Comparison of the accuracy of bracket axial positioning with and without radiographic support and according to practitioner experience: A three-dimensional study.

INTRODUCTION: Accurate bracket positioning remains challenging. To avoid angulation errors, some recommend examining the panoramic radiograph during bonding. However, it can cause distortions. Cone-beam computed tomography (CBCT) provides a more precise panoramic reconstruction but with higher radiation doses. The main objective of this study is to compare the accuracy of axial positioning between direct bonding without radiography, with conventional panoramic radiograph, and with panoramic reconstruction from CBCT. The secondary objectives are to evaluate positioning accuracy of each tooth and to assess the influence of practitioner level of experience. METHODS: Thirty practitioners, divided into two groups based on their experience performed direct bonding on a model thrice: without radiography, then with the conventional panoramic radiograph, then with the panoramic reconstruction from CBCT. Models were scanned, and angulation errors were measured using OrthoAnalyzer. Values were compared using the Friedman's test followed by the Bonferroni correction for multiple comparisons (P-value = 0.05). RESULTS: For the low level of experience group, angulation errors were significantly greater than the accepted limit without radiographic reference, and significantly lower with CBCT reconstruction. For the high level of experience group, angulation errors were significantly lower than the accepted limit for the three bonding methods. For every tooth, using the panoramic reconstruction from CBCT as a reference, was the most accurate method, regardless of the level of experience. More experienced practitioners made fewer errors for the three methods. CONCLUSIONS: Panoramic reconstruction from CBCT is the most accurate method to limit angulation errors during direct bonding. Conventional panoramic radiography remains a reliable tool if used with caution. Bonding without any radiographic reference should be avoided especially for less experienced practitioners.

Effect of Compressive Stress on Copper Bonding Quality and Bonding Mechanisms in Advanced Packaging.

The thermal expansion behavior of Cu plays a critical role in the bonding mechanism of Cu/SiO2 hybrid joints. In this study, artificial voids, which were observed to evolve using a focused ion beam, were introduced at the bonded interfaces to investigate the influence of compressive stress on bonding quality and mechanisms at elevated temperatures of 250 °C and 300 °C. The evolution of interfacial voids serves as a key indicator for assessing bonding quality. We quantified the bonding fraction and void fraction to characterize the bonding interface and found a notable increase in the bonding fraction and a corresponding decrease in the void fraction with increasing compressive stress levels. This is primarily attributed to the Cu film exhibiting greater creep/elastic deformation under higher compressive stress conditions. Furthermore, these experimental findings are supported by the surface diffusion creep model. Therefore, our study confirms that compressive stress affects the Cu-Cu bonding interface, emphasizing the need to consider the depth of Cu joints during process design.

Effect of Cu Film Thickness on Cu Bonding Quality and Bonding Mechanism.

In the hybrid bonding process, the final stage of chemical mechanical polishing plays a critical role. It is essential to ensure that the copper surface is recessed slightly from the oxide surface. However, this recess can lead to the occurrence of interfacial voids between the bonded copper interfaces. To examine the effects of copper film thickness on bonding quality and bonding mechanisms in this study, artificial voids were intentionally introduced at the bonded interfaces at temperatures of 250 °C and 300 °C. The results revealed that as the thickness of the copper film increases, there is an increase in the bonding fraction and a decrease in the void fraction. The variations in void height with different copper film thicknesses were influenced by the bonding mechanism and bonding fraction.

Enhanced Nanotwinned Copper Bonding through Epoxy-Induced Copper Surface Modification.

For decades, Moore's Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore's Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu-Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface.

Nanoscale osseointegration of zirconia evaluated from the interfacial structure between ceria-stabilized tetragonal zirconia and cell-induced hydroxyapatite.

BACKGROUND: The osseointegration of zirconia implants has been evaluated based on their implant fixture bonding with the alveolar bone at the optical microscopic level. Achieving nano-level bonding between zirconia and bone apatite is crucial for superior osseointegration; however, only a few studies have investigated nanoscale bonding. This review outlines zirconia osseointegration, including surface modification, and presents an evaluation of nanoscale zirconia-apatite bonding and its structure. HIGHLIGHT: Assuming osseointegration, the cells produced calcium salts on a ceria-stabilized zirconia substrate. We analyzed the interface between calcium salts and zirconia substrates using transmission electron microscopy and found that 1) the cell-induced calcium salts were bone-like apatite and 2) direct nanoscale bonding was observed between the bone-like apatite and zirconia crystals without any special modifications of the zirconia surface. CONCLUSION: Structural affinity exists between bone apatite and zirconia crystals. Apatite formation can be induced by the zirconia surface. Zirconia bonds directly with apatite, indicating superior osseointegration in vivo.

