Classical Bubble Research Articles

High Yield, Near Void-Free Assembly Process of a Flip Chip in Package Using No-Flow Underfill

The advanced assembly process for a flip chip in package (FCIP) using no-flow underfill material presents challenges with high I/O density (over 3000 I/O) and fine-pitch (down to 150 μm) interconnect applications because it has narrowed the feasible assembly process window for achieving robust interconnect yield. In spite of such challenges, a high yield, nearly void-free assembly process has been achieved in the past research using commercial no-flow underfill material with a high I/O, fine pitch FCIP. The initial void area (approximately 7% ) could cause early failures such solders fatigue cracking or solder bridging in thermal reliability. Therefore, this study reviewed a classical bubble nucleation theory to predict the conditions of underfill void nucleation in the no flow assembly process. Based on the models prediction, systematic experiments were designed to eliminate underfill voiding using parametric studies. First, a void formation study investigated the effect of reflow parameter on underfill voiding and found process conditions of void-free assembly with robust interconnections. Second, a void formation characterization validated the determined reflow conditions to achieve a high yield and void-free assembly process, and the stability of assembly process using a large scale of assemblies respectively. This paper presents systematic studies into void formation study and void formation characterization through the use of structured experimentation which was designed to achieve a high yield, void-free assembly process leveraging a void formation model based on classical bubble nucleation theory. Indeed, the theoretical models were in good agreement with experimental results.

Ultrasonic emissions from conifer xylem exposed to repeated freezing

Ultrasonic emission measurements enable the analysis of xylem cavitation induced by drought and freeze–thaw events. Several studies have indicated that ultrasonic acoustic emissions (UAE) in conifers occur upon freezing and not upon thawing, although classical theory has postulated gas bubble formation during freezing and cavitation during thawing. We analyzed the pattern and quality of freeze–thaw-induced UAE in seven conifers ( Abies alba, Larix decidua, Juniperus communis, Picea abies, Pinus cembra, Pinus mugo, Pinus sylvestris). Axes samples dehydrated to different water potentials were exposed to repeated frost cycles. The number, amplitude and energy of UAE signals were registered and related to water potential, temperature course and wood characteristics (wood density, tracheid diameter). For P. abies, ultrasonic emission analysis was also performed on bark samples, xylem samples without bark, as well as on stems of young potted trees. In all conifers, UAE were registered in water-stressed samples but not in saturated or dehydrated samples. No signals were emitted by the bark of P. abies. Ultrasonic activity occurred only upon freezing, and identical patterns were observed in axes samples and stems of potted P. abies trees. A weak positive relationship between tracheid diameter and UAE energy was observed, indicating wide tracheids to emit signals with higher energy. The classical bubble formation hypothesis cannot sufficiently explain the occurrence of UAE during freezing and upon repeated temperature cycles, as demonstrated in this study. We suggest that the low water potential of ice induces air-seeding near the ice-water interface, and consequently, causes UAE.

Non-classical Nucleation Model for Cold Production of Heavy Oil

Abstract We examine the gas bubble nucleation phenomenon encountered in extra heavy oil during cold production. The nucleation model described in this work is based on so-called non-classical nucleation. Using this method, we show mesoporous cavities could be at the origin of the nanobubble trapping mechanism. The results obtained show this physical approach tends to demonstrate the pre-existence of gas bubbles in these crevices (surface roughness). The physics of capillarity used here is based on traditional Laplace's law and an original disjoining pressure expression. We test for several wettabilities in our mathematical model. The first configuration envisaged is for oil-wet rocks, although the cavity is assumed to be gas-wet. Water wettability is considered a second time, taking into account a precursor water film between the rock and the entrapped bubbles. The mix of these two configurations could represent nucleation in a global mixed-wet porous media. However, we show in the first part of this article that water presence does not affect the initial bubble radius. Nevertheless, a bubble growth model developed in the second configuration shows that bubble confinement could play an important role on gas bubble nucleation and the early first steps of its development. Introduction Macroscopic nucleation mechanisms have been the subject of many studies over the last decades because of both its fascinating underlying physics and its technological importance in many domains. The physics of gas bubble generation and growth in supersaturated solutions is a confusing subject in the literature. Jones et al.(1) proposed a classification system for the kinds of nucleation that occur experimentally. They define mechanistically four types of nucleation and place the specific forms of nucleation into a better defined context. Several authors concluded that the heterogeneous nucleation form is the most plausible mechanism in porous media. Nevertheless, homogeneous or heterogeneous nucleation on molecularly smooth surfaces requires a very high level of supersaturation. During a depletion experiment with heavy oil in porous media, the supersaturations reached are low, so another type of nucleation has to be envisaged. The opposite of the classical bubble nucleation theory which requires very high levels of supersaturation, is one where the activation of the pre-existing gas cavities needs very low levels. Therefore, to study the nucleation phenomenon in heavy oil we assume the pre-existence of trapped gas bubbles in contact with the supersaturated liquid. Lubetkin(2) focused on this and claimed that theory predicts a need for a much higher supersaturation to cause bubble nucleation than is found experimentally. Moreover, the theory predicts that the nature of the liquid influences the conditions required for nucleation and experimental works show a strong influence with the chemical nature of the gas. Considering this, we try to take into account the influence of the physical and chemical properties of the liquid and gas in equilibrium in the crevice and develop a detailed net analysis of the various existing forces. Most previous work relates to spontaneous bubble formations which occur after a rapid decompression of a liquid solution initially saturated with dissolved gas molecules.

