Reduced thermal strain in flip chip assembly on organic substrateusing low CTE anisotropic conductive film

Flip chip assembly directly on organic boards offers miniaturization of package size as well as reduction in interconnection distances, resulting in a high performance and cost-competitive packaging method. This paper describes the usefulness of low cost flip-chip assembly using electroless Ni/Au bump and anisotropic conductive films on organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au plating was performed as a low cost bumping method. Effect of annealing on Ni bump characteristics informed that the formation of crystalline nickel with Ni₃P precipitation above 300°C causes an increase of hardness and an increase of the intrinsic stress. As interconnection material, modified ACFs composed of nickel conductive fillers for conductive fillers, and nonconductive fillers for modification of film properties, such as coefficient of thermal expansion (CTE), were formulated for improved electrical and mechanical properties of ACF interconnection. Three ACF materials with different CTE values were prepared and bonded between Si chips and FR-4 boards for the thermal strain measurement using moire interferometry. The thermal strain of the ACF interconnection layer, induced by temperature excursion of 80°C, was decreased according to the decreasing CTEs of ACF materials. This result indicates that the thermal fatigue life of ACF flip chip assembly on organic boards, limited by the thermal expansion mismatch between the chip and the board, could be increased by low CTE ACF     

Quantitative analysis of the size distributions and elements of the precipitates in Fe-3%Si alloy during secondary recrystallization annealing using HAADF imaging and XEDS

The distribution of precipitates on grain boundaries and their role in abnormal grain growth during secondary recrystallization annealing in Fe-3 %Si alloy is studied. The precipitates and grain boundaries were observed simultaneously using high angle annular dark field scanning transmission electron microscopy. The chemical composition of the precipitates was also analyzed by X-ray energy dispersive spectroscopy. During secondary recrystallization annealing, the number of small precipitates (<9000 nm²) increased in the samples heated up to 900°C and decreased in the samples heated up to 1000°C. The increase (of the small precipitates) was strongly correlated with the onset temperature of abnormal grain growth above 900°C. In all samples, 50 % to 80 % of the precipitates consisted of complexes containing both Al and Mn.     

Modeling of vehicle dynamics from real vehicle measurements using a neural network with two-stage hybrid learning for accurate long-term prediction

This paper describes a neural network (NN) model of a real vehicle and the associated hybrid learning scheme. The NN vehicle models the actual vehicle dynamic behavior with the architecture of a real-time recurrent network. The NN was trained to predict the next state of the vehicle, given the current vehicle state, the current input steering angle of the front wheel, and the vehicle's speed. A hybrid training scheme for the network has been proposed, which consists of two phases: open-loop training for stabilization of the NN weight learning and closed-loop training for long-term prediction of the vehicle behavior. The open-loop training is necessary to avoid learning instability at initial stages. The closed-loop training then follows in such a way that the NN correctly predicts the vehicle's next state in a recursive mode. The outcome is that the model can correctly generate the vehicle trajectory, given the initial state and the steering and speed sequence of the vehicle. Furthermore, after this training procedure, it not only learns the vehicle's lateral dynamics along the trained trajectories, but can also generalize to similar trajectories. This modeling technique has been successfully applied to model the actual dynamics of a Daewoo Leganza vehicle. It is an intelligent vehicle that is fully autonomous in that steering, braking, and accelerating were all done via computer control. The training data were taken from a four-vehicle platoon demonstration in which four vehicles were automatically controlled in a convoy mode.     

A decision support system for quantitative measurement of operational efficiency in a blood collection facility

A decision support system (DSS) is presented that allows users to input, analyze, and output data derived from blood banking operations. The DSS developed is a hybrid system that is both data and model driven. The system provides information, models, and data manipulation tools to assist users in the quantitative measurement of the operational efficiency in a blood collection facility. A relational database was developed to address the four major variables, which impact the cost per unit of blood being collected. Using visual basic, a user interface and mathematical model were developed establishing the relationships to analyze cost per unit of collected blood. Using inputs from users and historical financial data, the DSS calculates the cost per unit as each of the major variables is altered. Real life situations by the mobile operations team at a blood collection facility were used to test the DSS.     

L'effet du molybdène sur l'oxydation partielle du méthane par l'oxygène-pur

An investigation was carried out to establish the influence of molybdenum powder on the partial oxidation of methane with pure oxygen and to find the reaction conditions that lead to its complete conversion to synthesis gas without excess oxygen nor formation of carbon dioxide, water vapor and carbon deposits. Carbidization of molybdenum by methane and its decarbidization by oxygen lead one to suggest steps that explain the observed products. Thermodynamic feasibility of the steps suggested was established from equilibrium constants. Gas compositions at equilibrium were calculated for various reaction conditions. Sixty experiments were carried out to verify the calculated compositions. The temperature was varied from 1200 to 1900°K; the weight of molybdenum, from 0 to 5 grams; the methane to oxygen ratio, from 1.6 to 2.2 and the hourly space velocity, from 50 to 250. Above 1600°K, 2 to 1 ratio stoichiometric mixtures of methane and oxygen in the presence of molybdenum, generally yield pure synthesis gas (no carbon deposits, water vapor or carbon dioxide). X-ray diffraction analysis of the solids in the reactor confirmed the presence of large amounts of molybdenum carbide (but no oxide). This is strong evidence in support of the role assigned to molybdenum in eliminating carbon deposits.     

