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A Railgun-concept for the launch of small payloads into low-Earth orbits is currently under investigation. The first major project milestone foresees a 32-MJ railgun system able to launch nonpropelled projectiles with experiments for high-atmospheric research to an altitude of 115 km. This will be followed by a system to launch single-stage rocket-propelled projectiles to put in orbit nanosatellites using a 3.4-GJ railgun with a length of 180 m. One of the main issues to be investigated is the extreme thermal conditions the projectile's surfaces are exposed to, namely high temperatures and high thermal loads. These are caused by friction and turbulent flow properties, when the projectile rushes through the dense Earth's atmosphere in less than 30 s. The important questions to be answered for the design of a hypersonic projectile are the determination of the duration, magnitude, and location of the maximum temperatures with respect to the projectile's surface and its corresponding internal structure. For the determination of the complicated physical conditions, a two-step approach is used. In a so-called predesign phase, the HF3T code of the DLR is applied to estimate time-dependent temperature changes on the projectile's surface and/or within the material's structure as a function of the trajectory parameters. Finally, the three-degree-of-freedom trajectory program TRAJECTORY 3D of DLR is used to generate a detailed time-dependent data set, which includes the values for projectile velocity, Mach and Reynolds numbers, and atmospheric properties as a function of altitude. This data set is exchangeable with the TAU code of DLR for the solution of the Navier--Stokes equations, enabling pseudo-unsteady flow solutions along the trajectory. The solutions resulting from both approaches are then compared with emphasis on the surface temperature distributions. This strategy allows the verification of the feasibility of the proposed design solution for the railgun launched hypersonic projectiles. Index Terms--Aerothermodynamics, coupled calculations, heat load, railgun, unsteady flow.

The throat region of solid armatures is subjected to significant stress and temperature during a railgun launch. Recovered aluminum alloy armatures show evidence of plastic deformation, melting, and even cracking in the throat region. Plastic deformation can result from magnetic pinch or thermal expansion forces and melting from ohmic heating. Although cracking is historically associated with grain boundary melting, the cracks observed in recently recovered armatures are likely a result of thermal stresses. Finite-element codes EMAP3D and DYNA3D were linked to assess stresses generated by magnetic forces, inertial loading, wear, and thermal expansions. For low-speed armatures, thermal stresses were found to be as important as magnetic stresses. The observed cracking is likely due to rapid cooling, similar to quench cracking, and may or may not occur during launch. Index Terms--Cracking, solid armatures, throat region.

This paper summarizes experiments to investigate the possibility of delaying the onset of transition by using armatures with high melting temperatures. The rationale for the experiments was that armature materials with high melting points might outperform aluminum by reducing melting and erosion at the rail--armature interface. The tests used a novel technique that consists of placing thin claddings on the rail-contacting surfaces of the armatures. Two low-speed tests with copper armature claddings proved that claddings affixed to the trailing arms can survive a railgun launch. These tests were followed by four tests at about 2 km/s that used titanium armature claddings. These tests showed that titanium-clad armatures can perform well; however, this performance cannot be maintained beyond the first shot because the titanium armature claddings cause significant damage to the rails. Index Terms--Armature, cladding, railgun, titanium, transition to arcing contact.

Insights from recovered armatures suggest re-examining historical modeling assumptions for railguns. The finite-element codes EMAP3D and DYNA3D were linked to explore the effects of temperature-dependent material properties, thermal diffusion, armature wear, inertial loading, thermal stresses, and 2-D model approximations. Temperatures and principal stresses for each of these cases were compared. Thermal diffusion and thermal stresses in armatures cannot be ignored past the first millisecond of launch; material properties under pulsed heating can significantly differ from equilibrium and room-temperature values. Armature wear and inertial loading can be ignored at low speeds, but not at high speeds (>1 km/s). Models in 2-D can approximate 3-D models with appropriate boundary conditions, but only for the first few milliseconds of launch. With a detailed EMAP3D model and minimal assumptions, simulations that agree within a few percentage points of microstructural measurements from recovered armatures are possible. Index Terms--Model assumption, railguns.