Multi-vapor embryos nucleation process and spinodal temperature analysis of expandable superheated water system

This study uses molecular dynamics simulation to analyze the homogeneous nucleation process in superheated water. The temperature and pressure of the system are controlled with Langevin dynamics method while the system volume is variable. In this way, the expanding process of the liquid system into vapor system is studied phenomenologically. In metastable liquid system with higher superheating degree, there can be seen large quantities of regions with no liquid moleculer inside: i.e., the vapor embryos. These vapor embryos are unstable in nature and are deforming with time. By analyzing the attraction and repulsion between molecules, we find the mechanisms that govern the merging, formation and dying out of vapor embryos. Vapor embryo violates some predictions of classical bubble dynamics theory, it indicates that formation of vapor embryo may have a more microcopic nature than the formation of bubble. We compared systems under different temperatures to study the effects of superheating degree. The spinodal temperature of water at atmospheric pressure determined under our simulation condition is about 535 K, within the scope of available experimental results.

Nonexistence of classical steady Hele–Shaw bubble

This paper concerns nonexistence of steadily translating bubbles in a Hele–Shaw cell for small but nonzero surface tension. It is proved that for any fixed bubble velocity U relative to the fluid velocity at infinity in the interval ( 2 , ∞ ) , there can be no classical steady bubble solution.

A novel nano‐bubble inflation method for determining the viscoelastic properties of ultrathin polymer films

We describe a novel experimental technique for measuring the absolute creep compliance of ultrathin polymer films. The method is based on the classical bubble inflation technique for measuring the biaxial creep compliance of films, reduced in size to measure films with thicknesses down to at least 11.3 nm. The method uses the imaging capabilities of the atomic force microscope (AFM) to determine the time evolution of the geometry of nano-bubbles and thus avoids the problems with data interpretation that can arise due to "contact mechanics" issues when the AFM is used as a direct mechanical testing device.

The role of viscosity and surface tension in bubble entrapment during drop impact onto a deep liquid pool

The phenomenon of liquid drop impact onto the surface of a deep pool of the same liquid is studied in the context of bubble entrapment, using high-resolution digital photography. Three liquids, pure water, glycerin/water mixtures, and silicon oil, have been used to investigate the effect of viscosity (μ) and surface tension (σ) on regular bubble entrapment, and the associated impact crater signatures. The global viscous effect is seen as a shift in the classical inviscid bubble entrapment limits, whereas, at the impact crater, the local effect is seen as a weakening of the capillary wave, which is responsible for bubble pinching, and a weakening of the intensity of crater rebound. Bubble entrapment, which results from a competition between concentric capillary pinching of the crater cusp and viscous damping, is captured well by the capillary number Ca (Ca = mu Viσ, where Vi is the drop impact velocity). The measured peak entrapped bubble size decreases exponentially as capillary number increases, with the cut-off capillary number for bubble entrapment estimated to be around 0.6. The critical crater cone angle for peak bubble pinch-off weakly increases with capillary number, with the measured value in agreement with theory in the inviscid limit (low Ca). Additionally, the growth of the main body of the high-speed thin jet, formed immediately following bubble pinch-off, is fitted to a power-law singularity model. This suggests that the thin jet is similar to the hydraulic jets produced by the collapse of free-surface standing waves.

