Hybridization of FDTD and device behavioral-modeling techniques [interconnected digital I/O ports]

We present a systematic methodology for the electromagnetic modeling of interconnected digital I/O ports. Digital drivers and receivers are represented through behavioral models based on radial basis functions expansions. Such a technique allows a very accurate representation of nonlinear/dynamic effects as well as switching behavior of real-world components by means of carefully identified discrete-time models. The inclusion of these models into a finite-difference time-domain solver for full-wave analysis of interconnected systems is presented. A rigorous stability analysis shows that use of nonlinear/dynamic discrete-time models can be easily integrated with standard full-wave solvers, even in the case of unmatched sampling time. A set of numerical examples illustrates the feasibility of this method.     

Effect of Stand-Off Height on Microstructure and Tensile Strength of the Cu/Sn9Zn/Cu Solder Joint

To investigate the effect of stand-off height (SOH) on the microstructure and mechanical behavior of certain solder joints, Cu/Sn9Zn/Cu solder joints with a SOH of 100 μm, 50 μm, 20 μm, and 10 μm were prepared and studied. It was found that, as the SOH is reduced, the Zn content in the solder bulk experiences a rapid decrease due to consumption by metallurgical reaction in the reflow process; hence, the microstructure of the solder bulk is changed significantly from a Sn-Zn eutectic structure to a hypoeutectic structure. By contrast, Cu content in the solder bulk experiences a rapid increase with reducing SOH, and this leads to more dissociative intermetallic compounds (IMCs) in the solder bulk. These compositional and microstructural changes induced by reducing the SOH correlate closely with the mechanical properties of the solder joints. In our study it is found that, as SOH is reduced, the tensile strength of the solder joints decreases, the fracture path of the solder joint transfers from the solder bulk into the interface between the IMC layer and the solder bulk, and the fracture mode tends to change from ductile to brittle. These findings point to a probable way to improve the mechanical properties of miniaturized solder joints by controlling the composition and dissociative IMCs in the solder bulk.     

Milling time effects on the magnetic and structural properties of the Fe70Si30 system

The magnetic and structural properties of the Fe_0,70Si_0,30 alloy are analyzed by using X-ray diffraction and Mössbauer spectrometry. The samples were prepared by mechanical alloying in a planetary ball mill pulverisette 5 during 1, 5, 9, 15, 75 and 100 h milling, with a ball mass to powder mass relation of 10:1. The X-ray diffraction patterns showed a coexistence of BCC, DO₃ and FeSi structural phases; however, for 1-5 h process, we observed additional peaks which correspond to iron and silicon elements. These results indicate us that the alloy is still a non-fully consolidated sample. The grain size decreases drastically from 1 to 5 h, then slowly up to 15 h, and finally it remains nearly constant. The lattice parameter for each phase remains nearly constant (2838 A for the BCC structure). The shape of hyperfine field distributions used to describe the Mössbauer spectra is discussed.     

The equivalence of the total least squares and minimum norm methods[signal processing]

It is shown that the minimum norm solution is equivalent to the total least squares solution. It is noted that two versions of the total least squares solution exist, one based on the signal subspace and another based on the noise subspace     

Overview of MM and UTD methods at the Ohio State University [radartarget scattering]

Techniques appropriate for low and high frequency numerical evaluation of the scattered fields from complex shapes are discussed. Object size in terms of wavelengths dictates the type of solution to be used. For targets in and just above resonance, the method of moments (MM) is used. The limitation in this case is that the scatterer cannot be too large in terms of the wavelength. For radar targets in the microwave band, the uniform geometrical theory of diffraction (UTD) and modifications thereof form the basis for the computation. This has the basic limitation that the scattering mechanisms need to be known and included in the model. Examples are given for both frequency regimes     

Effect of Ag micro-particles content on the mechanical strength of the interface formed between Sn–Zn binary solder and Au/Ni/Cu bond pads

In this study, addition of Ag micro-particles with a content in the range between 0 and 4 wt.% to a Sn–Zn eutectic solder, were examined in order to understand the effect of Ag additions on the microstructural and mechanical properties as well as the thermal behavior of the composite solder formed. The shear strengths and the interfacial reactions of Sn–Zn micro-composite eutectic solders with Au/Ni/Cu ball grid array (BGA) pad metallizations were systematically investigated. Three distinct intermetallic compound (IMC) layers were formed at the solder interface of the Au/electrolytic Ni/Cu bond pads with the Sn–Zn composite alloys. The more Ag particles that were added to the Sn–Zn solder, the more Ag–Zn compound formed to thicken the uppermost IMC layer. The dissolved Ag–Zn IMCs formed in the bulk solder redeposited over the initially formed interfacial Au–Zn IMC layer, which prevented the whole IMC layer lifting-off from the pad surface. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces.     

