Nondestructive evaluation of elastic properties of advanced materials was performed with short surface acoustic wave (SAW) pulses in the 10 MHz-300 MHz range. The elastic surface pulses were launched thermoelastically with pulsed laser radiation and detected with a piezoelectric foil transducer. This technique was used, for example, to determine the mechanical and elastic properties of superhard materials, such as microcrystalline CVD diamond films and submicrometer thick nanocrystalline films of cubic boron nitride. These results are compared with the properties of the corresponding single-crystal material, In layered systems or graded materials the introduction of a length scale leads to dispersion of the surface acoustic waves (SAWs), which allows the simultaneous determination of several properties, such as the density, Young's modulus, and Poisson ratio. In free-standing polycrystalline CVD diamond plates dispersion of elastic surface pulses was observed. This material is neither isotropic nor homogeneous because the grain size and structure vary from nucleation side to the growth side. In some samples anomalous dispersion of SAWs was observed on the nucleation side with the finer grains. Amorphous SiC_xN_y films with various compositions were investigated to compare the microscopic bonding characteristics, determined by molecular dynamics (MD) simulations, with the macroscopic mechanical properties obtained by surface acoustic wave spectroscopy (SAWS).

Laser-ultrasound spectroscopy, a non-contact ultrasonic technique was used to characterize the Lame coefficients ((lambda) ,(mu) ) and thickness (h) of a zinc layer on a steel substrate. This characterization is based on fitting the measured velocity dispersion curve of surface acoustic waves (SAW) to the dispersion calculated one using the conjugates gradients algorithm (C.G). A short laser pulse was used to generate a wideband pulse of ultrasound and a laser interferometer was used for its detection. From a large number of echoes we identified the one corresponding to the SAW. Furthermore other useful information were obtained from these data like attenuation and surface skimming longitudinal wave. Measurements of the velocity dispersion of the Rayleigh wave were achieved up to 50 MHz. The evaluation of layer's parameters performed for similar cases, on a pseudo-experimental model, were obtained with accuracy better then 1% for (h, (mu) ) and about 4% to 6% for (lambda) .

Optical techniques for monitoring acoustic waves excited in thin films or micro-structures with ultrashort laser pulses are useful for the accurate and nondestructive evaluation as well as for the characterization of material properties. The pump-probe laser-based acoustic methods generate acoustic bulk waves in a thermo-elastic way by absorbing the pump laser pulses at the surface of the thin film. The acoustic waves are partly reflected at the interface of thin film and substrate. Back at the film surface the reflected acoustic wave causes a change of the optical reflection coefficient, which is measured by the probe laser pulse. One-dimensional, thermo-elastic models are developed to investigate the laser-based excitation and propagation of the longitudinal acoustic pulses in thin aluminium films. The change of the optical reflection coefficient is governed by the temperature distribution and the mechanical strain caused by the traveling acoustic pulse. The presented comparison of the simulation results of thin aluminium films with the pump-probe-measurements allows to determine film thickness or Young's modulus. Furthermore material properties like thermal conductivity and photoacoustic properties are estimated. The thermo-elastic modeling of the two-dimensional case and the resulting new possibility to use the pump-probe technique for the nondestructive evaluation of micro-structures is discussed. Further directions of the ongoing research project are presented.

Ceramic sensor based on TiO₂-Al₂O₃ systems were thermally cycled in the temperature range of 21 degree(s)C to 685 degree(s)C for different number of cycles. Thermal wave imaging technique (TWI), a non-destructive and non-contact evaluation method was used to characterize the bonding of sensor films with the substrate. Based on the thermal wave signal amplitudes, an assessment of bond strength was made. The results indicate that samples with 700 degree(s)C heat treatment show the best bonding characteristics. Furthermore, with increasing number of thermal cycles, bonding quality turns out to decrease as damage occurs. Thermal wave imaging is a powerful NDE tool. Results from a number of material evaluation efforts indicate that the technique has great promise.

The real time change of surface morphology during the RF magnetron sputtering Ta₂O₅ films on Si substrates was studied by the fixed angle X-ray reflectivity measurement. During the early stage of polycrystalline Ta₂O₅ growth, the surface roughness change reveals a surface morphology of island nucleation and island coalescence processes. After the thickness of 7 nm, the surface roughness increases up to more than 2 nm at the thickness of 80 nm. For crystalline Ta₂O₅ films, the density of the sputtering Ta₂O₅ films was also increased and reaches the value of bulk value only when the thin film thicker than 80 nm. For the amorphous sputtering film, the surface roughness is smoother and density is smaller.