We present a finite-element-based analysis to determine if there are potential reliability concerns due to thermally induced stresses in interwafer copper via structures in three-dimensional (3-D) ICs when benzocyclobutene (BCB) is used as the dielectric adhesive to bond wafers. We first partially validate our approach by comparing computed results against two types of experimental data from planar ICs: 1) volume-averaged thermal stresses measured by X-ray diffraction in an array of parallel Cu lines passivated with TEOS and 2) studies of failures induced by thermal cycling via chain structures embedded in SiLK or SiCOH. In the volume-averaged thermal stress study, predicted stress slopes (d[sigma]/dT) agree well with other modeling results. Our computed stress slopes agree reasonably well with experimental data along the Cu line direction and normal to the Cu lines surface, but we underestimate the stress slope across the Cu line. In the case of via chains, computed von Mises stresses agree with the results of thermal cycle experiments; we predict failure when SiLK is used as a dielectric and predict no failure when SiCOH is used as the dielectric. The approach is then employed to study thermal stresses in interwafer Cu vias in 3-D IC structures bonded with BCB. Simulations show that the von Mises stresses in interwafer Cu vias decrease with decreasing pitch at constant via size, increase with decreasing via size at constant pitch, and decrease with decreasing BCB thickness. We conclude that there is a concern regarding the stability of interwafer Cu vias. Guidelines for design parameter values are estimated, e.g., interwafer via size, pitch, and BCB thickness. For 2.6-/[micro]m-thick BCB, computations indicate that via size should be larger than 3 [micro]m at a pitch of 10 [micro]m to avoid plastic yield of Cu vias. Index Terms--Benzocyclobutene (BCB), Cu, interwafer vias, low-k dielectronics, thermo-mechanical stresses, three-dimensional (3-D) ICs.

In integrated power modules, mechanical properties of interfaces between deposited copper traces and substrates are important for reliable operation. This paper investigates the values of thermomechanical stresses by IDEAS simulation and describes an experimental method to calculate intrinsic residual stresses using the Stoney equation based on the bending curvature of the sample. Index Terms--Intrinsic residual stress, planar metallization, thermomechanical stress.

The aim of this paper is to define a procedure for the design of induction coilguns in order to obtain thermal and mechanical stress that do not exceed the allowed values in the sleeve. The magnetic vector potential is determined considering a cylindrical sheet current model both for the barrel and the sleeve and solving the related modified Bessel equation. Then the flux, the current density and the propulsive force for each section are determined. By considering the constraints due to mechanical and thermal stress, the maximum muzzle velocity for a one-section launcher is determined. Supposing that the muzzle velocities in the first and in the last section are established, and assuming that all sections, from the second to the last, work with the same mean slip and the same relative velocity, the number of sections and their length are determined. Moreover the surface current density in the barrel is calculated. The design criterion is compared with other criteria, and then used to design an 8km/s muzzle velocity launcher. Index terms - induction coilguns stresses.

A study was conducted to analyze delamination growth for a couple of delamination configurations in large scale integrating packages under a temperature cyclic loading environment. A 350-mil-wide J-lead package was utilized to examine delamination growth while a thermoeleastic finite element technique was used to carry out delamination computations. Results indicated quantitative grasp of stress intensity factors and their mode ratio at the tips at the delamination tips.

A study was conducted to carry out a materials properties and thermal stress evaluation of epoxy molding compound used in electronic packaging using fabricated specimens. A simple tension method was utilized to determine the elastic moduli at room temperature. Results indicated that the elastic modulus was inversely proportional with temperature. Findings also suggested possible failures at the edge sections of packages.

The ionizing radiation response of several semiconductor process technologies has been shown to be affected by preirradiation thermal stress. Data on bipolar linear circuits are presented and discussed in terms of the mechanisms previously proposed for CMOS.

Analytical thermomechanical models were proposed for the computation of thermally induced stress in flip chip assembly leadless solder interconnections. The structural mechanics-based analytical models are capable of estimating the magnitude and characterizing the nature of joint stresses. The models reveal that the largest stresses in flip chip assembly solder joints are at the connection's top and bottom surfaces.

A study was conducted on the thermal strain and stress distribution on silicon-based Planar-Lightwave-Circuits (PLC) substrates and the stress concentration on silicon terrace structures prepared for mounting active optical equipment. Three-point-bending tests were used to determine the fracture strength of silicon. The findings indicate the reliability of the PLC substrate for a new family of optical components.

A study was conducted on the fatigue life of an underfilled flip-chip package using Coffin-Manson relation and finite element modeling-computed solder shear strain. The results of the numerical simulations were employed in the analysis of the parametric sensitivity of the thermal strain in the solder joints and the axial and shear stress in the underfill material. The findings indicate an agreement between the predicted improvement in the number of cycles-to-failure of the underfilled flip-chip and the empirical observation.

A study was conducted on the plastic-creep behavior and stress relaxation behavior due to temperature cycling or isothermal cyclic loading. The findings indicate that long high-temperature and low-temperature dwell times do not contribute to the increase of the cyclic inelastic equivalent strain range in solder joints in an accelerated temperature cycling test. Proposals on some testing processes of temperature cycling and isothermal fatigue tests are also presented.

A study was conducted on thermally induced viscoplastic deformation and low cycle fatigue behavior of the lead-tin solder joints in a 32 mm ceramic ball grid array (CBGA) surface mount package. The nonlinear finite element model results indicate that the maximum viscoplastic strains happen in and around the edge CBGA solder joint. Moreover, the cyclic creep strain was found to be highly significant. The equivalent plastic strain is directly proportional to cyclic frequency and ramp rate but inversely proportional to hold time.

