Evaluation of reliability and metallurgical integrity of wire bonds and lead free solder joints on flexible printed circuit board sample modules

This paper presents a study of the optimization of the gold plating thickness for the use of both wire bonding and soldered interconnects on a flexible printed circuit board sample module. Wire bondability is typically better, when the gold plating thickness is greater than 30 μin.; however, the risk of problems with solder joint embrittlement becomes a concern with thick gold plating. In order to better understand the effect of the gold plating thickness on wire bondability and solder joint embrittlement, an evaluation was performed on samples with three ranges of gold plating thicknesses (10–20 μin., 20–30 μin., and 30–45 μin.), on flexible printed circuit board (PCB), substrates. Mechanical shear testing and metallurgical analyses were conducted on chip component solder joints in this three thickness gold study. Thermal shock and drop testing were conducted to evaluate the reliability of the sample modules. Drop testing is especially critical for determining the reliability of the sample modules, which are used in portable consumer electronics products. Reliability testing and metallurgical analyses have been performed to characterize the effect of gold embrittlement on the mechanical integrity of the solder joints with a gold content ranging from 1 to 4 wt.%.     

Synthesis and photochemical performance of morphology-controlled CdS photocatalysts for hydrogen evolution under visible light

Novel CdS nanomaterials were synthesized by a simple “one-pot” hydrothermal biomolecule-assisted method using glutathione (GSH) as the sulfur source and structure-directing reagent. Various morphologies of CdS photocatalysts, such as solid nanospheres (s-CdS), hollow nanospheres (h-CdS) and nanorods (r-CdS), were obtained by controlling only the hydrothermal temperatures. The X-ray diffraction patterns confirmed that all of the samples were typical hexagonal wurtzite CdS. It was found that the absorption edge of s-CdS was at 465 nm with a greater blue shift compared to that of h-CdS and r-CdS. The photocatalytic activity of s-CdS was superior to that of h-CdS and r-CdS under visible light. Photoluminescence measurements revealed their different photogenerated electron/hole recombination ability, which was in accordance with the order of s-CdS < h-CdS < r-CdS. The excellent photocatalytic activity of s-CdS was ascribed to the small sizes of sub-nanocrystallites, which make it easy for photoinduced electrons and holes on the solid sphere to migrate to the surface and react with water and the sacrificial agent quickly. It was crucial to control the temperature for preparing CdS photocatalysts via hydrothermal methods. The formation mechanism of different morphology might be due to complexation, S-C bond rupture, spherical aggregation and Ostwald ripening processes.     

忻州市中型水库病险成因分析及加固对策

忻州市现有五座中型水库不同程度地存在防洪标准低，坝体填筑质量差，坝基、坝肩渗漏严重，观测、管理配套孕施不健全等问题，结合除险加固工程实践，通过对水库病险成因的分析，阐述了相应的加固措施。     

The Effect of Oxygen Concentration on the Reaction of NOx with Soot Over BaAl2O4

The effect of oxygen concentration on the catalytic reaction of NO_x with soot over BaAl₂O₄ has been studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The introduction of O₂ into the NO flow can result in a reactant mixture of NO/NO₂/O₂. Increasing the O₂ concentration from 2 % to 5 % in the NO‐containing flow promotes the formation of NO₂ from the gas phase oxidation of NO. The reactant mixture with high O₂/NO flow, allows for the formation of greater amounts of nitrate species than that with low O₂/NO flow, which further promotes the reaction of soot with NO_x and leads to a high conversion efficiency of NO_x into N₂ and N₂O. In the absence of O₂, N₂O is not observed since the N₂O produced at high temperatures has reacted with soot before it can be detected.     

Controlled cooling of an aluminum alloy casting based on 3D printed rib reinforced shell mold

3D printing technology has been used for sand molding and core printing, but they simply substitute the traditional molding and core making method without changing the shape or size of the sand mold(core) and their dense structure. In this study, a new type of hollow mold based on 3D printing is presented. The new type of mold is a rib reinforced thickness-varying shell mold. This mold design can realize the controlled cooling of castings, i.e., different cooling rates at different areas, and improve the temperature uniformity of a casting after its solidifi cation. Therefore, the performance of castings can be improved and their residual stress and deformation can be reduced. This kind of new mold was applied to a stress frame of A356 aluminum alloy. The 3D printed rib reinforced thickness-varying shell mold was compared with the traditional dense mold, and the castings obtained by these two kinds of molds were also compared. The experimental results showed that the rib reinforced shell mold increased the cooling rate of the casting by 30%, tensile strength by 17%, yield strength by 11%, elongation by 67%, and decreased its deformation by 43%, while sand consumption was greatly reduced by 90%.     

