Morphology Control and Mechanism of Different Bath Systems in Cu/SiCw Composite Electroplating.

With the rapid development of electronic technology and large-scale integrated circuit devices, it is very important to develop thermal management materials with high thermal conductivity. Silicon carbide whisker-reinforced copper matrix (Cu/SiCw) composites are considered to be one of the best candidates for future electronic device radiators. However, at present, most of these materials are produced by high-temperature and high-pressure processes, which are expensive and prone to interfacial reactions. To explore the plating solution system suitable for SiCw and Cu composite electroplating, we tried two different Cu-based plating solutions, namely a Systek UVF 100 plating solution of the copper sulfate (CuSO4) system and a Through Silicon Via (TSV) plating solution of the copper methanesulfonate (Cu(CH3SO3)2) system. In this paper, Cu/SiCw composites were prepared by composite electrodeposition. The morphology of the coating under two different plating liquid systems was compared, and the mechanism of formation of the different morphologies was analyzed. The results show that when the concentration of SiCw in the bath is 1.2 g/L, the surface of the Cu/SiCw composite coating prepared by the CuSO4 bath has more whiskers with irregular distribution and the coating is very smooth, but there are pores at the junction of the whiskers and Cu. There are a large number of irregularly distributed whiskers on the surface of the Cu/SiCw composite coating prepared with the copper methanesulfonate (Cu(CH3SO3)2) system. The surface of the composite is flat, and Cu grows along the whisker structure. The whisker and Cu form a good combination, and there is no pore in the cross-section of the coating. The observation at the cross-section also reveals some characteristics of the toughening mechanism of SiCw, including crack deflection, bridging and whisker pull-out. The existence of these mechanisms indicates that SiCw plays a toughening role in the composites. A suitable plating solution system was selected for the preparation of high-performance Cu/SiCw thermal management materials with the composite electrodeposition process.

Application of Ni/SiCw Composite Material in MEMS Microspring.

The microspring is a typical type of device in MEMS devices, with a wide range of application scenarios and demands, among which a popular one is the microelectroformed nickel-based planar microspring prepared by the UV-LIGA technology based on the SU-8 adhesive. It is worth noting that the yield strength of the electrodeposited nickel microstructure is low, and the toughness of the structure is not high, which is unbeneficial for the enduring and stable operation of the spring. The paper mainly presents the methods of preparing high-aspect-ratio Ni/SiCw microstructures for MEMS devices based on UV-LIGA technology, developing Ni/SiCw-based microspring samples with a thickness of 300 µm, and applying a DMA tensile tester for mechanical property tests and characterization. In addition, the paper explores the influence of heat treatment at 300 °C and 600 °C on the tensile properties and microstructure of composite coatings. The results show that the W-form microspring prepared from Ni/SiCw composites not only has a wider linear range (about 1.2 times wider) than that of pure nickel material but also has a stronger resistance capacity to plastic deformation, which is competent for MEMS device applications in environments below 300 °C. The research provides a frame of reference and guidance for improving the stable cyclic operating life of such flat springs.

Advancements in SiC-Reinforced Metal Matrix Composites for High-Performance Electronic Packaging: A Review of Thermo-Mechanical Properties and Future Trends.

With the advancement of semiconductor technology, chip cooling has become a major obstacle to enhancing the capabilities of power electronic systems. Traditional electronic packaging materials are no longer able to meet the heat dissipation requirements of high-performance chips. High thermal conductivity (TC), low coefficient of thermal expansion (CTE), good mechanical properties, and a rich foundation in microfabrication techniques are the fundamental requirements for the next generation of electronic packaging materials. Currently, metal matrix composites (MMCs) composed of high TC matrix metals and reinforcing phase materials have become the mainstream direction for the development and application of high-performance packaging materials. Silicon carbide (SiC) is the optimal choice for the reinforcing phase due to its high TC, low CTE, and high hardness. This paper reviews the research status of SiC-reinforced aluminum (Al) and copper (Cu) electronic packaging materials, along with the factors influencing their thermo-mechanical properties and improvement measures. Finally, the current research status and limitations of conventional manufacturing methods for SiC-reinforced MMCs are summarized, and an outlook on the future development trends of electronic packaging materials is provided.

