Individual Balls Research Articles

Effect of thermo-mechanically induced microstructural coarsening on the evolution of creep response of SnAg-based microelectronic solders

The creep response of solder joints in a microelectronic package, which are subjected to aggressive thermo-mechanical cycling (TMC) during service, often limits the reliability of the entire package. Furthermore, during TMC, the microstructures of the new lead-free solders (Sn–Ag and Sn–Ag–Cu) can undergo significant in situ strain-enhanced coarsening, resulting in in-service evolution of the creep behavior. In this paper, the coarsening kinetics of Ag 3Sn particles in SnAg-based solder are studied, and the results are correlated with impression creep data from individual microelectronic solder balls subjected to thermal aging treatments. Coarsening influences creep behavior in two ways. At low stresses, the creep rate increases proportionately with precipitate size. At high stresses, precipitate coarsening influences creep response by altering the threshold stress for particle-limited creep. Based on these observations, a microstructurally adaptive creep model for solder interconnects undergoing in situ coarsening is presented.

Miniaturized impression creep testing of ball grid array solder balls attached to microelectronic packaging substrates

This article reports on the design and implementation of a miniaturized impression creep apparatus for characterizing the creep behavior of tiny solder balls attached to a ball grid array (BGA) microelectronic packaging substrate. The technique requires no special sample preparation, can probe individual solder balls, and proffers high data throughput by allowing numerous creep curves to be obtained from one substrate, as well as by minimizing the time required to achieve steady state creep. The apparatus reported here uses a 100-μm-diameter cylindrical WC punch to characterize the creep behavior of 750-μm-diameter BGA solder balls from ambient temperature to 423 K. A video imaging system facilitates precise alignment and placement of the indenter on the specimen at the test temperature. The possible effect of substrate curvature on the experimental solder creep curves was evaluated and was deemed to be insignificant. Example creep curves and data based on 90Pb-10Sn BGA solder balls are presented. The test is further scalable for testing of smaller flip-chip joints, using a smaller punch. The present work reports on the implementation of impression creep for testing nonbulk specimens.

Effect of soy supplementation on the physicochemical and sensory qualities of ‘Akara' from cowpea flour

Effect of supplementation on the physiochemical properties of cowpea flour and the sensory qualities of its akara balls were investigated. Akara is a deep-fat-fried product prepared from cowpea (Vignia unguinculata) flour or paste consumed in some parts of West and East Africa. Cowpea flour was supplemented with Soy flour in ratios 0, 20, 30 and 100% levels. The mixtures of the flours were subjected to physicochemical analyses while the akara balls were subjected to sensory evaluation. Analyses showed that as the level of supplementation increased, the protein content, specific gravity, bulk density, swelling capacity and the foaming capacity decreased while on the other hand the water absorption capacity initially decreased before increasing gradually. Supplementation up to 20% level produced pastes of good dispensing and frying characteristics which were well separated upon contact with the frying oil and formed uniformly shaped balls that floated and retained their integrity during frying. Above 20% supplementation level, the pastes exhibited opposite characteristics. They had a thick batter-like consistency, with difficulty in dispensing and failure to separate into individual balls and were submerged during frying. They were distorted and scattered in shape. However, they produced Akara of higher nutrient contents. KEY WORDS: Akara, Cowpea flour, Soybean flour, supplementation, frying. Global Jnl Pure and Applied Sciences Vol.10(4) 2004: 509-514

A novel form of carbon micro-balls from coal

A novel form of ball-like carbon material with its size in micrometer range was prepared from coal with nickel as catalyst by arc plasma method. The carbon material has been systematically studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and ultraviolet laser Raman spectroscopy. The SEM observation shows that the novel carbon material exists in various forms such as individual balls, net-like and plate-like forms, all of which have a quite smooth surface. The diameters of these carbon spheres are quite uniform and in a narrow range of 10–20 μm. The EDS analysis reveals that the ball-like carbon material contains more than 99.5% of carbon and a little amount of other elements such as nickel, silicon and aluminum. The XRD and UV–Raman results reveal that the novel carbon material is a kind of highly graphitized carbon. The growth mechanism of the ball-like carbon material was proposed and discussed in terms of arc plasma parameters and the chemical structure of coal-based carbon.

Grain dynamics in a two-dimensional granular flow.

We have used particle tracking methods to study the dynamics of individual balls comprising a granular flow in a small-angle two-dimensional funnel. We statistically analyze many ball trajectories to examine the mechanisms of shock propagation. In particular, we study the creation of, and interactions between, shock waves. We also investigate the role of granular temperature and draw parallels to traffic flow dynamics.