Comparison Between the Induced Changes in the Intensities of Mid and Near Infrared Absorption Bands of Poly[Vinyl Alcohol] Due to Temperature and Solvents

The temperature induced changes in the intensities of the infrared absorption bands of PVA in both MID and NIR regions are presented. The absorption band at 1141cm^-1 is the only band among the bands in the mid region which is markedly affected by temperature. This band is taken as a measure of crystallinity of PVA. PVA shows two phase transitions at 80c⁰ and 120c⁰. The absorbances of the 1940nm in the near region is also temperature sensititve. The temperature dependence of the other bands in either mid or near regions is very weak. The effect of non polar and polar solvents such as n-hexane, carbon tetrachloride, toluene, chloroform, methanol and acetone is discussed. Comparison between the solvent induced changes in the intensities of the bands in mid and near regions is carried out. The data demonstrate that the bands in the near region ( overtone and combinations) are more sensitive to solvents than the bands in the mid regions. The combined effect of temperature and solvents on the intensities of absorption bands of PVA is also studied.     

Effect of nano Al2O3 additions on the microstructure, hardness and shear strength of eutectic Sn–9Zn solder on Au/Ni metallized Cu pads

Nano-sized, nonreacting, noncoarsening Al₂O₃ particles have been incorporated into eutectic Sn–Zn solder alloys to investigate the microstructure, hardness and shear strength on Au/Ni metallized Cu pads ball grid array substrate (BGA). In the plain Sn–Zn solder joint and solder joints containing Al₂O₃ nano-particles, a scallop-shaped AuZn₃ intermetallic compound layer was found at the interfaces. In the solder joints containing Al₂O₃ nano-particles, a fine acicular-shaped Zn-rich phase and Al₂O₃ nano-particles were found to be homogeneously distributed in the β-Sn matrix. The shear strengths and hardness of solder joints containing higher percentage of Al₂O₃ nano-particles exhibited consistently higher value than those of plain solder joint and solder joints containing lower percentage of Al₂O₃ nano-particles due to control the fine microstructure as well as homogeneous distribution of Al₂O₃ nano-particles acting as a second phase dispersion strengthening mechanism. The fracture surfaces of plain Sn–Zn solder joints exhibited a brittle fracture mode with smooth surfaces while Sn–Zn solder joints containing Al₂O₃ nano-particles showed a typical ductile failure with very rough dimpled surfaces.     

Comment, on `A 1/f noise technique to extract the oxidetrap density near the conduction band edge of silicon' [and reply]

For the original article see ibid., vol.36, no.9, p.1773-82 (1989). The commenters show that, contrary to the calculations in the above-titled paper by R. Jayaraman and C.G. Sodini, the correlated noise power spectra of number and surface mobility fluctuations in n-channel MOSFETs are functions of the relative densities of the positive and neutral traps at the Si-SiO₂ interface. The authors, along with B.J. Gross, disagree with the commenters' assessment and support their calculations. The contend that the distribution of active traps assumed by the commenters is not representative of the distribution active in real MOSFET devices     

Temperature and magnetic field dependence of the critical current density for a mass-produced Nb/sub 3/Al multifilamentary strand fabricated by a jelly-roll method [for ITER]

JAERI has been developing jelly-roll processed multifilamentary Nb/sub 3/Al-Cu strands for the toroidal field (TF) coils of fusion tokamak machines since 1986, in cooperation with Sumitomo Electric Industries. One ton of mass-produced strands were successfully manufactured for the 13 T-46 kA Nb/sub 3/ Al insert which will be tested in the ITER Central Solenoid model coil. The critical current of the Nb/sub 3/Al strand developed for the ITER project was measured in temperatures from 4.2 to 15 K and in applied magnetic fields up to 16 T. An empirical equation for the critical current density Was obtained by using these data and the pinning force scaling method. The obtained equation is useful in evaluating the performance of the full-size conductor and in establishing the optimum design criteria for the conductor in fusion machines. In this work, we did not take into account the influence of mechanical strain on the strand. I/sub C/ measurement of the strands under mechanical strain will be carried out and an expression for J/sub C/ with the strain will be completed in the next phase.     

The photoionization cross sections of the Rg*2[3Σ+u] excimer states for Ne*2, Ar*2, and Kr*2

Based on the recently determined Rydberg series of the³Sigma+_{u}excimer states of Ne*2, Ar*2and Kr*2, the photoionization cross sections of these molecules are calculated using a single-channel quantum defect method. These cross sections are found to differ considerably from those of the asymptotic metastable atomic Rg*(ns^{3}P_{2}) states, but are in good agreement with recently reported experiments at isolated wavelengths. The implications of these results for VUV and XUV lasers are discussed.