Imaging of packaging-related problems in electronic components by scanning acoustic microscopy

Low-frequency (50 MHz) scanning acoustic microscopy has been applied to the problem of imaging defects in semiconductor packages. The results have been compared with the more established technique of X-ray shadow imaging. The scanning acoustic microscope has been found to be able to image a greater variety of defects than X-ray shadow imaging, although the acoustic image could often only be fully interpreted after comparison with the corresponding X-ray image. Scanning acoustic microscopy is now proving to be a valuable analysis technique for the detection and characterisation of packaging related problems.     

Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy

We introduce voltage-contrast scanning electron microscopy (VC-SEM) for visual characterization of the electronic properties of single-walled carbon nanotubes. VC-SEM involves tuning the electronic band structure and imaging the potential profi le along the length of the nanotube. The resultant secondary electron contrast allows to distinguish between metallic and semiconducting carbon nanotubes and to follow the switching of semiconducting nanotube devices, as confi rmed by in situ electrical transport measurements. We demonstrate that high-density arrays of individual nanotube devices can be rapidly and simultaneously characterized. A leakage current model in combination with fi nite element simulations of the device electrostatics is presented in order to explain the observed contrast evolution of the nanotube and surface electrodes. This work serves to fill a void in electronic characterization of molecular device architectures. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Investigation of crossed SAW fields by scanning acoustic force microscopy

We used multimode scanning acoustic force microscopy (SAFM) for studying noncollinearly propagating Rayleigh and Love wave fields. By analyzing torsion and bending movement of SAFM cantilever, normal and in-plane wave oscillation components are accessible. The SAFM principle is the down-conversion of surface oscillations into cantilever vibrations caused by the nonlinearity of the tip-sample interaction. Through mixing of complementary oscillation components, phase velocities of crossed Rayleigh waves on GaAs and crossed Rayleigh and Love waves on the layered system SiO2/ST-cut quartz were obtained simultaneously. Now, it is possible to investigate elastic properties of submicron areas through multimode SAFM measurements. Finally, we present mixing experiments of four SAWs on GaAs and discuss the various influences on the measured SAFM amplitude and phase contrast.     

Imaging properties of scanning holographic microscopy

Scanning heterodyne holography is an alternative way of capturing three-dimensional information on a scattering or fluorescent object. We analyze the properties of the images obtained by this novel imaging process. We describe the possibility of varying the coherence of the system from a process linear in amplitude to a process linear in intensity by changing the detection mode. We illustrate numerically the properties of the three-dimensional point-spread function of the system and compare it with that of a conventional imaging system with equal numerical aperture. We describe how it is possible, by an appropriate choice of the reconstruction algorithm, to obtain an ideal transfer function equal to unity up to the cutoff frequency, even in the presence of aberrations. Some practical implementation issues are also discussed.     

Cavitation asymmetry in silicon nitride by scanning laser acoustic microscopy

Scanning laser acoustic microscopy (SLAM) was used to visualize creep damage distribution in the gas-pressure-sintered silicon nitride after creep at 1300°C in 4-point bending. SLAM revealed asymmetrical distribution of creep damage beneath the tensile surface and in a narrow zone that spread continuously across the neutral axis toward the compression surface. Scanning and transmission electron microscopy confirmed the presence of cavities in tensile zone of bending bar. The combination of the homogeneous cavity development in the zone of tensile stresses and formation of the damage zone ahead of main crack was proposed to explain such cavity distribution. Current SLAM observation is a direct evidence of cavitation asymmetry in vitreous bonded ceramics. Such distribution supports the model of simultaneous presence of cavitation and non-cavitation creep mechanisms in silicon nitride and similar ceramics.     

Recent advances in scanning tomographic acoustic microscopy

We present the recent developments of the Scanning Tomographic Acoustic Microscope (STAM). The STAM was proposed as a method to achieve 3D imaging capability for the Scanning Laser Acoustic Microscope (SLAM). With the addition of a quadrature receiver, the complex scattered wave field can now be detected, and consequently the STAM is capable of subsurface holographic and tomographic imaging. The resolution improvement of the STAM can be attributed directly to the detection of the phase information and the image reconstruction technique. The STAM is sensitive to phase errors in the tomographic projections. In particular, the quadrature phase error and the initial phase error in the complex projections are critical to the tomographic reconstruction process. For multiple-angle tomography, high-precision projection registration and alignment become necessary. By obtaining solutions to these implementation problems, we have succeeded in obtaining images superior to the original SLAM images. In addition, quantitative ultrasonic imaging is possible with the STAM, and a method is presented to image the velocity parameter of simple specimens. With these capabilities, the STAM may become a useful tool for high-resolution subsurface nondestructive evaluation.     