Neurotrophin channeling of neural progenitor cell differentiation

The act of defining neuropoietic progenitor/stem cells is still in its early phases. Epidermal growth factor (EGF) stimulates extended proliferation of aggregates of subventricular striatal cells, taken from E15 mouse striatum, termed neurospheres in liquid culture. We have shown here and in previous work, using either immunohistochemistry or RT-PCR, that neurosphere cells express 13 cytokines (32 tested) and 20 cytokine receptors (28 tested), with 11 potential paracrine and nine potential autocrine loops. The neurotrophin receptors, Trk A, B, and C, were all expressed. Using a newly developed FACS single cell deposition technique, we evaluated the capacity of single EGF stimulated neurosphere cells to respond to the ligands for Trk A and B, nerve growth factor (NGF), and brain-derived neurotrophin factor (BDNF). Addition of NGF or BDNF to EGF for 14 days had no effect, but removal of EGF at day 14 with subsequent addition of BDNF or NGF resulted in an increase in neuronal and astroglial, but not oligodendrocyte, colony cells at 21 and 28 days of culture for BDNF, and of both cell types at 28 days for NGF. Tri-lineage colonies increased at day 21 with BDNF and at day 28 for both NGF and BDNF. Gross colony morphology also showed changes with neurotrophin addition, forming multiple individual cell balls or filamentous spreads. When EGF was withdrawn, a threshold effect was observed, with small, but not large, colonies ceasing growth. BDNF and NGF showed no effects on cell proliferation when compared to EGF controls, as determined by 5'-bromo-2-deoxyuridine (BrdU) incorporation and thus, they appear to affect differentiation of progenitor cells. These data indicate a sequential action of cytokines with EGF maintaining viability and proliferation and blocking differentiation. Removal of EGF is then permissive for the differentiating effects of BDNF and NGF. These data further indicate that the majority of EGF neurosphere clones have neurotrophin dependent tri-lineage potential.

Application of the Taguchi method to chip scale package (CSP) design

A three-dimensional (3-D) nonlinear finite element model of an overmolded chip scale package (CSP) on flex-tape carrier has been developed by using ANSYS/sup TM/ finite element simulation code. The model has been used to optimize the package for robust design and to determine design rules to keep package warpage within acceptable Joint Electron Device Engineering Council (JEDEC) limits. An L/sub 18/ Taguchi matrix has been developed to investigate the effect of die thickness and die size, mold compound material and thickness, flex-tape thickness, die attach epoxy and copper trace thicknesses, and solder bail collapsed stand-off height on the reliability of the package during temperature cycling. For package failures, simulations performed represent temperature cycling 125/spl deg/C to -40/spl deg/C. This condition is approximated by cooling the package which is mounted on a multilayer printed circuit board (PCB) from 125/spl deg/C to -40/spl deg/C. For solder ball coplanarity analysis, simulations have been performed without the PCB and the lowest temperature of the cycle is changed to 25/spl deg/C. Predicted results indicate that for an optimum design, that is low stress in the package and low package warpage, the package should have smaller die with thicker overmold. In addition to the optimization analysis, plastic strain distribution on each solder ball has been determined to predict the location of solder ball with the highest strain level. The results indicate that the highest strain levels are attained in solder balls located at the edge of the die. The strain levels could then be used to predict the fatigue life of individual solder balls.

Charged Molten Metal Droplet Deposition as a Direct Write Technology

ABSTRACTThe formation of highly uniform charged molten metal droplets from capillary stream breakup has recently attracted significant industrial and academic interest for applications requiring high-speed and high-precision deposition of molten metal droplets such as direct write technologies. Exploitation of the high droplet production rates intrinsic to the phenomenon of capillary stream break-up and the unparalleled uniformity of droplet sizes and speeds attained with proper applied forcing to the capillary stream make many new applications related to the manufacture of electronic packages, circuit board printing and rapid prototyping of structural components feasible. Recent research results have increased the stream stability with novel acoustic excitation methods and enable ultra-precise charged droplet deflection. Unlike other modes of droplet generation such as Drop-on-Demand, droplets can be generated at rates typically on the order of 10,000 to 20,000 droplets per second (depending on droplet diameter and stream speed) and can be electrostatically charged and deflected onto a substrate with a measured accuracy of ±12.5 µm. Droplets are charged on a drop-to-drop basis, enabling the direct writing of fine details at high speed. New results are presented in which fine detailed patterns are “printed” with individual molten metal solder balls, and issues relevant to the attainment of high quality printed artifacts are investigated.

