Acoustic Microscopy Research Articles

Nanostructural Characterization of Luminescent Polyvinyl Alcohol/Graphene Quantum Dots Nanocomposite Films.

This study focuses on the fabrication of polymer nanocomposite films using polyvinyl alcohol (PVA)/graphene quantum dots (GQDs). We investigate the relationship between the structural, thermal, and nanoscale morphological properties of these films and their photoluminescent response. Although according to X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and differential thermal analysis (DTA), the incorporation of GQDs does not significantly affect the percentage crystallinity of the PVA matrix, for a range of added GQD concentrations, atomic force microscopy (AFM) showed the formation of islands with apparent crystalline morphology on the surface of the PVA/GQD films. This observation suggests that GQDs presumably act as nucleating agents for island growth. The incorporation of GQDs also led to the formation of characteristic surface pores with increased stiffness and frictional contrast, as indicated by ultrasonic force microscopy (UFM) and frictional force microscopy (FFM) data. The photoluminescence (PL) spectra of the films were found to depend both on the amount of GQDs incorporated and on the film morphology. For GQD loads >1.2%wt, a GQD-related band was observed at ~1650 cm-1 in FT-IR, along with an increase in the PL band at lower energy. For a load of ~2%wt GQDs, the surface morphology was characterized by extended cluster aggregates with lower stiffness and friction than the surrounding matrix, and the PL signal decreased.

Antimetastatic lung cancer therapy using alkaloid Piperlongumine noncovalently bound to С60 fullerene

A novel nanoformulation, C60 fullerene loaded with a plant alkaloid Piperlongumine (PL) molecules (C60-PL nanocomplex), as a potential drug for the treatment of highly metastatic lung cancer was created and characterized by using ultrasonic technology, computer simulation, atomic force and scanning tunneling microscopy. The aim of the study was to evaluate the antimetastatic potential of PL alone and the C60-PL nanocomplex using Lewis lung carcinoma (LLC) cell line as a model. Evidence has been obtained that the 2:1C60-PL nanocomplex is a potent agent capable of effectively reducing the survival, migration and invasion of LLC cells in vitro, as well as tumor growth and metastasis in vivo compared to free PL. These effects in cell behavior were shown to be associated with an increased Bax expression and high level of cleaved PARP confirming the proapototic potential of C60-PL nanocomplex as well as down-regulation of the mRNA of epithelial-mesenchymal transition regulator Twist1 and cancer stem cell marker CD44, a reduced level of phosphorylated mTOR and adaptor protein Ruk/CIN85. Histological analysis of the lung tissue of LLC-bearing mice showed that in animals that received the C60-PL nanocomplex, the regression of metastases prevailed over their growth. The obtained results allow to conclude that the proposed C60-PL nanocomplex represents a promising drug for the treatment of metastatic lung cancer.

High frequency acoustic microscopy imaging of pellet cladding interface in nuclear fuel rods

In Pressurized Water Reactors (PWRs), fuel rods play a crucial role in generating nuclear energy. These rods consist of ceramic pellets, such as UO2 or (U,Pu)O2, enclosed in a zircaloy cladding tube, leaving an initial gap between the pellets and the cladding. As the reactor operates and the fuel undergoes irradiation, both the ceramic pellets and the zircaloy cladding experience transformations, causing the gap between them to gradually close. This phenomenon has a significant impact on the thermomechanical behavior of the fuel rod.Understanding the nature of the bonding that occurs during irradiation is essential for ensuring the safe and efficient operation of the reactor. To investigate the evolution of the contact state between the fuel pellets and the cladding during irradiation, a detailed analysis of the pellet-cladding interface after irradiation is necessary. However, traditional examination methods might be destructive or incapable of providing the desired level of precision and resolution.The Institute of Electronic and Systems at the University of Montpellier (IES – UMR CNRS 5214), in collaboration with the Alternative Energies and Atomic Energy Commission (CEA) and Electricité de France (EDF), has developed a specialized high-frequency acoustic microscope for imaging and non-destructively inspecting the pellet/cladding interface. The design of the acoustic microscope takes into account the complexity of the fuel rod's structure and the challenges associated with imaging the pellet/cladding interface by utilizing high-frequency ultrasound.In this paper, we present the ability of this acoustic microscope to acquire 2D images with controlled displacements of the sample rod along both its axial and circumferential directions thanks to a card with a high sampling frequency reaching 2 GHz. This capability is crucial because the geometrical, chemical, and mechanical properties of the fuel pellet-cladding contact are not uniform in these directions. By obtaining detailed acoustic images, we can identify specific regions where the fuel pellets and the cladding were in contact during irradiation. In this research, a resolution study is carried out to validate the microscope's ability to investigate the fuel rod and achieve the desired resolutions.Testing on real samples requires a specific configuration of the microscope, which must be adapted to the irradiation conditions. This is why, before proceeding to this stage, it is necessary to carry out tests on representative samples to validate the achievement of the desired resolution. So we’re also presenting the first acoustic images obtained on the zircaloy alloy claddings.

