3-D measurement of moving particles by circular image shifting

A new approach to the three-dimensional (3-D) measurement of position and velocity of moving particles is introduced. A single TV camera with an apparatus to add circular shift to the image enables us to record the 3-D movement of particles as spiral streaks on a single image. Every shape of the spiral streak on the image plane is related to the position and the velocity of the individual particle. The information about 3-D movement of particles is extracted from the image using an image processing technique. We applied the technique to the measurement of the 3-D water-flow field seeded with tracer particles in a test tank and obtained satisfactory results     

位相法三维形貌测量数值模拟系统

设计了位相法三维形貌测量数值模拟系统.实验结果表明,该系统可以模拟相位测量的主要过程,根据模拟物体和系统参数对投影光栅进行有效调制,并利用行列法对调制光栅得到的包裹相位图正确解包裹.本系统为研究各种高效健壮的相位解包裹算法提供了模拟平台.     

Rheological characterization of solder pastes

Solder paste is the strategic material for the electronic card assembly process, based on the surface mounting technology. The paste is a concentrated suspension (50% of volume) of metallic powder in an organic continuous phase and its screening on the printed circuit board is the first operation of the assembly. The result of the screening depends strongly on the rheological characteristics of the solder paste but, nevertheless the research activity on this material is so far very poor. In this paper, an analytical procedure for the rheological characterization is given and the most important rheological parameters, affecting the screening performance, are shown.     

Viscoelastic properties of solder pastes

Two solder pastes, used in an electronic card assembly process, were investigated under both oscillating and continuous shear fields, in order to characterize their viscoelastic and plastic properties. A further study on the vehicle used for the formulation of a paste was carried out in order to isolate the contribution of the disperse phase to the rheological properties of the corresponding system. The stress conditions for the departure from linear viscoelasticity and the transition from the solid- to liquid-like behavior, respectively, were defined on the basis of creep and oscillatory data. Appreciable elastic components were exhibited by the pastes examined, particularly at low stress conditions and, hence, can affect their screening performance. The contribution of the disperse phase is almost negligible at low shear or frequency, despite the high content of the disperse phase, and increases with increasing strain rate or frequency, essentially concerning only the viscous properties of the paste. This means that the rheological properties of the paste can be properly modulated by adjusting the formulation of the vehicle.     

一种基于相移技术的三维轮廓检测方法

光学三维轮廓检测技术在工业生产控制与检测、医学诊断和机器人视觉等领域正占有越来越重要的地位.提出了一种将莫尔投影法与单片机控制的相移技术相结合的物体表面三维轮廓测量方法,有效地实现了物体表面三维轮廓的高速、自动高精度测量.     

Solder balling of lead-free solder pastes

Solder balling in Sn/Ag/Cu solder pastes was studied in this work. Three different solder pastes, several different reflow profiles and conditions, and two stencil thicknesses were used in the investigation. During the first phase, called the verification phase, the solder pastes were checked to ensure they met the minimum requirements. In the process-screening phase, the reflow profile was varied. Results show that besides flux chemistry, reflow atmosphere plays the major role in solder balling. The average number of solder balls with the best paste was one fifth of that with the worst paste. Furthermore, with all the pastes, the number of solder balls dropped close to zero when nitrogen atmosphere was used. Another finding during the reflow process screening was the influence of the stencil thickness on the solder-balling result. With a thinner stencil, two of the pastes exhibited significant solder balling. This is assumed to be caused by the different ability of fluxes to withstand oxidation during the preheating in the reflow process. In the last phase, the effect of the solder-paste particle size on solder balling was studied more closely. The flux chemistry was kept unchanged, and the solder particle size was varied between type 3 and type 4. The results show that, with type 4 paste, significantly more solder balls are formed compared to type 3 paste. It was also confirmed that, regarding the reflow profile, the ramp-up rate from 150°C to 217°C and the reflow atmosphere were the most significant factors that determine the solder-ball formation for both types of paste.     

3-D radar imaging using range migration techniques

An imaging system with three-dimensional (3-D) capability can be implemented by using a stepped frequency radar which synthesizes a two-dimensional (2-D) planar aperture. A 3-D image can be formed by coherently integrating the backscatter data over the measured frequency band and the two spatial coordinates of the 2-D synthetic aperture. This paper presents a near-field 3-D synthetic aperture radar (SAR) imaging algorithm. This algorithm is an extension of the 2-D range migration algorithm (RMA). The presented formulation is justified by using the method of the stationary phase (MSP). Implementation aspects including the sampling criteria, resolutions, and computational complexity are assessed. The high computational efficiency and accurate image reconstruction of the algorithm are demonstrated both with numerical simulations and measurements using an outdoor linear SAR system     

