Current understanding and future research directions at the onset of the next century of sintering science and technology

Bordia, Rajendra K.; Kang, Suk–Joong L.; Olevsky, Eugene A.

doi:10.1111/jace.14919

Cited by 254 publications

(148 citation statements)

References 359 publications

(894 reference statements)

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“…Wang, 2016), and the activation energy which is relatively low for nanoscaled particles (Dai, 2018). The lower pressure and temperature of sintering imply less energy and time for densification, and that surface diffusion, a nondensifying mechanism, may play some role in the coalescence of the nanoparticles (Bordia et al, 2017). Thus, the attachment microstructure, which remains in an intermediate, thermodynamically unstable stage of incomplete sintering immediately postmanufacture, continues to densify under operation.…”

Section: Damage Formation Within the Sintered Attachment Layermentioning

confidence: 99%

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Agyakwa

Dai

et al. 2019

Journal of Microscopy

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Summary A time‐lapse study of thermomechanical fatigue damage has been undertaken using three‐dimensional X‐ray computer tomography. Morphologies were extracted from tomography data and integrated with data from microscopy modalities at different resolution levels. This enables contextualization of some of the fine‐scale properties which underpin the large‐scale damage observed via tomography. Lateral views of crack development are presented, which show networks analogous to mud‐cracks. Crack fronts which develop in the most porous regions within the sintered attachment layer travel across the boundary into the copper substrate. The propagation characteristics of these cracks within the substrate are analysed. Evidence is provided of heterogeneous densification within the sintered joint under power cycling, and this is shown to play a major role in driving the initiation and propagation of the cracks. Examination of the texture (differing levels of X‐ray absorption) of virtual cross‐sectional images reveals the origins of the nonuniformity of densification. Finally, cracks within the sintered joint are shown to have a negligible impact on the conduction pathway of the joint due to their aspect ratio and orientation with respect to the assembly. Lay Description This paper concerns the use of three‐dimensional (3D) X‐ray tomography, a nondestructive technique, to perform cradle‐to‐grave studies of sintered nanosilver die‐attachments under operation. Sintered nanosilver die‐attachments have been proposed as a more reliable and environmentally friendly alternative to solder alloy joints for emerging power electronics module designs. However, their degradation mechanisms are not as well understood. This same sample‐study is about observing how the fine‐scale structure of a sintered attachment evolves and degrades over time. Using 3D tomography affords otherwise infeasible perspectives, such as virtual cross‐sections in the lateral plane of the attachment. These perspectives provide qualitative information which elucidates the degradation mechanisms. They demonstrate, for example, that the structure of the sintered attachment densifies under operation, and a consequence of this is the formation of shrinkage cracks in the most porous regions, much like mud‐cracks. Other imaging techniques (metallographic etching and scanning electron microscopy) have been used in correlation with 3D renderings of these cracks to analyse their propagation and reveal their relationship both with the internal structure of the sintered attachment itself, and the structure of the substrate to which it is joined. It is shown that the cracks develop within the sintered attachment layer and eventually cross over into the substrate. A comparison of two sintered attachments with contrasting bulk porosities allows the effect of initial bond quality on crack development to be examined.

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Section: Damage Formation Within the Sintered Attachment Layermentioning

confidence: 99%

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Agyakwa

Dai

et al. 2019

Journal of Microscopy

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“…In the past 15 years, considerable effort has been put into investigating the effect of an electric field on the sintering behavior of ceramics. In Spark Plasma Sintering (SPS), for example, electric currents are used to directly heat a material enclosed in a graphite die while applying simultaneously mechanical pressure . Since 2010, another field‐assisted sintering process, named flash sintering, attracted attention .…”

Section: Introductionmentioning

confidence: 99%

Grain growth in strontium titanate in electric fields: The impact of space‐charge on the grain‐boundary mobility

et al. 2018

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This study investigates grain growth in the perovskite oxide strontium titanate in an electric field. The seeded polycrystal technique was chosen as it provides a sensitive and controlled setup to evaluate the impact of different parameters on grain growth due to the well‐defined driving force for grain growth. Current blocking electrodes were used to prevent Joule heating. The results show faster grain growth, and thus, higher grain‐boundary mobility at the negative electrode. It is argued that the electric field causes point‐defect redistribution, resulting in a higher oxygen vacancy concentration at the negative electrode. The local oxygen vacancy concentration is suggested to affect the space‐charge potential at the grain boundaries. A thermodynamic treatment of the grain‐boundary potential at a grain boundary without field shows that for a high oxygen vacancy concentration less space‐charge and less accumulation of cationic defects to the boundary occurs. Therefore, at the negative electrode, a higher oxygen vacancy concentration results in less space‐charge and less accumulation of cationic defects. The lower degree of defect accumulation requires less diffusion of segregated defects during grain‐boundary migration, so that at the negative electrode faster grain growth is expected, as found in the experiments.

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“…In Figure 2B, when samples are sintered at 1600°C, with the increase in yttrium oxide content from 3 wt% to 9 wt%, the amount of YAG phases is gradually increased. 20 In samples sintered at 1600°C, these connected pores between grain boundaries gradually become their own isolated pores, and continue to shrink. Figure 3 shows the map-scanning images of Al 2 O 3 -based ceramic cores produced with yttrium oxide of 9 wt% at 1600°C.…”

Section: Resultsmentioning

confidence: 99%

“…At this time, the diffusion mode is dominant, and the lattice and grain boundary diffusion occur. 20 In samples sintered at 1600°C, these connected pores between grain boundaries gradually become their own isolated pores, and continue to shrink. The movement of grain boundary causes the large particles to continue to grow.…”

Section: Resultsmentioning

confidence: 99%

Influence of yttrium oxide addition and sintering temperature on properties of alumina‐based ceramic cores

Zhao

Yang

et al. 2019

Int J Applied Ceramic Tech

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Al2O3‐based ceramic cores with a uniform microstructure were fabricated successfully by a traditional pressing forming method, in which Al2O3 powders were used as matrix and yttrium oxide as additive. The influences of yttrium oxide content and sintering temperature on properties of ceramic cores were studied carefully. Results indicated that a higher sintering temperature benefited the preparation of ceramic cores with excellent properties. As the temperature was above 1400°C, the reaction of Al2O3 and yttrium oxide occurred, leading to the formation of YAG phases. And, YAG was uniformly adhered on the surface of Al2O3 particles, exerting a good role in connecting Al2O3 particles. Based on XRD analyses, it was found that the increase in the sintering temperature could promote the formation of more YAG phases. When sintering temperature was adjusted to 1600°C, with the increase in the yttrium oxide content, their relative density developed a trend of decreasing first and then increasing, while the apparent porosity had an opposite change tendency. With the increase in the sintering temperature, the line shrinkage and bending strength of Al2O3‐based ceramic cores both increased gradually. In our research, their bending strength reached to 53.5 MPa and apparent porosity was 33.9% when the ceramic cores were prepared with 9 wt% yttrium oxide at 1600°C.

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Current understanding and future research directions at the onset of the next century of sintering science and technology

Cited by 254 publications

References 359 publications

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Grain growth in strontium titanate in electric fields: The impact of space‐charge on the grain‐boundary mobility

Influence of yttrium oxide addition and sintering temperature on properties of alumina‐based ceramic cores

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