Matched impedance amplifier design for shear-force acoustic near-field microscopy

Efficient detection of the acoustic signal constitutes the most critical aspect in Shear-force Acoustic Near-field Microscopy, for reliably characterize the dynamic response of confined fluids under shear stress. The near-field acoustic emission from the fluid is monitored as the probe gradually approaches to, and subsequently retracts from, the substrate. Herein we report a 7dB improvement in signal-to-noise sensitivity in detecting the acoustic emission from the fluid trapped between a flat sample and the apex of a tapered probe (the latter attached to a quartz tuning fork of 32 kHz resonance frequency). The new design capitalizes on the inherent capacitance of the SANM acoustic sensor (comprising a pile of piezoelectric plates) and a proper matching inductor/capacitance combination to, altogether connected in a tank-circuit fashion, optimize the sensor’s response at 32 kHz. A detailed construction of the circuit amplifier, as well as detailed frequency response bandwidth and noise characterization, is included herein.

Defluxing of Copper Pillar Bumped Flip Chips

Flip-chip technology has become increasingly prevalent within the electronics industry due to its lower cost, increased package density, improved performance while maintaining or improving circuit reliability, and increased I/O density. This technology is a method for interconnecting semiconductor devices such as IC chips and MEMS to external circuitry with solder bumps that have been deposited onto the chip pads. However, solder bump technology has proven to be problematic below 125µm pitch as it is challenging to manufacture and assemble. As pitch is reduced, both standoff height and joint reliability decrease, and the risk of shorts are increased. Given this, traditional solder bumps are being replaced by copper pillar technology. Used as first-level interconnect, copper pillar technology is increasing in popularity. Copper pillar technology has been documented to be efficient to pitches of 80 µm and appears to be promising down to pitches of 40µm. Along with reduced pitches, copper pillar brings several other benefits, including improved electrical performance. This technology is becoming popular since it allows for smaller devices, greater control of standoff height and reduces the number of package substrate layers which reduces cost. Devices utilizing copper pillar technology have more interconnects per surface area resulting in tighter pitch and lower standoffs heights. As standoff height reduces, flux residues have less area to outgas during reflow. For that reason, there is a critical need to investigate the conditions that would be required to successfully remove flux residues to ensure the functionality and reliability of the final product. Flux residues can affect reliability, especially with respect to underfill in two different ways. Firstly, if present on the solder bump, substrate or die, thin films of flux residue can significantly reduce interfacial adhesion between the underfill and the surfaces. Once the underfilled device is stressed by thermal shock, humidity or other factors, the underfill delaminates from the surface, and a gap can be detected using acoustic microscopy. Secondly, fluxes can affect reliability by physically impeding the flow of underfill material. Flux residue buildup in the gap between bumps or between the die and the substrate can narrow the gap to a point where the underfill cannot flow or the edges flow faster, encapsulating air and creating a void. To ensure a void-free underfill, homogenous wetting of the underfill must occur on all surfaces. If wetting is not homogeneous, voids in the uncured underfill may translate into reliability problems later. The study involved using straight DI-water and novel low-concentration alkaline cleaning agent on copper pillar bumped flip chips. The challenge was to effectively clean flux residues underneath these components. The outcome of this study could provide a benchmark for conducting further studies involving bump pitch lower than 15 µm and denser packages including 2.5Ds and 3Ds. The cleaning assessment methodologies employed analytical/functional testing including FTIR, Ion Chromatography, SEM/EDX, Thermal Cycling (TC) Test, Underfill Test, High Temp Storage Life (HTSL) Test and Moisture Sensitivity Level 3 (MSL-3) Testing.