Flip chip on board solder joint reliability analysis using 2-D and3-D FEA models

This study investigates the effects of employing different two-dimensional (2-D) and three-dimensional (3-D) finite element analysis (FEA) models for analyzing the solder joint reliability performance of a flip chip on board assembly. The FEA models investigated were the 2-D-plane strain, 2-D-plane stress, 3-D-1/8th symmetry and 3-D-strip models. The different stress and strain responses generated by the four different FEA models were applied to various solder joint low cycle fatigue life prediction relationships. The investigation shows that the 2-D-plane strain and 2-D-plane stress models gave the highest and lowest solder joint strains, respectively. The 3-D-strip and 3-D-1/8th symmetry model results fall in between the 2-D-plane strain and 2-D-plane stress model results. The 3-D-1/8th symmetry model agrees better with the 2-D-plane strain model, while the 3-D-strip model agrees better with the 2-D-plane stress model results. The results for the fatigue life prediction analyses also show similar trends     

High-temperature variable melting point Sn-Sb lead-free solder pastes using transient liquid-phase powder processing

During this investigation, a high-temperature, variable melting point (VMP) Sn-Sb solder paste was developed. The solder was created by mixing pure Sn and Sb powders together with a flux to form a paste. The proper choice of flux composition and Sn powder size resulted in a Sn-10wt.%Sb solder paste that had an initial melting point of 232°C and solder ball formation at peak temperatures as low as 241°C. This represents a significant reduction in the process temperature that would normally be required for a prealloyed solder with a melting point of 250°C. When this solder paste is reheated, significant remelting does not take place until a temperature above 241°C is reached. In this way, the solder exhibits a VMP. Experiments indicate that this VMP behavior is due to isothermal solidification (or freezing) at the solder temperature owing to the partial transient liquid-phase (TLP) behavior of the solder powder paste.     

Microwave phase shifting with gain using IMPATT diodes

The use of an IMPATT reflection amplifier to produce phase modulation at microwave frequencies has been demonstrated. By operating the IMPATT diode near to avalanche resonance frequency, phase-switching through 180° can be obtained, and the drive current can be set to give equal gain in the two phase states so that no amplitude modulation is produced. Possible application to high-frequency data-transmission systems is envisaged.     

Comparison of in-situ measurement techniques of solder joint reliability under thermo-mechanical stresses

Thermo Mechanical Cycle Lifetime (TMCL) test is a widely used test methodology for evaluating the reliability of solder joints in the microelectronics industry. The commonly used measurement techniques to monitor solder joint failures during the TMCL test are either event detector or data logger. In this study, TMCL test has been carried out on the same devices in parallel with both measurement techniques. The pros and cons of both techniques are compared. It is observed that the solder joint reliability results on the investigated samples by both techniques are comparable. The event detector can catch short intermittent events, while the data logger is able to capture the details of the solder joint degradation process. In applications for which performance is dependent on the transmission of signals with a frequency of several hundred megahertz or more, the event detector technique shall be used. In such cases the data logger technique may overestimate product lifetime. On the other hand, for some applications where the performance is less susceptible to intermittent solder joint interconnect interruption but more to the increase of the solder joint resistance, the data logger shall be used. In such cases the event detector technique may underestimate product lifetime. In conclusion depending on the end application of the device, the most suitable technique can be selected.     

3-D object recognition using 2-D views

We consider the problem of recognizing 3-D objects from 2-D images using geometric models and assuming different viewing angles and positions. Our goal is to recognize and localize instances of specific objects (i.e., model-based) in a scene. This is in contrast to category-based object recognition methods where the goal is to search for instances of objects that belong to a certain visual category (e.g., faces or cars). The key contribution of our work is improving 3-D object recognition by integrating Algebraic Functions of Views (AFoVs), a powerful framework for predicting the geometric appearance of an object due to viewpoint changes, with indexing and learning. During training, we compute the space of views that groups of object features can produce under the assumption of 3-D linear transformations, by combining a small number of reference views that contain the object features using AFoVs. Unrealistic views (e.g., due to the assumption of 3-D linear transformations) are eliminated by imposing a pair of rigidity constraints based on knowledge of the transformation between the reference views of the object. To represent the space of views that an object can produce compactly while allowing efficient hypothesis generation during recognition, we propose combining indexing with learning in two stages. In the first stage, we sample the space of views of an object sparsely and represent information about the samples using indexing. In the second stage, we build probabilistic models of shape appearance by sampling the space of views of the object densely and learning the manifold formed by the samples. Learning employs the Expectation-Maximization (EM) algorithm and takes place in a "universal," lower-dimensional, space computed through Random Projection (RP). During recognition, we extract groups of point features from the scene and we use indexing to retrieve the most feasible model groups that might have produced them (i.e., hypothesis generation). The likelihood of each hypothesis is then computed using the probabilistic models of shape appearance. Only hypotheses ranked high enough are considered for further verification with the most likely hypotheses verified first. The proposed approach has been evaluated using both artificial and real data, illustrating promising performance. We also present preliminary results illustrating extensions of the AFoVs framework to predict the intensity appearance of an object. In this context, we have built a hybrid recognition framework that exploits geometric knowledge to hypothesize the location of an object in the scene and both geometrical and intesnity information to verify the hypotheses.     

