Experimental and modeling analysis of the reliability of the anisotropic conductive films

Experiments as well as computer modeling methods have been used to investigate the effect of the solder reflow process on the electrical characteristics and reliability of anisotropic conductive film (ACF) interconnections. In the experiments, the contact resistance of the ACF interconnections was found to increase after a subsequent reflow and the magnitude of this increase was strongly correlated to the peak temperature of the reflow profile. In fact, nearly 40 percent of the joints were opened (i.e. lifted away from the pad) after the reflow with a peak temperature of 260 OC while no openings was observed when the peak temperature was 210 "C. It is believed that the CTE mismatch between the polymer particle and the adhesive matrix is the main cause of this contact degradation. To understand this phenomenon better, a 3-D model of an ACF joint structure was built and Finite Element Analysis was used to predict the stress distrihution in the conductive particles, adhesive matrix and metal pads during the reflow process. The effects of the peak temperature, the CTE of the adhesive matrix and the bump height on the reliability of the ACF interconnections were discussed.

Thermo-mechanical analysis of the packaging process for micro-electronic displays

Micro-electronic displays are sensitive devices and its performance is easily affected by external environmental factors. To enable the display to perform in extreme conditions, the device must be structurally strengthened, the effects of this packaging process was investigated. A thermo-mechanical finite element analysis was used to discover potential problems in the packaging process and to improve the overall design of the device. The main concern from the analysis predicted that displacement of the borosilicate glass and the Y stress of the adhesive are important. Using this information a design which reduced the variation of displacement and kept the stress to a minimum was suggested

Thermal-mechanical analysis of flexible substrates during lead-free solder reflow

This paper presents modeling results about the performance of flexible substrates when subjected to higher lead-free reflow temperatures. Both adhesiveless and adhesive types of polyimide substrates were studied. Finite element (FE) models of flex substrates were built, two copper tracks located in the centre of the substrate was considered. The thermal induced shear stress in the flex substrate during the lead-free reflow process was studied and the effect of the design changes including the track thickness, flex thickness, and copper width were studied. For both types of flexes, the one of most important variables for minimizing damage to the substrate is the height of the copper tracks. The height of flex and the width of copper track show less impact. Beside of the geometry effects, the increase in reflow peak temperature can also result in a significant increase in the interfacial stress between the copper track and flex. Higher stresses were identified within the adhesive flex due to the big CTE mismatch between the copper and adhesive/dielectric

An analysis of the changes to the mechanical and acoustical properties of paper caused by the damage mechanisms present in the fibre structure

This paper will analyse two of the likely damage mechanisms present in a paper fibre matrix when placed under controlled stress conditions: fibre/fibre bond failure and fibre failure. The failure process associated with each damage mechanism will be presented in detail focusing on the change in mechanical and acoustic properties of the surrounding fibre structure before and after failure. To present this complex process mathematically, geometrically simple fibre arrangements will be chosen based on certain assumptions regarding the structure and strength of paper, to model the damage mechanisms. The fibre structures are then formulated in terms of a hybrid vibro-acoustic model based on a coupled mass/spring system and the pressure wave equation. The model will be presented in detail in the paper. The simulation of the simple fibre structures serves two purposes; it highlights the physical and acoustic differences of each damage mechanism before and after failure, and also shows the differences in the two damage mechanisms when compared with one another. The results of the simulations are given in the form of pressure wave contours, time-frequency graphs and the Continuous Wavelet Transform (CWT) diagrams. The analysis of the results leads to criteria by which the two damage mechanisms can be identified. Using these criteria it was possible to verify the results of the simulations against experimental acoustic data. The models developed in this study are of specific practical interest in the paper-making industry, where acoustic sensors may be used to monitor continuous paper production. The same techniques may be adopted more generally to correlate acoustic signals to damage mechanisms in other fibre-based structures.

Reliability analysis for power electronics modules

This paper discusses the reliability of power electronics modules. The approach taken combines numerical modeling techniques with experimentation and accelerated testing to identify failure modes and mechanisms for the power module structure and most importantly the root cause of a potential failure. The paper details results for two types of failure (i) wire bond fatigue and (ii) substrate delamination. Finite element method modeling techniques have been used to predict the stress distribution within the module structures. A response surface optimisation approach has been employed to enable the optimal design and parameter sensitivity to be determined. The response surface is used by a Monte Carlo method to determine the effects of uncertainty in the design.

