Curing kinetics of anisotropic conductive adhesive film

Polymer-based conductive-adhesive materials have become widely used in many electronic packaging interconnect applications, such as chip-on-glass, chip-on-flex, etc. Among all the conductive-adhesive materials, anisotropic conductive adhesive film (ACF) is an attractive interconnect material because of its fine pitch capability. Anisotropic conductive-adhesive film is a thermosetting, epoxy matrix impregnated with a small amount of electrically conductive particles. During component assembly, the epoxy resin is cured to provide mechanical connection, and the conducting medium provides electrical connection in the z direction. The thermal cure process is critical to develop the ultimate electrical and mechanical properties of the ACF. In this paper, the curing reaction of ACF was studied with a differential scanning calorimeter (DSC) under isothermal conditions in the range of 120–180°C. An autocatalyzed kinetic model was used to describe the curing reaction. The rate constant and the reaction orders were determined and used to predict the progress of the curing reaction. A good agreement is found between the proposed kinetic model and the experimental reaction-rate data. The reaction-rate constants were correlated with the isothermal temperature by the Arrhenius equation. The glass-transition temperature also has been studied as a function of cure degree and moisture absorption.     

Radio-frequency transmission properties of carbon nanotubes in a field-effect transistor configuration

In this letter, the radio-frequency (RF) transmission properties of single-walled carbon nanotubes (CNTs) have been characterized up to the frequency of 12 GHz in a carbon nanotube field-effect transistor (CNFET) configuration using a two-port S-parameter method for the first time. The RF characteristics of the CNTs were measured from the drain to the source of the CNFET. A resistance, inductance, and capacitance model has been proposed, and the element values have been extracted. Without the effect of the parasitics, the RF signal transmission in the CNTs presents no degeneration even at 12 GHz. The capacitive contact between CNTs and metal electrodes is reported.     

Low-/spl kappa/ BCB passivation on AlGaN-GaN HEMT fabrication

Due to the stress-induced polarization effect on the GaN HEMTs, the surface passivation of the device is critical and is deserved to conduct a detailed study. It has been proven that the GaN HEMTs demonstrate nondispersive pulsed current-voltage (I-V) characteristics and better microwave power performances after passivating the Si/sub 3/N/sub 4/ film on the GaN surface. In this letter, we proposed to use the BCB material, a negative photoresist with a low-/spl kappa/ characteristic, as the surface passivation layer on GaN HEMTs fabrication. After comparing the dc I-V, pulsed I-V, RF small-signal, microwave power characteristics, and device reliability, this BCB-passivated GaN HEMT achieved better performance than the Si/sub 3/N/sub 4/ passivated device.     

Anisotropic in-plane permeability of fabric media

An elegant procedure is proposed for obtaining components of the orthotropic or anisotropic in-plane permeability tensor from experimental data on flow front position and time. A radial flow geometry allows the shape of the advancing flow front to be dictated by the in-plane permeability of the fabric media. The directional permeabilities in the fabric plane are directly calculated from fluid and fabric properties together with data from the mold filling experiment (resin injection pressure and flow front position with time). The simplicity of the apparatus and proposed analytical procedure permit easy testing and comparison of different types of fibrous media.     

Cytogenetic abnormalities in pediatric myelodysplastic syndrome: a report of three cases

Three consecutive cases of pediatric myelodysplastic syndrome (MDS) diagnosed over a three-year period in Queen Mary Hospital, Hong Kong, were described. Depending on the classification system used, they comprised two cases of chronic myelomonocytic leukemia (CMMoL) of which one can be reclassified as juvenile chronic myeloid leukemia (JCML) and one cases of refractory anemia with excess of blasts (RAEB) or an alternative diagnosis of atypical CML. Cytogenetic abnormalities were detected in all of them on examination of bone marrow cells. Of the two CMMoL, one had monosomy 21, whereas the other had hypodiploidy. The patient with RAEB had a complex karyotype of 46,X,del(X)(q24),t(1;7) (p22;q32),add(15)(q26)(8). The balanced translocation (1;7) seen in this patient was exceedingly rare and, to the best of our knowledge, was reported only twice in the literature. The karyotypic abnormalities that we saw in our patients were not well recognized in pediatric MDS. This report emphasizes the importance of cytogenetic study in children suspected of suffering from MDS, which remains a rare disorder of childhood, and a need to rationalize current classification schemes.     

A look-ahead Levinson algorithm for general Toeplitz systems

The authors present an extension of Levinson's algorithm that is guaranteed to be weakly stable for a large class of general Toeplitz matrices, namely, those that do not have many consecutive ill-conditioned leading principal submatrices. The new algorithm adapts itself to the given Toeplitz matrix by skipping over all the ill-conditioned leading principal submatrices encountered during the solution process. This is done by a look-ahead strategy that monitors the condition of the leading principal submatrices and, if necessary, switches to a block step of suitable size. The overhead of the look-ahead algorithm is typically small compared to the classical Levinson algorithm, and in addition a reliable condition number estimate is produced     

A software system for anticipating the size and shape of submerged arc welds

A software system for computing the size and shape of bead-on-plate submerged arc (SA) welds is described in this presentation. The system is based on algorithms originated by McGlone et al., Chandel et al. and Yang et al. Essentially the system consists of a specially designed interface for welding/materials/design/fabrication engineers, automated plotting for parametric studies, a simplified data base for storing/editing/retrieving frequently used welding parameters and pictorial graphics for displaying weld size and shape. The use of the system in engineering practice is discussed at some length.