Design and Optimization of Piezoelectric Cantilever Beam Vibration Energy Harvester.

Piezoelectric cantilever beams are commonly utilized to harvest energy from environmental vibrations due to their simple structures. This paper optimizes a single crystal trapezoidal hollow structure piezoelectric cantilever beam vibration energy harvester with a copper substrate to achieve high energy density at a low frequency. Finite element analysis (FEA) is adopted to optimize the size of the copper substrate at first, and the piezoelectric energy harvester (PEH) is further optimized with a trapezoidal hollow structure under the optimal size of the copper substrate. The developed PEH with a trapezoidal hollow structure (La = 20 mm, Lb = 15 mm, and Lh = 40 mm), with a copper substrate of 80 mm × 33 mm × 0.2 mm, can obtain the best output performance. Under the condition of 1 g acceleration, the resonance frequency and peak voltage output were 23.29 Hz and 40.4 V, respectively. Compared with the unhollowed PEH, the developed trapezoidal hollow structure PEH can reduce its resonant frequency by 12.18% and increase output voltage by 34.67%, while also supplying a power density of 7.24 mW/cm3. This study verified the feasibility of the optimized design through simulation and experimental comparison.

Process improvement of high aspect ratio nano-gratings based on synchrotron x-ray.

To achieve better structural accuracy and aspect ratio, nano-gratings with a vertical angle close to 90° and a depth-to-width ratio of about 8 were prepared by synchrotron radiation. The optimal exposure dose and development time were determined to be 0.006 (A·h) and 6 min, respectively, by observing the surface loss and roughness of the gratings with slit widths of 150 nm and 250 nm under different conditions. To obtain the desired rectangular grating structure, the experimental conditions were optimized with the help of controlled variables experimental method. With the mask-to-photoresist pitch and the development and drying temperatures of 20µm and 23 °C, the optimized depth-to-width ratio of the nano-gratings with a slit width of 250 nm can reach 8.28. The cone angle can reach 88.4°. The aspect ratio of the nano-gratings with a slit width of 150 nm is 7.18, and its cone angle is 87.1°.

Design, Manufacture and Test of Piezoelectric Cantilever-Beam Energy Harvesters with Hollow Structures.

This article presents a single-crystal piezoelectric energy harvester (PEH) with a trapezoidal hollow hole that can obtain high energy density at low frequency. Harvesters with a hollow structure were fabricated through a series of manufacturing processes such as thermocompression bonding, screen printing and laser cutting. Finite element analysis (FEA) and experimental results showed that using low modulus brass instead of stainless steel as the PEH substrate enhances the voltage output of the device, and the hollow design greatly increases the overall stress level and power density. In addition, the developed PEH with a trapezoidal hole obtained the best output performance; when the acceleration, resonance frequency and matched load resistance were 0.5 g, 56.3 Hz and 114 kΩ, respectively, the peak voltage was 17 V and the power density was 2.52 mW/cm3. Meanwhile, compared with the unhollowed device, the peak voltage and maximum power density of the proposed PEH were increased by 30.7% and 24.4%, respectively, and the resonance frequency was reduced by 7%. This study verified the feasibility of the optimized design through simulation and experimental comparison.

Preparation of Microneedle Array Mold Based on MEMS Lithography Technology.

As a transdermal drug delivery technology, microneedle array (MNA) has the characteristics of painless, minimally invasive, and precise dosage. This work discusses and compares the new MNA mold prepared by our group using MEMS technology. First, we introduced the planar pattern-to-cross-section technology (PCT) method using LIGA (Photolithography, Galvanogormung, Abformung) technology to obtain a three-dimensional structure similar to an X-ray mask pattern. On this basis, combined with polydimethylsiloxane (PDMS) transfer technology and electroplating process, metal MNA can be prepared. The second method is to use silicon wet etching combined with the SU-8 process to obtain a PDMS quadrangular pyramid MNA using PDMS transfer technology. Third method is to use the tilting rotary lithography process to obtain PDMS conical MNA on SU-8 photoresist through PDMS transfer technology. All three processes utilize parallel subtractive manufacturing methods, and the error range of reproducibility and accuracy is 2-11%. LIGA technology produces hollow MNA with an aspect ratio of up to 30, which is used for blood extraction and drug injection. The height of the MNA prepared by the engraving process is about 600 µm, which can achieve a sustained release effect together with a potential systemic delivery. The height of the MNA prepared by the ultraviolet exposure process is about 150 µm, which is used to stimulate the subcutaneous tissue.