Fracture mechanics analysis of cracks in solder joint intermetallic compounds

The trend towards miniaturization of electronic products leads to the need for very small sized solder joints. Therefore, there is a higher reliability risk that too large a fraction of solder joints will transform into Intermetallic Compounds (IMCs) at the solder interface. In this paper, fracture mechanics study of the IMC layer for SnPb and Pb-free solder joints was carried out using finite element numerical computer modelling method. It is assumed that only one crack is present in the IMC layer. Linear Elastic Fracture Mechanics (LEFM) approach is used for parametric study of the Stress Intensity Factors (SIF, KI and KII), at the predefined crack in the IMC layer of solder butt joint tensile sample. Contrary to intuition, it is revealed that a thicker IMC layer in fact increases the reliability of solder joint for a cracked IMC. Value of KI and KII are found to decrease with the location of the crack further away from the solder interfaces while other parameters are constant. Solder thickness and strain rate were also found to have a significant influence on the SIF values. It has been found that soft solder matrix generates non-uniform plastic deformation across the solder-IMC interface near the crack tip that is responsible to obtain higher KI and KII.

Transcriptome analysis of sulfate deficiency response in marine microalga Emiliania huxleyi

Summary The response to sulfate deficiency of plants and freshwater green algae has been extensively analysed by system biology approaches. By contrast, seawater sulfate concentration is high and very little is known about the sulfur metabolism of marine organisms. Here, we used a combination of metabolite analysis and transcriptomics to analyse the response of the marine microalga Emiliania huxleyi as it acclimated to sulfate limitation. Lowering sulfate availability in artificial seawater from 25 to 5 mM resulted in significant reduction in growth and intracellular concentrations of dimethylsulfoniopropionate and glutathione. Sulfate-limited E. huxleyi cells showed increased sulfate uptake but sulfate reduction to sulfite did not seem to be regulated. Sulfate limitation in E. huxleyi affected expression of 1718 genes. The vast majority of these genes were upregulated, including genes involved in carbohydrate and lipid metabolism, and genes involved in the general stress response. The acclimation response of E. huxleyi to sulfate deficiency shows several similarities to the well-described responses of Arabidopsis and Chlamydomonas, but also has many unique features. This dataset shows that even though E. huxleyi is adapted to constitutively high sulfate concentration, it retains the ability to re-program its gene expression in response to reduced sulfate availability.

Fracture Mechanics Analysis of the Dentine-Luting Cement Interface.

The objectives of this study were to determine the fracture toughness of adhesive interfaces between dentine and clinically relevant, thin layers of dental luting cements. Cements tested included a conventional glass-ionomer, F (Fuji I), a resin-modified glass-ionomer, FP (Fuji Plus) and a compomer cement, D (DyractCem). Ten miniature short-bar chevron notch specimens were manufactured for each cement, each comprising a 40 µm thick chevron of lute, between two 1.5 mm thick blocks of bovine dentine, encased in resin composite. The interfacial KIC results (MN/m3/2) were median (range): F; 0.152 (0.14-0.16), FP; 0.306 (0.27-0.37), D; 0.351 (0.31-0.37). Non-parametric statistical analysis showed that the fracture toughness of F was significantly lower (p

Extraction and radioimmunoassay quantitation of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) from human dental pulp tissue

The measurement of neuropeptides in complex biological tissue samples requires efficient and appropriate extraction methods so that immunoreactivity is retained for subsequent radioimmunoassay detection. Since neuropeptides differ in their molecular mass, charge and hydrophobicity, no single method will suffice for the optimal extraction of various neuropeptides. In this study, dental pulp tissue was obtained from 30 human non-carious teeth. Of the three different neuropeptide extraction methods employed, boiling in acetic acid in the presence of protease inhibitors yielded the highest levels of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP). High pressure liquid chromatography (HPLC) analysis of dental pulp tissue verified the authenticity of the neuropeptides extracted. © 2003 Elsevier Science Ltd. All rights reserved.

From the transformation to the bancarization of the spanishsaving banks: an analysis of the results pursued

This research arises due to the current restructuring process in which is immersed the Spanish banking sector. The above mentioned process is carried out to try to reduce the doubts on the viability of the bank companies to average and long term and to be able to return again the confidence in the sector. Though the economic and financial crisis has concerned the whole banking sector, the subsector of the Spanish savings banks is the one that has experienced a major number of integrations (articulated by means of mergers, absorptions and across Institutional Protection Schemes -IPSs-), and the one that has met submitted to the bancarization process. Considering what has been said, the present paper analyses Spanish saving banks to try to discern whether thanks to that process the objectives pursued by the bank rearrangement have been fulfilled. To do this, the evolution of some important financial variables will be studied over a long period of time (1999-2012). The results suggest that not all the savings banks have seen improved their ratios of efficiency, solvency, financial gap and social work, which indicates that there is still much to be done in order to rectify the problems affecting the studied sector.

