obtaining the win-win balance in China's economy, with its positive effects on economic growth being more significant than on environmental protection; (2) capital market development promotes both economic growth and environmental protection, while also playing a significant role in the win-win balance of China's economy. [ABSTRACT FROM AUTHOR]

The phase equilibria of the Mg-Pb-Sn ternary system were investigated using a combined method of electron probe microanalyzer and x-ray diffraction. Three isothermal sections of the Mg-Pb-Sn ternary system at 200, 300 and 400 °C were experimentally established. The phase equilibria of Mg-Pb-Sn ternary system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method on the basis of the presently determined experimental data. A consistent set of thermodynamic parameters has been derived for describing the Gibbs free energies of each solution phase and intermetallic compound in the Mg-Pb-Sn ternary system. The calculated phase diagrams and thermodynamic properties in the Mg-Pb-Sn ternary system are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the microstructure evolution and the resulting change in mechanical properties in a Ag@Sn TLP bondline during reflow and thermal aging. A Ag@Sn high-remelting-point bondline was rapidly achieved with thermocompression bonding of Ag@Sn powder in only 5 min at 250 °C. After reducing the thickness of the Sn coating on the Ag particles, the main phases in the resulting bondlines changed from Ag/Ag3Sn to Ag/ζ-Ag, increasing the remelting temperatures to 480 °C and above. The voids were effectively controlled by reducing the thickness of the Sn coating, thereby increasing the shear strength by 38%. The large surface area of the Ag/Sn interface, provided by a high density of core–shell Ag@Sn particles, enabled the rapid formation of an interconnection that is entirely composed of Ag and ζ-Ag. After thermal aging, the main phases transformed from Ag/ζ-Ag to Ag/Ag (Sn) solid solution/ζ-Ag, which causes an increase in the remelting temperature of aged interconnections up to 724 °C. The thermal aged samples showed slight decreases in shear strength, but the morphology of the fracture surfaces indicated better ductility. [ABSTRACT FROM AUTHOR]

Despite the consensus that activation of TWIK-related spinal cord K (TRESK) might contribute to the pathogenesis of chronic pain, the specific mechanisms underlying the transfer and development of pain signals still remain obscure. In the present study, we validated that TRESK was expressed in neurons instead of glial cells. Furthermore, in the SNI model of neuropathic pain (NP), downregulation of TRESK in spinal cord neurons resulted in upregulation of connexin 36 (Cx36) and connexin 43 (Cx43), both being subtypes of gap junctions in the spinal cord, with gliocytes in the spinal cord activated ultimately. Compared with SNI rats, intrathecal injection of TRESK gene recombinant adenovirus significantly downregulated the expression levels of Cx36 and Cx43 and suppressed the activation of gliocytes in the spinal cord, with hyperalgesia significantly reduced. In conclusion, TRESK contributes to the pathogenesis of NP by upregulation of synaptic transmission and activation of gliocytes. [ABSTRACT FROM AUTHOR]

We analyze a gradient recovery based linear finite element method to solve bi-harmonic equations and the corresponding eigenvalue problems. Our method uses only $$C^0$$ element, which avoids complicated construction of $$C^1$$ elements and nonconforming elements. Optimal error bounds under various Sobolev norms are established. Moreover, after a post-processing the recovered gradient is superconvergent to the exact one. Some numerical experiments are presented to validate our theoretical findings. As an application, the new method has been also used to solve 1-D fully nonlinear Monge-Ampère equation numerically. [ABSTRACT FROM AUTHOR]

In situ observation was performed on cross-sections of Sn-3.0Ag-0.5Cu solder interconnects to track the evolution of microstructure and grain orientation under electrical current stressing. Cross-sections of Cu/Ni-Sn-3.0Ag-0.5Cu-Ni/Cu sandwich-structured solder interconnects were prepared by the standard metallographic method and subjected to electrical current stressing for different times. The electron backscatter diffraction technique was adopted to characterize the grain orientation and structure of the solder interconnects. The results show that metallization dissolution and intermetallic compound (IMC) migration have close relationships with the grain orientation and structure of the solder interconnects. Ni metallization dissolution at the cathode interface and IMC migration in the solder bulk can be accelerated when the c-axis of the grain is parallel to the electron flow direction, while no observable change was found when the c-axis of the grain was perpendicular to the electron flow direction. IMC can migrate along or be blocked at the grain boundary, depending on the misorientation between the current flow direction and grain boundary. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the expression and clinical significance of miR-494 and PTEN (phosphatase and tensin homologue deleted on chromosome ten) in non-small cell lung cancer (NSCLC). Immunohistochemistry for PTEN and in situ hybridization (ISH) for miR-494 were performed in 92 NSCLC tissues and 10 normal lung tissues to detect their expression, and correlation between their expression with clinical characteristics and prognosis was analyzed. The expression of miR-494 was significantly higher in NSCLC than in normal lung tissues ( P = 0.004). The positive expression of PTEN protein in the lung carcinoma tissues was significantly lower than that in the normal lung tissues ( P = 0.013), while the level of miR-494 expression was negatively correlated with PTEN expression ( r = −0.577, P < 0.01). The high positive rate of miR-494 was positively correlated with pathological TNM (p-TNM) staging and lymph node metastasis. The expression of miR-494 was negatively correlated with grade of differentiation. However, the expression of PTEN was positively correlated with grade of differentiation. Patients with over-expression of miR-494 had a shorter overall survival (OS), while the negative group of PTEN was correlated with poor OS. MiR-494 over-expression and low PTEN expression are closely related to tumor p-TNM staging and lymph node metastasis, differentiation, and OS. Combined detection of PTEN and miR-494 can aid in determining malignancy degree and the prognosis of patients with NSCLC. MiR-494 may be served as a novel prognostic factor and may lead to new treatment strategies for NSCLC. [ABSTRACT FROM AUTHOR]