Multiphase fluidization in large-scale slurry jet loop bubble columns for methanol and or dimethyl ether production

A solution methodology is proposed for the process development and process engineering of a continuously operated jet loop bubble column including integrated external or internal steam generation for, e.g., a high-efficiency large-scale medium pressure methanol and or dimethyl ether production, or other gas to liquid Fischer–Tropsch applications. A jet loop bubble column is defined in the present process development to study the combined integration of a jet-eductor draft tube system with an upper bubble column. The major advantages resulting from the integrated jet-eductor draft tube system in large-scale bubble columns are the guidance and good mixing efficiency of the multiphase flow up to the upper part of the bubble column. Reducing the bubble column operating liquid level at about 2.5–3.0 times of the column diameter above the upper end of the draft tube results in a classical jet-eductor draft tube reactor suitable for small and or medium-scale industrial applications. Methanol synthesis is usually executed catalytically in multistage packed beds at higher pressure, e.g. 26 MPa, and about 350– 400 ∘ C , resulting in a higher plant installation and operating cost. The successful scale-up of a slurry jet loop bubble column can achieve a higher catalytic selectivity at a lower pressure ( ∼ 5 MPa ) and temperature ( ∼ 250 ∘ C ) , and therefore reduce the overall plant investment and production cost [ Toseland, 1999. Three phase flows under extreme conditions of pressure and temperature, Part II: industrial applications, Air products and Chemicals, Inc. Presented at the A.I.Ch.E. Annual Meeting, Dallas, TX; Fan, 1999. Three phase flows under extreme conditions of pressure and temperature, Part I: fundmental characteristics, Department of Chemical Engineering, The Ohio State University. Presented at the A.I.Ch.E. Annuxal Meeting, Dallas, TX]. In addition, the separate slurry production of dimethyl ether, or even coproduction with methanol, can be a more cost-effective process than the classical methanol dehydration process. The new Modified Slurry Process © for large-scale methanol and or dimethyl ether production is presented including internal or external heat exchanger location for steam production. A process concept is developed of a Large Scale Slurry Jet Loop Bubble Column © with external separator, auxiliary internal heat exchanger equipment and high-efficiency gas–liquid slurry jet-eductor mixing system including draft tubes and an upper bubble column. In addition, as comparison a simplified concept is discussed for a small-to-medium-scale slurry jet loop reactor including external steam production and bottom nozzle jet-eductor installation without the presence of an upper bubble column. The basic geometrical parameters of the proposed slurry jet loop bubble column and jet loop reactor are discussed. The influence of the selected geometrical parameters on the gas holdup, interfacial area and mixing is analyzed. Information about catalyst type and particle size distribution is also presented. The definition of optimal operating conditions related to the influence of the fluid dynamics and mixing on mass transfer efficiency and also information for the minimum required power input per unit volume for startup or stable reactor operation are discussed. A simplified estimation method is presented for the expected axial temperature difference across the overall length of the jet bubble column, and also the required heat transfer area of a new construction-type internal compact heat exchanger for efficient reactor cooling and operation. Scale-up is possible for large diameter jet loop bubble columns, typically up to 5 m diameter and 60 m height, including continuous three-phase slurry operation at higher power input and interfacial area, for more efficient synthesis gas absorption and reaction than in classical slurry bubble columns. Integration of suitable designed sieve trays can further guarantee an efficient operation of the lower jet loop draft tube system at higher column diameters and also achieve an efficient reactor operation in the upper bubble column section.

Rheological Measurements of the Thermoviscoelastic Response of Ultrathin Polymer Films

Measurement of the thermoviscoelastic behavior of glass-forming liquids in the nanometer size range offers the possibility of increased understanding of the fundamental nature of the glass-transition phenomenon itself. We present results from use of a previously unknown method for characterizing the rheological response of nanometer-thick polymer films. The method relies on the imaging capabilities of the atomic force microscope and the reduction in size of the classical bubble inflation method of measuring the biaxial creep response of ultrathin polymer films. Creep compliance as a function of time and temperature was measured in the linear viscoelastic regime for films of poly(vinyl acetate) at a thickness of 27.5 nanometers. Although little evidence for a change in the glass temperature is found, the material exhibits previously unobserved stiffening in the rubbery response regime.

On the formation mechanism of impurity–helium solids: evidence for extensive clustering

Optical emission studies of a discharged nitrogen–helium gas injected into superfluid helium near 1.5 K are described. Analysis of atomic (α group) and molecular Vegard–Kaplan transitions clearly indicates that the emitting species are embedded inside nitrogen clusters. Cluster formation is most efficient in the crater formed on the liquid surface. Model calculations based on the classical bubble model and density functional theory suggest that under the experimental conditions only clusters consisting of more than 1000 molecules have sufficient kinetic energy for stable cavity formation to occur inside liquid helium. The results obtained suggest that impurity–helium solids formation is a consequence of extensive clustering in the gas jet.