ボールミルシミュレーションによるメカニカルアロイング過程の解析とミリングシステムの設計

Theoretical analysis of mechanical alloying process conducted by ball mills is indispensa during mechanical alloying should be investigated. In this paper, some results of the author's computer-based motion simulation of individual balls during ball milling of metal powders were presented. One of the results was helpful to understand the metal powder coating behavior during mechanical alloying by a tumbling ball mill.

Comparing three DEM charge motion models

In comminution research, recent trends have been made to describe internal dynamics of mills using the discrete element method (DEM). In this work, three modelling approaches to DEM implementation to charge motion modelling are compared these being single ball trajectories, system of individual balls describing the mill charge and charge balls grouped together using an arbitrary discretization scheme. After presenting some charge motion fundamentals as well as a presentation of the three approaches to DEM implementation, charge profile results are presented for a 12 m mill. Further power predictions for a number of ball mills are presented along with a brief internal charge dynamics comparison. A discussion focuses on the needed future research to improving these approaches.

The role of olive oil in the preservation of yogurt cheese (labneh anbaris)

Small ‘balls’ of yogurt cheese (40 g 100 g‐1 total solids), derived by extracting moisture from concentrated yogurt (23% total solids), can be stored in retail outlets in the Middle East (20–25°C) under virgin olive oil for up to two years. The absence of over‐acidification appears to be due to the inhibitory effect of low pH (3.8), low available water (0.85) and salt (1.0 g 100 g‐1) on starter activity, while the anaerobic conditions created by the oil both reinforce these inhibitory factors and, additionally, prevent the growth of yeasts over the surface of the individual balls. The type of vegetable oil covering the balls was found to be unimportant, and sunflower, safflower and cottonseed oil were equally effective in preserving yogurt cheese inoculated with Kluyveromyces marxianus subsp marxianus and stored for three months at 25°C.

回転ボールミル内のボールの運動の３次元モデルシミュレーション

Mechanical alloying process, especially conducted by ball milling of metal powders, shows poor reproducibility, since we have few indices adequate for the mathematical description of the process. Energy consumption by the plastic deformation of metal powder particles in the mechanical alloying process can be a good index for the mathematical description. However, it is much difficult to measure the energy consumption only by the plastic deformation of metal powder particles. In this study, the authors tried to trace the motion of individual milling balls in a tumbling ball mill during ball milling of a metal powder, by using a three-dimensional model simulation based on discrete element method. From the motion of individual balls calculated by the simulation, frequency of collision event as well as distribution of impact velocity were estimated as a function of ball filling ratio, J. As a result, the motion of balls and therefore the distribution of impact velocity were affected signifficantly by the ball filling ratio. Especially, the frequency of collision event having higher impact velocities shows an maximum at J=0.5. This means that the plastic deformation of the metal particles is most promoted at J=0.5 if the plastic deformation requires higher impact velocity.

A model of fullerene conductance

An attempt has been made to describe fullerene conductance on the basis of the additive conductance Dresselhaus-Dresselhaus model for graphite, taking into account the topology of a fullerene molecule in the crystal lattice. It has been shown that fullerene conductance is related to the σ c component of the conductance of graphite through the relation σ full ≈ 10 −2 σ c graph , because only 1 out of 60 atoms in a fullerene molecule is involved in creating a path of conductance between electrodes and the ratio of fullerene to graphite density is ρ full / ρ graph = 0.74. Total resistivity of fullerene is determined by resistivites of individual fullerene balls. Doping, like in graphite, causes an increase in the conductivity of intercalated Me x C 60 for low value of x.

Spindle deflections in high-speed machine tools ? Modelling and simulation

This research attempts to develop spindle deflection error models for high-speed machining systems. A model for determining total spindle deflection at the tool-end is presented. The model incorporates spindle bearing characteristics, shifts in ball contact angles, and centrifugal force and gyroscopic moment effects at high speeds. It uses the transfer matrix method to determine the total deflections at the tool-end based upon the point contact deformations at the individual balls of an angular contact ball-bearing assembly. A simulator is also developed for simulating spindle end deflections for various spindle rotational speeds. The results of the simulation show contact angle variations and peak deflections at particular spindle rotational speeds. Important research issues are also presented.

