Gas flow simulations of a fluxless Si solder bonding oven

In this paper the technology of the “Linn” type Si fluxless solder bonding oven and gas flow simulations of the oven are discussed. This oven is used for fixing silicon chips on metal substrates with high temperature solder bonding process. The solder is applied in a foil form which is placed between the Si chip and the metal substrate. This does not contain any flux, therefore a reducing agent has to be applied to avoid the oxidation of the joints during the soldering process. In this technology the reducing agent is the Forming gas which is a mixture of 10 vol.% H₂ and 90 vol.% N₂. The key factors of this soldering process was studied which are the suitable temperature (350-370 °C for 13-15 min) and the adequate H₂ concentration (8-10 vol.%). A detailed 3D gas flow model of the Linn oven was prepared which is based on the finite volume model (FVM) method. The thermal and gas flow circumstances - used the basic and new theoretical oven settings - were compared by simulations applied the ANSYS-FLUENT system. The gas flow model was verified by the measurements of the H₂ concentration, the temperature and the pressure inside the oven. The aim was to find new oven settings in order to improve the mechanical stability and decrease the void percent of the solder joints.     

Investigation of the Electroless Nickel Plated Sic Particles in Sac305 Solder Matrix

Powder Metallurgy and Metal Ceramics - In the present study, an electroless nickel (EN) plating method is applied for the coating of silicon carbide (SiC) particles. The particles of SiC(Ni) were...     

Strategies for Volumetric Recovery of Large Scale Damage in Polymers

The maximum volume that can be restored after catastrophic damage in a newly developed regenerative polymer system is explored for various mixing, surface wetting, specimen configuration, and microvascular delivery conditions. A two‐stage healing agent is implemented to overcome limitations imposed by surface tension and gravity on liquid retention within a damage volume. The healing agent is formulated as a two‐part system in which the two reagent solutions are delivered to a through‐thickness, cylindrical defect geometry by parallel microvascular channels in thin epoxy sheets. Mixing occurs as the solutions enter the damage region, inducing gelation to initiate an accretive deposition process that enables large damage volume regeneration. The progression of the damage recovery process is tracked using optical and fluorescent imaging, and the mixing efficiency is analyzed. Complete recovery of gaps spanning 11.2 mm in diameter (98 mm²) is achieved under optimal conditions.     

Comparison of antepartum testing schemes for the management of the postdate pregnancy

We analyzed the outcome results of 583 postdate pregnancies managed prospectively by one of three antepartum testing schemes, each predicated on the nonstress test. In scheme 1, we relied upon the contraction stress test for evaluation of the nonreactive nonstress test. In scheme 2, we used a modified biophysical profile to evaluate the nonreactive nonstress test. In addition, patients were tested semiweekly. In scheme 3, we added routine weekly ultrasound evaluation of amniotic fluid volume to scheme 2. Only in scheme 3 did we induce labor for decreased amniotic fluid volume or fetal cardiac decelerations irrespective of reactivity. The incidence of fetal distress, perinatal mortality, and perinatal morbidity was increased in babies with decelerations or decreased amniotic fluid volume. Nevertheless, outcome results in scheme 2 were improved over those with scheme 1 and were best with scheme 3. These results suggest a benefit to both semiweekly testing and liberalized criteria for intervention in postdate pregnancies. We also compared the outcome results of scheme 3 with those reported for schemes in which the weekly contraction stress test was used as the primary form of surveillance. We found the outcome results comparable in that both schemes showed minimal mortality and morbidity statistics but high intervention rates (25% to 30%). Differences in methodology and test criteria, however, make such comparisons less than ideal.     

Seismic fragility of reinforced concrete structures in nuclear facilities

The failure and fragility analyses of reinforced concrete structures and elements in nuclear reactor facilities within the Seismic Safety Margins Research Program (SSMRP) at the Lawrence Livermore National Laboratory are evaluated. Receiving special attention are uncertainties in material modeling, behavior of low shear walls, and seismic risk assessment for nonlinear response. Problems with ductility-based spectral deamplification and prediction of the stiffness of reinforced concrete walls at low stress levels are examined. It is recommended that relatively low damping values be used in connection with ductility-based response reductions and that static nonlinear force-deflection curves be studied for better nonlinear dynamic response predictions.     

Seismic effects in secondary containments: Research needs

The purpose of this paper is to discuss the status of current and projected research on the behavior of nonprestressed secondary containment structures carrying combined pressurization and seismic shear. Ongoing experimental research at Cornell University on specimens carrying combined biaxial tension and static cyclic shear is described. The remainder of the paper treats research needed to better predict the response of containments to seismic effects and to serve as the basis for improved design methods for reinforced concrete containments.     

Isoenzymes of creatine kinase in the perinatal period (author's transl)

The serum of new-born children shows a higher catalytic concentration of creatine kinase than adult serum. These values reach normal adult levels within the first 10 days of life. In addition to the MM-, the MB- and BB-isoenzymes of creatine kinase are also found in the serum of women in labour, in cord-serum, and in the serum of newborn children. These findings should be taken into consideration in the analysis of creatine kinase isoenzymes.     

Graph Transformation in Relational Databases

We present a novel approach to implement a graph transformation engine based on standard relational database management systems (RDBMSs). The essence of the approach is to create database views for each rules and to handle pattern matching by inner join operations while negative application conditions by left outer join operations. Furthermore, the model manipulation prescribed by the application of a graph transformation rule is also implemented using elementary data manipulation statements (such as insert, delete, update).     

Torsional Strengthening of Spandrel Beams with Fiber-Reinforced Polymer Laminates

Research has shown that fiber-reinforced polymer (FRP) composites can increase flexural, axial, and shear capacity of beams, columns, and walls. The present paper describes both experimental and analytical programs focused on the torsional strengthening of reinforced concrete spandrel beams using composite laminates. The variables considered in this study included fiber orientation, composite laminate, and effects of a laminate anchoring system. The study proved that the FRP laminates could increase the torsional capacity of concrete beams by more than 70%. The analytical procedure developed revealed a good comparison between experimental and analytical results.