Bump Side Research Articles

Interpretation of topography and bed properties beneath Thwaites Glacier, West Antarctica using seismic reflection methods

Thwaites Glacier (TG), West Antarctica, is losing mass in response to oceanic forcing. Future evolution could lead to deglaciation of the marine basins of the West Antarctic Ice Sheet, depending on ongoing and future climate forcings, but also on basal topography/bathymetry, basal properties, and physical processes operating within the grounding zone. Hence, it is important to know the distribution of bed types of TG's interior and grounding zone, and to incorporate them accurately in models in order to improve estimates of retreat rates and stability. Here we estimate properties of the bed by determining its acoustic impedance from amplitude analysis of reflection seismic data. We report on the results from two lines – a longitudinal (L-Line) and a transverse (N-Line) – on a central flowline of TG ∼100 km inland from the grounding zone. The data show considerable spatial variability in bed forms and properties, similar to results from a comparable survey farther inland. Notably, we find the same pattern here of hard (presumed bedrock) material on the stoss side of bumps and soft (presumed till) on the lee side. Physical understanding indicates the basal flow law describing motion over different regions of TG's bed likely varies from nearly-viscous over the bedrock regions to nearly-plastic over till regions, providing guidance for modeling.

Underfill Flow Void Solutions Through Process and Materials Interaction

Silicon dies were thinned down and bump pitch became smaller to have a lot of input/output in electronic device packages especially in package on package configuration. This presents challenges on underfill (UF) dispense processing. UF voids occurred near the dispense side of bumps in multiple dispense pass technology. In this paper, we will review UF flow behavior on thin die technology, as well as the process and material interaction that cause UF void formation. Process optimization, such as the time between two dispense passes has become a critical parameter to eliminate UF voids without causing UF epoxy roll up that can cause reliability failure.

Modeling the effects of bed topography on fluvial bedrock erosion by saltating bed load

Abrasion by saltation is an important mechanism of fluvial incision into bedrock. Sklar and Dietrich (2004) introduced an abrasion model in which the erosion rate of an “approximately planar” bed is linearly dependent on the kinetic energy transferred by the vertical velocity of saltating grains. However, most bedrock-floored channels exhibit topographic variations that yield deviations from a planar surface, referred to as “bed topography.” Observations show that bed topography affects erosion. Here the saltation-abrasion model is extended for a nonplanar bed. A several-centimeter high bump, transverse to the flow, is repeated every 50 cm. The kinetic energy of grain impacts is calculated in two ways: (1) impact velocity normal to bed topography and (2) vertical impact velocity. By comparing the latter case with the planar model, it is possible to isolate the effects of topography on the interception of saltation trajectories. Incorporating bed topography changes erosion in three ways. First, erosion is 10 to 1000 times faster, depending upon transport stage and grain size. Enhanced erosion results from both the interception of grains by topography and the increased kinetic energy transfer associated with high-angle impacts on the stoss side of bumps. Second, erosion increases monotonically with transport stage, whereas maximum erosion occurs at low to intermediate transport stage with a planar bed. Third, erosion decreases monotonically with grain size, whereas maximum erosion occurs with intermediate-sized grains with a planar bed. Although the model is highly simplified, results show that bed topography should be considered when simulating erosion of bedrock.

Study of Factors Which Influenced to Bump Shape and Voids in Bumps during Bump Formation with Solder Paste

Regarding to inner bump formation using solder paste for FC-BGA and FC-CSP, the voids and abnormal bump shape generation are undesirable problems to achieve high quality assembly. The solder pastes which contain small solder particle and flux are applied to wafer bumping and substrate bumping method. However, as the bump pitch becomes tighter, the influence of those problems gets more serious especially for yield issue. In this study, we tried to solve the following issues 1)voids generation using 99.3mass%Sn-0.7mass% Cu solder paste and other alloys, 2)the dint bumps generation on the top of bumps using 95mass%Pb-5mass%Sn paste and 3)the needle and plate like intermetallic compound generation on the top and side of bumps using 96.5mass%Sn-3mass%Ag-0.5mass%Cu paste and 95.5mass%Sn-4mass%Ag-0.5mass%Cu paste. In terms of 1), it was available to understand when and where voids were generated by in-situ soft x-ray observation, and we could construct our original consideration why voids were generated during bumping process. In terms of 2) and 3), it was found that some kind of impurities affected on the dint, needle and plate like IMC generation. Furthermore, we tried to understand from the influence of reflow profile. By understanding these defects, we believe we can bring benefits to operating solder paste for printing method.

