Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part I: Creep constitutive relation and fatigue model

In this study, a new unified creep constitutive relation and a modified energy-based fatigue model have been established respectively to describe the creep flow and predict the fatigue life of Sn−Pb solders. It is found that the relation successfully elucidates the creep mechanism related to current constitutive relations. The model can be used to describe the temperature and frequency dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part II to develop the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly. The project supported by the National Natural Science Foundation of China (59705008)     

Sorption of methylene blue on an organoclay bearing thiol groups and application to electrochemical sensing of the dye

In this work, a thiol functionalized-clay was prepared by the covalent grafting of 3-mercaptopropyltrimethoxysilane (MPTMS) onto the surface of a natural smectite clay mineral originating from Cameroon. Effectiveness of the grafting process and properties of the resulting hybrid material were studied by various physico-chemical techniques, such as Fourier transform infrared (FTIR) spectroscopy, N(2) adsorption-desorption experiments (surface area measurements by the BET method) and thermal gravimetric analysis (TGA) coupled with mass spectrometry (MS). Sorption of methylene blue (MB), an electroactive cationic dye, was investigated for both the raw clay and its modified counterpart, as a function of shaking time, adsorbate concentration and pH, through batch experiments. A significant enhancement of the adsorption capacity towards MB was observed with the clay bearing thiol groups in comparison with the pristine one. The obtained sorption data matched the Langmuir isotherm model, from which it appeared that the organoclay adsorbed MB at a maximal loading of 1.04mmolg(-1), while the natural clay displayed a significantly poorer performance (0.31mmolg(-1)). The uptake of MB by the modified clay was found to be highly affected by pH, the cationic dye being more effectively adsorbed in alkaline medium. The possible use of the thiol functionalized-clay as electrode modifier for MB sensing purposes was then evaluated by means of carbon paste electrodes, using cyclic voltammetry. A calibration curve was obtained in the concentration range from 1x10(-6) to 1.4x10(-5)molL(-1), with a detection limit of 4x10(-7)molL(-1)(signal/noise=3).     

Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part II: Reliability experiment and numerical simulation

In the present study, a facility, i.e., a mechanical deflection system (MDS), was established and applied to assess the long-term reliability of the solder joints in plastic ball grid array (BGA) assembly. It was found that the MDS not only quickly assesses the long-term reliability of solder joints within days, but can also mimic similar failure mechanisms in accelerated thermal cycling (ATC) tests. Based on the MDS and ATC reliability experiments, the acceleration factors (AF) were obtained for different reliability testing conditions. Furthermore, by using the creep constitutive relation and fatigue life model developed in part I, a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results were found to be in good agreement with the test results from the MDS. As a result, a new reliability assessment methodology was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly. The project supported by the National Natural Science Foundation of China (59705008)     

HL—1M装置1998年物理实验进展报告

报道了ＨＬ－１Ｍ装置１９９８年度物理实验的进展情况。主要包括等离子体密度极限,中性束注入加热,离子回旋共振加热,低温杂波离子加热,多发弹丸注入,超声分子束注入等实验的情况。     

Astrophysical S-factors from asymptotic normalization coefficients

S-factors for direct capture reactions can be found at astrophysical energies from asymptotic normalization coefficients which provide the normalization of the tail of the overlap function. For example the overlap for ⁸B → ⁷Be+p defines the S-factor for ⁷Be (p, γ)⁸B. Peripheral transfer reactions offer a technique to determine these asymptotic normalization coefficients. As a test of the technique, the ¹⁶O(³He, d)¹⁷F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ¹⁷F. The S-factors for ¹⁶O(p, γ)¹⁷F calculated from these ¹⁷F → ¹⁶O+p asymptotic normalization coefficients are found to be in very good agreement with recent measurements. Following the same technique, the ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the asymptotic normalization coefficient for ⁷Be(p, γ)⁸B. This result provides an indirect determination of S ₁₇(0).     

Sensitive electrochemical detection of methyl parathion in the presence of para-nitrophenol on a glassy carbon electrode modified by a functionalized NiAl-layered double hydroxide