[Clinical Significance of the Bone Marrow Morphological Differences in the Differential Diagnosis of Megaloblastic Anemia and Refractory Anemia].

OBJECTIVE: To investigate the clinical significance of bone marrow morphological differences in the differential diagnosis of megaloblastic anemia (MM) and refractory anemia (R4). METHODS: A total of 60 anemia patients selected from our hospital between April 2004 and April 2015 were divided into MA group (30 cases) and RA group (30 cases) in accordance with their clinical diagnosis. Clinical manifestations, results of bone marrow morphology test, blood examination, peripheral blood smear, erythroid megaloblastic variability rate and nucleated red blood cell level in the 2 groups were compared and analyzed. RESULTS: Incidence of fever, hemorrhage, digestive reaction, splenomegaly and fatigue as well as hemoglobin level, platelets and white blood cell counts in patients of MA group were similar to those of RA group, there was no statistically significant difference between 2 groups (P>0.05). The percentages of dysplastic hematopoiesis in erythroid cells, granulocytic cells, magakaryoajtic cells, the PAS-positive rate and red blood cell distribution in the MA patients were obviously lower than those in the RA patients, while the erythroid megaloblastic variability rate (90%) in MA group was obviously higher than that in RA patients (10%) and with statistically significant difference (P<0.05). The percentage of immature red blood cells was similar between MA group (53.33%) and RA group (60.00%), without significant difference (P>0.05). CONCLUSION: Most of clinical manifestations and peripheral blood smear results are consistent in MA patients and RA patients, bone marrow morphology detection in RA group should be focused on lymphocytoid micromegakaryocytes, while the erythroid megaloblastic cell body is the focus in MA group, PAS can be used as a diagnostic criteria.

Integral equation theory study on the phase separation in star polymer nanocomposite melts.

The polymer reference interaction site model theory is used to investigate phase separation in star polymer nanocomposite melts. Two kinds of spinodal curves were obtained: classic fluid phase boundary for relatively low nanoparticle-monomer attraction strength and network phase boundary for relatively high nanoparticle-monomer attraction strength. The network phase boundaries are much more sensitive with nanoparticle-monomer attraction strength than the fluid phase boundaries. The interference among the arm number, arm length, and nanoparticle-monomer attraction strength was systematically investigated. When the arm lengths are short, the network phase boundary shows a marked shift toward less miscibility with increasing arm number. When the arm lengths are long enough, the network phase boundaries show opposite trends. There exists a crossover arm number value for star polymer nanocomposite melts, below which the network phase separation is consistent with that of chain polymer nanocomposite melts. However, the network phase separation shows qualitatively different behaviors when the arm number is larger than this value.

Integral equation theory study on the structure and effective interactions in star polymer nanocomposite melts.

The polymer reference interaction site model theory is used to investigate the radial distribution function, potential of mean force, depletion force, and second virial coefficient in star polymer nanocomposite melts. The contact aggregation of nanoparticles for relatively weak nanoparticle-monomer attraction and the bridging aggregation of nanoparticles for very large nanoparticle-monomer attraction are observed. The star architecture can well suppress the organization states of direct contact and bridging structure for the moderate nanoparticle-monomer attraction, and promote the bridging-type organization for relatively large nanoparticle-monomer attraction. At constant particle volume fraction, the arm length quantitatively affects the organization states of star polymer nanocomposite melt, and larger repulsive barriers are existent to prevent the contact aggregation of larger nanoparticles. These observations provide useful information for the development of new nanocomposite materials.

Prediction of phase behavior of nanoconfined Lennard-Jones fluids with density functional theory based on the first-order mean spherical approximation.