Optical Coherence Tomography (OCT) is an active optical imaging technique that is capable of three-dimensional resolution better than 10 microns in all dimensions. OCT was originally developed as a non-invasive technique in biomedical field. It also found uses in the NDE of various materials including ceramics, plastics and composites. In various ceramics OCT can be used to detect microscopic, subsurface defects at depths approaching hundreds of microns. The depth of penetration depends on the material and on the wavelength of light. Here we demonstrate an application of OCT to the subsurface imaging in various materials and, in particular, to the detection of a surface-penetrating Hertzian crack in a Si₃N₄ ceramic ball. We present measured subsurface trajectory of the crack and compare it to theoretical predictions. These cracks represent one of the most important failure mechanisms in advanced ceramic materials. The ability to map subsurface trajectories of cracks is a valuable tool in the evaluation of different existing theories. Better theoretical understanding of various properties of crack initiation and propagation can lead to engineering of improved ceramic materials.

Dynamic Atomic Force Microscopy (AFM) modes, where the cantilever is vibrated while the sample surface or tip is scanned, belong to the standard features of most commercial instruments. With these techniques images can be obtained the contrast of which depend on the elasticity of the sample surface. Quantitative determination of Young's modulus of a sample surface with AFM is a challenge, especially when stiff materials such as hard metals or ceramics are encountered. The evaluation of the cantilever vibration spectra at ultrasonic frequencies provides a way to discern local elastic data quantitatively using the flexural vibration modes. Nanocrystalline magnetic materials, multi- domain piezoelectric materials, polymeric materials, diamond-like carbon layers, silicon, and soft clay have been examined. Images obtained at the contact resonance frequencies are presented whose contrast is based on the elastic differences of the surface structure of the various materials examined. The spatial resolution is approximately 10 nm. Applying an electrical ac-field between the tip and the surface of a piezoelectric sample, images can be generated whose contrast is additionally influenced by the piezoelectric and dielectric properties of the sample. Furthermore, we present a new approach for studying friction and the stick-slip phenomenon using the torsional resonances of AFM cantilevers.

To investigate nanoscale mechanical behavior, new approaches using dynamic modes of the atomic force microscope cantilever are being developed. One method, atomic force acoustic microscopy (AFAM), measures cantilever resonances in the acoustic frequency range to obtain elastic-property information. We describe quantitative AFAM measurements and compare them to results from techniques like surface acoustic waves and instrumented indentation. With AFAM we examined a niobium film using two separate calibration samples and two cantilever geometries. Depending on the cantilever type we found M=105-114 GPa, in good agreement with literature values of M=116-133 GPa for bulk niobium and M=120 GPa obtained with surface acoustic waves. We also obtained AFAM values of M=54-81 GPa for the indentation modulus of an aluminum film. In comparison, literature values for bulk aluminum are M=76-81 GPa, while other results on the same film yielded M=78-85 GPa. To understand the results more thoroughly, we compare two methods of AFAM spectrum analysis. The analytical approach assumes a cantilever of uniform rectangular cross-section while the finite-element model accounts for spatial variations in cantilever dimensions. The same data are interpreted with the two approaches to better understand measurement uncertainty and accuracy.

Recent atomic force microscopy research has focused on dynamical methods in which AFM probes are vibrated while in contact with a specimen during scanning. The nonlinear tip-sample interactions can induce nonlinear features into the dynamic response. Nonlinear responses observed experimentally include the DC shift (or lift-off) and primary response softening as well as the development of subharmonics and superharmonics. Here, this problem is formulated in terms of a nonlinear boundary value problem which is solved using the method of multiple scales. The main result of this analysis is the amplitude-frequency relation for all vibration modes. The nonlinear normal modes are comprised of terms representing the softening effect of the resonance, the static offset, and harmonics. The softening effect on the primary response is shown to be a function of the particular vibration mode as expected. The contact mechanics model used here is restricted to Hertzian contact, but can be generalized to more complex models. Results of the primary response for various excitations are presented. The amplitude-frequency behavior is dependent on the linear contact stiffness, the forcing amplitude, and contact damping. It is also shown that the modes have a differing sensitivity to the nonlinearities present in the contact.

Ultrasonic atomic force microscopy (UAFM) is a new scientific tool realizing reliable measurement of nano-scale elasticity from resonance vibration of cantilever in the contact mode AFM. The elasticity is evaluated from the resonance frequency, and the loss modulus may be evaluated from Q the factor. This paper describes recent progress on the theoretical model, subsurface imaging, inverse analysis, nonlinearity due to a dislocation, and theory and experiment of Q control for improving resolution and stability.