Monitoring near-field acoustic emission from confined water under shear interaction with blunt tips

Mesoscopic water adhered to a surface at ambient conditions is typically reported to behave as sticky glue. Still, Shear-force Acoustic Near-field Microscopy (SANM), complemented with the Whispering Gallery Acoustic Sensing (WGAS) technique, has demonstrated the ability of a water meniscus, formed at the nanometer-sized gap between a sharp probe and a flat surface, to remain flexible enough for emitting near-field acoustic waves while being subjected to shear interactions exerted by a laterally oscillating probe. To gain insights on the meniscus formation process, as well as to better understand its viscoelastic response, purposely blunt probes (composed of multiple sharp asperities) are used. The experimental results suggest the stochastic formation and break of water bridges at multiple asperities on the probe, each providing an energy dissipation channel from the lateral motion of the probe to the fluid. Despite heavily damping the lateral motion of the probe, the ability of the large fluid meniscus to emit acoustic wave is recovered by properly increasing the amplitude of the lateral oscillations of the probe. Overall, monitoring the behavior of large meniscus adhered to a blunt probe allows to infer the behavior of smaller volume meniscus adhered to sharp probes.

Acoustic monitoring humidity effects on the formation of water bridges at sharp contacts

Shear-force Acoustic Near-field Microscopy (SANM) and Whispering Gallery Acoustic Sensing (WGAS) are used to evaluate the role of humidity on the formation and rupture of water meniscus bridges that form between a laterally oscillating tapered probe and a flat substrate. SANM monitors the near-field acoustic wave emitted by the meniscus, while WGAS monitors acoustically the probe’s amplitude of oscillation, as a function of the probe-sample distance. In the instances reported here, the SANM/WGAS measurements are performed in frequency modulation modality, which allows to discriminate the elastic and inelastic components of the probe-fluid-substrate interaction. The response signal traces, acquired when the probe first approaches and then retracts from the sample at 56% relative humidity (or below), revealed absence of hysteresis; this result persists when performing the same experiment a few days later. However, as the humidity increases (different trials from 56% to 67% are included) a notorious hysteresis is observed between the approach and retraction traces. The results indicate that, as the probe approaches the substrate, a higher humidity promotes an increase of stochastic instabilities in the probe-fluid-substrate interactions (reflected in higher damping effects on the probe, and instabilities in the probe-sample distance feedback control). However, the elastic response of the water meniscus prevails over damping effect, as revealed by the greater acoustic emission despite a decrease in the probe’s amplitude. These measurements are relevant to investigations on the dynamic behavior of fluids near hydrophobic/philic substrates, and wetting properties of solids and nanotribology phenomena in general.