The recently proposed first-order mean spherical approximation (FMSA) [Y. Tang, J. Chem. Phys. 121, 10605 (2004)] for inhomogeneous fluids is extended to study the phase behavior of nanoconfined Lennard-Jones fluids, which is consistent with the phase equilibria calculation of the corresponding bulk fluid. With a combination of fundamental measure theory, FMSA provides Helmholtz free energy and direct correlation function to formulate density functional theory, which implementation is as easy as the mean-field theory. Following previous success in predicting density profiles inside slit pores, this work is focused specially on the vapor-liquid equilibrium of the Lennard-Jones fluids inside these pores. It is found that outside the critical region FMSA predicts well the equilibrium diagram of slit pores with the sizes of 5.0, 7.5, and 10 molecular diameters by comparing with available computer simulation data. As a quantitative method, FMSA can be treated as an extension from its bulk calculation, while the mean-field theory is only qualitative, as its bulk version.

Structure and effective interactions in polymer nanocomposite melts: an integral equation theory study.

The polymer reference interaction site model from integral equation theory is used to investigate the structure and effective interactions in polymer nanocomposite melts where strong nanoparticle-monomer interactions are principally considered in this work. For finite particle volume fraction, the compromise for the interference between polymers and nanoparticles results in an optimum particle volume fraction for nanoparticle dispersion in polymer melts. At constant particle volume fraction, the effects of degree of polymerization become insignificant when it reaches a threshold value, below which quantitative effects on the organization states of polymer nanocomposite melts are found and help nanoparticles to well disperse in polymer. The aggregation of large nanoparticles decreases with the increase of the nanoparticle-monomer attraction strength. These observations may provide useful information for the development of new polymer materials.

Structure and adsorption of a hard-core multi-Yukawa fluid confined in a slitlike pore: grand canonical Monte Carlo simulation and density functional study.

Because of the increasing interest in studying the phenomenon exhibited by charge-stabilized colloidal suspensions in confining geometry, we present a density functional theory (DFT) for a hard-core multi-Yukawa fluid. The excess Helmholtz free-energy functional is constructed by using the modified fundamental measure theory and Rosenfeld's perturbative method, in which the bulk direct correlation function is obtained from the first-order mean spherical approximation. To validate the established theory, grand canonical ensemble Monte Carlo (GCMC) simulations are carried out to determine the density profiles and surface excesses of multi-Yukawa fluid in a slitlike pore. Comparisons of the theoretical results with the GCMC data suggest that the present DFT gives very accurate density profiles and surface excesses of multi-Yukawa fluid in the slitlike pore as well as the radial distribution functions of the bulk fluid. Both the DFT and the GCMC simulations predict the depletion of the multi-Yukawa fluid near a nonattractive wall, while the mean-field theory fails to describe this depletion in some cases. Because the simple form of the direct correlation function is used, the present DFT is computationally as efficient as the mean-field theory, but reproduces the simulation data much better than the mean-field theory.

First-order mean spherical approximation for attractive, repulsive, and multi-Yukawa potentials.

The first-order mean spherical approximation (FMSA) theory proposed by Tang et al. [Fluid Phase Equilib., 134, 21(1997)] is applied for studying several typical Yukawa fluids, including attractive, repulsive, and multi-Yukawa cases. The FMSA study is particularly advantageous in providing thermodynamics and structure information in a simple, analytical, and consistent manner. Comparisons with the latest reported computer simulation data for compressibility factor, internal energy, and radial distribution function show that FMSA performs very well and the performance is very close to the full MSA and to several other theories, developed individually for the above-mentioned cases or properties. The present study provides solid evidence to support FMSA applications to more complex fluids.

Prediction of global vapor-liquid equilibria for mixtures containing polar and associating components with improved renormalization group theory.

Our recently improved renormalization group (RG) theory is further reformulated within the context of density functional theory. To improve the theory for polar and associating fluids, an explicit and complete expression of the theory is derived in which the density fluctuation is expanded up to the third-order term instead of the original second-order term. A new predictive equation of state based on the first-order mean spherical approximation statistical associating fluid theory (FMSA-SAFT) and the newly improved RG theory is proposed for systems containing polar and associating fluids. The calculated results for both pure fluids and mixtures are in good agreement with experimental data both inside and outside the critical region. This work demonstrates that the RG theory incorporated with the solution of FMSA is a promising route for accurately describing the global phase behavior of complex fluids and mixtures.

Integral equation theory for atactic polystyrene melt with a coarse-grained model.