The analysis of the dynamic behavior of the micro- cantilevers employed in atomic force microscopy (AFM) is often limited to linear or weakly nonlinear behavior without damping. Finite element simulations are used here to study the cantilever dynamics outside of these restrictions. The nonlinear contact mechanics between the AFM tip and the material surface are modeled using the JKR model with different damping. This model is most appropriate for AFM cantilevers that are most compliant than the specimen. The focus is on the contact case in all analyses to simplify the problem. Thus, the AFM cantilever tip is assumed to remain in contact with the specimen surface at all times during the motion. Applications for both weakly and strongly nonlinear behavior are examined. The properties of the vibration, the influence of different initial loads and different damping models on the behavior, like nonlinear shifts of the resonance frequencies, the eccentricity and asymmetry of the amplitude, of the nonlinear vibration are calculated by FEM. The numerical analysis shows that the eccentricity and the asymmetry of the amplitude are more sensitive to the change of damping and the contact stiffness than the resonance frequencies. The response of the cantilever and the evaluation of elastic properties of the sample can be studied appropriately using this model.

The quest for technical advancements is leading scientists to study how devices interact on the nanometer scale. There is a growing need for material characterization techniques, which can image, detect damage/changes, and characterize the material and its engineered structures in the nanometer region. One of the most powerful tools that are routinely used for characterization of nanostructured materials is Atomic Force Microscopy. The Atomic Force Microscope (AFM) provides a 3 dimensional surface topographic image of a sample. When imaging a sample's surface, a 10-micron or smaller area maybe fairly flat so that the AFM image provides very little detail and contrast even though the overall sample surface is quite rough. Ultrasonic Force Microscopy (UFM) has been developed in order to improve the image contrast on flat areas of interest where the AFM topography images are limited in contrast. The combination of AFM-UFM allows a near field acoustic microscopic image to be generated. The AFM tip is used to detect the ultrasonic waves and overcomes the lateral resolution limit of the acoustic wavelength that occurs in acoustic microscopy. By using the elastic changes under the AFM tip, an image of much greater detail than the AFM topography can be generated. Nondestructive evaluation and material characterization on ceramic and copper applications in which the addition of UFM has greatly improved upon the AFM images is presented.

The Micro Materials Center Berlin (MMCB) located at the Fraunhofer Institute IZM belongs to three German Centers for Materials Research in Microtechnology funded by the German Ministry for Education and Research (BMBF). The paper presents some recent results obtained in the field of electronic packaging for MEMS. A survey is given concerning advanced interconnection technologies (chip size packaging, BGA, wafer level packaging etc.) taking into account new developments in the field of materials research for packaging in various applications, e.g. in automotive and telecommunication systems. Special attention will be given to overcome the reliability gap which can be found in the field of microsystem reliability (e.g. high temperature electronics, lead-free solder applications in MEMS etc.). The authors present recent results obtained in the different branch labs of MMCB situated in Berlin, Munich, Chemnitz, Oberpfaffenhofen, and Teltow. New fields of applications are dealt with e.g. polytronics, micromechatronics.

Smart materials based on carbon fiber-reinforced plastics with embedded PZT sensors and actuators are expected to be a favorite composite for vibration damping and noise reduction. Due to the wide variety of physical properties of the components various damage mechanisms may reduce or even remove the sensing and actuating capabilities of the piezoceramic material. Comprehensive non-destructive characterization and integral health monitoring help to optimize the structure and its manufacturing and are essential prerequisites to ensure performance and availability of smart components during their life time. The first part of the paper presents high resolution non- destructive imaging methods including microfocus X-rays, ultrasonics and eddy currents. These methods are used to characterize damages resulting from non-optimal manufacturing and external load. The second part is dedicated to newly developed imaging techniques using the active piezoceramics as transmitters of acoustic, electromagnetic and thermal fields. The third part focuses on health monitoring by impedance spectroscopy using the same piezoceramics as for vibration damping. Electromechanical finite-element-modeling and experimental investigations at strip-shaped specimens have shown the close connection between mechanical properties and electrical impedance.

