Synchrotron Radiation X-ray Microtomography Research Articles

J0601-5-5 チップ抵抗鉛フリーはんだ接合部の熱疲労き裂の放射光X線CTを応用した非破壊観察([J0601-5]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(5))

A synchrotron radiation X-ray micro-tomography system called SP-μCT with a spatial resolution of about 1μm has been developed in SPring-8. In this work, SP-μCT was applied to the nondestructive observation of fatigue crack propagation appearing due to thermal cyclic loading in lead-free solder joints of chip type resistor. In order to show the whole image of crack propagation process, 3D rendered images of fatigue cracks was extracted from CT images. The results show that nondestructive inspection of lead-free solder joints of chip type resistor by the micro CT system is useful in combination with three-dimensional visualization of the thermal fatigue cracks.

Three-dimensional fatigue crack growth behavior in an aluminum alloy investigated with in situ high-resolution synchrotron X-ray microtomography

The fatigue crack propagation process in an Al–Mg–Si alloy was investigated using in situ high-resolution synchrotron radiation X-ray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120,000 fatigue cycles. Three-dimensional rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and closure levels was discussed and interpreted.

放射光X線マイクロCTによるフリップチップはんだ接合部における熱疲労寿命の非破壊評価(<小特集>電子機器の熱・機械信頼性と機械工学)

A synchrotron radiation X-ray microtomography system called SP-μCT with a spatial resolution of about 1μm has been developed in SPring-8. Our research group first applied SP-μCT to the nondestructive evaluation of phase growth and fatigue crack propagation due to thermal cyclic loading in flip chip solder micro-bumps. The obtained CT images enabled us to evaluate the lifetime of the bumps to the initiation of fatigue cracks by estimating the increase in phase growth parameter. Additionally, a refraction-contrast imaging technique was used to visualize the crack propagation process of the fatigue cracks, and then the propagation lifetime was also estimated precisely. These results show the possibility that nondestructive inspection by synchrotron radiation X-ray microtomography system can be useful for the clarification of fatigue mechanism and the evaluation of fatigue lifetime in micro-joints.

Wavelet-based local region-of-interest reconstruction for synchrotron radiation x-ray microtomography

Synchrotron radiation x-ray microtomography is becoming a uniquely powerful method to nondestructively access three-dimensional internal microstructure in biological and engineering materials, with a resolution of 1μm or less. The tiny field of view of the detector, however, requires that the sample has to be strictly small, which would limit the practical applications of the method such as in situ experiments. In this paper, a wavelet-based local tomography algorithm is proposed to recover a small region of interest inside a large object only using the local projections, which is motivated by the localization property of wavelet transform. Local tomography experiment for an Al–Cu alloy is carried out at SPring-8, the third-generation synchrotron radiation facility in Japan. The proposed method readily enables the high-resolution observation for a large specimen, by which the applicability of the current microtomography would be promoted to a large extent.

Nondestructive Evaluation of Thermal Phase Growth in Solder Ball Microjoints by Synchrotron Radiation X-Ray Microtomography

In high-density packaging technology, one of the most important issues is the reliability of the microjoints connecting large scale integrated circuit chips to printed circuit boards electrically and mechanically. The development of nondestructive testing methods with high spatial resolution is expected to enhance reliability. An X-ray microtomography system called SP-μCT has been developed in Super Photon ring-8 GeV (SPring-8), the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied in the nondestructive evaluation of microstructure evolution, that is, the phase growth due to thermal cyclic loading in solder ball microjoints. Simulating solder microjoints used in a flip chip, specimens were fabricated by joining a Sn–Pb eutectic solder ball 100 μm in diameter to a steel pin in the usual reflow soldering process. The phase growth process was determined by observing the computed tomography (CT) images obtained consecutively at the fixed point of the target joining. In the reconstructed CT images, the distribution of the constituent phases in the Sn–Pb eutectic solder was identified based on the estimation value of the X-ray linear attenuation coefficient. Consequently, the microstructure images obtained nondestructively by SP-μCT provided us with the following useful information for evaluating the reliability of the solder microjoints. First, each phase involves not dispersing particles but a three-dimensional monolithic structure like a sponge. Second, the phase growth proceeds in such a way that the average phase size to the fourth power increases proportionally to the number of cycles. Finally, in the vicinity of the joining interface, more rapid phase growth occurs compared to the other regions because local thermal strain due to the mismatch of thermal expansion leads to a remarkable phase growth.