Study of cellular adhesion with scanning acoustic microscopy

A mechanical scanning acoustic reflection microscope was applied to living cells (e.g., osteoblasts) to observe their undisguised shapes and to evaluate their adhesive conditions at a substrate interface. A conditioned medium was collected from a bone-metastatic breast cancer cell line, MDA-MB-231, and cultured with an immature osteoblast cell line, MC3T3-E1. To characterize the cellular adhesion, MC3T3-E1 osteoblasts were cultured with or without MDA-MB-231 conditioned medium for 2 days, then assayed with the scanning acoustic reflection microscope. At 600 MHz the scanning acoustic reflection microscope clearly indicated that MC3T3-E1 cells cultured with MDA-MB-231 conditioned medium had both an abnormal shape and poor adhesion at the substrate interface. The results are compared with those obtained with laser scanning confocal microscopy and are supported by a simple multilayer model.     

The pyramidal-mirror detector for scanning laser acoustic microscopy

The pyramidal-mirror detector has important advantages over the knife-edge detector currently in use in scanning laser acoustic microscopy. A key element of this new detector is a four-sided pyramid with mirrored surfaces. In the operation of the microscope, the zero-order component of the light of the scanning laser beam that has been reflected from the microscope's coverslip is centered on the tip of the pyramid. Thus, each mirror face reflects one fourth of the light in this component. Making use of an arrangement of four photodetectors, one for each of the four faces of the pyramidal mirror, the light reflected from each face goes to a different photodetector and is processed separately from the light reflected from the other faces. This detector has an almost isotropic transfer function with no negative responses and fourfold symmetry around a null point in the center which coincides with the zero-frequency point in the spatial spectrum. This property makes it possible to detect spatial frequencies in all directions simultaneously with almost equal sensitivity. Oblique insonification, required for best operation with the knife-edge detector because of its region of negative response, is not preferred in the pyramidal-mirror detector and double side-band detection can be employed. Since there is no requirement that a negative response region be avoided, the spatial spectrum of this detector can be more than twice that of the knife-edge detector. The tighter the focusing of the scanning laser beam onto the coverslip, the higher the spatial frequencies detectable in the object. In fact, if the coverslip occupies a position in the very-near field of the object, evanescent-wave detection is possible. Low-frequency, highly penetrable ultrasound can be used and at the same time high spatial frequencies can be detected for obtaining high resolution. © 1999 John Wiley & Sons, Inc. Int J Imaging Syst Technol 10, 323–327, 1999     

Detection systems for scanning laser tomoholographic acoustic microscopy

A new microscope, called the scanning laser tomoholographic acoustic microscope, will employ three insonifying transducers to obtain holographic projections from three different directions for use in reconstructing tomograms of microscopic objects. To do this, the detection system should detect with equal sensitivity in all directions of propagation the traveling ultrasonic waves that emerge from the object with the image information. Two such laser-beam detectors, the heterodyne detector and the time-delay interferometric detector, have been examined to find the one best suited for rapid data acquisition and direction-insensitive optical computing. Although each has its own advantages and disadvantages, we find the latter more suitable for our purpose. © 1996 John Wiley & Sons, Inc.     

Study of overgrowth heterostructure InSb/GaAs by scanning electron acoustic microscopy

An overgrowth InSb epilayer on GaAs substrate with large lattice-mismatch was grown by metalorganic chemical vapor deposition (MOCVD), and the heterogeneous crystalline state was observed by scanning electron acoustic microscopy (SEAM). The middle stage of relaxation of the large mismatch InSb/GaAs epilayer is observed by SEAM images of crystalline state of the buried subsurfaces. A macroscopical heterogeneous distribution is formed by large compression stress fields. It was a very important result to observe and study semiconductor epitaxial heterostructures by SEAM uniquely imaging mechanism.     