Polymeric aerospace coating systems are subject to environmental degradation from ultraviolet light, water exposure and thermal cycling. This paper discusses the current progress in a novel study to develop nondestructive evaluation (NDE) methods for monitoring coating degradation during service. In the current study, weathering tests were conducted for varying lengths of time. The examined specimens were single layer epoxies on aluminum alloy (AA2024-T3) substrates. Artificial weathering of the coated samples was conducted using simulated sunlight exposure (Xenon arc lamps), combined with heat and humidity. The coatings were characterized using spectroscopic and NDE techniques after each exposure interval. The NDE included infrared microscopy and scanning acoustic microscopy (SAM). IR absorption spectra as a function of UV radiation exposure were obtained by using attenuated total reflection- infrared spectroscopy (ATR-FTIR). These spectra provide quantitative measures of coating degradation and enabled a correlation with SAM measurements. Thus, potential acoustic parameters could be identified that can be used to track coating degradation. Degradation in the coating as indicated by the IR spectra and NDE data will be correlated with physical changes observed in the coating morphology.

TOFD method has attracted attention as the most accurate crack depth measurement technique in industrial inspection field. Since this method utilizes the crack tip ultrasonic diffraction echo and the amplitude of this echo is weak, enhancement of S/N ratio of received signal is required for accurate and reliable measurement. The most harmful defect for industrial structures is a crack and a crack closure sometimes causes failure in nondestructive crack detection by TOFD method. However, quantitative behavior of crack tip diffraction echo depending on crack closure for longitudinal wave used in TOFD method have not been investigated yet. In this paper, we prepared 7075-T6 aluminum alloy specimens with a penetrating surface fatigue crack by three point bending test. During the fatigue test, maximum applied load Kmax was reduced gradually according to the crack extension to control the maximum stress intensity factor to be constant. Using the specimen with a closed fatigue crack, crack tip opening displacement (CTOD) was controlled by loading within Kmax. The amplitude of the crack tip diffraction echo of 5 MHz ultrasonic longitudinal wave depending on CTOD was measured. Using the obtained relation as a calibration curve, the minimum CTOD required for stable TOFD measurement of fatigue crack was estimated to be 0.1 micrometers .

Miniaturized dogbone tensile specimens are used to determine mechanical properties when only a small amount of material is available. Because of the high surface to volume ratio, surface finishing becomes critical for specimens with diameters less than 2 mm. Barkhausen noise technique was used to characterize the machined surfaces of small diameter tensile specimens. Full surface scans were conducted using a new magnetization technique. The Barkhausen noise profile curves for several different analyzing frequencies were compared to those obtained on electro-polished specimens using correlation techniques in order to characterize the penetration depth of the surface treatment.

We present a modeling technique for the interaction of an elliptical-shape crack in a metal with an open-ended waveguide. The crack is first modeled by an appropriate number of short rectangular waveguides. The mode-matching technique is then used to calculate the scattering matrix of the new segmented waveguide structure. The probe reflection coefficient of the dominant mode is finally calculated for various positions of the crack in order to predict the probe output signal. To demonstrate the accuracy of the model, we consider cracks of various aspect ratios. The comparison of our results with those obtained using a commercial finite element code validates the model introduced in this paper.

Accelerated life tests (ALTs) are aimed at the revealing and understanding the physics of the expected or occurred failures, i.e. are able to detect the possible failure modes and mechanisms. Another objective of the ALTs is to accumulate representative failure statistics. Adequately designed, carefully conducted, and properly interpreted ALTs provide a consistent basis for obtaining the ultimate information of the reliability of a product - the predicted probability of failure after the given time of service. Such tests can dramatically facilitate the solution to the cost effectiveness and time-to-market problems. ALTs should play an important role in the evaluation, prediction and assurance of the reliability of microelectronics and optoelectronics devices and systems. In the majority of cases, ALTs should be conducted in addition to the qualification tests, which are required by the existing standards. There might be also situations, when ALTs can be (and, probably, should be) used as an effective substitution for such standards, or, at least, as the basis for the improvement of the existing qualification specifications. We describe different types (categories) of accelerated tests, with an emphasis on the role that ALTs should play in the development, design, qualification and manufacturing of microelectronics and photonics products. We discuss the challenges associated with the implementation and use of the ALTs, potential pitfalls (primarily those associated with possible shifts in the mechanisms and modes of failure), and the interaction of the ALTs with other types of accelerated tests. The role of the nondestructive evaluations is also briefly outlined. The case of a laser welded optoelectronic package assembly is used to illustrate the concepts addressed.