In this work, an integral equation approach to investigate the atactic polystyrene (aPS) melt based on polymer reference interaction site model (PRISM) theory is proposed. The intramolecular structure factors, required as input to PRISM theory, are obtained from the semiflexible chain model. With a novel coarse-graining procedure and the explicit-atom molecular-dynamics (MD) simulations for aPS, the parameters needed for the coarse-grained model are obtained by using an automatic simplex optimization. These parameters can be used to describe the structure and thermodynamic properties of the complex aPS melt and good agreement is obtained between the theory and MD simulations. The proposed integral equation approach provides a basis for describing the structure and properties of PS nanocomposites where the application of molecular simulation is difficult.

An improved renormalization group theory for real fluids.

On the basis of White's theory, an improved renormalization group (RG) theory is developed for chain bonding fluids inside the critical region. Outside the critical region, the statistical associating fluid theory based on the first-order mean sphere approximation [Fluid Phase Equilibria 171, 27 (2000)] is adopted and all the microscopic parameters are taken directly from its earlier application of real fluids. Inside the critical region, the RG transformation for long-range density fluctuation is derived in the k space, which illustrates explicitly the contributions from the mean-field term, the local density fluctuation, and the nonlocal density fluctuation. The RG theory is applied to describe physical behavior of ten n alkanes (C1-C10) both near to and far from the critical point. With no additional parameters for chain bonding fluids, good results are obtained for critical specific heat and phase coexistence curves and the resulting critical exponents are in good agreement with the reported nonclassic values.

Effect of the range of attractive interactions on crystallization, metastable phase transition, and percolation in colloidal dispersions.

The equilibrium as well as nonequilibrium phase behaviors of colloidal dispersions have been investigated using statistical-mechanical theories of fluids and solids in complement with the renormalization-group (RG) theory. It is shown that the osmotic second virial coefficient at the critical point of the fluid-fluid transition varies with the range of attractions and is sensitive to specific forms of the attractive potential in contrast to a common speculation that it remains practically constant. However, for colloids with short-ranged forces, the critical temperature of the fluid-fluid phase transition is well correlated with the range of attractions in good agreement with an earlier empirical correlation based on simulation results. A comparison of the relative positions of the fluid-fluid coexistence curve, freezing, melting, and percolation lines in the phase diagram indicates that the gelation in colloidal systems has significant effects on the equilibrium phase transitions and crystallization, especially when the attractions between colloidal particles are short ranged.

Study on osmotic pressures for aqueous lysozyme and alpha-chymotrypsin-electrolyte solutions with two Yukawa potentials.

The equation of state (EOS) of Duh and Mier-y-Terán for one Yukawa potential is expanded to two Yukawa potentials to describe the nonidealities of the charged lysozyme and alpha-chymotrypsin solutions. Instead of the classical DLVO theory, the attractive dispersion and double-layer repulsion interactions are represented by two Yukawa potentials, respectively. For the aqueous lysozyme solutions, the only adjustable dispersion energy parameter epsilon/k is regressed and the average deviation is 1.76%. For the aqueous alpha-chymotrypsin solutions, two adjustable parameters (the molecular weight and dispersion energy parameter) are regressed and the average deviation is 7.62%. Some correlation and prediction results are discussed.

Correlation and Prediction of Osmotic Pressures for Aqueous Bovine Serum Albumin-NaCl Solutions Based on Two Yukawa Potentials.

A new equation of state is proposed to correlate and predict the osmotic pressure data for aqueous bovine serum albumin (BSA) solutions with different NaCl concentrations and pH values with only one adjustable parameter. The Carnahan-Starling equation represents the contribution of the hard sphere repulsion to the osmotic pressure. The attractive dispersion and double-layer repulsion interactions are represented by two Yukawa potentials, respectively. The equation of state of Duh and Mier-Y-Teran for one Yukawa potential is expanded to two Yukawa potentials to describe the nonidealities of the charged BSA-aqueous NaCl solution, instead of the classical DLVO theory. The average relative deviation of correlation of the osmotic pressure in 0.15 M NaCl solution is 18%. The average relative deviation of prediction in 1-5 M NaCl solutions is 20.33%. A comparison with other models and the limitations of our model are discussed. Copyright 2001 Academic Press.