A finite element approach to anisotropic damage of ductile materials in large deformations Part II: finite element formulation and applications

A finite element analysis model for material and geometrical non-linearities due to large plastic deformations of ductile materials is presented using the continuum damage mechanics approach. To overcome limitations of the conventional plastic analysis, a fourth-order tensor damage, defined in Part I of this paper to represent the stiffness degradation in the finite strain regime, is incorporated. General forms of an updated Lagrangian (U.L.) finite element procedure are formulated to solve the governing equations of the coupled elastic–plastic-damage analysis, and a computer program is developed for two-dimensional plane stress/strain problems. A numerical algorithm to treat the anisotropic damage is proposed in addition to the non-linear incremental solution algorithm of the U.L. formulation. Selected examples, compared with published results, show the validity of the presented finite element approach. Finally, the necking phenomenon of a plate with a hole is studied to explore plastic damage in large strain deformations. This revised version was published online in August 2006 with corrections to the Cover Date.     

2-Iminothiazolidine-4-carboxylic acid produces hippocampal CA1 lesions independent of seizure excitation and glutamate receptor activation

Impaired wound healing is a common complication of diabetes mellitus. The underlying pathophysiology of diabetes-impaired healing is poorly understood. In the present study we have compared cell proliferation rates, apoptosis (programmed cell death), the myofibroblast marker alpha-smooth muscle actin and procollagen I mRNA expression, between diabetic and control mice. Full-thickness skin wounds were made in non-obese diabetic (NOD) mice and C57B6 controls. NOD mice showed a marked retardation of wound healing at both 7 and 14 days after wounding. Comparison of cell proliferation rates 7 days after wounding, using 5-bromo-2'-deoxy-Uridine incorporation, showed higher rates of cell proliferation in controls (88.1 +/- 12.8) than in NOD wounds (52.1 +/- 9.9, p < 0.02, n = 4). Immunohistochemical detection of alpha-smooth muscle actin, showed a later onset in diabetic wounds, suggesting that wound contraction may be delayed in the diabetic animals. In situ hybridisation for alpha 1 (I) procollagen mRNA expression, showed reduced procollagen I expression in the diabetic wounds when compared with controls. Lastly, there appeared to be higher levels of apoptosis in diabetic wounds, shown by the terminal transferase mediated UTP nick end-labelling technique. Apoptotic cells were rare in control wounds confirming previous studies, which showed that apoptosis occurs late in normal wound healing as the wound matures into scar tissue. In conclusion, we hypothesize that reduced cell proliferation, retarded onset of the myofibroblast phenotype, reduced procollagen I mRNA expression and aberrant control of apoptotic cell death may contribute to impaired wound healing seen in this diabetic model.     

The relationship of the -5, -8, and -24 variant alleles in African Americans to triosephosphate isomerase (TPI) enzyme activity and to TPI deficiency

In 424 African-American and 75 white subjects, we found that the -5 (TPI 592 A-->G), -8 (TPI 589 G-->A), and -24 (TPI 573 T-->G) variants in the triosephosphate isomerase (TPI) gene occurred frequently (41.0%) in the African-American subjects but did not occur in the whites. These data suggest that this set of polymorphisms may turn out to be one of the higher-incidence molecular markers of African lineage, a surprising finding because others had reported that these nucleotide substitutions were restricted to a small subset of African Americans who had been characterized as TPI-deficiency heterozygotes. Additionally, we investigated the relationship of these variants to TPI-enzyme activity. Although the variant substitutions (occurring in three haplotypes: -5 alone, -5 -8, and -5 -8 -24) were associated with moderate reduction in enzyme activity, severe-deficiency heterozygotes could not be identified with certainty, and none of the haplotypes were restricted to subjects with marked reduction of enzyme activity. Three subjects were homozygous for the -5 -8 haplotype, a finding inconsistent with the putative role of this haplotype as the cause of a null variant incompatible with life in homozygotes. Despite these findings, the possibility remains that the -5 -8 or -5 -8 -24 haplotypes may in some instances contribute to compound heterozygosity and clinical TPI deficiency.     

Oxidation Prevention and Electrical Property Enhancement of Copper-Filled Isotropically Conductive Adhesives

This paper describes the development and characterization of isotropically conductive adhesives (ICAs) incorporating copper (Cu) powders as electrically conductive fillers, along with a silane coupling agent for oxidation protection of copper powders, for environmentally friendly, low cost and high thermal reliability applications in microelectronics packaging. The effect of silane coupling agent materials and concentration on the electrical conductivity, thermal stability and reliability of Cu-filled ICAs was investigated for potential alternatives of conventional silver-filled ICAs. The surface characteristics of silane thin films on copper surfaces, such as their hydrophobicity and thermal stability, were also evaluated to compare the performance of antioxidant behaviors of different silane coupling agents for Cu-filled ICAs. The low contact resistance and high thermal stability of the contact resistance of Cu-filled ICAs were achieved by addition of an optimized silane coupling agent. Greater thermal stability and improved reliability of Cu-filled ICAs under high temperature and humidity conditions were achieved with a silane coupling agent of high molecular weight and hydrophobicity. The bulk resistivity of ∼10⁻⁴ Ωcm of Cu-filled ICAs was achieved with bimodal filler loading.     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.