Electro-migration Behavior in Micro-joints of Sn-57Bi solder and Cu Post Bumps

The bonding technique for high density Flip Chip(F.C.) packages requires a low temperature and a low stress process to achieve high reliability of the micro joining. Sn-Bi solder has been noted as a low temperature bonding material. Electromigration behavior of Sn-57wt%Bi flip chip interconnection with Cu post bumps was investigated. The flip chip bumps used for this experiments consisted of Cu post formed with plating and Sn-57wt%Bi solder. Two types of under bump metal(UBM) of organic substrate were studied, that is, electroless Ni(6μm)/Au(0.5μm) on Cu pad and Cu pad. Electron flow to induce the electro-migration was from organic substrate side (Cu pad) to chip side (Cu post) with current density of 40000A/cm2 at 125 degree C. At both types of the UBM, Bi migrated and accumulated to the anode side (Cu post) and Sn migrated to the cathode side (substrate pad). Each interconnect resistance has increased to about 25% and 46% within 100 hours, respectively. However, after more than 3000 hours, they were stabilized. With Ni/Au UBM pad, Cu3Sn/Cu6Sn5 intermetallic compounds (IMCs) were formed at the Cu bump side. And under the Bi layer Cu6Sn5/Ni-Sn compounds were formed. But we didn’t observe the failure like cracks or voids at the Ni layer. With Cu pad, only Cu3Sn IMC at the Cu bump side and under the Bi layer Cu6Sn5/Cu3Sn compounds were formed after 4000 hours. Although the voids were observed at Cu3Sn/Cu interface, good electrical connection was obtained.

Four-Wheel Independent Steering (4WIS) System for Vehicle Handling Improvement by Active Rear Toe Control.

This paper presents the enhancement of vehicle cornering stability through active and independent rear toe control. Because toe change in the rear wheel during high-speed turning maneuvers is an important factor influencing vehicle stability, the active rear toe control vehicle such as four-wheel steering(4WS)vehicle has been developed in past years. Especially, a toe in the rear outer wheel(bump side)plays a dominant role in cornering, hence the four-wheel independent steering(4WIS)system which selectively or simultaneously controls the rear wheels, could be suggested. In the proposed system, there are some advantages not only in energy consumption, but also in control responsiveness. The independent rear steering strategy using rear toe control scheme has been developed and its performances were evaluated with the ADAMS full vehicle model. Also, 4WIS system is compared to the conventional four-wheel steering(4WS)system through the step input and the double lane change test. The simulation results of 4WIS system show the similar handling performance with those of the conventional 4WS system and the total consumed power to control the system in rear wheels was much reduced.

Modifications to the Theory of Intraglacial Waterways for the Case of Subglacial Ones

AbstractIt is argued that in temperate mountain glaciers, waterways are subglacial. It is shown that the theory of Spring and Hutter (1981) for intraglacial flooded conduits leads to an equation for the grade line which differs from Röthlisberger’s (1972) only by negligible terms, and a slight modification of the exponent of the discharge. For a subglacial flooded waterway two important processes should instead be introduced: the enhancement of plastic deformation on the up-stream side of bumps, and the heat afforded by ground water (which in winter accounts for most of the discharge). The theory modified in this way explains why Röthlisberger had to adopt an unrealistic value for the rheological parameter of ice. It leads to the conclusion that in areas which are not overdeepened, most of the year subglacial waterways should remain not flooded and at atmospheric pressure. The case of overdeepening is examined. Finally the implications of this new model for glacier sliding theory are demonstrated.

Modifications to the Theory of Intraglacial Waterways for the Case of Subglacial Ones

AbstractIt is argued that in temperate mountain glaciers, waterways are subglacial. It is shown that the theory of Spring and Hutter (1981) for intraglacial flooded conduits leads to an equation for the grade line which differs from Röthlisberger’s (1972) only by negligible terms, and a slight modification of the exponent of the discharge. For a subglacial flooded waterway two important processes should instead be introduced: the enhancement of plastic deformation on the up-stream side of bumps, and the heat afforded by ground water (which in winter accounts for most of the discharge). The theory modified in this way explains why Röthlisberger had to adopt an unrealistic value for the rheological parameter of ice. It leads to the conclusion that in areas which are not overdeepened, most of the year subglacial waterways should remain not flooded and at atmospheric pressure. The case of overdeepening is examined. Finally the implications of this new model for glacier sliding theory are demonstrated.

Simulated Glacier Sliding over an Obstacle

AbstractThe sliding of temperate ice over two obstacles with sine-wave profiles (wavelength, 0.53 m; maximum slope, 0.22) and low thermal conductivity has been reproduced at full scale within a steel chamber. As expected, large cavities form between the ice and the obstacles so that the drag is limited. However, the delayed elasticity of bubbly ice modifies the expected behaviour. At the base of the ice a fine-grained, bubble-free blue ice layer develops. The shear strain concentrates on the up-stream side of bumps and in the blue ice layer. Tap-water ions enhance tertiary creep-rates.

Simulated Glacier Sliding over an Obstacle

Abstract The sliding of temperate ice over two obstacles with sine-wave profiles (wavelength, 0.53 m; maximum slope, 0.22) and low thermal conductivity has been reproduced at full scale within a steel chamber. As expected, large cavities form between the ice and the obstacles so that the drag is limited. However, the delayed elasticity of bubbly ice modifies the expected behaviour. At the base of the ice a fine-grained, bubble-free blue ice layer develops. The shear strain concentrates on the up-stream side of bumps and in the blue ice layer. Tap-water ions enhance tertiary creep-rates.