This paper describes the concept of a three-dimensional histogram used for the statistical interpretation of randomly varying harmonics. The new method is based on the measurement of the time duration of each harmonic value. This idea is consistent with the existing instrumentation technology and can enhance the effectiveness of real-time data acquisition to determine the effect and the limits of voltage and current distortions.

A fundamentally based chemical-thermodynamic multifactor stress aging functional relation requiring experimentally based constants is developed, based upon various theoretical models. The specific example presented is that for 120 V aromatic polyimide insulated wire. The stresses of water, temperature, and mechanical strain are included and electrical stress is considered. The results of over 2000 specimens are fitted to the theoretical trends. For a single independent variable function, the resulting relation reduces to the classical Arrhenius curve. The three independent variable relations presented here is applied to data from laboratory aging experiments that simulate insulation deterioration occurring in actual aircraft service experience. The results used in age categorization of US Navy aircraft are generated from wire specimens taken from active aircraft. The paradigm does not use ab initio based constants because of uncertainties in the theoretical development, two forms of which are presented. It is the aim of this presentation to provide a plausible, intuitively meaningful syllogism having elements transferable to other insulation materials/devices/systems. That transfer will require proper recognition of specific chemical mechanisms in the life calculation routine, constrained by practical secondary effects and the need of nonstandard statistics.

The finite element method is proposed as a method to solve for the thermal stresses in passivated and unpassivated lines. Results show that increases in unpassivated line stresses are in direct proportion to increases in linewidth and substrate rigidity. On the other hand, increases in passivated line stresses are inversely dependent on linewidth decreases as these approach a square cross section.

A proposed method in predicting solder joints' fatigue life is based on fracture mechanics and performs well in simulation tests. Results show that, for the cases studied, an n = 3 stress exponent is appropriate. A time-dependent plastic strain introduced into the constitutive equation contributes to 20-30% of the overall strain and to the increase of fatigue cracks. The suggested failure standards used in the study is shown to be conservative although conform well with theoretical predictions.

Twenty-nanometer FePt films with 40% Fe content were deposited on MgO substrates at 300[degrees]C. A perfect (001) preferred orientation of FePt L[1.sub.0] phase was obtained. After 700[degrees]C annealing in vacuum, a room temperature perpendicular anisotropy of as high as 4.5 x [10.sup.7] erg/[cm.sup.3] can be obtained. The Curie temperature of the sample with 40% Fe content is far below the 50% Fe sample, which can effectively reduce the temperature of the thermal writing process. Furthermore, decay of magnetic anisotropy energy ([K.sub.u]) is much faster than saturated magnetization ([M.sub.s]) with rising temperature, which results in a domination of demagnetization (DM) energy at high temperature. Therefore, a further reduction of the switching field can be achieved. Finally, the films show almost the same magnetic properties during 10 times thermal writing processes from 25[degrees]C to 300[degrees]C, implying this media has high reliability for thermal writing process. Index Terms--Demagnetization, FePt with 40% Fe content, MgO substrate, perpendicular anisotropy, thermal writing.

The thermoelastic interaction problem of surface acoustic waves (SAW) in solids, namely the velocity dispersion and thermoelastic attenuation of SAW in continuous and layered type material, can be investigated by the thermal impedance approach. The weak thermoelastic coupling approximation in isotropic solids gives the value of thermal impedance. The thermoelastic SAW attenuation becomes zero in an ideal heat conductive layer.

A response to a research paper on compensation law and its relation to the thermal aging of electric insulators is presented. It defends against the paper's criticism of the aging compensation effect (ACE) correlation culled from life test results as being empirical in origin and quality. It also points out the formal ACE correlation obtained from a later analysis of experimental data on a round robin life test. This is undermines the research paper's assertion, based on Eyring's rate theory, of the ACE correlation's physical significance.

The multilevel interconnection vias is examined using the finite-element method. Thermal stress and electron mobility is stunted due to increases in current density in integrated circuits, which can be estimated using coupled thermal and electrical conduction model in three dimensions. The ratio of via to track width determines the influence of geometry to temperature profile of the device while Joule heating and current density affects position of peak temperature.

The Arrhenius model is extended to model the life data of a power-transformer insulation subjected to electrical and thermal stress. Thermal aging and combined thermal/electrical aging tests are conducted on Fish paper insulation to validate the theoretical model. A good fit is obtained between life predictions of the model and experimental results. The latter indicate a reduction in material life with increased thermal and combined thermal/electrical stress.

