Bump Shape Research Articles

Indium Bump Bonding: Advanced Integration Techniques for Low-Temperature Detectors and Readout

We have examined the influence of bump shape and bonding pressure on low-temperature electrical properties of indium bump connections including superconducting transition temperature, normal state resistance, and superconducting critical current. We describe our test structures, bonding process, and methods of characterization. At temperatures below 1 K, we observe critical currents greater than 70 mA for indium bump connections with a nominal bump size of 17 µm × 17 µm.

Drag Reduction Analysis of Optimal Three-dimensional Bumps on the M6 Wing

Based on Isight optimization software and evolutionary strategy algorithm, this paper builds a bump optimization design platform by integrating the three-dimensional bump shape generator program, grid generation software Gridgen and flow field simulation software Fluent. This platform is successfully validated on the RAE2822 supercritical infinite straight wing, which reduces the drag coefficient by 11 counts and increases the lift-drag ratio by 11.48 percent. Through this platform, the drag reduction characteristics of optimal three-dimensional bumps on the M6 wing are numerical studied. The results show that the three-dimensional bumps can weaken shock waves and have spanwise characteristics, the stronger the shock waves, the more obvious the drag reduction effect of the three-dimensional bumps, and the wing with optimal three-dimensional bumps can improve flow field characteristics and prevent flow separations.

Inferring the presence of very massive stars in local star-forming regions

Context. Very massive stars (VMS) have masses in excess of 100 M⊙ and are rare. However, owing to their powerful winds, very high luminosity, and efficient nucleosynthesis, they are key players of star-forming regions. In particular, their strong ionizing fluxes impact the surrounding interstellar medium. Aims. We aim at detecting VMS in local star-forming region from the imprint they leave on the integrated UV and optical light. Methods. We analyzed a sample of 27 star-forming regions and galaxies in the local Universe. We selected sources with a metallicity close to 12+log(O/H) = 8.3, which is typical of the Large Magellanic Cloud. We defined empirical criteria to distinguish sources dominated by VMS and Wolf-Rayet stars (WR), using template spectra of VMS- and WR-dominated regions. We subsequently built population synthesis models with an updated treatment of VMS. We investigated the successes and failures of these new models in accounting for the UV-optical spectroscopy of our sample sources. Results. We show that the UV range alone is not sufficient to distinguish between VMS- and WR-dominated sources because their spectra are almost identical in this range. The region of the WR bumps in the optical breaks the degeneracy. In particular, the morphology of the blue bump at 4640–4686 Å is a key diagnostic. Beyond the prototypical R136 region, which contains VMS, we identify two galaxies showing clear signatures of VMS. In two other galaxies or regions the presence of VMS can be suspected, as already discussed in the literature. The stellar population is clearly dominated by WR stars in seven other sources. The most recent BPASS population synthesis models can neither account for the strong He II 1640 emission, nor for the shape of the blue bump in VMS- and WR-dominated sources. Our models that include VMS more realistically reproduce the UV-optical spectra of VMS-dominated sources. Conclusions. We conclude that VMS are present in some local star-forming regions, but that separating them from WR-dominated populations requires optical spectroscopy with a high signal-to-noise ratio. A high equivalent width of He II 1640 is not a sufficient condition for identifying VMS. Populations synthesis models need to take VMS into account by incorporating not only evolutionary tracks, but also dedicated spectral libraries. Finally, we stress that the treatment of WR stars needs to be improved as well.

A simple way to predict the flip–chip gap

Using laser scanning confocal microscopy measurement, a concise method for extracting the indium bump shape in microelectronics was first established. The extracted bump shape was then used as the input for finite element analysis. The modeled one-bump deformation was used to predict the final flip–chip gap after bonding. Dovetailed with the results of cross-sectional scanning electron microscopy, this simple and non-destructive method for predicting a flip–chip gap of the order of 10 microns or less was eventually validated.

Manipulation of bumpy surface cylinders for flow control and heat transfer improvement

The present work aims at investigating laminar flow effects over bumped-surface circular cylinders at Reynolds number ≤ 200. Three bumpy cylinder surfaces are considered and studied, comprising square, triangular, and dimple surface shapes. The bumpy surfaces are placed on the upper surface of the cylinder and arranged between 0° and 90° from the front stagnation point of the cylinder. These angles include θ = 0○, 45○, and 90○. The flow characteristics, such as the lift and drag coefficients, as well as the Strouhal and Nusselt numbers, are evaluated. For all three examined bump shapes, it is demonstrated that when θ ≤ 45°, the amplitude of the drag coefficient is smaller than larger angles. It is also found that at θ = 90°, the magnitude of the drag coefficient is about 40% larger than test cases with θ ≤ 45°. It is found that the Nusselt number is dependent on the location of the bump on the leading surface of the cylinder. The critical angle of the bump's location is identified and introduced, which is θcm = 45°. While the minimum Nusselt number is obtained once the bump is located at θcm = 45°, the maximum Nusselt number is assessed at θ = 90° with approximately a 12% increment.

