Residual stress evaluation in resin-molded IC chips using finite element analysis and piezoresistive gauges

The high residual stress in a resin-molded electronic package sometimes makes the electronic functions unstable. Therefore the residual stress in electronic packages, especially on the top surfaces of semiconductor chips, should be evaluated. The objective of this study is to present a simple method for evaluating residual stress in resin-molded semiconductor chips using a combination of experimental and numerical methods. The actual residual stress of the packaging process was measured by using test chips that included piezoresistive gauges. A linear thermoelastic finite element analysis was then carried out using a three-dimensional model. The finite element analysis was performed under a stress-free temperature determined by the temperature dependence of the residual stress, which was experimentally measured by using the piezoresistive test chips. The measured residual stress using the test chips agreed well with the results of the finite element analysis. It was therefore confirmed that the present evaluation method, combining experimental and numerical methods, is reliable and reasonable.     

A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

HVEM study of crack-tip dislocations in Si crystals prepared by FIB and twin-blade cutting method

Crack-tip dislocations in silicon crystals have been examined by using high-voltage electron microscopy. Cracks were introduced by the Vickers indentation method at room temperature and the indented specimens were annealed at high temperatures to induce dislocations around crack tips under the presence of residual stress due to the indentation. A selected area around a crack tip was thinned by a focused ion beam (FIB) technique. Specimens were thinned in advance by a twin-blade cutting (TBC) method, which is a simple cutting process for saving FIB machine time. A combination of FIB and TBC can be a useful thinning procedure for the efficient preparation of transmission electron microscopy specimens. Characteristic dislocation structures were observed around the tip of a crack, aiding the elucidation of dislocation processes, which is essential to increase the fracture toughness of materials.     

Experimental and numerical analysis of channel-length-dependent electrical properties in bottom-gate,bottom-contact organic thin-film transistors with Schottky contact

Channel length dependence of field-effect mobility and source/drain parasitic resistance in pentacene thin-film transistors with a bottom-gate, bottom-contact configuration was investigated. Schottky barrier effect such as nonlinear behaviors in transistor output characteristics appeared and became more prominent for shorter channel length less than 10 μm, raising some concerns for a simple utilization of conventional parameter extraction methods. Therefore the gate-voltage-dependent hole mobility and the source/drain parasitic resistance in the pentacene transistors were evaluated with the aid of device simulation accounting for Schottky contact with a thermionic field emission model. The hole mobility in the channel region shows smaller values with shorter channel length even after removing the influence of Schottky barrier, suggesting that some disordered semiconductor layers with low carrier mobility exist near the contact electrode. This experimental data analysis with the simulation enables us to discuss and understand in detail the operation mechanism of bottom-gate, bottom-contact transistors by considering properly each process of charge carrier injection, carrier flow near the contact region, and actual channel transport.     

Carbon nanotube enables quantum leap in oil recovery

A novel sealing material based on a CNT-rubber composite was developed for use in producing oil from deep, hot reservoirs. Fully dispersed and better bondings are two critical advances that enhance its mechanical properties. Authors solved the critical issues and clarified the mechanism of nano network reinforcement using test data. The resulting sealing solution underwent field tests around the world, and it marks a rare success story for the use of nanotechnology in the oilfield.     

Multilayered reasoning by means of conceptual fuzzy sets

The real world consists of instances of events and continuous numeric values, while people represent and process their knowledge in terms of symbols. Fuzzy sets provide a strong notation connecting the symbolic representation to the real world. In previously proposed Conceptual Fuzzy Sets (CFS), the meaning of a concept is represented by the distribution of activations of labels in a bidirectional associative memory. In particular, a multilayered structured CFS represents the meaning of the same concept as it is used in various expressions in each layer. The propagation of activations corresponds to reasoning. Therefore, we propose a multilayered reasoning method associated to a multilayered structured CFS, which has the following features: (1) capable of simultaneous symbolic and quantitative processing, (2) capable of simultaneous top-down and bottom-up processing. The effectiveness of the proposed method is illustrated by practical examples of decision regarding the amount of steering in the task of parking a car, and recognition of facial expressions for an image understanding system. © 1996 John Wiley & Sons, Inc.     