Chip to Wafer Hybrid Bonding Development for High Volume Manufacturing

The adoption of 3D architectures in advanced packaging between chips is driven by high performance computing and artificial intelligence requirements [1,2]. Hybrid bonding (HB) is essential for this transition, as it offers high I/O connectivity with fine pitch (<10µm), increases system level bandwidth and speed, and improves thermal budget. Chip-to-Wafer (C2W) HB further offers the benefit of using known-good-die to achieve higher yield, especially for heterogeneous integration. This paper describes the necessary conditions to achieve a successful C2W HB suitable for high volume manufacturing (HVM) production. HB can be achieved in a 2-step process; firstly, by leveraging on the initial forces of surface interaction at atomic proximity of dielectric-dielectric interface to form the “tacking,” which is the initiation of the bonding, and finally, following up with a fusion process by annealing at an elevated temperature (100°C-400°C) to form both stronger dielectric-dielectric covalent bonds with the release of excessive water (H2O) molecules, as well as metal-metal diffusion which will enable the electrical connection. A successful bond can be achieved with careful surface engineering of the dielectric [3], typically with dielectric surface roughness values of <0.4nm. Figure 1 shows an optimized result, demonstrating C2W HB with Cu-Cu interdiffusion. Die-to-die (D2D) or C2W HB has many challenges. Removal of barrier spikes/protrusions in the nm-scale that is not critical in wafer-to-wafer HB is paramount in C2W HB, likely attributed to the reduced volume/weight and no physical pressure applied after the die-tacking process. A chemical-mechanical polishing (CMP) is a critical step to create necessary pre-conditions for HB and must be carefully and meticulously optimized. Prior to bonding, a proper activation step is required on the dielectric surfaces. The delay between activation and bonding can weaken the initial bonds. Q-time control and surface cleanliness are critical for consistent performance and high bonding yield. A repeatable process performance with low contact angles, no degradation of dielectric roughness, and Cu dishing performance is imperative. Results will show that such milestones were achieved with the state-of-the-art systems at the HB Centre of Excellence. Cleanliness is undoubtedly a salient criterion for successful C2W HB. Contaminants such as particles and volatile organic compounds can be detrimental to bonding strength and metal-metal contact resistance. Unlike other advanced packaging methods such as TCB, there is no gap between the die and substrate, nor is there solder or glue that can help to mitigate the impact of any particles present. Since the bonding occurs between flat dielectric to dielectric surfaces, any particle entrapped will result in big voids, rendering the device useless. As such, this paper will also outline the cleanliness levels achieved in the system. Equivalent to this criterion is also the mechanics behind the bonding mechanism itself. At the core of an HB, the process is the bond front propagation, which, if not controlled, can lead to voids, die damage, and loss of accuracy, amongst other things. As such, BESI has developed a series of tools allowing controlled die shaping to initiate bonding at specific locations as well as to control the die release. Die placement accuracy is typically measured using IR equipment. This paper will show and analyze the accuracy results of actual C2W HB dies. This paper will also discuss additional data from post-bond confocal scanning acoustic microscopy (cSAM), contact resistance, and daisy-chain continuity E-test.

Observations of amyloid breakdown by proteases over time using scanning acoustic microscopy

Amyloid consists of insoluble beta-fibrillar proteins with stable structures. The Congo red staining method for histologically detecting amyloid is unsuitable for quantitatively assessing amyloid fibers. Scanning acoustic microscopy (SAM) detects the attenuation of sound (AOS) through sections. This study aimed to clarify whether AOS values reflected the amount of amyloid fibril degradation in tissues. Formalin-fixed paraffin-embedded unstained sections of various types of amyloidosis were digested with different endopeptidases. The AOS images after digestion were observed over time via SAM. The corresponding Congo red-stained images were followed to identify the amyloid. The amyloid and nonamyloid portions were statistically examined over time to determine the changes in the AOS values. Most of the amyloid areas showed significantly different AOS values from nonamyloid portions before digestion and significantly decreased after digestion; these findings corresponded with the disappearance and waning of the Congo red staining in the light microscopic images. Some nonamyloid areas with high AOS masked the reduction in AOS in the amyloid areas. The method used in this study may help detect the amyloid quantity and determine the appropriate treatment method for removing amyloid deposits from tissues.

Noninvasive imaging of rat-derived microglia and its reactivity to inflammatory molecules via acoustic impedance microscopy.

Microglia, the brain's immune cells, play important roles in neuronal differentiation, survival, and death. The function of microglia is deeply related to the morphologies; however, it is too complex to observe conventionally and identify the condition of living microglia using optical microscopes. Herein, we proposed a new method to observe living cultured microglia and their reactivity to inflammation via the acoustic impedance mode of a scanning acoustic microscope. Primary cultured microglia collected from rat pups exposed to acetamiprid, an insecticide, in utero were observed with both acoustic interface impedance mode (C-mode) and transparent three-dimensional impedance mode (B-mode). We characterized microglia into four types based on the results obtained from acoustic impedance, cytoskeletal information, and laser confocal imaging. Biphasic acoustic observation using B-mode and C-mode gave us information regarding the dynamic morphologies of living microglia treated with adenosine triphosphate (ATP) (600μmol/L), which reflects distress signals from inflamed neurons. Acetamiprid exposure induced microglia response even in the neonatal period. ATP stimulus altered the shape and thickness of microglia with a change in the bulk modulus of the cell. Three-dimensional alteration with ATP stimulus could be observed only after biphasic acoustic observation using B-mode and C-mode. This acoustic observation was consistent with confocal observation using anti-Iba-1 and P2Y12 immunocytochemistry. This study demonstrated the adequacy of using a scanning acoustic microscope in analyzing microglia's shape, motility, and response to inflammation.

