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.%.     

A Semiautomatic Approach to Deriving Turbine Generator Diagnostic Knowledge

Condition monitoring of turbine generators, housed at British Energy nuclear power stations throughout the U.K., is implemented to diagnose incipient faults at an early stage, so corrective action can be taken to avoid the associated high costs of an unplanned shutdown. A prototype expert system has been developed that provides decision support to condition monitoring experts who monitor British Energy turbine generators. The expert system automatically interprets data from strategically positioned sensors and transducers on the turbine generator by applying expert knowledge in the form of heuristic rules. This paper reviews the application domain and describes the work undertaken in developing the prototype expert system. The paper also outlines a learning module design that uses an approach based on an analytical symbolic machine learning technique, explanation-based generalization, to semiautomatically derive heuristic rules for turbine generator fault diagnosis. The approach adopted by the learning module is explained in detail and a worked example demonstrates how the learning module can derive a fault heuristic from a single training example. The modular approach to capturing the causal fault and behavioral models is described, and the method in which the module will be integrated with the existing expert system has been outlined. A preliminary evaluation of the learning module design is discussed.     

Facile Preparation of Multifunctional WS2/WOx Nanodots for Chelator‐Free 89Zr‐Labeling and In Vivo PET Imaging

While position emission tomography (PET) is an important molecular imaging technique for both preclinical research and clinical disease diagnosis/prognosis, chelator‐free radiolabeling has emerged as a promising alternative approach to label biomolecules or nanoprobes in a facile way. Herein, starting from bottom‐up synthesized WS₂ nanoflakes, this study fabricates a unique type of WS₂/WO_x nanodots, which can function as inherent hard oxygen donor for stable radiolabeling with Zirconium‐89 isotope (⁸⁹Zr). Upon simply mixing, ⁸⁹Zr can be anchored on the surface of polyethylene glycol (PEG) modified WS₂/WO_x (WS₂/WO_x‐PEG) nanodots via a chelator‐free method with surprisingly high labeling yield and great stability. A higher degree of oxidation in the WS₂/WO_x‐PEG sample (WS₂/WO_x (0.4)) produces more electron pairs, which would be beneficial for chelator‐free labeling of ⁸⁹Zr with higher yields, suggesting the importance of surface chemistry and particle composition to the efficiency of chelator‐free radiolabeling. Such ⁸⁹Zr‐WS₂/WO_x (0.4)‐PEG nanodots are found to be an excellent PET contrast agent for in vivo imaging of tumors upon intravenous administration, or mapping of draining lymph nodes after local injection.     

Trellis: Portability across architectures with a high-level framework

The increasing computational needs of parallel applications inevitably require portability across parallel architectures, which now include heterogeneous processing resources, such as CPUs and GPUs, and multiple SIMD/SIMT widths. However, the lack of a common parallel programming paradigm that provides predictable, near-optimal performance on each resource leads to the use of low-level frameworks with architecture-specific optimizations, which in turn cause the code base to diverge and makes porting difficult. Our experiences with parallel applications and frameworks lead us to the conclusion that achieving performance portability requires a common set of high-level directives and efficient mapping onto each architecture.     

The optimal level of fuzz: case studies in a methodology for psychological research

Cognitive science research is hard to conduct, because researchers must take phenomena from the world and turn them into laboratory tasks for which a reasonable level of experimental control can be achieved. Consequently, research necessarily makes tradeoffs between internal validity (experimental control) and external validity (the degree to which a task represents behaviour outside of the lab). Researchers are thus seeking the best possible trade-off between these constraints, which we refer to as the optimal level of fuzz. We present two principles for finding the optimal level of fuzz, in research, and then illustrate these principles using research from motivation, individual differences and cognitive neuroscience.     

On hypoxia and fish kills along the north shore of Lake Erie

Hypoxia is a common feature in the offshore central basin of Lake Erie. In the late summer of 2012, a strong wind-induced upwelling event transported oxygen depleted water to the nearshore zones of northern Lake Erie. Wind speed, duration and direction relative to the shoreline of individual wind events determined the extent of nearshore zone affected by the hypoxic waters. The upwelling event resulted in adverse water quality along some stretches of the northern shoreline of Lake Erie with persistent anoxia, which was mainly responsible for the mortality of fish.     

Confocal fluorescence microscopy in alumina-based ceramics: Where does the signal come from?

Confocal Cr³⁺ fluorescence microscopy is an ideal technique for investigating residual stresses in alumina-based ceramics. Due to their transparency, however, it is important to understand where the collected signal comes from by characterising the probe response function (PRF). Here, a PRF is proposed that captures all the relevant physical effects, including a newly identified consequence of scattering by pores and grain boundaries. The new PRF describes the response of a range of alumina-based ceramics to depth scanning in a high resolution confocal fluorescence microscope in a manner that balances physical significance with the accuracy of empirical fitting. The results showed that measurements could be made deep within single crystals of sapphire and ruby, although refraction degraded the depth resolution from about 3 μm at the surface to 25 μm at a depth of 500 μm. Scattering and absorption limited the depth to which polycrystalline alumina could be probed to ～15 μm. This was further reduced to ～4 μm for an alumina–10 vol.% SiC nanocomposite. However, the absorption increased the accuracy of near surface measurements in these materials by preventing contamination from subsurface fluorescence.     

Lean NOx Trap Chemistry Under Lean-Gasoline Exhaust Conditions: Impact of High NOx Concentrations and High Temperature

The primary technical barrier to deployment of fuel saving lean gasoline engines is NOx emissions control. We conducted automated flow reactor experiments on a commercial LNT catalyst to identify opportunities and challenges associated with the higher temperatures and higher NOx concentrations expected in lean gasoline applications. Overall NOx conversion was quite high at low to moderate temperatures, but dropped off at high temperatures. The decrease in NOx conversion with temperature was worse for higher inlet NOx concentrations. As expected from equilibrium considerations, the catalyst stored more NOx under higher gas phase NOx concentrations, but that NOx was rapidly released during the rich phase and slipped out of the catalyst before it could be converted to N₂ by incoming reductant. This rich phase NOx release was the primary factor limiting performance of the catalyst at high temperatures, and resulted in significant spikes of NOx that would likely exceed any not-to-exceed regulated emissions levels. N₂O production was also significant, and increased with NOx concentration. The catalyst made very little NH₃ at high temperatures. NH₃ yield was significant at the lowest operating temperature studied, but it decreased with increasing NOx concentration.     

Cr3+ microspectroscopy measurements and modelling of local variations in surface grinding stresses in polycrystalline alumina

Surface residual stresses caused by grinding and polishing of alumina are thought to influence materials properties but have previously been measured only by low spatial resolution techniques which sample average stresses. In this work confocal Cr³⁺ fluorescence microscopy has been used to investigate the spatial distribution of the residual stresses. A model for the residual stresses, accounting for both surface plastic deformation and “pullout” of material from the surface by brittle fracture, was developed to help in analysing the results. After coarse diamond grinding, the results showed that the residual stresses fluctuate greatly with position. Large tensile stresses (up to ～600 MPa) were found below the plastically deformed surface layer in regions between the “pullouts”. These tensile stresses are expected to aid crack propagation and further surface pullout. They arise because pullout removes parts of the plastically deformed surface layer. The stresses beneath the pullout sites themselves were compressive, but the largest compressive stresses (≈?1.5 GPa) were within the plastically deformed surface regions and extended to a depth of 1.3 μm. The plastically deformed surface layer was much shallower following polishing with 3 μm diamond paste but the compressive stress within it was of similar magnitude to that in the plastically deformed surface layer caused by grinding.