Analysis of electromigration phenomenon in thick-film and LTCC structures at elevated temperature

Studies on electromigration phenomenon in thick-film structures on alumina and LTCC substrates are presented in this paper. The effects of storage of Au and Ag electrode patterns in temperature range up to 300 °C under voltage bias were examined. The leakage characteristics of electrodes with 100 μm spacing at 50 V dc bias as a function of time and temperature are presented and analyzed. Scanning electron microscope (SEM) equipped with the energy-dispersive X-ray spectroscopy (EDX) detector was applied for determination of metal ions transport. Test structures with Au-based conductive material are much more resistant to electromigration than Ag-based layers.     

Effect of laser irradiation on microstructure and electromigration in aluminum films

Optical and transmission electron microscopy were employed to study the effect of ruby laser irradiation on the microstructure and electromigration properties of thin aluminum films. At low energy levels a single pulse creates multiple regions of localized grain growth; grain size in the irradiated area can be an order of magnitude larger than the matrix. Vaporization, melting, and grain growth are observed and related to the input laser energy. In some cases, the morphology of the laser-damaged film resembles that of cast ingots, i.e., a columnar structure radiating from an equiaxed boundary network and bounded by a circular chill zone.     

Observations on the electromigration in various thin films of group I–IV

The transport of ions under the influence of a direct current has been found to be directed towards the cathode in thin films of silver, copper and gold, and towards the anode in aluminum, magnesium, indium, tin and lead films. The direction of electromigration in silver, copper and gold films is opposite to the one usually found in bulk samples of these metals. In silver films with large as well as with small grains the direction of electrotransport is the same. The experiments show that electromigration in single-crystalline silver films is small. This suggests that grain boundary electrotransport predominates in silver films over surface and volume electrotransport, which is also true for aluminum films.     

Study of the influence of thermal effects on the electromigration tests

A simple one-dimensional thermal model of the electromigration phenomenon shows that the usual measurement methods of the temperature during lifetime tests usually lead to an erroneous determination of Black's relation parameters n and Q. The effects of the current density and the temperature estimation method on the errors on n and Q are analysed. An estimation of the temperature of the site where the flux divergence is maximum allows us to understand the behaviour of n and Q. The difference between real and apparent activation energy, at low current densities, is also calculated.     

Hydrolysis behavior of aluminum nitride in various solutions

The AlN powder was immersed in deionized water, HCl aq, NaOH aq and H₃PO₄ aq to investigate their hydrolysis behavior at 283 to 373 K. The pH of the solutions were not varied at the initial stage in the case of deionized water, and they increased abruptly after the incubation time with evolution of NH₃. Time until the evolution of NH₃ decreased with increasing temperature. The hydrolysis at the higher temperature was different from at the lower. Below 351 K a crystalline bayerite was produced on the surface of AlN particle, while a crystalline boehmite was produced at higher than 351 K. The AlN powder was hydrolyzed more efficiently in HCl aq and NaOH aq compared with in the deionized water. While, H₃PO₄ aq restrained hydrolysis of AlN powder.     

Design of solder joints for fundamental studies on the effects of electromigration

The continuous miniaturization of high performance electronic devices has reached a level at which current densities are large enough to make electromigration (EM) a significant issue affecting the electrical and mechanical reliability of solder joints. A new design of solder joints that controls the extent of regions experiencing relatively uniform current density, as well as regions with large current density gradient was developed. Current density distribution of this newly designed solder joint was calculated using finite element analysis (FEA), which was used to guide the characterization of EM of real solder joints. As a part of the effort in evaluating the suitability of the new joint configuration for evaluating the fundamental issues in EM, eutectic PbSn solder joints were fabricated using this design. EM effects due to applied current, current density distribution, and joint thickness of eutectic PbSn solder joints present in this joint configuration were investigated. Findings based on this new design can facilitate fundamental studies of EM issues that affect the reliability of solder joints.     

Analysis and approximation for the performance of a workstation with various types of setups

Setups commonly exist in flexible manufacturing systems. Modelling the queue time correctly is of fundamental importance in evaluating the performance of manufacturing systems. An insightful classification is the first step towards correct modelling. Through the observation of practical production lines, two types of setups are classified: state-induced setups and product-induced setups. The product-induced setups can be a changeover setup or a replacement setup. Changeover setups are induced by switching manufacturing processes between products, whereas replacement setups are caused by changing components or consumables. Approximate models for the mean queue time of different setup types are proposed based on their distinct properties. The proposed models are validated with simulations and perform well in the examined cases.     