硝基苯催化加氢制苯胺的热力学分析

用基团估算法计算了硝基苯的热力学数据。对硝基苯催化加氢制苯胺进行了比较详细的热力学分析,首次建立了该反应的反应焓变、Gihbs自由能以及反应平衡常数的变化与反应温度的关系。得出该反应为自发放热反应,反应温度越高,趋于热力学平衡程度越低。     

基于加装叶尖小翼风电机组发电量提升试验研究

针对老旧风电场由于风电机组风轮和风资源未能很好匹配等原因导致的发电量不理想问题,提出一种基于加装叶尖小翼风电机组发电量提升方法,该方法在增加叶片扫掠面积的同时有效改善叶片的气动性能。通过加装叶尖小翼增加叶尖部分切向力,增加主轴扭矩从而提高风轮吸收功率,达到提升发电量的目的。基于风电场实际试验数据对提功增效效果进行分析,结果表明所提方法在满足安全性的前提下可有效提高机组输出功率,提升发电量。同时该方法成本低,展现了良好的性价比。     

Regeneration of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-based high-temperature coal gas desulfurization sorbent in atmosphere with sulfur dioxide

Regeneration of a high-temperature coal gas desulfurization sorbent is a key technology in its industrial applications. A Fe₂O₃-based high-temperature coal gas desulfurizer was prepared using red mud from steel factory. The influences of regeneration temperature, space velocity and regeneration gas concentration in SO₂ atmosphere on regeneration performances of the desulfurization sorbent were tested in a fixed bed reactor. The changes of phase and the composition of the Fe₂O₃-based high-temperature coal gas desulfurization sorbent before and after regeneration were examined by X-ray diffraction (XRD) and X-ray Photoelectron spectroscopy(XPS), and the changes of pore structure were characterized by the mercury intrusion method. The results show that the major products are Fe₃O₄ and elemental sulfur; the influences of regeneration temperature, space velocity and SO₂ concentration in inlet on regeneration performances and the changes of pore structure of the desulfurization sorbent before and after regeneration are visible. The desulfurization sorbent cannot be regenerated at 500°C in SO₂ atmosphere. Within the range of 600°C–800°C, the time of regeneration becomes shorter, and the regeneration conversion increases as the temperature rises. The time of regeneration also becomes shorter, and the elemental sulfur content of tail gas increases as the SO₂ concentration in inlet is increased. The increase in space velocity enhances the reactive course; the best VSP is 6000 h^?1 for regeneration conversion. At 800°C, 20 vol-% SO₂ and 6000 h^?1, the regeneration conversion can reach nearly to 90%.     

Synthesis and characterization of high-density non-spherical Ni(OH)2 cathode material for Ni–MH batteries

Positive electrode active materials of non-spherical nickel hydroxide powders with a high tap-density for alkaline Ni–MH batteries have been successfully synthesized using a polyacrylamide (PAM) assisted two-step drying method. The tap-density of the powders reaches 2.32 g cm⁻³, which is significantly higher than that of nickel hydroxide powders obtained by the conventional co-precipitation method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge–discharge test were used to characterize the physical and electrochemical properties of the synthesized material. The results show that the as-prepared nickel hydroxide materials have an irregular tabular shape, a high density of structural disorder, and a high specific surface area. The charge–discharge tests indicate that nickel hydroxide powders synthesized by the new method have better electrochemical performance than those obtained by the conventional co-precipitation method. This performance improvement could be attributable to a more compact electrode microstructure, a lower amount of intercalated anions, better reaction reversibility, a higher proton diffusion coefficient, and lower electrochemical impedance, as indicated by TG-DTA, CV, and EIS. The results clearly show that better electrochemical activity can be achieved using nickel hydroxide that has a higher tap-density. Moreover, the new synthesis process is simple, cost-effective, and facile for large-scale production.