Pad Geometry Research Articles

1521 接触片形状がフレッティング疲労強度に及ぼす影響 : ブリッジパッド脚高さの影響

In order to investigate the effect of contact pad geometry on the fretting fatigue strength, the fretting fatigue tests and interrupted fretting fatigue tests were carried out for Ni-Cr-Mo steel. In this paper, the fretting fatigue test were conducted with; a stress ratio R=0.05,a contact pressure P=200 MPa and bridge pads leg height h=0.5,1.0 and 3.0 mm. The main features in this study are as follows : the fretting fatigue strength decreased with the increase in height of bridge pad legs because of the decreasing of frictional force, and the interrupted fretting fatigue tests showed that crack initiation behavior was affected by the bridge pad leg in the fretting fatigue.

Improving the performance of spring-supported thrust bearing by controlling its deformations

The performance of the spring-supported thrust bearing is studied with three-dimensional thermo-elastic hydrodynamic lubrication theory. The generalized Reynolds equation, the energy equation, the heat conduction equation, and the thermo-elastic deformation equation are solved simultaneously using the combination of the finite difference method and finite element method. Thermo-elastic deformation plays an important role in the performance of the spring-supported thrust bearing. Several factors such as spring pattern, pad thickness and initial pad geometry are analyzed. The results show that the above factors influence the performance of the bearing significantly. Suggestions based on the results are put forward to assist design considerations.

The PHOBOS silicon sensors

PHOBOS is one of the four experiments at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. PHOBOS almost exclusively utilizes silicon sensors to measure charged particle multiplicity distributions and to track particles in a 2-arm spectrometer. The detector consists of about 450 silicon pad sensors. Nine different pad geometries are used to match the different physics needs of the experiment. A relatively high granularity, of up to 1536 channels per sensor, is used in the spectrometer. The multiplicity detector uses 128 and 64 channel sensors and the charge deposition per pad is measured to determine the multiplicity of single events. All sensors are of the double-metal silicon pad type with pad sizes from 1 cm 2 up to 4 cm 2. They are produced in Taiwan by the ERSO foundry under supervision of Miracle Co. and National Central University. An extensive testing procedure makes it possible to select sensors suited for use in PHOBOS. Detector modules consisting of up to five sensors are read out with integrated chips of either 64 or 128 channels. The testing of the sensors and the performance of assembled detector modules is discussed.

An apparatus for quantitative fretting testing

The design and construction of an apparatus for performing quantitative fretting fatigue experiments is described. The device allows accurate measurement and control of normal contact force, tangential contact force, relative displacement between contacting surfaces and bulk fretting loads, as well as measurement of average friction coefficients. Its design is simple, and includes interchangeable fretting contact pads, allowing the use of various pad geometries without major adjustment. The device incorporates many points of adjustment for alignment and compliance, making it a robust frame for a wide variety of fretting fatigue conditions involving different materials. The capabilities of this device are also verified by results of fretting fatigue experiments conducted on a 7075‐T6 aluminium alloy.

Layout and tests of silicon pad detectors for the PHOBOS experiment at RHIC

The PHOBOS experiment at RHIC, which is currently under construction, is designed to measure the particle multiplicity and to reconstruct low-momentum tracks in heavy ion Au–Au collisions. Both tasks are accomplished with silicon pad detectors. The silicon pad detectors are single-side devices with up to 1540 pads per detector. A special double-metal readout scheme for pad detectors provides a cost-effective method to connect detectors with different pad geometries to identical standard VLSI electronics. Different pad geometries have been designed and tested to optimise the pulse height and position measurement. Results of tests on the signal response and detector parameters for different pad configurations are be presented.