Enhanced Copper Bonding Interfaces by Quenching to Form Wrinkled Surfaces.

For decades, Moore's Law has been approaching its limits, posing a huge challenge for further downsizing to nanometer dimensions. A promising avenue to replace Moore's Law lies in three-dimensional integrated circuits, where Cu-Cu bonding plays a critical role. However, the atomic diffusion rate is notably low at temperatures below 300 °C, resulting in a distinct weak bonding interface, which leads to reliability issues. In this study, a quenching treatment of the Cu film surface was investigated. During the quenching treatment, strain energy was induced due to the variation in thermal expansion coefficients between the Si substrate and the Cu film, resulting in a wrinkled surface morphology on the Cu film. Grain growth was observed at the Cu-Cu bonding interface following bonding at 300 °C for 2 and 4 h. Remarkably, these procedures effectively eliminated the bonding interface.

Thermal Transport and Mechanical Stress Mapping of a Compression Bonded GaN/Diamond Interface for Vertical Power Devices.

Bonding diamond to the back side of gallium nitride (GaN) electronics has been shown to improve thermal management in lateral devices; however, engineering challenges remain with the bonding process and characterizing the bond quality for vertical device architectures. Here, integration of these two materials is achieved by room-temperature compression bonding centimeter-scale GaN and a diamond die via an intermetallic bonding layer of Ti/Au. Recent attempts at GaN/diamond bonding have utilized a modified surface activation bonding (SAB) method, which requires Ar fast atom bombardment immediately followed by bonding within the same tool under ultrahigh vacuum (UHV) conditions. The method presented here does not require a dedicated SAB tool yet still achieves bonding via a room-temperature metal-metal compression process. Imaging of the buried interface and the total bonding area is achieved via transmission electron microscopy (TEM) and confocal acoustic scanning microscopy (C-SAM), respectively. The thermal transport quality of the bond is extracted from spatially resolved frequency-domain thermoreflectance (FDTR) with the bonded areas boasting a thermal boundary conductance of >100 MW/m2·K. Additionally, Raman maps of GaN near the GaN-diamond interface reveal a low level of compressive stress, <80 MPa, in well-bonded regions. FDTR and Raman were coutilized to map these buried interfaces and revealed some poor thermally bonded areas bordered by high-stress regions, highlighting the importance of spatial sampling for a complete picture of bond quality. Overall, this work demonstrates a novel method for thermal management in vertical GaN devices that maintains low intrinsic stresses while boasting high thermal boundary conductances.

Integration of High-Performance InGaAs/GaN Photodetectors by Direct Bonding via Micro-transfer Printing.

The integration of dissimilar semiconductor materials holds immense potential for harnessing their complementary properties in novel applications. However, achieving such combinations through conventional heteroepitaxy or wafer bonding techniques presents significant challenges. In this research, we present a novel approach involving the direct bonding of InGaAs-based p-i-n membranes with GaN, facilitated by van der Waals forces and microtransfer printing technology. The resulting n-InP/n-GaN heterojunction was rigorously characterized through electrical measurements, with a comprehensive investigation into the impact of various surface treatments on device performance. The obtained InGaAs/GaN photodetector demonstrates remarkable electrical properties and exhibits a high optical responsivity of 0.5 A/W at the critical wavelength of 1550 nm wavelength. This pioneering work underscores the viability of microtransfer printing technology in realizing large lattice-mismatched heterojunction devices, thus expanding the horizons of semiconductor device applications.

Deep learning for virtual orthodontic bracket removal: tool establishment and application.