Part of anti-covid therapy based on a theoretical model describing mechanics of contact interaction between coronavirus and cell membrane

This article proposes a theoretical model of mechanical feedback in pattern formation on deforming a membrane when coronavirus enters a cell. Coronavirus stiff and flexible spike proteins attach to ACE2 receptors on the cell membrane of the target cell. TMPRSS2 triggers the fusion of the viral and cell membranes with the formation of a fusion pore leading to opening of a capsid surrounded by the coronavirus envelope and viral RNA release into the cell. Based on mechanical feedback analysis of contact interaction and elastic shell theory, a critical value of cell radius, at which a fusion pore is formed and membrane damage occurs locally, is determined. The results revealed that the smaller the cell size, the less likely that the cell will be damaged mechanically when exposed to the virus. One of the ways to reduce the cell size is to decrease intracellular fluid volume through the use of medicines - diuretics. The critical value of cell radius is inversely proportional to the value of binding energy at the time of attachment of the coronavirus to the cell membrane. Further research is required to improve our knowledge of the dependency of binding energy on the shape and sizes of spikelike bumps for various types of coronavirus strains. It may be predicted that when a new coronavirus strain will emerge, it may produce lower binding energy to cell surface and the severity of the disease may decrease. It is necessary to verify the conclusions of the theoretical study by experimental methods.

Impact of TSV bump and redistribution layer on crosstalk delay and power loss

The performance of a 3D IC is primarily reliant on the selection of an appropriate bump shape. The most prevalent bump shape (cylindrical) is experiencing substantial stress, power loss and crosstalk issues. TSV bump with a tapered structure have recently attracted considerable attention owing to its low volume fraction and coupling capacitance, that can substantially reduce the stress and crosstalk concerns. An impact of the redistribution layer (RDL), intermetal dielectric and high frequency skin effect are appropriately taken into account for the tapered TSV (T-TSV) with a cylindrical, barrel and tapered bump shape. A mathematical framework of the resistance–inductance–conductance–capacitance (RLGC) structure of the proposed T-TSV have been formulated by effectively considering the coupling, passivation and fringing capacitance of the RDL. In order to benchmark the proposed electrical equivalent circuit, the structural model of the T-TSV is validated against the fabrication based experimental results, and a subsequent analysis have been performed for the stress, crosstalk induced delay, and power loss. The proposed TSV structure is in good agreement with the experimental results with an average deviation of only 2.8%. Furthermore, irrespective of bump height, the tapered bump based T-TSV can effectively reduce the overall crosstalk induced delay, stress, power delay product (PDP), insertion and reflection losses with an average deviation of 20.22%, 22.30%, 23.55%, 8.01%, and 10.32%, respectively, when compared to the barrel and cylindrical bumps. In addition, it has been observed that the overall rate of change in PDP, power losses and crosstalk induced delay with considering RDL are 18.8%, 20.50%, and 25.22%, respectively independent of the bump shapes.

On Optimal Control of a Multichamber Air Spring and Experimental Validation over Speed Bumps

This paper deals with a preview-based optimal control of a multichamber suspension over speed bumps. A multichamber suspension is an innovative type of road vehicle suspension whose spring is composed of multiple auxiliary air reservoirs connected to a main pneumatic chamber. A set of controllable valves regulate the airflow among the different chambers, allowing the modulation of the spring equivalent stiffness. Multichamber suspensions are the only existing architecture in the market capable of vertical stiffness regulation. The first goal of this paper is to find an optimal valve position sequence which minimizes the vertical acceleration over some known speed bump profiles, under the hypothesis of perfect road preview. This optimization is carried out in simulation considering a control-oriented model of the multichamber suspension. A sensitivity study is then performed considering different bump shapes and vehicle speeds. The second goal of this work is to apply and validate the control sequence on a real vehicle equipped with commercial multichamber suspensions. Experimental results successfully reported improvements in corner vertical acceleration up to 16% and chassis pitch rate up to 12% compared to the passive benchmark.