Experimental assessment of barely visible impact damage carbon fiber reinforced epoxy composite using ultrasound method

Background Carbon fiber reinforced epoxy (CFRP) is susceptible to impact damage which could resulted in reduction of the mechanical properties. This paper studies the architecture of barely visible impact damage (BVID) to comprehend the extent of damage on quasi-isotropic CFRP laminates of varying thickness (i.e. 16, 24 and 32-ply laminates of 3, 4 and 5 mm respectively). Methods Quasi-static indentation is chosen to produce BVID on CFRP laminates, followed by using non-destruction evaluation method, namely conventional contact-type ultrasonic testing (UT) and C-mode scanning acoustic microscopy (C-SAM) method. Results The findings revealed (1) the size and shapes of the BVID on CFRP laminates, (2) no damage was found at the center of the impact point, and (3) the bridging between the point of impact to the outer damaged diameter due to the consequence of diverse orientation of carbon fiber strips which exhibit excellent mechanical properties before structural failure. Conclusions The results concluded that the UT and C-SAM method can identify both the pristine region and the internal damaged structures in CFRP laminates.

Laser Processing of Polyimide and Molybdenum Substrates for Extreme Environment Electronics

A desire in today’s electronic packaging technologies is to create more dense electronic packaging schemes. One method to achieve more dense electronic package integration is to use three-dimensional interconnects to minimize interconnect physical dimensions. Three-dimensional interconnect technologies, such as interposers, require a method of connecting electronics to electronic packages vertically. Thru silicon vias are a widely studied and explored vertical interconnect technology used in a variety of electronic packaging applications. Though silicon has high material hardness, the brittle nature of silicon substrates is a concern for robustness and reliability. These concerns only increase when the desired interconnect application is in extreme environments, such as cryogenic temperatures. A potential alternative to silicon in thru-via applications in extreme environments is molybdenum. Molybdenum is a commonly used material in many applications, such as automotive and aerospace, and has high material strength. Molybdenum is also a low coefficient of thermal expansion material, comparable to silicon, which in combination with high material strength lends to high reliability at extreme temperatures. A challenge of working with refractory metals such as molybdenum is that conventional CNC machining techniques require the use of machining coolants that may not be compatible with fabricated electronics and/or processes can become costly due to tool wear and the need for specialized equipment. Additionally, using molybdenum as a thru-via substrate requires the need for an electrically insulated layer, such as polyimide, within drilled molybdenum thru-holes to prevent the molybdenum substrate from shorting via connections. One potential solution to the above challenges is developing laser processing techniques to cut and drill molybdenum and polyimide. Laser processing is becoming a preferred method for inexpensive prototyping with high resolution and design versatility. This work seeks to meet the challenges described by developing laser cutting and drilling techniques for both molybdenum and polyimide for the use in cryogenic applications. This work will describe two laser processing configurations utilizing two different lasers to laser machine molybdenum and polyimide. This work will first describe the process strategies of laser cutting and drilling molybdenum as a stand-alone substrate. Aspects of laser processing on molybdenum, such as pattern repetitions and scanning speeds, will be described. Process parameter variations will be compared directly and evaluated. Additionally, post-laser processing steps, such as abrasive blasting, will be described and discussed. Next, the fabrication steps to achieve an insulating layer of polyimide in laser drilled holes as well as on each surface of the molybdenum will be detailed. Once polyimide has been cured, laser processing parameters to realize thru-holes in the polyimide-filled molybdenum drills will be presented. Adhesion of polyimide on the molybdenum substrate will be verified and demonstrated through the use of confocal scanning acoustic microscopy before and after polyimide laser processing. Cryogenic performance will be verified by completing confocal scanning acoustic microscopy after submersion in liquid nitrogen (~77 K) and compared with the pre-submersion microscopy images. Processes detailed in this work will open opportunities for future development of molybdenum-based interconnect structures for use in cryogenic applications. Acknowledgement We thank the Alabama Micro/Nano Science and Technology Center (AMNSTC) for providing access to fabrication and characterization facilities used in this work.