Polymeric Foaming Simulation for Extrusion Processes

A numerical simulation for polymeric foaming extrusion processes was conducted. Combining classical nucleation rate and bubble growth models with a non-Newtonian fluid model of a flow, a simultaneous bubble nucleation and growth behavior in a flow field was simulated. Simulation results were compared with the experimental data obtained by visual observations at a foaming extruder, where a polypropylene resin was physically foamed. The effects of physical parameters in foaming model on bubble size and number density calculation were intensively examined by sensitivity analysis.

Financial Bubbles: Excess Cash, Momentum, and Incomplete Information

We report on a large number of laboratory market experiments demonstrating that a market bubble can be reduced under the following conditions: 1) a low initial liquidity level, i.e., less total cash than value of total shares, 2) deferred dividends, and 3) a bid-ask book that is open to traders. Conversely, a large bubble arises when the opposite conditions exist. The first part of the article is comprised of twenty-five experiments with varying levels of total cash endowment per share (liquidity level), payment or deferral of dividends and an open or closed bid-ask book. We find that the liquidity level has a very strong influence on the mean and maximum prices during an experiment (P < 1/10,000). These results suggest that within the framework of the classical bubble experiments (dividends distributed after each period and closed book), each dollar per share of additional cash results in a maximum price that is $1 per share higher. There is also limited statistical support for the theory that deferred dividends (which also lower the cash per share during much of the experiment) and an open book lead to a reduced bubble. The three factors taken together show a striking difference in the median magnitude of the bubble ($7.30 versus $0.22 for the maximum deviation from fundamental value). Another set of twelve experiments features a single dividend at the end of fifteen trading periods and establishes a 0.8 correlation between price and liquidity during the early periods of the experiments. As a result, calibration of prices and evolution toward equilibrium price as a function of liquidity are possible.

A Model of Bubble Nucleation on a Micro Line Heater

The bubble nucleation mechanism on a cavity-free micro line heater surface was studied by using the molecular cluster model. A finite difference numerical scheme for the three-dimensional transient conduction equation for the liquid was employed to estimate the superheated volume where homogeneous bubble nucleation could occur due to heat diffusion from the heater to the liquid. Calculation results revealed that bubble formation on the heater is possible when the temperature at the hottest point in the heater is greater than the superheat limit of the liquid by 6°C–12°C, which is in agreement with the experimental results. Also it was found that the classical bubble nucleation theory breaks down near the critical point where the radius of the critical bubble is below 100 nm.

Investigation of the bubble behaviour at the free surface of a large three-dimensional gas fluidized bed

Gas fluidization is generally associated with the formation of bubbles that critically influence the performance of fluidized bed processes (FBPs). Therefore, in the design, simulation and operation of FBPs, it is very essential to know the behaviour of the bubbles at the free surface. The size and growth of bubbles play an important role for determining properties such as bed expansion, solids entraiment, in-bed heat transfer and solid mixing. This paper presents a study on the behaviour of bubbles at the free surface of a large three dimensional gas-fluidized bed with square section of 61×61 cm2. Measurements were carried out to determine the effects of bed height and excess air velocity on the bubble eruption diameter, frequency and bubble fraction. All experiments were performed at freely bubbling mode and the flow characteristics of bubbles were recorded by a video camera. Bed materials used were 593 μm raw perlite and 1233 μm sand falling within the categories of Geldarts Groups B and D, respectively. The fixed bed height ranged from about 8–18 cm for raw perlite and 9–26 cm for sand. The excess air velocity was varied between 0·5 and 1·75 cm s−1 for raw perlite and 13 and 25 cm s−1 for sand. Equations related to the bubble count, frequency, flow area shape factor and through-flow coefficient were given using a modified form of two-phase theory of fluidisation. Observations were made to validate the two-phase theory for two different particles. The flow area shape factor was in the range of 0·47–0·81 for raw perlite and 0·20 to 0·57 for sand, with mean values of 0·6 and 0·4, respectively. The through-flow coefficient was found to be between −0·68 and 2·82 for raw perlite and between 3·27 to 15·87 for sand, and was larger than predicted values of classical bubble models. © 1998 John Wiley & Sons, Ltd.

Treatment of gases and dust using “droplet columns”

AbstractThe properties of the air‐water state diagram, representing the liquid holdups according to gas velocities, in a 0.075 m diameter column are restated. After measurement of the interfacial areas and mass‐transfer coefficients, the part of the diagram corresponding to high gas velocities and low liquid contents (10 &lt; UG &lt; 14 m/s and 0.005 &lt; UL &lt; 0.04 m/s) was chosen for the treatment of polluted gas streams. Under these conditions, it was shown that a “droplet column” is very efficient for the treatment of gases polluted by acid vapors (SO2, HCl) and dust (iron oxide, talc, etc.). The cost of energy appeared more favorable than for classical bubble columns.