OBJECTIVE: We aimed to develop a tool for virtual orthodontic bracket removal based on deep learning algorithms for feature extraction from bonded teeth and to demonstrate its application in a bracket position assessment scenario. MATERIALS AND METHODS: Our segmentation network for virtual bracket removal was trained using dataset A, containing 978 bonded teeth, 20 original teeth, and 20 brackets generated by scanners. The accuracy and segmentation time of the network were tested by dataset B, which included an additional 118 bonded teeth without knowing the original tooth morphology. This tool was then applied for bracket position assessment. The clinical crown center, bracket center, and orientations of separated teeth and brackets were extracted for analyzing the linear distribution and angular deviation of bonded brackets. RESULTS: This tool performed virtual bracket removal in 2.9 ms per tooth with accuracies of 98.93% and 97.42% (P < 0.01) in datasets A and B, respectively. The tooth surface and bracket characteristics were extracted and used to evaluate the results of manually bonded brackets by 49 orthodontists. Personal preferences for bracket angulation and bracket distribution were displayed graphically and tabularly. CONCLUSIONS: The tool's efficiency and precision are satisfactory, and it can be operated without original tooth data. It can be used to display the bonding deviation in the bracket position assessment scenario. CLINICAL SIGNIFICANCE: With the aid of this tool, unnecessary bracket removal can be avoided when evaluating bracket positions and modifying treatment plans. It has the potential to produce retainers and orthodontic devices prior to tooth debonding.

Recrystallization and Grain Growth in Cu-Cu Joints under Electromigration at Low Temperatures.

The behavior of recrystallization and grain growth was examined in Cu-Cu joints during electromigration at 150 °C. Recrystallization and grain growth were observed in all the joints after electromigration for 9000 h. Voiding was formed in Cu current-feeding lines and in bonding interfaces, and resistance increased with time due to the void formation. However, instead of rising abruptly, the resistance of certain Cu joints dropped after 7000 h. Microstructural analysis revealed that a large grain growth occurred in these joints at 150 °C, and the bonding interface was eliminated. Therefore, the electromigration lifetime can be prolonged for these joints.

Orthodontic Approaches in the Management of Mandibular Fractures: A Scoping Review.

Non-surgical approaches have been proposed in the management of mandibular fractures, especially in children, but there is a lack of clear guidelines on the clinical indications of conservative approaches. The aim of this scoping review is to provide the available evidence of the role of the orthodontist in the management of mandibular fractures. The PRISMA-ScR guidelines were followed to select eligible articles from the PubMed, Scopus, and Web of Science databases according to precise inclusion criteria. The research questions were formulated as follows: "what is the scientific evidence concerning the rule of orthodontists in the management of mandibular fractures" and "the preferential use of the direct bonding technique with orthodontic brackets rather than rigid arch bars"? Seventeen articles were included. Five articles presented the use of removable acrylic splints or functional appliances, six articles concerned the employment of cemented acrylic or rigid splints, and six articles described the management of mandibular fractures in adults and children using orthodontic brackets or mini-screws. Most of these techniques have been employed in children and growing subjects, while fewer data were available regarding conservative treatments in adults. Preliminary evidence suggests that condylar and some minor parasymphyseal fractures in children may be managed with conservative approaches. In adults, minor condylar and stable body mandibular fractures with minimal displacement have been reduced similarly. However, there are no sufficient elements that could suggest the preferential use of orthodontic brackets over rigid arch bars in adults. Further randomized and non-randomized clinical trials with long follow-ups will be needed to better define the clinical indications of the orthodontic approaches in the management of mandibular fractures based on severity, location, and age.

Cimifugin suppresses type 2 airway inflammation by binding to SPR and regulating its protein expression in a non-enzymatic manner.

BACKGROUND: Cimifugin is one of the main bioactive components of Yu-Ping-Feng-San, a well-known traditional Chinese medicine, which can effectively relieve Allergic asthma (AA) and atopic dermatitis and reduce recurrence in clinic. However, the underlying mechanism of cimifugin on AA is still unknown. PURPOSE: In the present study, we aimed to investigate the effect and mechanism of cimifugin on AA. STUDY DESIGN: In vivo and in vitro experimental studies were performed. METHODS: The effect of cimifugin on AA was demonstrated in vivo and in vitro. Sepiapterin reductase (SPR) was predicted as the most potent target of cimifugin in treating AA by reverse docking. Molecular docking and microscale thermophoresis (MST) were used to analyze the direct binding between cimifugin and SPR. Overexpression and interference of SPR were performed to verify whether targeting SPR is a key step of cimifugin in the treatment of AA. QM385, an inhibitor of SPR, was administrated in vivo and in vitro to evaluate the role of SPR in AA. Further, HPLC and cell-free direct hSPR enzyme activity assay were performed to research whether cimifugin regulated SPR by influencing the enzyme activity. Simultaneously, the inhibitors of protein degradation were used in vitro to explore the mechanism of cimifugin on SPR. RESULTS: We found cimifugin effectively alleviated AA by reducing airway hyperresponsiveness, inhibiting type 2 cytokines-mediated airway inflammation, and restoring the expression of epithelial barrier proteins. Molecular docking predicted the direct binding ability of cimifugin to SPR, which was further verified by MST. Notably, the therapeutic effect of cimifugin on AA was dampened with SPR interfering, in contrast, the phenotypic features of AA were significantly alleviated with QM385 application both in vivo and in vitro. Interestingly, cimifugin showed no effect on the enzyme activity of SPR, as the level of its substrate sepiapterin was not affected with cimifugin treatment by cell-free enzyme activity assay. Furthermore, we found cimifugin could reduce SPR protein expression without affecting its mRNA expression probably through autophagosome pathway. CONCLUSIONS: To our knowledge, we're reporting for the first time that cimifugin can suppresses type 2 airway inflammation to alleviate AA by directly binding to SPR and regulating its protein expression in a non-enzymatic manner.