A detailed micro-characterization of a MEMS ultrasonic transducer was done using a scanning heterodyne interferometry technique. Both temporal and spatial measurements were made of the out-of-plane displacement levels of the transducer under normal operating conditions. Spatial resolution levels approaching the optical diffraction limit of 1 mm were achieved, which allowed characterizations of individual micro-transducer elements to be made. The resonance characteristics of individual transducer membranes were evaluated for drive frequencies between 1 MHz and 7 MHz. Although the majority of transducer elements showed nearly identical frequency response characteristics, several of the MEMS elements showed evidence of shifted resonance response features, which dramatically altered their performance level. Displacement levels in excess of 100 nm were observed for peak DC and AC drive voltage input levels. Time-sequenced measurements of the oscillating MEMS structures were also studied, and showed phase-reversal effects near the edges of transducer membranes. The scanning interferometry technique proved to be a very useful NDE tool for micro-characterization, and provided a wealth of information regarding the micro-features of the MEMS ultrasonic transducer which are currently not available with any other advanced NDE.

Recent advances in microelectronics and electronic packaging technology have led to a strong need in strain and stress analysis on micro and nano scale as well. Smallest cracks, delaminations and defects are a concern and can initiate defect propagation and can also cause failure of whole components. Crack detection and evaluation for crack lengths of very small microcracks are required. The authors present an approach to deformation measurement based on local correlation analysis on captured micrographs. Incremental displacement and strain fields are extracted from SEM and AFM images picked up for different object loading states. The application of the method is demonstrated by investigations of electronic packages. Fracture mechanics has been applied to combine the experimental results with advanced fracture and reliability concepts. Displacement fields in the immediate vicinity of micro and nano crack tips and crack opening displacements as small as some nanometers have been measured. They are used to determine fracture parameters. The results have also been used as input parameters in parametrized finite element simulation.

In this overview the mechanical, thermal and electrical properties of CVD (Chemical Vapor Deposition) diamond, determined by various non-destructive techniques, are highlighted and compared with calculations. In the case of Young's modulus the measurement results of high quality samples leads to an average value of 1126 GPa which is in good agreement with the calculated value of 1143 GPa and close to the Young+s modulus of single crystalline diamond. However, values as low as 242 GPa were determined on 300 +m thick bulk CVD diamond. The differences in the measurement results can be traced back to extended voids in the sample. A traditional heated bar technique was used to measure the temperature dependent thermal conductivity of CVD-diamond. High quality polycrystalline diamond films reached a room temperature thermal conductivity of 20.5 W cm^-1 K^-1. This value is comparable to the thermal conductivity of the best single crystal diamonds available. For the lower quality samples, boundary scattering and point defects are most likely responsible for the lower thermal conductivity. The electrical properties of B-doped polycrystalline diamond films were characterized by temperature dependent Hall and conductivity measurements. These measurements together with a semi-empirical model give insight in to the current transport mechanism. The model indicates, that the electrical mobility in diamond thin films is lower compared with single crystal diamond. However, the current conduction mechanism are essentially the same when compared with single crystal diamond.

For a long time quantitative data analysis for nondestructive evaluation of material properties with flash thermography meant a simple comparison of the measured temperature to a standard at a fixed time after excitation. With the advent of modern infrared camera technology a few improved concepts for extracting measurement data were developed, but no testing technique used for industrial applications took advantage of the physical properties of thermal diffusion. We present an analytical 1-dimensional model for a multi-layer sample that predicts the time evolution of the surface temperature after excitation. Based on an experimentally confirmed model for thermography with periodic excitation, this calculation tool permits to determine parameters like layer thickness or heat conductivity taking into account the complete data set instead of a single image. For samples with a geometry and thermal properties specified before measuring, an unknown parameter could be extracted from experimental data without further calibration standards. The model is also capable of accommodating arbitrary excitation and semitransparent layers. We present calculations of different test scenarios like layer thickness measurement. Finally, we compare the model calculation to test samples with known characteristics.

Thermal imaging is one of the fastest growing areas of nondestructive testing. The basic idea is to apply heat to a material and study the way the temperature changes within the material to learn about its composition. The technique is rapid, relatively inexpensive and most importantly has a wide coverage area with a single experimental measurement. One of the main goals in thermal imaging has been to improve flaw definition through advanced image processing. Tomographic imaging is a very attractive way to achieve this goal. Although there have been some attempts to implement tomographic principles for thermal imaging, they have been only marginally successful. One possible reason for this is that conventional tomography algorithms rely upon wave propagation (either electromagnetic or acoustic) and are inherently unsuitable for thermal diffusion without suitable modifications. In this research program, a modified approach to thermal imaging is proposed which fully accounts for diffusion phenomena in a tomographic imaging algorithm. Here, instead of the large area source commonly used in conventional thermal imaging applications, a raster scanned point source is employed in order to provide the well defined source- receiver positions required for tomographic imaging. A thermal diffusion modified version of ART is used for image reconstruction. Examples of tomographic images are presented from synthetically generated data to illustrate the utility of the approach.