Interactions between inclusions and various types of cracks

The problems of a crack inside, outside, penetrating or lying along the interface of an anisotropic elliptical inclusion are considered in this paper. Because the crack may be represented by a distribution of dislocation, integrating the analytical solutions of dislocation problems along the crack and applying the technique of numerical solution on the singular integral equation, we can obtain the general solutions to the problems of interactions between cracks and anisotropic elliptical inclusions. Since there are no analytical solutions existing for the general cases of interactions between cracks and inclusions, the comparison is made with the numerical results obtained by other methods or with the analytical results for the special cases which can be reduced from the present problems. These results show that our solutions are correct and universal     

Diluting and annealing effects on electromigration and morphology of chemical vapor-deposited copper films

The crystallization and orientation of chemical vapor-deposited copper films were investigated by means of X-ray diffraction. The ratios of Cu (1 1 1) peak intensity to Cu (2 0 0) [I(1 1 1)/I(2 0 0)] of the film deposited at different temperatures were plotted as a function of temperature. Then it can be found that the ratio of I(1 1 1)/I(2 0 0) increased with the deposition temperature, and 400 °C is the best one for electromigration when the films are grown in diluting N₂, and/or annealing by N₂ or by H₂. In addition, the morphology of copper films was characterized by atomic force microscopy, and it was found that the smoothness of the films grown in diluting N₂ and/or annealing by N₂ are improved, while the films annealing by H₂ have no significant changes.     

Controllable motions of compressible simple materials of various types

Summary It is shown that a motion is possible in every compressible homogeneous isotropic simple solid having a certain range of memory, in the presence of a constant body force field, if and only if it is homogeneous and uniformly accelerated after a certain time. In the class of solids having perfect memory, the only motion of this kind which can be smoothly initiated in a body at rest is a rigid one. For the class of solids having finite memory of durationT and initially at rest, the motions of the type considered need be homogeneous and uniformly accelerated only after timeT. For those solids having fading memory, the motion must reduce to a fixed homogeneous deformation. Similar results are developed for simple fluids and anisotropic simple solids.

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Steuerbare Bewegungen verschiedener kompressibler einfacher Stoffe

Zusammenfassung Es wird gezeigt, daß in jedem kompressiblen, homogenen und isotropen einfachen Festkörper mit einem gewissen Erinnerungsbereich und in Gegenwart eines konstanten Massenkraftfeldes eine Bewegung dann und nur dann möglich ist, wenn sie homogen und nach einer gewissen Zeit gleichmäßig beschleunigt ist. Bei Festkörpern mit vollkommener Erinnerung ist die einzige Bewegung dieser Art, die bei einem ruhenden Körper glatt eingeleitet werden kann, eine starre. Bei Festkörpern mit begrenzter ErinnerungsdauerT, die anfangs in Ruhe waren, müssen die Bewegungen der betrachteten Art homogen und nur nach der ZeitT gleichmäßig beschleunigt sein. Für Festkörper mit schwindendem Gedächtnis reduziert sich die Bewegung auf eien feste homogene Verformung. Ähnliche Ergebnisse werden für einfache Flüssigkeiten und anisotrope einfache Festkörper entwickelt.

     

Thermal buckling of various types of FGM sandwich plates

The sinusoidal shear deformation plate theory is used to study the thermal buckling of functionally graded material (FGM) sandwich plates. This theory includes the shear deformation and contains the higher- and first-order shear deformation theories and classical plate theory as special cases. Material properties and thermal expansion coefficient of the sandwich plate faces are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. Several kinds of symmetric sandwich plates are presented. Stability equations of FGM sandwich plates include the thermal effects. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. Numerical examples cover the effects of the gradient index, plate aspect ratio, side-to-thickness ratio, loading type and sandwich plate type on the critical buckling for sandwich plates.     

Peculiarities of the long-range effects in GaAs-Based transistor structures upon combined irradiation with ions of various masses

Anomalous distinctions in the depth profiles of charge carrier density in the active regions of GaAs-based structures were observed for samples irradiated from the rear side (through substrate) with molecular hydrogen and argon ions either separately or in a certain combined sequence. The maximum effect of ion irradiation was observed in the structures characterized by increased density of defects in the buffer layer. The experimental results are explained by reconstruction of the impurity-defect complexes at the layer interfaces under the action of elastic waves arising both as a result of relaxation of the atomic displacement peaks in the ion stopping zone and due to the reverse piezoelectric effect.     