Segmentation and measurement of the cortex from 3-D MR images using coupled-surfaces propagation

The cortex is the outermost thin layer of gray matter in the brain; geometric measurement of the cortex helps in understanding brain anatomy and function. In the quantitative analysis of the cortex from MR images, extracting the structure and obtaining a representation for various measurements are key steps. While manual segmentation is tedious and labor intensive, automatic reliable efficient segmentation and measurement of the cortex remain challenging problems, due to its convoluted nature. Here we present a new approach of coupled-surfaces propagation, using level set methods to address such problems. Our method is motivated by the nearly constant thickness of the cortical mantle and takes this tight coupling as an important constraint. By evolving two embedded surfaces simultaneously, each driven by its own image-derived information while maintaining the coupling, a final representation of the cortical bounding surfaces and an automatic segmentation of the cortex are achieved. Characteristics of the cortex, such as cortical surface area, surface curvature, and cortical thickness, are then evaluated. The level set implementation of surface propagation offers the advantage of easy initialization, computational efficiency, and the ability to capture deep sulcal folds. Results and validation from various experiments on both simulated and real three-dimensional (3-D) MR images are provided.     

Ultrasonic liver discrimination using 2-D phase congruency

In this paper, we present an experiment to extract liver features using two-dimensional phase congruency, which is invariant to changes in intensity or contrast, to try to avoid the influence of machine settings. The effectiveness of our method was tested on three classes of liver images and shows the potential for physicians to quantify liver pathology in clinical diagnosis.     

Wide-band photonically phased array antenna using vector sum phase shifting approach

In this paper, a wide-band photonically phased array antenna is demonstrated. The array configuration consists of a 4 /spl times/ 1 Vivaldi single-polarization antenna array and an independent photonic phasing system for each element. The phasing network of this array is implemented using two novel photonic phase shifters based on the vector summation approach. A vector sum phase shifter (VSPS), which exhibits a frequency-linear characteristic from dc to 15 GHz and can be continuously tuned from 0 to 100/spl deg/, is presented. A second-order VSPS (SO-VSPS), a modification of the VSPS that is capable of 0-430/spl deg/ phasing range, is also demonstrated. This paper presents the operation and characterization of each component of the array, including the radiating elements and the various photonic phase shifters and, finally, a demonstration of the combined system. A discussion on the practicality of this system for airborne applications is presented, along with suggestions for simplification and improvement.     

Fundamental limitations in RF switching and phase shifting using semiconductor diodes

When semiconductor diodes are used as variable impedance switching elements in RF transmission networks, the maximum power and minimum attenuation depend upon the characteristics of the diodes and the function being performed. Equations and theorems are derived which define these limits for quantized RF control networks used in on-off switches, selection switches, and phase-shift devices. The relationships are quite general and the limits are shown to apply to a wide variety of network configurations. It is shown that the maximum power of a switch is proportional to the maximum RF current of the forward-biased diode and also to the maximum RF voltage when reverse-biased. The maximum power in phase shifters is a sinusoidal function of the phase change required. Minimum attenuation depends upon the switching function performed, the frequency of operation, and a newly defined cutoff frequency which includes diode resistance in both forward-bias and reverse-bias states.     

Ray phase space approach for 3-D imaging and 3-D optical data representation

We propose a framework to model, analyze and design three-dimensional (3-D) imaging systems. A system engineering approach is adopted which relates 3-D images (real or synthesized) to 3-D objects (real or synthesized) using a novel representation of the optical data which we call "ray phase space". The framework provides a powerful tool for determining the performance of 3-D imaging systems, for generating computational reconstruction of 3-D images and for optimizing 3-D imaging systems.     

Forming high temperature solder joints through liquid phase sintering of solder paste

Eutectic lead-tin has been the solder of choice throughout the history of the electronics industry. Alternatives to this material are now being considered because of environmental concerns, as well as the strength and temperature limitations of eutectic lead-tin. Identifying and using these alternative materials poses significant challenges, many of which we believe can be addressed if one forms solder joints through liquid phase enhanced sintering. First, most alternative solder materials have significantly higher melting temperatures (than eutectic lead-tin), and their use would require the replacement of much of the manufacturing infrastructure. In this work joints with shear stresses approaching that of eutectic lead-tin solder were formed by sintering a eutectic tin-sliver solder paste (T_m=221°C) doped with 3 v/o eutectic Sn-Bi powder at 210°C for 30 min. Second, to date the industry has limited its consideration to eutectic or near-eutectic alloys because of the concern of forming cold solder joints. In this work joints have been prepared by sintering solder pastes with a wide thermal range at temperatures just above the solidus, where a small amount of liquid will form and therefore enhance the rate of sintering, which have shear strengths of 6 MPa or higher. These findings indicate that it may be worthwhile to investigate developing a sinterable solder paste, which can be used to prepare surface mount assemblies.     

Multiplexing of interferometric sensors using phase carrier techniques

This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity ofsim 18 murad/sqrt{Hz}. Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstratedsim 2-murad performance with both single sensor and four element array operation.     

Motion measurement using shape adaptive phase correlation

For video objects that have large displacements between frames, standard motion estimation techniques may not be suitable. A modification to the phase correlation motion measurement technique is proposed that avoids using frequency components from the background and offers a better compromise between range and accuracy of measured motion parameters