Effect of the reflow process on IMC growth for different devices and complex components

Intermetallic compound (IMC), as an inevitable part between pad and solder, has a severe effect on the strength and reliability of microelectronic interconnection. Here, an investigation was carried out on IMC growth for different devices and complex components. The device-level experiments were conducted with five factors: peak temperature, time duration above solder liquidus temperature, the thickness of solder paste, surface finish types, and package types including ball grid array (BGA) and quad flat package (QFP). Meanwhile, four complex components with the same reflow profile were conducted and compared for component-level experiments. A scanning electron microscopy (SEM) was used to measure the thickness and determine the spatial distribution of the elements through the IMC. The multivariate analysis of the formation and growth of IMC during reflow soldering was studied based on Nernst–Shchukarev’s equation and the results of the experiments. The difference in IMC thickness between BGA and QFP with different factors was discussed and compared separately. The results showed that the peak temperature and time above liquidus played a vital role in the IMC growth and the solder paste thickness and different pad metallization could not be ignored. SEM pictures of the solder and statistical results were revealed that the surface finish type has a marked impact on the formation of the IMC. For printed circuit board (PCB) with numbers of components, the IMC thickness and uniformity of solder joints at corner and center positions showed some regularity differences. Meanwhile, the bump shape (Cu1−x Ni x )6Sn5 IMC was observed for small size BGA with electroless nickel and immersion gold during the reflow process. The results have a significant meaning to optimize its reflow process parameters for complex components, to improve the interconnection reliability in engineering.

A study of micro-scale solder bump geometric shapes using minimizing energy approach for different solder materials

Demand for more interconnection joints between semiconductor devices can be realized with solder bump technology. Surface tension and density are usually material properties related factors that affect solder bump geometric shape. Therefore, to cope with this fast-changing microarchitecture design in semiconductor technology, a better understanding of the solder bump geometric shape is needed. This study used a static equilibrium force approach to integrate the surface tension and gravitational energy into the solder energy content. Surface Evolver software was used to perform calculations and deliver the final solder bump shape. Perfect agreement with less than 10 % comparison between previous studies and the current Surface Evolver results was found. According to statistical analysis using SPSS, the maximum width of solder shape is closely related to the surface tension. In contrast, the maximum standoff is highly correlated with the solder density. By changing the solder volume, the solder bump changes from standard flip-chip bump to Cu pillar bump with consistency in maximum width to maximum standoff height ratio of 1.5. This study shows that the bumping technology can produce various sizes of solder bumps to meet new electronic packaging requirements.

Finite element analysis of a modified weigh-in-motion sensor

The weigh-in-motion (WIM) sensors can measure the weight on each wheel, on the axle and thus can then determine the weight of the entire vehicle. These sensors are also used for traffic monitoring, both in volume (number of vehicles) and structure (classification by vehicle type). This paper presents the finite element analysis (FEA) of a sensor for urban traffic, which is carried out at medium speeds (around 50km / h). The sensor has the shape and dimensions of a speed bump and is mounted on the road in the same way. With FEA, the state of stress, strain and displacement in the elastic element of the sensor were determined, as well as the contact pressures between the tire and the sensor. For FEA different types of vehicles (a car and a truck) were considered which cross the sensor in the central area or in the side areas.

Chipping Energy Threshold in MEMS Sensors

This research faces the problem of identifying the impact energy for which silicon chips are generated after shocks in microdevices, with the aim of providing design guidelines for next generation robust inertial sensors. The issue is tackled through the design of an on-chip test structure capable of generating up to 100 nJ of impact energy onto a stopping bump, corresponding to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> gravity units of acceleration for a wide range of state-of-the art gyroscopes and accelerometers. The additional challenge of identifying the presence of debris without the need to uncap the dice is faced through the design of interdigitated electrodes underneath the impact area, and the measurement of small leakage currents caused by debris-induced short circuits between them. Statistical tests performed on 27 samples of different bump shape not only enable to identify an energy threshold for debris generation at about 10 nJ, valid at least for the considered process, but also suggest how the bump shape significantly influences this phenomenon. [2021-0257]

Passive control of 3D adaptive shock control bumps using a sealed cavity

This paper presents a Fluid–Structure-Interaction study of a novel passive adaptive shock control bump concept. A flexible plate, clamped on all sides and placed above a sealed cavity, was tested beneath a Mach 1.4 normal shock in the Imperial College London supersonic wind tunnel. The plate was actuated into the shape of a 3D shock control bump by passively controlling the cavity pressure through an array of breather holes. Preliminary experiments were performed with active control of cavity pressure (via a vacuum tank) at Mach 1.4 and 2 to illustrate the potential of this concept. Full-field surface measurement techniques, namely photogrammetry and pressure sensitive paint, were employed in addition to static pressure tappings and schlieren photography. Results confirmed that cavity pressure plays a key role in determining the aerostructural behaviour of the flexible plate. In addition, it was found that carefully placed breather holes allowed the plate to deform into a 3D shock control bump when a shock was on the flexible region and remain flat otherwise. This shows significant potential for improving the off-design behaviour of adaptive shock control bumps.

