倒装芯片焊点可靠性的有限元模拟法探讨

随着集成电路封装技术的发展,倒装芯片技术得到广泛应用.由于材料的热膨胀失配,使倒装焊点成为芯片封装中失效率最高的部位,而利用快捷又极具参考价值的有限元模拟法是研究焊点可靠性的重要手段之一.简单介绍了集成电路芯片焊点可靠性分析的有限元模拟法,重点概括了利用该方法对芯片焊点进行可靠性评价常见的材料性质和疲劳寿命预测模型.     

PDZ proteins bind, cluster, and synaptically colocalize with Eph receptors and their ephrin ligands

Localizing cell surface receptors to specific subcellular positions can be critical for their proper functioning, as most notably demonstrated at neuronal synapses. PDZ proteins apparently play critical roles in such protein localizations. Receptor tyrosine kinases have not been previously shown to interact with PDZ proteins in vertebrates. We report that Eph receptors and their membrane-linked ligands all contain PDZ recognition motifs and can bind and be clustered by PDZ proteins. In addition, we find that Eph receptors and ligands colocalize with PDZ proteins at synapses. Thus, PDZ proteins may play critical roles in localizing vertebrate receptor tyrosine kinases and/or their ligands and may be particularly important for Eph function in guidance or patterning or at the synapse.     

Binding of double-stranded DNA by Escherichia coli RecA protein monitored by a fluorescent dye displacement assay

We have developed a new assay to characterize the double-stranded DNA (dsDNA) binding properties of RecA protein. This assay is based on measurement of changes in the fluorescence of a 4',6-diamidino-2-phenylindole (DAPI)-dsDNA complex upon RecA protein binding. The binding of RecA protein to a complex of DAPI and dsDNA results in displacement of the bound DAPI, producing a decrease in the observed fluorescence. DAPI displacement is dependent on both RecA protein and ATP; dATP and, to a lesser extent, UTP and dCTP also support the DAPI displacement reaction, but dGTP, GTP, dITP and TTP do not. Binding stoichiometry for the RecA protein-dsDNA complex measured by DAPI displacement is 3 bp per RecA protein monomer in the presence of ATP. These results, taken together with data for mutant RecA proteins, suggest that this DAPI displacement assay monitors formation of the high affinity DNA binding state of RecA protein. Since this state of RecA protein defines the form of the nucleoprotein filament that is active in DNA strand exchange, these findings raise the possibility that the RecA protein-dsDNA filament may possess a homologous pairing capacity.     

Assumption testing in population pharmacokinetic models: illustrated with an analysis of moxonidine data from congestive heart failure patients

Deriving a population pharmacokinetic model from real data is always associated with numerous assumptions. Violations of these assumptions, especially if undetected, may lead to inappropriate conclusions being made from the analysis. Routinely, only a few of the assumptions are explicitly stated and justified in the reporting of a population model. Here, we attempt to be exhaustive in the presentation of the assumptions made in the course of an analysis of moxonidine pharmacokinetics. The different ways that assumptions were justified, through experience, graphical examination, or additional modeling, are outlined. Models for relaxing assumptions regarding the covariate and statistical submodels, not previously reported in the area of population pharmacokinetic modeling, are also described.     

Probing the topography of HIV-1 nucleocapsid protein with the alkylating agent N-ethylmaleimide

Retroviral nucleocapsid (NC) proteins contain one or two zinc fingers (ZFs) consisting of a CCHC peptide motif that coordinates Zn(II). Mutational and biochemical analyses have shown that NC ZFs are directly involved in multiple stages of viral replication, including genomic RNA encapsidation, virus maturation, and the early infection process. The multiple roles of the conserved retroviral ZFs make them attractive targets for antiviral agents. We have previously shown that a variety of chemical compounds can inactivate the whole virus by attacking NC ZFs. For the enhancement of the specificity of antiviral reagents, it is desirable to have a detailed knowledge of the spatial organization of reactive sites on the NC protein in its free and oligonucleotide-bound states. A method has been developed using chemical probes to assess the reactivity of specific Cys residues in the NC protein, and is being used to investigate the topography of ZFs in different contexts. In this study we focus on the reaction mechanism of N-ethylmaleimide (NEM) with free HIV-1 NCp7 protein. Our results show that the conformation of free NCp7 restricts the initial site of attack to Cys-49 (the most distal Cys residue in the second ZF) and that the reactivity of thiols in full-length protein differs from that of the isolated ZF peptides. A moderate to near complete reduction in reaction rate was observed when NCp7 was complexed with different oligonucleotides. These findings provide a set of experimentally determined parameters that can serve to guide computational modeling of the NC protein and will be useful for the rational design of drugs directed against retroviral ZFs.     

泡沫铝填充帽型结构轴向冲击吸能特性的试验研究

利用冲击试验系统,通过试验方法研究了泡沫铝填充帽型结构在轴向冲击工况下的吸能特性。首先进行了泡沫铝、空心帽型结构以及泡沫铝填充帽型结构的轴向冲击试验;然后根据试验结果,对泡沫铝填充帽型结构轴向冲击工况下的吸能特性进行了分析,评估了填充泡沫铝以及应变率对帽型结构吸能特性的影响。试验结果表明, 与空心结构相比,填充泡沫铝之后帽型结构的轴向压缩稳定性和吸能特性有明显的改善;由于材料对应变率敏感, 与准静态压缩相比,结构的吸能特性有一定的提高。     

根据行为级模型方法对CMOS 图像传感器的BJPG 晶体管的分析

本文提出一种新的用于CMOS图像传感器像素的光电检测器－－双极结型光栅晶体管。由于引入p^ n注入结，光电荷的读出速率大大增加，改善了CMOS图像传感器的工作速率和响应灵敏度。尽管传统的光电集成电路的电路级模拟采用微电子集成电路的模拟方法，但是光电子集成电路不仅含有微电子器件和电信号还含有光电检测器和光信号，采用传统的集成电路模拟方法有其局限性。本文提出一种行为级模拟方法（光电子检测器设计的新方法，利用C、MATLAB和HSPICE等语言写出光电子器件的模拟器）来模拟分析双极结型光栅晶体管的特性。基于0.6μm CMOS工艺的分析结果表明双极结型光栅晶体管在不同栅氧化层厚度随栅压变化与传统光栅晶体管的特性一样，但光电流密度呈指数式增长且光电流密度增大，因此改善了CMOS图像传感器的工作速率和响应灵敏度。     

FCBGA封装器件的失效分析与对策

FCBGA(Flip-chip ball grid array)封装形式器件是近年来集成电路封装的最佳选择,其可靠性日益引起重视.本文简要介绍了FCBGA封装形式器件的结构特点以及相关的可靠性问题,通过两个FCBGA封装器件失效的案例,分析了两只FCBGA器件失效的原因,一个是由于芯片上的焊球间存在铅锡焊料而导致焊球短路,另一个则是因封装内填料膨胀分层而导致的焊球开路.本文提出了针对这种形式封装的器件在使用过程中的注意事项及预防措施,以减少该类失效情况的发生.