Affinity Matured CD72 CAR-T Improves Efficacy Versus Low Antigen Density B-Cell Non-Hodgkin Lymphoma Models

Background: Even in the CD19 CAR-T era, many patients with relapsed/refractory B cell non-Hodgkin lymphoma (B-NHL) need additional therapeutic options. Our group has identified CD72 as a therapeutic target for high-risk B-cell malignancies and validated anti-CD72 CAR-Ts (“nanoCAR”s) for these indications in relevant preclinical models (Nix et al., Cancer Discovery 2021, Temple et al., ASH 2022). However, patient B-NHL tumors may express a wide distribution of surface CD72, and our current CAR-T designs may be less efficacious for tumors with low antigen density. We previously described the development of affinity-matured binders extending from our initial published anti-CD72 nanobody clone (NbD4), with ~20-60x higher target affinity (Temple et al.). Here, we tested the hypothesis that these higher affinity binders would better eliminate low antigen density B-NHL models, both in vitro and in vivo, and impact other properties including avidity, and antigen binding epitopes. Methods: Anti-CD72 affinity-matured binders were developed by random mutagenesis of CDR regions of the nanobody clone NbD4 (described in Temple et al.). CAR-T cells were generated by lentiviral transduction. CAR-T cell efficacy was tested by in vitro cytotoxicity assays and Incucyte live-cell imaging against lymphoma cell lines. For in vivo studies, JeKo-1 tumor cells were implanted at 1e6 per mouse and then mice were treated with 3.5e6 CAR+ T-cells at day 7. Tumors from mice bearing JeKo-1 that relapsed on CAR-T treatment were isolated and used in Incucyte assays. Results: We analyzed publicly available datasets of patient cohorts and found that CD72 is widely expressed, though with a broad distribution, across diffuse large B cell lymphoma (DLBCL), follicular lymphoma, and Burkitt lymphoma patient samples. In both DLBCL and chronic lymphocytic leukemia (CLL), high expression of CD72 correlated with significantly shorter overall survival (DLBCL: GSE10846, n=233, p = 0.0382; CLL: GSE22762, n=107, p = 0.00124, log-rank test). We confirmed expression of CD72 on 8 lymphoma cell lines by flow cytometry. In vitro against a subset of these lines, affinity-matured clone NbD4.13 showed improved cytotoxicity compared to parental NbD4 and similar cytotoxicity to a humanized variant (H24 clone). We developed a JeKo-1 model of low CD72 antigen density (4.7x MFI reduction) by CRISPR/Cas9 knockout of endogenous CD72 and re-expression of a recombinant construct. In this “CD72 low” model, affinity matured clone NbD4.13 led to improved cytotoxicity vs. H24 ( p = 5.1e-4 by t-test). We previously showed that tumor isolated from JeKo-1 mice treated with H24 CAR appear to have reduced antigen expression at relapse (Temple et al.). We cocultured these post-relapse JeKo-1 tumors with various CD72 nanoCARs and found that NbD4.13 eliminates tumor significantly faster at 24 hours than H24 by live-cell imaging (p = 0.0054 by t-test). In vivo in a JeKo-1 model, NbD4.13 also out-performed the H24 clone with respect to survival benefit (p = 0.011 by log-rank for survival) ( Fig. 1). To assess if additional differences beyond affinity may determine the efficacy of NbD4.13, we performed structural modeling using AlphaFold and HADDOCK. However, this analysis predicts NbD4, NbD4.13 and H24 bind a similar non-linear epitope on the CD72 monomer. Furthermore, acoustic force microscopy did not reveal a significant difference in binding avidity for any of the compared CD72 nanoCAR constructs. Finally, we evaluated whether it could be possible to pharmacologically increase CD72, as co-treatment strategy to enhance efficacy of CD72 nanoCARs. We found that the Protein Kinase C inhibitor Bryostatin-1, previously demonstrated to increase CD22 antigen density (Ramakrishna et al., Clin Cancer Res 2019), could also significantly increase surface CD72 in vitro in both B-ALL and B-NHL models ( Fig. 2). Conclusion: NbD4.13-based anti-CD72 CAR is a promising candidate for further preclinical development for treatment of relapsed/refractory B-cell non-Hodgkin lymphoma. Given anticipated heterogeneity in CD72 expression in various lymphomas, pharmacologic co-treatment strategies may be considered to modulate tumor antigen density.