Physical model for the broadband energy spectrum of X-ray illuminated accretion discs: Fitting the spectral energy distribution of NGC 5548

Aims. We develop a new physical model for the broadband spectral energy distribution (SED) of X-ray illuminated accretion discs that takes into account the mutual interaction of the accretion disc and the X-ray corona, including all the relativistic effects induced by the strong gravity of the central black hole (BH) on light propagation and on the transformation of the photon energy, from the disc to or from the corona rest-frames, and to the observer. Methods. We assumed a Keplerian optically thick and geometrically thin accretion disc and an X-ray source in the lamp-post geometry. The X-ray corona emits an isotropic, power-law-like X-ray spectrum, with a high-energy cut-off. We also assumed that all the energy that would be released by thermal radiation in the standard disc model in its innermost part is transported to the corona, effectively cooling the disc in this region. In addition, we include the disc heating due to thermalisation of the absorbed part of the disc illumination by the X-ray source. X-ray reflection due to the disc illumination is also included. The X-ray luminosity is given by the energy extracted from the accretion disc (or an external source) and the energy brought by the scattered photons themselves, thus energy balance is preserved. We computed the low-energy X-ray cut-off through an iterative process, taking full account of the interplay between the X-ray illumination of the disc and the resulting accretion disc spectrum that enters the corona. We also computed the corona radius, taking the conservation of the photon number during Comptonisation into account. Results. We discuss in detail the model SEDs and their dependence on the parameters of the system. We show that the disc-corona interaction has profound effects on the resultant SED, it constrains the X-ray luminosity and changes the shape and normalisation of the UV blue bump. We also compare the model SEDs with those predicted from similar models currently available. We use the new code to fit the broadband SED of NGC 5548, which is a typical Seyfert 1 galaxy. When combined with the results from previous model fits to the optical and UV time-lags of the same source, we infer a high black-hole spin, an intermediate system inclination, and an accretion rate below 10% of Eddington. The X-ray luminosity in this source could be supported by 45–70% of the accretion energy dissipated in the disc. The new model, named KYNSED, is publicly available to be used for fitting AGN SEDs inside the XSPEC spectral analysis tool. Conclusions. X-ray illumination of the accretion disc in AGN can explain both the observed UV and optical time-lags and the broadband SED of at least one AGN, namely NGC 5548. A simultaneous study of the optical, UV, and X-ray spectral and timing properties of these AGN with multiwavelength, long monitoring observations in the past few years will allow us to investigate the X-ray and disc geometry in these systems, and to constrain their physical parameters.

요철판을 이용한 새우 선별 방법 연구

Shrimp sorting from the catch requires a lot of time and efforts. So, this study proposes an automatic shrimp sorting method using a bumpy plate and investigates the performance by the shape and spacing of the bump and the contact angle. 2 species (Palaemon gravieri, Metapenaeopsis dalei) of shrimp and 3 species of fish were used in the experiment. As a result, the average sorting rate by the bump shape was high in the order of cutter blade hook sharp cutter blade, that by the bump spacing decreased as the spacing increased and that by the contact angle decreased as the angle increased. The highest sorting rate was 61.7% in the cutter blade type/5 mm/20°, which was very low. So, the sorting rate for the case where the fish contained only P. gravieri and that only M. dalei were calculated, respectively. As a result, the highest sorting rate of P. gravieri group showed 91.7% in the cutter blade type/5 mm/20°, and that of M. dalei group showed 46.7% in the cutter blade type/3 mm/30°. Therefore, it was determined that the method of sorting shrimp using bumpy plate was effective in sorting P. gravieri, but not in M. dalei.

Metrology for Measuring Bumps in a Protection Layer Based on Phase Shifting Fringe Projection

We developed a telecentric 3D measurement system based on the fringe projection technique to measure phases corresponding to the 3D shape of bumps on a surface. A measurement algorithm based on an area scan camera with a flexibly programmable region of interest (ROI) was applied to reconstruct the 3D model. Only the pixel information within the ROI is stored, which reduces the data volume and processing and accelerates the area scan acquisition. Experiments showed that the fringe projection system provided good linearity between the calibration and optical data with excellent accuracy. A reflectometry sensor was implemented to provide a correction offset to the bump height in a protection layer in a subsequent high-speed inspection.