Lividins: Novel antimicrobial peptide homologs from the skin secretion of the Chinese Large Odorous frog, Rana (Odorrana) livida: Identification by “shotgun” cDNA cloning and sequence analysis.

Odorous frogs of the sub-genus Odorrana are of oriental distribution, and are so called due to the foul smell of their defensive skin secretions released from specialized skin glands following stress or predator attack. Here we report the application of a “shotgun” skin secretion cDNA library cloning technique which can rapidly expedite identification of secretion bioactive peptides. From a library constructed from the skin secretion of the Large Chinese Odorous frog, Rana (Odorrana) livida, we have identified four novel peptides whose primary structures were deduced initially from cloned precursors. Subsequently, mature peptides were located in and structurally characterized from reverse phase HPLC fractions of skin secretion. Named lividins 1–4, these were found to be structural homologs of known antimicrobial peptide families from Rana frogs. Rapid identification of novel peptides can thus be rapidly achieved using this non-invasive, non-destructive technology and the extensive similarities revealed between antimicrobial peptide precursor organization and nucleic acid sequences would lend support to the hypothesis that they have a common ancestral origin.

Surveying nursing students on their sources of stress: A validation study

This study tested the psychometric properties of a questionnaire that measured sources of distress and eustress, or good stress, in nursing students. The Transactional model of stress construes stress in these different ways and is frequently used to understand sources of stress, coping and stress responses. Limited research has attempted to measure sources of distress and eustress or sources that can potentially enhance performance and well-being. A volunteer sample of final year nursing students (n = 120) was surveyed in the United Kingdom in 2007. The questionnaire measured sources of stress and measures of psychological well-being were taken to test construct validity. This was tested through an exploratory factor analysis. This reduced the questionnaire from 49 to 29 items and suggested three factors: learning and teaching, placement related and course organization; second, it was analysed by testing the assumptions of the Transactional model, the model on which the questionnaire was based. In line with the assumptions of the model, measures of distress related to adverse well-being, and measures of eustress related to healthier well-being responses. The test–retest reliability estimate was 0.8. While certain programme issues were associated with distress, placement-related experiences were the most important source of eustress.

Neuropeptide YY1 receptor in human dental pulp cells of noncarious and carious teeth

Aim To determine the distribution of the NPY Y1 receptor in carious and noncarious human dental pulp tissue using immunohistochemistry. A subsidiary aim was to confirm the presence of the NPY Y1 protein product in membrane fractions of dental pulp tissue from carious and noncarious teeth using western blotting. Methodology Twenty two dental pulp samples were collected from carious and noncarious extracted teeth. Ten samples were processed for immunohistochemistry using a specific antibody to the NPY Y1 receptor. Twelve samples were used to obtain membrane extracts which were electrophoresed, blotted onto nitrocellulose and probed with NPY Y1 receptor antibody. Kruskal-Wallis one-way analysis of variance was employed to test for overall statistical differences between NPY Y1 levels in noncarious, moderately carious and grossly carious teeth. Results Neuropeptide Y Y1 receptor immunoreactivity was detected on the walls of blood vessels in pulp tissue from noncarious teeth. In carious teeth NPY Y1 immunoreactvity was observed on nerve fibres, blood vessels and inflammatory cells. Western blotting indicated the presence and confirmed the variability of NPY Y1 receptor protein expression in solubilised membrane preparations of human dental pulp tissue from carious and noncarious teeth. Conclusions Neuropeptide Y Y1 is expressed in human dental pulp tissue with evidence of increased expression in carious compared with noncarious teeth, suggesting a role for NPY Y1 in modulation of caries induced pulpal inflammation. © 2008 International Endodontic Journal.

Analysis and comparison of displacement granular pile anchors

Granular piles can resist only compressive and shear loads owing to their inherent nature. By a simple modification of providing a pedestal/geogrid at the bottom and attaching a cable to the same, they are made to resist pullout/uplift forces. This paper presents an analysis of granular pile anchor (GPA), considering it and the in situ soil to behave linearly and the in situ ground to be semi-infinite. A parametric study presents results in the form of variations of normalised shear stress, displacement influence coefficient and axial uplift force with depth with relative stiffness factor. Two methods for the estimation of deformation moduli of the GPA and the in situ soil are proposed. Based on the estimated values of the moduli, the displacements of GPA were estimated and the results compared with test results of Kumar (2002). The predicted displacements compare well with the measured ones.