Image analysis of delamination cracks in carbon-fibre composites by scanning acoustic microscopy

Fibre-reinforced composite laminates have been widely applied to many kinds of structures because of their superior properties. The delamination resistance of such composites is a weak point, however, and one of the most important problems is the non-destructive detection of delamination cracks. In this study, high-resolving-power observations with a recently developed scanning acoustic microscope (SAM) have been conducted for a study of the applicability of the technique for non-destructive inspection of delamination. The high-resolving-power observations were applied to carbon-fibre/epoxy and carbon-fibre/PEEK unidirectional, multidirectional reinforced and fabric composites. From the results obtained, the delamination micro-mechanisms are discussed and knowledge of non-destructive inspection with a SAM has been obtained.     

Characterization of heterogeneous matrix composites using scanning acoustic microscopy

Acoustic microscopy was used to examine the morphology of multi-phase matrices and composites. The acoustic microscopy imaging could easily resolve the rubber domains dispersed within a thermosetting or thermoplastic continuous phase. However, because the thermoplastic and thermosetting phase domains had comparable elastic moduli, the resolution between them was not always clear. Rayleigh wave distortion of imaging remained as one of the serious limitations that needed to be overcome in order for this technique to be widely utilized in heterogeneous/anisotropic media. In its present form, the acoustic imaging technique can be used to augment other existing analytical tools in order to generate more detailed morphological information that is useful in understanding structure-property relationships for multi-phase toughened matrices used in advanced composites.     

Thermal effects in scanning acoustic microscopy for fine resolutionapplications

A novel scanning acoustic microscopy technique for achieving high resolution acoustic images by employing thermal effects and image subtraction has been studied and demonstrated. Experiments were performed on a perspex block patterned with a machined grid on the reverse surface, and on a buried channel in similar material. If was found that using the image subtraction technique, short periods of sample heating can lead to a stronger pattern selectivity, because of the strong temperature dependency of the elastic parameters of the polymer. In previous SAM techniques improvement in signal has been achieved through the use of special liquids as acoustic coupling media between the acoustic lens and the sample. The reported technique retains water as the coupling medium and the acoustic impedance matching is performed by varying the elastic parameters of the sample itself through direct heating. The temperature increase in the sample decreases the velocity of propagation of acoustic waves in the solid, and brings the acoustic impedance close to that of water. A theoretical model, including expressions for the acoustic aberrations, depth dependence and acoustic impedance matching has been derived. Examples of the results obtained are presented     

Three-dimensional measurement of short fatigue cracks using scanning acoustic microscopy

Abstract

The three-dimensional crack growth of short fatigue cracks in Al–Li 8090 alloy has been examined using time resolved acoustic microscopy. Two sets of specimens were machined having different orientations of the elongated grains. Depending on the orientation of the pancake shaped grains with respect to the propagation direction of the cracks different growth rates were obtained. Furthermore, the influence of the microstructure (e.g. grain boundaries) on the crack path in the two sets of specimens could be determined.

MST/1838     

Residual stress measurements in welded steel beam column connections by scanning acoustic microscopy

Residual stresses which arise from thermal expansion and contraction due to welding may have contributed to the brittle fracture exhibited by welded steel beam-to-column connections during the Northridge Earthquake. These residual stresses have a strong influence on crack initiation and crack propagation in the vicinity of stress concentrations (i.e., unfused backup bar in welded steel beam-to-column connections) and account for changes in the driving force for fracture. They affect material toughness by changing the constraint condition under which fracture occurs. Currently, all methods of dealing with residual stresses are hampered by the lack of a consistent means of measuring the magnitudes and distribution of these stresses. This paper describes a new acoustic microscopy technique that allows the mapping of residual stresses in welded connections with high spatial resolution. The technique is based on the sensitivity of polarized acoustic modes to local elastic anisotropy induced by stress. The technique furthermore allows the mapping of residual stresses in a tomographic way by changing the frequencies of the acoustic waves. The results reveal that the magnitude of the residual stresses is influenced by the local microstructure of the steel and the weld metal. Ductile microstructures within the weld and the heat affected zone release residual stresses by yielding, whereas brittle microstructures retain residual stresses.