Non‐destructive evaluations of water uptake in epoxy coating

AbstractA commercial epoxy coating was studied on steel panels and as free films to investigate water uptake using non‐destructive techniques (gravimetric analysis, Electrochemical Impedance Spectroscopy [EIS], Attenuated Total Reflection‐Fourier Transform Infrared Spectroscopy [ATR‐FTIR], and Scanning Acoustic Microscopy [SAM]) after immersion in 3.5 wt% NaCl solution. In epoxy free films, water uptake showed rapid absorption initially, slowing down due to the counteracting process between water uptake and leachable content. Later, a mass decrease indicated leaching dominance. On coated steel, EIS revealed rapid water absorption within 72 h, followed by slower uptake up to 336 h. The continuous increase in water content resulted from observed coating layer swelling, confirmed by SAM. ATR‐FTIR analysis indicated hydrogen bonding of most absorbed water molecules to the epoxy matrix. By combining non‐destructive techniques, water uptake mechanisms into the epoxy coating film were proposed.

Automatic Classification of C-SAM Voids for Root Cause Identification of Bonding Yield Degradation

Wafer-level direct bonding technology is a key process for the production of backside illuminated (BSI) CMOS image sensor (CIS). Usually, constant-depth mode scanning acoustic microscope (C-SAM) 300mm wafer images are acquired and defect size distribution is provided to monitor defects that degrade bonding yield. This acquisition technique is used as it is nondestructive and is able to capture the full wafer. Current solutions are not providing information detailed enough to identify the root cause of this degradation. A consequence is that most measurements and classification is currently done manually which take time and have reproducibility issues. In this paper, we propose a rule-based method for the classification of the defects and automatic segmentation of the defects to extract precise measurements depending on the type of defect. The classes of defects are precisely defined based on their origin in the process. All these information will allow to reduce the time to analyze the images and improve the precision and consistency of the analysis. These results will allow to identify more precisely the defects thus the causes of yield degradation during bonding process.

Effect of competitive interactions on the structure and properties of blends prepared from an industrial lignosulfonate polymer

To explore the possibility of applying lignin in practice, an industrial lignosulfonate (0–50 vol%) was blended with four ionomers. The concentrations of carboxyl and carboxylate groups were systematically varied in the ethylene-acrylic acid copolymers to study the competition of hydrogen and ionic bonds forming between the components. The mechanical properties of the blends were determined by tensile testing. The structure was investigated by scanning electron microscopy, while deformation and failure processes were studied by acoustic emission measurements and microscopy. Interfacial interactions were quantitatively characterized by analyzing local deformation processes and by evaluating the composition dependence of the tensile strength using appropriate models. Molecular dynamics simulations indicated that carboxylate groups preferably form clusters in the ionomer phase, consequently, the increasing degree of neutralization results in ionomers with more and more self-interactions of components deteriorating ionomer-lignin interactions. The novel combination of experiments, modeling, and simulation was done for the first time on such materials, and it pointed out that the role of hydrogen bonds is more critical in determining blend properties. Blends can be prepared for practical applications with a good combination of stiffness (0.8 GPa), tensile strength (22 MPa), and elongation-at-break (25 %) at 30 vol% lignosulfonate content and 33 % neutralization.