Solder Joint Formation Simulation and Component Tombstoning Prediction During Reflow

The failure of electrical devices associated with solder joints has become one of the most critical reliability issues for surface-mounted devices. Solder joint reliability performance has been found to be highly dependent on the solder joint configuration, which, in turn, is governed by bond pad size, alloy material, and leadframe structure, as well as solder reflow characteristics. To investigate tombstone effects causing solder joint failure during leadless component reflow process, this work has focused on (1) developing a numerical model for the simulations of the solder joint formation during the reflow process, and (2) determining possibility that a tombstone effect for the leadless component may occur by analyzing the force and torque in the problem. Using this methodology, the tombstone effect associated with different pad geometry configurations and solder paste amount has been analyzed through the application of the public domain software tool Surface Evolver. Simulations show that the tombstoning is very sensitive to pad/component geometry design, solder surface tension, solder paste volume, wetting area, and wetting angle. This model simulation can be used to determine optimal solder paste volume, pad geometry configurations, and solder material for avoiding tombstone effects.

Fretting fatigue in engineering alloys

The experimental procedures which have been used to carry out fretting fatigue tests are reviewed and the preferred specimen and contact pad geometries and method of testing are identified. The S–N curves generated with and without fretting and subsequent analysis have been used to satisfy a number of objectives: (1) to establish the important variables which can significantly affect fretting fatigue behaviour; (2) to increase our fundamental understanding of the fretting fatigue process; and (3) to give a ranking of a diverse range of materials in terms of their resistance to fretting fatigue. The analytical methods which have been used to predict fretting fatigue crack initiation are briefly discussed. With some specimen/fretting pad material combinations, small fretting fatigue cracks are introduced at a very early stage in life and fracture mechanics methods are developed in order to model their growth. Analytical procedures for fretting fatigue based on either S–N endurance or fracture mechanics methodologies are discussed.

Electrical conduction models for isotropically conductive adhesive joints

An electrical conduction model for silver filled isotropically conductive adhesives (ICA) was developed. The model combines the microscopic resistance of the bulk silver particles and the contact between silver flakes with the macroscale resistor network calculation by percolation theory. The resistivities of the composites were calculated by resistor network simulations considering both contact effects and particle size effects. Three different types of film typically exist on the silver surface: residual organic films; tarnish films; and a thin epoxy layer. The contact resistance between silver flakes can be due to a constriction resistance, to the tunneling resistance through insulating films, or to the resistance of more conductive layers. The constriction resistance is produced by the restriction of the current flow by small contact spots and is controlled by the actual contact spot area (metallic contact), which is dependent on the contact force between flakes. The tunneling resistance is caused by the very thin layer which may reside on the silver flakes between the metallic contact spots, and is dependent on a barrier film thickness and potential. Oxide and sulfide tarnish films are typically degenerate semiconductors. Two- and three-dimensional (2-D and 3-D) computer simulations were performed to predict the effects of particle sizes, shapes, and distribution on the percolation conduction thresholds and cluster sizes. The model predicts that the percolation threshold decreases with broad particle size distributions and high aspect ratio particles. The effective resistivity of the adhesive depends on the thickness dimension of the adhesive pad geometry, with very thin layers resulting in high percolation thresholds and high resistivities. Resistivity does not change with the pad thicknesses greater than a certain thickness level. Silver flake orientation on the surface increases the resistivity of the conductive adhesive pads, but in the same magnitude range. The resistivities of the materials are controlled by silver flake sizes and the nature of the contacts.

Progress in diamond and GaAs detectors

Substantial progress has been made in CVD diamond and GaAs detectors (in both pad and microstrip geometry). The former have achieved charge collection distances around 100 μm and have been used successfully in an electromagnetic calorimeter prototype. In microstrip detectors, both types have functioned satisfactorily, with good spatial resolution. The diamond detectors are shown to have excellent radiation hardness to gamma-rays, pions and protons GaAs detectors have been shown to perform adequately for LHC applications with respect to neutron hardness, but give indications of greater sensitivity to high-energy protons.