Copper Ions Absorbed on Acrylic-Acid-Grafted Polystyrene Enable Direct Bonding with Tunable Bonding Strength and Debonding on Demand.

Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal of adhesive residues. To tackle this problem, adhesive technologies are needed allowing debonding on demand and which do not contaminate the surface of the substrate. Direct bonding enabled by oxygen plasma treatment has already achieved substantial adhesion between flat substrates. However, debonding takes place by water, thus limiting the applications of this technology to water-free environments. The work presented in the following shows that this drawback can be overcome by grafting acrylic acid and adding copper(II) ions on the surface of polystyrene. In this process, the number of functional groups on the surface was significantly increased without increasing the surface roughness. The bonding strength between the substrates could be increased, and the process temperature could be lowered. Nevertheless, the samples could be debonded by exposure to EDTA solution under ultrasound. Hence, by combining acrylic acid grafting, variations in the bonding temperatures and the use of copper(II) ions, the bonding strength (5 N to >85 N) and the debonding time under the action of water can be tuned over large ranges (seconds to complete resistance).

Comparison of the accuracy of bracket positioning between direct and digital indirect bonding techniques in the maxillary arch: a three-dimensional study.

BACKGROUND/OBJECTIVES: When the indirect bonding technique was developed in 1972 by Silverman and Cohen, many authors wondered whether this technique would improve bracket positioning accuracy compared to the direct bonding technique. Studies have found little to no difference between them regarding positioning accuracy. Recently, technological advances have improved the indirect method by allowing the user to position the brackets virtually using software applications such as OrthoAnalyzer™. To the best of our knowledge, no studies have compared direct positioning to this new digital indirect technique. Thus, the aim of this study was to compare the accuracy of placement between the two techniques in the maxillary arch using two different bracket types: conventional twin brackets and self-ligating brackets. A secondary objective was to evaluate whether bracket type affected positioning accuracy. METHODS: A maxillary arch of a patient was scanned by digital impression. Forty resin duplicates of this model were printed and then mounted on a mannequin head, on which 20 practitioners performed direct bonding using the aforementioned brackets. Later on, they performed a virtual indirect bonding of the same case virtually, with the digital impression superimposed to the patient's CBCT (cone-beam computed tomography). Afterwards, the direct bonded models were unmounted, scanned, and then superimposed to the indirect models. Differences in height, angulation and mesio-distal position of the brackets were evaluated. RESULTS: Regarding height, the differences between direct and indirect methods were not significant. Height difference was significantly greater for self-ligating brackets compared to conventional brackets. Regarding mesio-distal positioning, significant differences were noted for teeth 13 and 15 with self-ligating brackets (p-value = 0.019 and p-value = 0.043, respectively). The deviation was also greater for these brackets. Regarding angulation, the difference was significant on tooth 12 when using conventional brackets (p-value = 0.04) and on 12 and 22 when using self-ligating brackets (p-value = 0.09). CONCLUSION/IMPLICATIONS: There were no major significant differences between direct and indirect bonding. Differences were significant only on the laterals for of angulation, and on teeth 13 and 15 for mesio-distal centering. The bracket type seems to influence positioning accuracy, since self-ligating brackets had a larger deviation range than conventional brackets.

Langasite Bonding via High Temperature for Fabricating Sealed Microcavity of Pressure Sensors.

