Enthalpy relaxation and fragility in polychlorinated biphenyls

We employ temperature modulated DSC (TMDSC) to determine the dependence of the fictive temperature on cooling rate for a series of polychlorinated biphenyls (PCB). From the slopes of semi-logarithmic plots of cooling rate vs. fictive temperature, the latter normalized by the fictive temperature for an arbitrary cooling rate, we determine the enthalpic fragilities. Despite significant differences in glass transition temperature and chemical structure (specifically chlorine content), the PCB have the same fragility. The value of the fragility determined using TMDSC is consistent with the fragility previously determined using dielectric relaxation spectroscopy.     

PCB separation by HRGC-MS. Fourier analysis for characterizing Aroclor chromatograms

Aroclor and Aroclor mixture chromatograms obtained using temperature programmed high resolution capillary GC coupled with mass spectrometric selective detection have been investigated by Fourier analysis developed for the study of multicomponent chromatograms. The experimental autocorrelation function (EACF), i.e. peak shape and position correlation, showed a retention - structure pattern which could be associated with both the type of Aroclor and the ion used for selective ion monitoring (m/z value). In particular, o-m and m-m isomerization effects were singled out by EACF analysis. By fitting EACF with previously developed theoretical models, it was possible to characterize a specific Aroclor in terms of the number of PCB congeners present in it. The results obtained agreed closely with the typical Aroclor content. For the Aroclor mixture, the distribution of inter-distance between successive peaks was derived. The two first distribution moments obtained agreed with those derived from retention data reported in the literature. The consequences on the separation performance, i.e. the number of singlets, doublets, etc. in the chromatogram, are discussed.     

Total ranking models by the genetic algorithm variable subset selection (GA–VSS) approach for environmental priority settings

Total order ranking (TOR) strategies, which are mathematically based on elementary methods of discrete mathematics, seem to be attractive and simple tools for performing data analysis. Moreover order-ranking strategies seem to be a very useful tool not only to perform data exploration but also to develop order ranking models, a possible alternative to conventional quantitative structure–activity relationship (QSAR) methods. In fact, when data material is characterised by uncertainties, order methods can be used as alternative to statistical methods such as multilinear regression (MLR), because they do not require specific functional relationships between the independent and dependent variables (responses). A ranking model is a relationship between a set of dependent attributes, experimentally investigated, and a set of independent attributes, i.e. model attributes, which are calculated attributes. As in regression and classification models, the variable selection model is one of the main steps in finding predictive models. In this work the genetic algorithm–variable subset selection (GA–VSS) approach is proposed as the variable selection method for searching for the best ranking models within a wide set of variables. The models based on the selected subsets of variables are compared with the experimental ranking and evaluated by the Spearmans rank index. A case study application is presented on a TOR model developed for polychlorinated biphenyl (PCB) compounds, which have been analysed according to some of their physicochemical properties which play an important role in their environmental impact.     

Thermochemical and physical properties of printed circuit board laminates and other polymers used in the electronics industry

Theories behind four thermal analysis techniques are reviewed, and relevant case studies are used to illustrate the application of these techniques to measure; various parameters relevant to printed circuit board laminates and engineering polymers.Thermogravimetric analysis (TGA) is used to determine the filler content of polymers and composites and when combined with Fourier transform infrared (FTIR) spectroscopy can be used for the chemical analysis of evolved gases.Differential scanning calorimetry (DSC) is used to measure the melting point of polymers and the degree of cure of prepregs, laminates and adhesives.Thermomechanical analysis (TMA) is used to measure the coefficient of thermal expansion (CTE) and the glass transition temperature (Tg) of laminates, and dynamic mechanical analysis (DMA) is used to measure the storage modulus, loss; modulus and Tan δ of polymers.     

嵌入式应用系统中高速PCB设计技术的研究及实现

为了能够消除高速PCB技术中信号完整性的问题,需要在高速PCB设计过程中解决时序、噪声、电磁干扰等关键问题。通过对嵌入式RTU的高速PCB设计过程中出现的串扰、电磁干扰、振铃和电源完整性等信号问题的研究,提出削弱或消除以上噪声的方法。用Altium Designer、PADS软件绘制电路原理图和PCB,借助Hyper Lynx和ADS仿真软件进行前端和后端可靠性可靠性验证,根据仿真结果确定元器件和接插件的布局以及走线规则,最后通过对完成布线的PCB进行信号完整性验证。设计的嵌入式RTU电路板通过电磁兼容测试,表明该方法能够有效抑制噪声,增强高速数字电路设计的稳定性,提高产品设计的成功率,对从事相关工作的人员有很重要的参考价值,在智能设备的升级替换和推进物联网的建设方面有重要的借鉴作用。     

用于非金属目标非接触位置检测的单片式电容传感器

利用印刷电路板加工工艺研制成了一种适于非金属目标位置检测的单片式电容传感器,工作原理是金属电极的近场效应。研究了传感器的阻抗频率特性以及传感器工作频率与检测系统灵敏度的关系,得到了使检测系统灵敏度最大的工作频率(1MHz)。用该传感器对36g/m2的胶片和10mm厚的玻璃体两种非金属目标位置进行检测。结果表明:在0.1mm量程内,检测系统的线性较好;在0.2mm量程内,非线性也不超过16.5%。     

355 nm DPSS UV laser cutting of FR4 and BT/epoxy-based PCB substrates

The 355 nm DPSS UV laser cutting of electronics printed circuit board (PCB) substrates including FR4, and BT/epoxy-based PCB substrates was investigated. The effects of various laser conditions such as scanning speed, assisting gas, repetition rate, and interval between scans on the heat affected zone (HAZ) and charring were studied. The quality and morphology of laser cut PCB substrates were evaluated with optical microscope, and scanning electron microscope (SEM). It was found that multi-pass cutting at high scanning speed can achieve high quality cutting with little charring. It was also found that with O₂ assist gas, a certain amount of interval time between scans and higher repetition rate led to less HAZ and less charring. High quality laser cutting of PCB substrates with no delamination, very little charring and minimum HAZ was demonstrated. The developed process has important potential applications in the electronics industry.     

高速DSP系统的PCB板设计研究

介绍了高速DSP系统PCB板的特点以及基于信号完整性设计应注意的几个问题,包括电源线设计、地线设计、阻抗匹配端接技术。测试结果表明,该设计方案可靠、合理,很好地解决了系统的信号完整性问题。     

利用CP-150萃取回收PCB碱性蚀刻废液中的铜

利用CP-150萃取剂萃取碱性蚀刻废液中的铜,并利用硫酸进行反萃取。考察不同因素对萃取和反萃取的影响。萃取实验表明,铜的萃取率随着萃取剂浓度和相比增大而增大,随着料液铜浓度的升高而降低。反萃实验表明,反萃速率随着硫酸反萃液浓度的增大而增大。     

基于Linux的进程调度研究

通过对Linux进程调度函数源码的分析,深入剖析了kernel核进程调度流程、调度时机、进程PCB和进程调度的依据．针对进程调度中出现的优先级反向问题,给出了基本优先级继承协议和优先级上限继承协议两种解决方法。