Development of a new heterojunction structure (ACJ -HIT) and its application to polycrystalline silicon solar cells

A new solar cell structure named HIT (Heterojunction with Intrinsic Thin layer) has been developed based on new artificially constructed junction (ACJ) technology. In this structure a non-doped a-Si thin layer was inserted between the p(a-Si)/n(c-Si) heterojunction, improving the output characteristics and achieving a conversion efficiency of 18.1%. This structure was applied to cast polycrystalline silicon solar cells of a practical size. A high conversion efficeincy of 13.6% was obtained with a cell size of 10 cm × 10 cm using various technologies, including hydrogen plasma passivation.     

Photoacoustic Spectroscopy of Some Energetic Materials

To find an effective laser source to ignite energetic materials, the absorption spectra of some energetic materials are obtained by means of a photoacoustic spectroscopy (PAS). In this experiment, PAS covers the wavelength region of 400 nm-1600 nm in which no other conventional method can take absorption spectra for powdered energetic materials. Photoacoustic spectra of 18 energetic materials are reported. In general, energetic materials tested showed peaks in 600 nm–800 nm and 1400 nm–1600 nm ranges. It is found that the energy required to initiate explosives in the case of ruby laser initiation were correlated with their photoacoustic signal intensities.     

What are the sciences of relationship-centered primary care

Steroidogenic acute regulatory protein (StAR), a 30-kDa protein involved in the transport of cholesterol to inner mitochondrial membrane during stimulation of steroid hormone biosynthesis, has recently been cloned from human adrenals and MA-10 mouse Leydig tumor cells. We examined the regulation of StAR mRNA accumulation upon induction of steroidogenesis in immortalized rat granulosa cells. Granulosa cells were transfected with SV40 DNA alone (POGS5); with SV40 DNA and Ha-ras oncogene (POGRS1); with SV40 DNA, Ha-ras oncogene and LH/CG receptor (GLHR15) or with FSH receptor (GFSHR17) or with the beta 2-adrenergic receptor (G beta 2AR13) expression plasmids. Cells were cultured to confluency and then stimulated for 24 h with oFSH (4 nM), hCG (2.4 nM), isoproterenol (10 microM) or forskolin (50 microM). By quantitative RT-PCR, StAR mRNA was undetectable in non-steroidogenic cells (transfected with SV40 DNA alone, POGS5) either in the presence or in the absence of forskolin. In contrast, variable amount of the message was detected in all steroidogenic cell lines cotransfected with SV40 DNA and Ha-ras. Moreover, an increase in the StAR mRNA expression was evident in all steroidogenic cells upon stimulation with their respective agonists, concomitantly with enhanced progesterone production. The RT-PCR product was sequenced and the 379 base pairs of rat StAR were found to be 93% and 86% identical to mouse and human cDNA, respectively. The deduced 126 amino acid sequence was 95%, 88% and 88% identical to the mouse, human and bovine deduced protein sequences. We conclude that StAR message is expressed only in the steroidogenic rat granulosa cells and can be upregulated by FSH, hCG, isoproterenol and forskolin in the appropriate cell lines. In addition, we find that the rat StAR cDNA exhibit a high degree of homology with the mouse and human sequences.     

Studies on biaxial stretching of polypropylene film. IX. Melting behavior of biaxially stretched film in one step

Melting temperature of a film biaxially stretched in one step in air at 152 or 140°C increases with increase of vA, whereas heat of fusion and density decrease with increase of vA, where vA is the degree of stretching in area. The rapid decrease in density occurs for vA > 10. Extrapolation of the plot of the density versus vA^?1/2 gives a value of 0.870 g/cm³ at infinite vA, which has been reported as the amorphous density of isotactic polypropylene by Farrow. This is so because the fine structure of the film becomes more and more amorphous with further stretching and reaches completely amorphous state at infinite vA. The temperature of stretching has a strong effect on the thermal behavior of a film; a low stretching temperature (140°C) brings about lower melting temperature, heat of fusion, and density. Crystallinity after melt press has not so large an effect on the melting behavior as the stretching temperature. Melting temperature and the shape of the thermogram also depend on the heating rate. There is an appropriate heating rate depending on vA which gives the minimum melting temperature. With stretched samples, a small side peak or a shoulder appears at a relatively low temperature in the thermogram when a high heating rate is used.