Effect of Chip and Pad Geometry on Solder Joint Formation in SMT

An analytical model of solder joint formation during a surface mount reflow process is developed for two-dimensional fillets whose flow may be restricted due to “finite” metallizations on a leadless component and the printed circuit board. Although these height and length constraints on the fillet geometry may result in obtuse contact angles, the solution is obtained in the form of an explicit integral, similar to that previously derived by the authors for the case of acute contact angles. This solution may also be recast into the form of elliptic integrals of the first and second kinds, thereby permitting one to evaluate the fillet geometry using mathematical tables or special function software, if desired, rather than resorting to a computer-based numerical quadrature. In addition an approximate zero-gravity solution is given by means of simple closed-form expressions relating the height, length, contact angles, and cross-sectional area of the fillet. Numerical results generated by implementing the “exact” integral solution for the joint profile are given in the form of dimensionless plots, relating fillet geometry to the solder properties (surface tension and density), amount of solder, chip height, and pad length. Also presented in dimensionless form are the approximate results from the zero-gravity model, which are independent of solder properties, yet are of sufficient accuracy for “small” joints. Because of their dimensionless nature, the results of the present paper may be of maximum utility to process engineers aiming to achieve desired joint geometries (e.g., to maximize fatigue life or to eliminate bridging problems), or to board designers responsible for selecting efficient footprint patterns to maximize board density. Models of solder joint formation, such as the one presented here, may be of most value when used in conjunction with stress analysis packages (e.g., finite element programs) and appropriate fatigue models. In this way an integrated approach to the design of solder joints and circuit boards may be taken, resulting in improved product reliability and performance.

Improved equivalent circuit for determination of MESFET and HEMT parasitic capacitances from "Coldfet" measurements

An improved equivalent circuit for MESFET and HEMT devices under zero drain bias pinched-off conditions is proposed. Parasitic gate and drain capacitances evaluated from low-frequency Y parameters using this circuit are approximately equal under conditions where equality would be expected from bond pad geometry considerations. In contrast, the previously used circuit considerably overestimates parasitic drain capacitance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of Experimental Design to the Solder Paste Screen Printing Process

Experimental design has proved to be a useful statistical tool in reducing process variation. The technique has been applied to a wide range of processes, including electronics assembly and soldering processes. For effective SMT assembly the screen printing of solder paste requires tight process control, especially as pad geometries become ever smaller. However, printing of solder paste is a rather complex process which is affected by machine, material, environmental and human factors, which make it difficult to characterise effectively. This paper examines the practical application of experimental design to solder paste printing for SMT and also the results from a number of experiments carried out on a semi‐automatic ‘clamshell’ type screen printer. The experimentation concentrates on the important printer and squeegee parameters and their effect on paste deposition, with measured solder paste height and ‘measle’ diagrams used as process outputs. The usefulness of the experimental results in determining the best printer settings, as well as the problems encountered during the experimentation, are highlighted.

Dynamic behavior of SMT chip capacitors during solder reflow

A dynamic model of a SMT (surface mount technology) type 1206 chip capacitor is developed. The model is used to determine the effects of pad geometry, chip metallization and dimensions, amount of solder, and chip displacement on the ability of the chip to lift (tombstone) and to self-align itself during solder reflow. Both static and dynamic characterizations are shown. The model simulations show that the chip capacitor will begin to lift initially for some geometries, but tombstoning does not appear to be a problem. Thus, to help the self-alignment capabilities, the simulations show that system configurations with smaller pad lengths, smaller pad gaps, larger solder volume, and smaller metallization are best. These conclusions are confirmed when compared to existing recommendations based upon experimental tests. It is concluded that the model is a powerful tool that can be used to optimize these system parameters. >