1928 放射光X線CT装置を用いたフリップチップ接合部における熱疲労き裂進展過程の評価(J16-4 電子情報機器,電子デバイスの熱制御と強度・信頼性評価(4),J16 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)

1928 放射光X線CT装置を用いたフリップチップ接合部における熱疲労き裂進展過程の評価(J16-4 電子情報機器,電子デバイスの熱制御と強度・信頼性評価(4),J16 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)

放射光X線マイクロCTによるSn-Pbはんだ接合部における微細組織変化の観察

放射光X線マイクロCTによるSn-Pbはんだ接合部における微細組織変化の観察

Characterisation of fretting fatigue damage using synchrotron X-ray micro-tomography

The fretting fatigue damage of mechanical joints is studied experimentally by considering the following scenario: first, the crack nucleation in the joint is investigated via fretting tests. Second, the propagation of the fretting cracks under cyclic uniaxial tensile loading is carried out and analysed. Synchrotron radiation X-ray micro-tomography is used to image for the very first time the three-dimensional shape of the initial fretting cracks as well as that of the propagating cracks at different stages of the fatigue life, thanks to a dedicated set-up. This technique brings new experimental data on the influence of the local microstructure on fretting fatigue damage, initiation and growth.

Advances in synchrotron radiation microtomography

Abstract The use of synchrotron radiation X-ray microtomography rests on the exploitation of the beam coherence, the high spatial (submicron) or temporal resolution (s), in situ and real time experiments and quantitative measurements. Selected original applications showing these capabilities are presented. They include the phase contrast imaging of Si particles in Al alloys, the nucleation of fatigue cracks in structural materials, the visualization of hollow silica spheres within polymer foams, and the real time observation of the semi-solid state in Al–Cu alloys.

Fatigue crack propagation: In situ visualization using X-ray microtomography and 3D simulation using the extended finite element method

The propagation of a semi-elliptical crack in the bulk of an ultrafine-grained Al–Li alloy has been investigated using synchrotron radiation X-ray microtomography. In this material, the studied crack, despite its small dimension, can be considered as “microstructurally long” and described in the frame of the linear elastic fracture mechanics. The extended finite element method is used to calculate the stress intensity factors along the crack front taking into account the three-dimensional geometry extracted from the tomographic images. For the same nominal value of the stress intensity factor range, crack propagation is faster in the bulk than at the surface. The observed anisotropy is attributed to the variation of the closure stress along the crack front between surface and bulk. The experimentally observed fatigue crack propagation is compared to numerical simulations. Good agreement is found when a linear variation of closure stress along the crack front is taken into account in the “3D crack propagation law” used for the simulation.

3D Visualisation of Short Crack Propagation in Al Alloy Using High Resolution Synchrotron X-Ray Microtomography

In-situ fatigue tests monitored by Synchrotron Radiation X-ray microtomography were carried out in order to visualize the three dimensional (3D) shape and evolution of short cracks in the bulk of a cast Al alloy. After the in-situ fatigue test the sample has been infiltrated with liquid Gallium (Ga) in order to visualize the grain structure of the material. Irregularities of the crack advance along the crack front can clearly be correlated to the grain structure of the material.

In situ high resolution synchrotron x-ray tomography of fatigue crack closuremicromechanisms

Fatigue crack closure has been identified as an important factor in determining crack growthrates. However, the methods of measurement of crack closure remain the subject of ongoingcontroversy. To date, computed finite element models, analytical models and widelyestablished compliance-based experimental methods have offered limited micromechanicalinsight and/or direct information on the active crack tip region within bulk material. Tounderstand the absolute contributions of crack closure mechanisms, such as plasticity-inducedand roughness-induced closure, to fatigue properties, an internal, three-dimensional insightinto crack behaviour during loading and unloading is clearly of value. In this work,synchrotron radiation x-ray microtomography is carried out at a high resolution of0.7 µm to provide unique three-dimensional in situ observation of steady state plane strain fatiguecrack growth in a 2024-type Al alloy (Al–Cu–Mg–Mn). Using such high resolution imaging(additionally exploiting the phase contrast effect in interface imaging), the details of fatiguecracks are readily observed, along with the occurrence of closure. A novel microstructuralcrack displacement gauging method is used to quantify the mixed mode character of crackopening displacement and the closure effect. A liquid gallium grain boundary wettingtechnique is used in conjunction with the microtomography to visualize the correlationbetween the three-dimensional structure of the grains and fatigue crack behaviour.Subsequently, electron backscattering diffraction assessment of the grain orientation on thesamples provides a uniquely complete 3D description of crack–microstructure interactions.