Deep learning and analytical study of void regional formation in flip-chip underfilling process

PurposeThis paper aims to study the relationship between the ball grid array (BGA) flip-chip underfilling process parameter and its void formation region.Design/methodology/approachA set of top-down scanning acoustic microscope images of BGA underfill is collected and void labelled. The labelled images are trained with a convolutional neural network model, and the performance is evaluated. The model is tested with new images, and the void area with its region is analysed with its dispensing parameter.FindingsAll findings were well-validated with reference to the past experimental results regarding dispensing parameters and their quantitative regional formation. As the BGA is non-uniform, 85% of the test samples have void(s) formed in the emptier region. Furthermore, the highest rating factor, valve dispensing pressure with a Gini index of 0.219 and U-type dispensing pattern set of parameters generally form a lower void percentage within the underfilling, although its consistency is difficult to maintain.Practical implicationsThis study enabled manufacturers to forecast the void regional formation from its filling parameters and array pattern. The filling pressure, dispensing pattern and BGA relations could provide qualitative insights to understand the void formation region in a flip-chip, enabling the prompt to formulate countermeasures to optimise voiding in a specific area in the underfill.Originality/valueThe void regional formation in a flip-chip underfilling process can be explained quantitatively with indicative parameters such as valve pressure, dispensing pattern and BGA arrangement.

Effects of moisture content and fibrous structure on the uniaxial compression behavior of natural bamboo

The compression properties of natural bamboo were tested, and the crush morphologies with different moisture contents and fibrous structure were observed. Real-time acoustic emission (AE) and optical microscope videos captured the compression behaviors. Dry bamboo internodes showcased 100% higher compression strength with shearing as the predominant failure mode, while the wet samples demonstrated delamination and splitting. AE and fracture morphology indicated five compression behavior categories. Bamboo node samples exhibited heightened compressive strength and modulus than internodes due to their coarser 3D fibrous structures. This investigation offers valuable insights for the development of engineering bamboo materials.

Single-crystalline LiNbO3 integrated onto Si-based substrates via Ar plasma-activated low-temperature direct bonding

Lithium niobate (LiNbO3) crystals are multifunctional materials with excellent performance and are widely used in integrated optical devices. In this study, 4-inch LiNbO3/Si and LiNbO3/SiO2/Si bonded pairs were obtained by optimizing Ar plasma activation. After pre-bonding was completed, a slicer was used to cut the LiNbO3/Si and LiNbO3/SiO2/Si pairs into 10 × 10 mm2 squares, respectively. The optimal annealing temperature was determined through multiple annealing experiments. Scanning acoustic microscopy was used to confirm the high bonding rates of the two bonding pairs. Based on hydrophilic experiments and atomic force microscopy, the changes in the hydrophilicity and roughness of the LiNbO3, Si, and SiO2 surfaces before and after activation can be compared. X-ray photoelectron spectroscopy was used to characterize the chemical structure composition of LiNbO3, Si, and SiO2 surfaces. The dense interface without defects was observed by transmission electron microscopy. In addition, we explained the bonding mechanism between LiNbO3 and Si-based materials. The reasons for the different bonding strengths of LiNbO3 with Si and SiO2 were also analyzed. Finally, the high bonding quality of LiNbO3 and Si-based materials can meet the stringent material requirements of Si-based LiNbO3 devices.

In-situ delamination detection in multi-layered semiconductor packages

Accurately determining the material properties of large-area solder joints is crucial for developing precise lifetime models in modern power electronic devices, as these joints play a vital role in providing both electrical and mechanical connections between components. This study presents a novel, non-destructive, and in-situ technique based on laser Doppler vibrometry for detecting crack initiation and monitoring crack growth in semiconductor structures. This method was successfully applied to determine various stages of die attach degradation during accelerated mechanical cyclic tests of large area solder joints, and was verified by scanning acoustic microscopy (SAM) measurements as well as optical methods. Furthermore, analysis of the acoustic emission (AE) signal was conducted as an alternative method for monitoring crack propagation. Optical and electron microscopy were employed to analyse crack initiation, crack paths, and crack surface morphologies. The in-situ delamination detection technique can provide essential information for robust lifetime prediction modelling of material systems in advanced semiconductor components.