Simulation of charge motion in ball mills. Part 1: experimental verifications

A numerical tool known as the discrete element method (DEM) is used to study the motion of the ball charge in ball mills. In particular, the motion of individual balls in the ball charge is simulated. An interesting aspect of this simulation is that it yields the frequency distribution of ball collisions as a function of collision energy. The results of numerical simulations are compared with experiments: The angular positions of the toe and shoulder, the trajectory of two balls, and the power draft — all of these predictions are reasonably close to experimental measurements. An interesting sidelight of this study is that the collision frequency can be combined with the breakage property of particles to carry out direct simulation of particle fragmentation in ball mills. The rudiments of such a simulation are illustrated.

Evaluation of a method to assess plasma viscosity: The falling ball viscometer

Several methods are presently used to evaluate plasma viscosity and its variation. The falling ball viscometer, in spite of its cheap running cost, has been only used by a limited number of laboratories. We wish in this article to give our own appraisal of the technique. We studied the influence of the individual glass syringes and stainless steel balls, as well as the temperature dependence on plasma viscosity value. Freezing plasma samples did not appear to affect the value of plasma viscosity, as well as the mode and frequency of thawing, since the variations (0.01 mPa.s or less) were equivalent to the reliance of the technique (0.01 mPa.s, 1 %). A reference range for healthy controls was determined. We could not detect any significant difference between men and women for plasma viscosity values. In spite of the fibrinogen increase with aging or smoking, we could not observe any significant variation for plasma viscosity values in healthy controls. However, in a large range of fibrinogen values, a good correlation was found between plasma viscosity and fibrinogen concentration (r2 = 0.460; p = 0.0001). In 9 patients with IgG myeloma, a significant correlation between serum viscosity and IgG concentration was obtained (r2 0.797; P 0.001). Concomittant measurements of plasma viscosity with a

Jahn-Teller distortions in solid C 20 and other fullerene structures

We have used first principles molecular dynamics to determine the energies of Jahn-Teller distortions in a variety of neutral and negatively charged fullerene structures. We find that smaller structures have larger Jahn-Teller distortion energies. Solid C 28 and solid C 20, which have covalent bonds connecting the individual fullerene balls, are found to have energies which are much lower than the energies of their molecular components. The charged state of solid C 20 is found to have a total distortion energy which is about six times larger than that of C − 60.

Numerical simulation of charge motion in ball mills — Lifter bar effect

This paper focuses on the use of a numerical tool known as the discrete element method (DEM) to study the motion of ball charge in ball mills. DEM is employed to simulate the motion of individual balls. While doing so, the effect of liner design on the grinding performance of the mill is studied. Two important factors, such as the configuration of the liner and the geometry of the lifting surfaces, are correlated with the overall mill performance. An attempt is made to show the effectiveness of the lifter bars in transmitting power from the mill, shell to the interior of the mill with particular emphasis on large diameter mills.

Numerical Simulation of Ball Motion in a Tumbling Ball Mill.

The two dimensional motion of the individual balls in a tumbling ball mill was analyzed numerically by a Distinct Element Method using the extended Kelvin model composed of nonlinear spring and nonlinear dashpot. A parameter related to the coefficient of viscosity is determined from the data of imperfect restitution between ball and mill shell. The simulation of the dynamic motion of the individual balls is based on the nonlinear perfect elasticity, nonlinear viscosity and Newton's law of motion. The dynamic motion of balls during milling calculated was compared with the actual three dimensional motion of balls observed in a mill. The effects of ball charge fraction and mill speed on the impact velocity of balls estimated were also discussed.It can be concluded that the model simulation developed in the present study predicts approximately the actual motion of the balls in a tumbling mill. The motion reproduced from the simulation is strongly influenced by the ball charge fraction and mill speed. The impact frequency of the individual balls and their impact velocities at individual collisions can be estimated by the simulation technique proposed.

Image analysis methods for solderball inspection in integrated circuit manufacturing

Machine vision methods are presented for the analysis of solder balls in integrated circuits. The algorithms are founded on counter fitting using a multiparameter Hough transform and on polynomial-classifier-based pattern recognition. The first method is used to show the complexity of the inspection problem, especially in the presence of high-precision requirements. In this connection, it is shown that subpixel accuracy is not obtainable even under the assumption of a perfect camera system which determines the resolution necessary for the measurement of a given maximum-volume distortion. The second method is carried out by computing a large number of features on the original image after individual solder balls are segmented by a projection technique. This approach can be considered as a control-free image segmentation paradigm, since it does not rely on properly sequencing several image-analysis modules. Further experimentation with a large pool of defective solder balls is necessary to confirm the applicability of these machine vision algorithms to a real-world manufacturing inspection systems. A general image-segmentation architecture is proposed, which enables the computation of the necessary low-level image features as well as pixel classification at video-rate speed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>