Three-dimensional quantitative analysis of polymer foams from synchrotron radiation x-ray microtomography

We propose a three-dimensional and high-resolution quantitative image analysis technique for the investigation of the internal microstructure of polymer foams. Microscopy, which is the conventional method of investigation of foams, images only the surface of samples, though, three-dimensional x-ray computed microtomography (μCT) enables the non-destructive imaging of multiple slices of a sample. It is a powerful technique for the examination of porous and multiphase materials. In this paper, we present the application of three-dimensional synchrotron radiation μCT for the characterization of foam samples. After a brief description of the imaging system, we present three-dimensional image-processing tools developed to extract structural parameters quantifying the internal structure of foams. Results of this three-dimensional quantitative image analysis on various types of plasticized poly vinyl chloride foams are presented. This approach provides a tool to study the relationships between the foam microstructures and their physical properties.

Study of the interaction of a short fatigue crack with grain boundaries in a cast Al alloy using X-ray microtomography

Synchrotron Radiation X-ray microtomography is used to visualize and analyze simultaneously the three-dimensional shape of crystallographic grains containing a short fatigue crack in a cast Al alloy. The visualization of the grains is based on the decoration of Al grain boundaries by liquid Ga which serves as a selective contrast agent. The intricate three-dimensional shape of the fatigue crack, as well as the crack stops observed on the sample surface, are correlated to the grain structure of the material. Complementary measurements of the grain orientation on the sample surface by electron backscattering diffraction (EBSD) allow us to discuss and interpret the observations in terms of possible crack propagation mechanisms.

High resolution three-dimensional visualization and characterization of coronary atherosclerosis in vitro by synchrotron radiation x-ray microtomography and highly localized x-ray diffraction

Human atherosclerotic plaques in both native and bypass arteries have been visualized using microtomography to provide additional information on the nature of coronary artery disease. Plaques contained within arteries removed from three white males aged 51, 55 and 70 are imaged in three-dimensions with monochromatic synchrotron x-ray radiation. Fields of view are 658 × 658 × 517 voxels, with cubic voxels ranging from 12 to 13 µm on a side. X-ray energies range from 11 to 15 keV (bandpass approximately 10 eV). At lower energies, high local absorption tends to generate reconstruction artefacts, while at higher energies the arterial wall is scarcely visible. At all energies, calcifications are clearly visible and differences are observed between plaques in native arteries (lifetime accumulations) versus bypass arteries (plaques developing in the interval between the heart bypass operation and the autopsy). In order to characterize coronary calcification, a micro-focused, 50 µm2, 25 keV x-ray beam was used to acquire powder diffraction data from selected calcifications. Also, large calcifications were removed from the native arteries and imaged with 25 keV x-ray energy. Calcifications are composed of hydroxyapatite crystallites and an amorphous phase. In summary, native calcifications are larger and have a higher fraction of hydroxyapatite than calcifications from the bypass arteries.

Penetration of liquid gallium into the grain boundaries of aluminium: a synchrotron radiation microtomographic investigation

The penetration of liquid metals into the grain boundaries of polycrystalline solid metals is a precursor process triggering liquid metal embrittlement for some specific metal couples. Synchrotron radiation X-ray microtomography is used to investigate the penetration of liquid gallium into the grain boundaries of aluminium. The large difference in absorption coefficients between Ga and Al allows micrometer thick liquid Ga films to be observed as they are wetting grain boundaries of Al. The effects of annealing are presented and discussed. This technique opens the way for in-situ measurements of the kinetics of liquid metal penetration in materials. It might also be used to visualise and analyse the three-dimensional grain structure of a metallic polycrystal.