Micromagnetic simulations are performed to investigate the reversal process and the thermal stability of a grain of a typical perpendicular recording, media (Co-Cr). The integration of the LLG equation yields that the reversal process changes slowly and steadily from coherent rotation to nucleation with increasing column length. The region between homogeneous rotation and nucleation becomes smaller and is shifted to smaller column lengths if the damping constant is reduced from [Alpha] = 1 to [Alpha] = 0.02. In the weakly damped case very fast switching modes exist if the switching field is only slightly larger than the coercive field. In this small regime the switching time increases with higher switching fields. Using solutions of LLG simulations, energy barriers between the two stable states at zero field are estimated. For column lengths larger than 30 nm the energy barrier for inhomogeneous reversal processes are smaller than for coherent rotation. Index Terms--Energy barriers, fast switching, micromagnetics, perpendicular recording, thermal stability.

We investigated coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer for high thermal stability and a granular host layer to reduce noise. The addition of Co/Pt multilayers increased the nucleation field of the Co[Cr.sub.18][Pt.sub12] medium from 0 to -2000 Oe. Moreover, the moment decay was reduced from 4.8% to 0.1% per decade. Compared to Co/Pd multilayer media, the CGC medium had a 10 dB higher signal-to-noise ratio (SNR). The granular host layer significantly improved the SNR in the high-density region over 10 kfc/mm. Compared to the Co[Cr.sub.20][Pt.sub.10] medium, the CGC medium had a 3 dB higher SNR in the low-density region. The medium noise for the CGC medium increased with the recording density, while the noise for the Co[Cr.sub.20][Pt.sub.10] medium remained constant from 10 to 20 kfc/mm. The approach using CGC medium improves both the SNR and the thermal stability. Index Terms--Continuous layer, granular layer, perpendicular media, signal-to-noise ratio, thermal stability.

The thermal stability in exchange coupled CoPtCrB trilayer structure medium (TL) is discussed and compared to that for the corresponding single layer (SL) medium. The time dependence of magnetization shows a nonlinear behavior. The magnetization decay rate is found to be reduced in TL when the applied field is close to the coercivity. The DC demagnetization (DCD) reversal mechanisms are investigated by magnetic force microscopy. It is observed that for the reversed field close to remanent coercivity of the TL and SL, very coarse magnetic structures appear. Index Terms--Antiferromagnetic coupling, magnetic recording, magnetic viscosity, MFM observation.

Schemes for SNR enhancement for advanced longitudinal recording media are discussed. SNR improvement is obtained by utilizing a bi-magnetic layer media, where the initial magnetic layer has lower magnetization, coercivity, and magnetic anisotropy, in comparison to the top magnetic layer. Further improvements in SNR and thermal stability are achieved using synthetic ferrimagnetic media. The selection of proper thickness and composition of the initial magnetic layer is important for the high performance of the synthetic ferrimagnetic media. Index Terms--High-density longitudinal recording, recording media, signal to noise ratio, thermal stability.

In this paper, we present a micromagnetic and analytical analysis of double layer media with antiferromagnetic exchange coupling. It has been found that in order to achieve good recording performance, strong interlayer exchange coupling and large thickness ratio are desired. When the thickness of the bottom layer is small, thermal activation assists the bottom layer to switch, which requires a smaller interlayer exchange coupling constant. Thermal stability of double layer AFC media has also been investigated with comparison to single layer media in the case of strong and weak interlayer exchange coupling. Index Terms--Antiferromagnetic exchange coupling, multilayer media, thermal activation, thermal stability.

We report magnetic measurements made on two CoCrPtTa thin film media, which were sputter deposited in identical conditions onto either CrMn or NiAl/CrMn underlayers grown on glass substrates. This produced films with [1120] and [1010] preferred orientations respectively. The films had stacking fault densities of 8 [+ or -] 1% and 13 [+ or -] 1% respectively. Increased magnetic viscosity and switching at low fields in the switching field distributions were observed which correlates well with the level of fcc-like regions. We find that the energy barriers to reversal in these films are dominated by the anisotropy field distribution rather than the distribution of grain-sizes. Furthermore, it is clear that even relatively low levels of stacking faults cause significant levels of thermally activated magnetization reversal which may cause reduced thermal stability of written information. Index Terms--Stacking faults, thermal activation.

A pre-irradiation elevated-temperature stress is shown to have a significant impact on the radiation response of a linear bipolar circuit. Thermal cycling can lead to part-to-part variability in the radiation response of circuits packaged from the same wafer. In addition, it is demonstrated that a pre-irradiation elevated-temperature stress can significantly impact the enhanced low dose rate sensitivity (ELDRS) of the LM111 voltage comparator. Thermal stress moderates and, in some cases, eliminates ELDRS. The data are consistent with space charge models. These results suggest that there may be a connection between the mechanisms responsible for thermal-stress effects and ELDRS in linear circuits. Implications of these results for hardness assurance testing and mechanisms are discussed.