INSPAD: a system for automatic bond pad inspection

A method of detecting probe mark defects in semiconductor bond pads is presented that uses digitized images of color Polaroid photographs from an optical microscope. INSPAD inspects the bond pads in a magnified IC circuit image taken after the electrical testing stage. These are: probe marks must not extend beyond pad boundaries such that they damage glassivation; scratches on the bond pads must not exceed 50% of the bond pad width; and the probe marks must not exceed 25% of the bond pad area. Three types of commonly used bond pad geometries have been addressed. Morphological filtering is performed on the bond pad, to isolate and identify the major probe mark regions. Inspection of each pad takes approximately 2 to 3 s on an Apollo DN-4000 workstation which makes it suitable for real-time applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Limit Cycles for Pad Bearings Under Fluid Excitation

Pad bearings for turbine rotors are known to exhibit unstable limit cycles due to steam flow excitation in the power generation stages. To simulate the rotor-bearing system, static and dynamic behavior of a tilting pad have been modeled by means of phenomenological laws expressed as nonlinear function of pivot distance and the time derivative. These functions have been obtained experimentally for some common pad geometries. The pad functions are further assembled to express the static and dynamic behavior of tilting pad bearings in functional form. Popular linear properties, such as spring and damping constants can be obtained also by differentiation. The functional description of individual pads offers: a) a great reduction in the variety of pad bearing geometries and properties which need to be tabulated, b) feasibility of inexpensive experimental determination of the essential data, and c) a convenient utilization in large numerical rotor dynamic analysis programs, as compared with the on-line numerica...

Solder pad geometry studies for surface mount of chip capacitors : Elizabeth A. Kress. IEEE Trans. Compon. Hybrids mfg Technol.CHMT-8 (4), 505 (1985)

Solder pad geometry studies for surface mount of chip capacitors : Elizabeth A. Kress. IEEE Trans. Compon. Hybrids mfg Technol.CHMT-8 (4), 505 (1985)

Solder Pad Geometry Studies for Surface Mount of Chip Capacitors

An optimized solder pad geometry for surface mounting chip capacitors is developed. In surface mount production poor design can cause low yields and may require expensive redesign, retooling, and reprogramming of equipment. The solder fillets were examined visually for three types of defects. The general procedure used was to surface mount capacitors onto epoxy and alumina substrates using vapor phase reflow and infrared reflow. The solder used was 60Sn/40 Pb. Capacitors used were palladium/silver frit terminated (five-sided termination) and thin-film terminated (end termination only). Visual defects observed as a function of solder pad geometry were opens, misalignment Of chips (rotation), and drawbridges. Geometry of the solder pads was seen to play an important role in the visual defects observed. Of particular importance were the overlap of the pad and the capacitor, the width of solder pads, and the extension of the solder pad outside the capacitor (in the length dimension). Capacitor sizes used were 0805, 1206, and 1210 components.

Centrifugal effects on the thermohydrodynamic performance of circular pad thrust bearings

The thermohydrodynamic performance of a thrust bearing with circular pads is analysed taking into consideration the three-dimensional variation in lubricant viscosity. The effect of centrifugal forces is included. A Reynolds' equation incorporating centrifugal forces is derived for the thermohydrodynamic case. The system of equations is solved by a finite difference method. The results show that at the upper limits of laminar operation centrifugal forces alter considerably the load, the frictional force and the lubricant inflow. They might either overestimate or underestimate the bearing performance characteristic, depending on the pad's geometry and the operating conditions of the bearing.

An experimental investigation into the performance of externally pressurized rectangular air bearings

An experimental programme which was designed to investigate the performance characteristics of externally pressurized rectangular air bearings considering the effects of pad geometry and inlet gas conditions is presented. Three forms of rectangular bearings were considered: one arrangement consisted of continuous plane surfaces, the second had a recessed pad and a plane bed and the third had a plane bed and a recessed pad with a step in the bearing area following the recess. The results revealed that the recess length has a dominant effect on the pressure distribution in the air film. The effect of pressure depression is obvious at extremely small clearances and supply pressures. Such an effect is exaggerated when a step is introduced in the pad surface. The introduction of the step improves the load-carrying capacity of the bearing as long as the bearing is free from shock-wave formation.

An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.