The effects of test temperature and humidity on the mixed-mode fatigue behavior of a toughened adhesive aluminum joint

The effects of test environment humidity and temperature on the fatigue threshold and crack growth behavior of P2-etched and commercial coil-coated (CC) aluminum adhesive joints were studied under mixed-mode loading using aluminum asymmetric double cantilever beam (ADCB) specimens. Under dry conditions, increasing the temperature to 80 °C had an insignificant effect on the fatigue threshold, but caused an increase in the crack growth rates. At 40 °C, the fatigue behavior was insensitive to moisture at higher crack growth rates, but became sensitive to moisture level in the test environment as crack growth rates slowed to the threshold. The effect of moisture and temperature were explained by the observed changes in the crack path, which in general moved progressively closer to the more highly-strained adherend as the applied strain energy release rate, and consequently the crack growth rate, decreased. Furthermore, the residual adhesive thickness on the more highly-strained adherend, t_r, increased with increasing temperature, and the crack path shifted to the hydrated aluminum oxide interface when the test environment was saturated with moisture. The degrading effect of a hot-wet environment was similar for both P2-etch and CC pretreatments. At higher crack growth rates, the joint fatigue performance was degraded solely due to the effect of the increased temperature, whereas at low crack growth rates, the fatigue performance was degraded predominantly because of elevated moisture.     

Comparison of fracture toughness test procedures for aluminum alloys

The Dynamic Tear (DT) test permits the measurement of fracture propagation energy across the toughness spectrum for metals which are definable by linear elastic analyses to those requiring gross plastic strains for fracture. The linear elastic fracture mechanics parameter K_ic provides a relationship between critical flaw size and stress level at which crack instability will occur. Unlike the DT test, the K_ic toughness test cannot be utilized for fracture under conditions of elastic-plastic or gross plastic strain.

A correlation has been developed between the DT test and the K_IC parameter for ahuminum alloys. The relationship may also be expressed in terms of β_ic-DT and _ic-DT. The K_ic values were determined with several specimen types and a comparison of the values for different specimens is provided.

The correspondence between K_ic and DT serves several purposes. It provides a frame of reference for DT values obtained from frangible metals that fracture under linear elastic conditions. Accordingly, it permits utilization of the inexpensive DT test to approximate the flaw size-stress instability conditions which otherwise must be determined by the more expensive K_ic test. Furthermore, through extrapolation, it is possible to utilize the DT test to estimate the critical flaw size under an elastic-plastic strain field.     

Synthesis of amorphous calcium phosphate using various types of cyclodextrins

Amorphous calcium phosphate (ACP) was synthesised in aqueous solution at room temperature using cyclodextrins. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis (DTA/TGA) were performed on the calcium phosphate precipitates obtained from solutions. We observed that only β-CD could stabilise the amorphous phase in the mother solution because of the lower solubility of β-CD in water and the ACP remained stable in aqueous solution for more than 24 h at room temperature. The ACP particle has an initial particle size of less than 40 nm, Ca/P molar ratio of 1.67 and β-CD absorbed on its surface. The mechanism for the stabilisation of ACP is proposed.     

Properties of self-compacting mortar made with various types of sand

Higher cement and fines content is needed in self-compacting mortars (SCMs) to increase their flowability and stability. Different inert fillers and supplementary cementitious materials are usually added. The use of sands rich in fines may be a cost effective alternative source of filler. This paper presents the results of an experimental study on the rheological and mechanical properties of self-compacting mortars (SCMs) made with various types of sands: crushed sand (CS), river sand (RS), dune sand (DS) and a mixture of different sands. The mini-slump flow, V-funnel flow time and viscosity measurement tests were used to study the rheological properties. The experimental results indicate that the rheological properties and strength improve with mixtures of crushed and river sands but decrease with mixtures of crushed and dune sands especially for higher dune sand content. Crushed sand with (10–15%) of limestone fines can be used successfully in production of SCM with good rheological and strength properties. However, a reduction in compressive strength with increasing dune sand content (up to 50%) in mortar with binary and ternary sands was observed.     

Properties of self-compacting mortar made with various types of sand

Higher cement and fines content is needed in self-compacting mortars (SCMs) to increase their flowability and stability. Different inert fillers and supplementary cementitious materials are usually added. The use of sands rich in fines may be a cost effective alternative source of filler. This paper presents the results of an experimental study on the rheological and mechanical properties of self-compacting mortars (SCMs) made with various types of sands: crushed sand (CS), river sand (RS), dune sand (DS) and a mixture of different sands. The mini-slump flow, V-funnel flow time and viscosity measurement tests were used to study the rheological properties. The experimental results indicate that the rheological properties and strength improve with mixtures of crushed and river sands but decrease with mixtures of crushed and dune sands especially for higher dune sand content. Crushed sand with (10–15%) of limestone fines can be used successfully in production of SCM with good rheological and strength properties. However, a reduction in compressive strength with increasing dune sand content (up to 50%) in mortar with binary and ternary sands was observed.