Concave Bump for Impinging-Shock Control in Supersonic Flows

In the present study, a novel concave bump for impinging-shock control in two-dimensional supersonic flows is investigated. An analytical method for preliminary bump design based on a generalized shape of a shock-canceling bump has been developed and verified numerically. An extensive proof-of-concept study was performed at a freestream Mach number ranging from 2.5 to 5.0 for shock-generator angles varying from 6 to 12 degrees. It could be demonstrated that a concave bump designed for a given flow-deflection angle is capable of significantly reducing the size of the separation bubble as well as the total pressure losses throughout the Mach number range investigated. The achievable gains depend on the Mach number, the flow-deflection angle, and the relative impingement position of the incident shock front on the bump. The highest values of separation-length reduction (up to 100%), momentum thickness reduction (up to 31%), and pressure recovery factor increase (up to 33%) were obtained at the optimum shock impingement position for the largest deflection angle studied. The concave bump is less effective, and in some cases even disadvantageous, when the incident shock wave does not optimally strike the bump crest.

High-Fidelity Simulation of Turbulent Flow Past Gaussian Bump

A spanwise-periodic computation of a turbulent flow past a Gaussian bump is performed in the form of a hybrid direct numerical simulation and wall-resolved large-eddy simulation. A fourth-order spatially accurate flow solver is employed to perform the simulation, using 10.2 billion grid points for a Reynolds number of 170,000 based on the bump height. The key findings from the simulation are reported in the acceleration and deceleration flow regions associated with the bump shape. Significant anisotropy in the normal Reynolds stresses, along both the wall-normal and streamwise directions, is observed within the acceleration region. The ratio between the Reynolds shear stress and turbulent kinetic energy in that region also experiences significant deviations from the norms of a zero pressure gradient turbulent boundary layer. The chosen Reynolds number generates strong flow separation in the adverse pressure gradient region, which is in contrast with a previous simulation at half the Reynolds number that only indicated incipient separation. An internal layer generated in the acceleration region evolves into a free shear layer that develops in the deceleration region and separates. Proper modeling of this inner layer appears crucial to predict the flow separation. Surface curvature effects on the attached flow development are also discussed.

A Surface Energy Approach to Developing an Analytical Model for the Underfill Flow Process in Flip-Chip Packaging

Abstract This paper presents a new approach to formulating an analytical model for the underfill process in flip-chip packaging to predict the flow front and the filling time. The new approach is based on the concept of surface energy along with the energy conservation principle. This approach avoids the need of modeling the flow path to predict the flow front and the filling time, and thus it is suitable to different configurations of solder bumps, including different shapes and arrangements of solder bumps in flip-chip packaging. An experiment along with the computational fluid dynamics simulation was performed based on a proprietarily developed testbed to verify the effectiveness of this approach. Both the experimental and simulation results show that the proposed approach along with its model is accurate for flip-chip packages with different configurations besides the configuration of a regular triangle arrangement of solder bumps and a spherical shape of the solder bump.

Numerical simulation of the solidification phenomena of single molten droplets impinging on non-isothermal flat plate using explicit moving particle simulation method

In jet engines and gas turbines, the deposition phenomenon is attributed to the adhesion of molten droplets on walls. In this study, numerical simulations of the deposition phenomena on a substrate were performed using the explicit moving particle simulation (E-MPS) method. We adopted a non-isothermal condition for the substrate using a coupling method including wall particles and a regular grid to estimate the heat conduction to and within the substrate for enhanced numerical accuracy. This coupling method was validated by comparing the theoretical values of the one-dimensional unsteady heat conduction. Simulations were performed to study the solidification phenomena of a single molten stannum (Sn) droplet impinging and solidifying on a vertical substrate. The droplet behavior from impingement to solidification shows reasonable agreement with experimental results in terms of spread factor, taking into account the heat exchange between the droplet and substrate, including the substrate temperature change. Although temperature change in the substrate is limited to areas near the impinging droplet, temperature distributions on the interface differ between the early and later stages. The high-temperature region appears near the impinging center except near the stagnation point for the former stage, while it is near the center for the latter stage. The finger and bump shapes around the impinging droplet are explained via Rayleigh–Taylor and Plateau–Rayleigh instabilities, respectively, using the actual expanding acceleration of the liquid film.