The Performance of a Semi-Lagrangian Transport Scheme for the Advection–Condensation Problem

Abstract A series of numerical experiments are carried out solving a coupled set of equations for advection and condensation with a semi-Lagrangian (SL) transport scheme. Canonical validation tests in one dimension show that SL suffers less numerical aberrations than many Eulerian transport schemes. Some monotonic transport constraints are experimented with. These tests confirm, for an SL transport, the statement first enunciated by Grabowski and Smoladdewicz within the context of Eulerian transport that monotonic transport constraints are not sufficient to prevent the development of false ripples when integrating coupled field equations. A constraint is developed and successfully applied to the simplified advection–condensation problem. A two dimensional dynamical model based on the fully elastic equations solved with a semi-implicit semi-Lagrangian scheme is used to simulate the classical moist bubble convection problem; these SL solutions are compared to published results obtained with Eulerian models....

Measuring Unsteady Velocity Profiles and Integral Parameters Using Digital Image Processing of Hydrogen Bubble Timelines

To aid in the investigation of artificially generated turbulent spots a technique was developed to make instantaneous measurements of full velocity profiles in an unsteady water boundary layer. These profiles were used to document the unsteady behavior of scalar descriptors such as the displacement thickness. The classical hydrogen bubble flow visualization technique was augmented to yield quantitative information by incorporating digital image processing of videotaped boundary layer flow. Digital images were converted into velocity fields using a corrected time-of-flight technique. The capability and limitations of this method in both steady and unsteady flows have been verified using an analytical uncertainty analysis and through comparison with laser-Doppler anemometry measurements. Recommendations are made for effective use of this technique.

Bubble point measurements on large areas of microporous membranes

The classical bubble point measurement can only be applied to membrane areas limited in size. In the case of areas larger than approx. 0.05 m2 the diffusion flow exceeds the convective flow through individual pores. This difficulty can be avoided by using a microphone as a flow sensor which responds only to convective flows. Filter cartridges with membrane areas of 1 m2 were tested by this method, and the maximum pore sizes compared with the retention capacity with respect to Pseudomonas diminuta. The maximum pore diameters correlate with bacterial retention within a tolerance of ± 0.3 μm.

Bubble Dynamics and Cavitation Inception in Cavitation Susceptibility Meters

To improve the understanding of the scaling effects of nuclei on cavitation inception, bubble dynamics, multibubble interaction effects, and bubble-mean flow interaction in a venturi Cavitation Susceptibility Meter are considered theoretically. The results are compared with classical bubble static equilibrium predictions. In a parallel effort, cavitation susceptibility measurements of ocean and laboratory water were carried out using a venturi device. The measured cavitation inception indices were found to relate to the measured microbubble concentration. The relationship between the measured cavitation inception and bubble concentration and distribution can be explained by using the theoretical predictions. A tentative explanation is given for the observation that the number of cavitation bursting events measured by an acoustic device is sometimes an order of magnitude lower than the number of microbubbles measured by the light scattering detector. The questions addressed here add to the fundamental knowledge needed if the cavitation susceptibility meter is to be used effectively for the measurement of microbubble size distributions.

Flame Propagation Through Layered Fuel-Air Mixtures

Abstract It is observed that a layered, unconfined combustible mixture supports a flame propagation velocity of 4 to 5 times the laminar flame speed of the stoichiometric mixture of fuel and air. This effect which has been observed by some and more recently in this laboratory, has never been adequately explained. It is in contrast to the classical soap bubble experiment, in which the flame propagation velocity is of the order of 7 to 8 times the laminar flame speed, that is, the order of the unburned to burned gas density ratio To explain this new effect two physical models with different degrees of complexity are explored here. The first is a step-wise premixed fuel-air and pure air case in a gallery of infinite length. The second deals with one of finite length. Both have been mathematically defined to give quantitative results so that the effects of environmental factors can be explicitly determined Solutions of the first model show that the maximum flame propagation speed occurs when the gallery is of infinite height. In that case the ratio of the propagation speed to the laminar flame speed is equal to the square root of the ratio of the unburned to the burned gas density. For the second model, in which the galleries have finite length with open ends, the interesting result is that for all but a gallery of infinite height the flame propogation speed is unsteady and accelerating. These results have been experimentally verified.