An inorganic–organic composite material was prepared by the insertion of bis(ethylhexyl)hydrogen phosphate (BEHP) within the interlayer space of a nickel-aluminum–layered double hydroxide (NiAl LDH). X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared were used to characterize the pristine and modified LDH (NiAl–BEHP), which together confirm the intercalation of BEHP in the mineral structure. Cyclic voltammetry using [Fe(CN)₆]^3? as an anionic redox probe demonstrated a significant decrease in the anion exchange capacity of NiAl upon modification. Used as electrode modifier for methyl parathion (MP) detection, a remarkable increase in MP signal on NiAlBEHP–modified glassy carbon electrode (GCE/NiAl–BEHP) was observed, because of the high hydrophobicity character of the modified LDH. The signal assigned to the electroactivity of the nitro group being less stable than that of the reduction of the nitroso group, the use of both functions was explored for the calibration experiments. Sensitivities of 0.79 μA μM^?1 and 0.14 μA μM^?1 were obtained, with detection limits of 2.28 × 10^?8 and 12.4 × 10^?8 mol L^?1 for nitro and nitroso groups, respectively. However, the linearity range was more important for the nitroso group (0.5–12 μM) as compared to the nitro group (0.5–3.5 μM). Moreover, the signal of the nitroso group showed poor interference with some chemical species likely to be encountered in the presence of MP. The GCE/NiAl-BEHP–modified electrode was particularly effective for the differentiation of 4-nitrophenol (4-NP) from MP. Interestingly, the decrease in the sensor sensitivity was negligible (0.13 μA μM^?1) when the calibration curve of MP was plotted in the presence of 1 μM of 4-NP. The poor efficiency of the sensor to quantify 4-NP was probably because of the high organophilic character of the electrode material. The developed method was successfully applied to quantify MP in spring water.     

中国环流器新一号装置总体联调

本文介绍中国环流器新一号装置工程总体联合调试的内容和主要结果。该装置总体联调是非常成功的，获得了重复性很好，环电流平顶宽的稳定平稳的放电波形，这对物理实验的开展非常有利。     

Surfactant-intercalated smectite modified electrode: sensitive electrochemical detection of methyl orange dye

This work describes the use of organosmectite modified electrode to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for the determination of methyl orange (MO) dye in natural water. Organosmectites were prepared by intercalation of hexadecyltrimethylammonium cations at various ratios into the interlayer of smectite. The synthesised organosmectites were characterised by various physicochemical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. An amperometric sensor based on organosmectite as electrode modifier for MO sensing purposes was then evaluated by means of clay-film modified electrode using square wave voltammetry (SWV). The electrochemical procedure for MO analysis by stripping voltammetry involves two successive steps: accumulation of MO at open circuit conditions followed by a voltammetric detection in a same medium by the SWV technique. The peak current obtained (after 5 min preconcentration of 15 µmol L^?1 MO solution) on a glassy carbon electrode coated by a thin film of the modified clay was more than 2.5 times higher than that exhibited by the same substrate covered by a film of the pristine clay. Under optimised conditions, a linear calibration curve for MO was obtained in the concentration range from 0.1 to 1.6 µmol L^?1, leading to a detection limit of 4 × 10^?8 mol L^?1 (signal-to-noise ratio equal to 3). The interfering effect of various inorganic and organic ions likely to influence the stripping determination of the MO was also examined. To further validate application of this sensor, the proposed method was successfully used to the determination of MO in natural water with satisfactory results.     

Electrochemical analysis of methylparathion pesticide by a gemini surfactant-intercalated clay-modified electrode

In this study, an hybrid material obtained by the intercalation of a gemini surfactant between the layers of smectite-type clay, was fully characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and N₂ adsorption-desorption experiments (BET method). To ascertain the intercalation process of the starting clay by the dimeric surfactant, the permselectivity and ion exchange properties of the organoclay were investigated by ion exchange voltammetry using [Fe(CN)₆]³⁻ and [Ru(NH₃)₆]³⁺ as redox probes, by the means of a clay film-modified electrode. Due to its organophilic character, the surfactant-intercalated complex was evaluated as electrode modifier for the accumulation of methylparathion (MP) pesticide. The electroanalytical procedure involves two steps: preconcentration under open-circuit followed by voltammetric detection by square wave voltammetry: the peak current obtained (after 5 min preconcentration in 4 × 10⁻⁵ mol L⁻¹ MP) on a glassy carbon electrode coated by a thin film of the modified clay was more than five times higher than that exhibited by the same substrate covered by a film of the pristine clay. This opens the way to the development of a sensitive method for the detection of the pesticide. Many parameters that can affect the stripping response (surfactant loading of the hybrid material, film composition, pH of the detection medium, preconcentration time, electrolysis potential and duration as well as some other instrumental parameters) were systematically investigated to optimize the sensitivity of the organoclay-modified electrode. After optimization, a linear calibration curve for MP was obtained in the concentration range from 4 × 10⁻⁷ to 8.5 × 10⁻⁶ mol L⁻¹ in acetate buffer (pH 5), with a detection limit of 7 × 10⁻⁸ mol L⁻¹ (signal-to-noise ratio equal to 3). The interference effect of various inorganic ions likely to influence the stripping determination of the pesticide was also examined, and the described method was applied to spring water analysis.