We proposed a novel Langasite (LGS) bonding method only using high temperature to solve the manufacturing difficulty of the sealed microcavity of pressure sensors. The optimal bonding parameters by comparative experiments were defined as 1350 °C for 3 h. Due to simple experimental conditions, low experimental cost, and be suitable for bonding wafers with various sizes, the method is convenient for popularization and mass-production, thus promoting the development of surface acoustic wave (SAW) devices at high temperatures. Simultaneously, an intact microcavity was observed by scanning electron microscopy, and a tight and void-free bonding interface with a transition layer thickness of 2.2 nm was confirmed via transmission electron microscopy. The results of tensile and leakage experiments indicated that the bonded wafer with the sealed microcavity exhibited a high bonding strength of 4.02 MPa and excellent seal performance. Compared to the original wafer, the piezoelectric constant of the LGS bonded wafer had a reduction of only 4.43%. The above characteristics show that the sealed microcavity prepared by this method satisfies the conditions for fabricating the LGS SAW pressure sensors. Additionally, based on the bonding interface characterizations, the mechanism of LGS bonding has been investigated for the first time.

Low Temperature Hydrophilic SiC Wafer Level Direct Bonding for Ultrahigh-Voltage Device Applications.

SiC direct bonding using O2 plasma activation is investigated in this work. SiC substrate and n- SiC epitaxy growth layer are activated with an optimized duration of 60s and power of the oxygen ion beam source at 20 W. After O2 plasma activation, both the SiC substrate and n- SiC epitaxy growth layer present a sufficient hydrophilic surface for bonding. The two 4-inch wafers are prebonded at room temperature followed by an annealing process in an atmospheric N2 ambient for 3 h at 300 °C. The scanning results obtained by C-mode scanning acoustic microscopy (C-SAM) shows a high bonding uniformity. The bonding strength of 1473 mJ/m2 is achieved. The bonding mechanisms are investigated through interface analysis by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Oxygen is found between the two interfaces, which indicates Si-O and C-O are formed at the bonding interface. However, a C-rich area is also detected at the bonding interface, which reveals the formation of C-C bonds in the activated SiC surface layer. These results show the potential of low cost and efficient surface activation method for SiC direct bonding for ultrahigh-voltage devices applications.

Effect of Bonding Strength on Electromigration Failure in Cu-Cu Bumps.

In microelectronic packaging technology for three-dimensional integrated circuits (3D ICs), Cu-to-Cu direct bonding appears to be the solution to solve the problems of Joule heating and electromigration (EM) in solder microbumps under 10 µm in diameter. However, EM will occur in Cu-Cu bumps when the current density is over 106 A/cm2. The surface, grain boundary, and the interface between the Cu and TiW adhesion layer are the three major diffusion paths in EM tests, and which one may lead to early failure is of interest. This study showed that bonding strength affects the outcome. First, if the bonding strength is not strong enough to sustain the thermal mismatch of materials during EM tests, the bonding interface will fracture and lead to an open circuit of early failure. Second, if the bonding strength can sustain the bonding structure, voids will form at the passivation contact area between the Cu-Cu bump and redistribution layer (RDL) due to current crowding. When the void grows along the passivation interface and separates the Cu-Cu bump and RDL, an open circuit can occur, especially when the current density and temperature are severe. Third, under excellent bonding, when the voids at the contact area between the Cu-Cu bump and RDL do not merge together, the EM lifetime can be more than 5000 h.

An LC Wireless Passive Pressure Sensor Based on Single-Crystal MgO MEMS Processing Technique for High Temperature Applications.

An LC wireless passive pressure sensor based on a single-crystalline magnesium oxide (MgO) MEMS processing technique is proposed and experimentally demonstrated for applications in environmental conditions of 900 °C. Compared to other high-temperature resistant materials, MgO was selected as the sensor substrate material for the first time in the field of wireless passive sensing because of its ultra-high melting point (2800 °C) and excellent mechanical properties at elevated temperatures. The sensor mainly consists of inductance coils and an embedded sealed cavity. The cavity length decreases with the applied pressure, leading to a monotonic variation in the resonant frequency of the sensor, which can be retrieved wirelessly via a readout antenna. The capacitor cavity was fabricated using a MgO MEMS technique. This MEMS processing technique, including the wet chemical etching and direct bonding process, can improve the operating temperature of the sensor. The experimental results indicate that the proposed sensor can stably operate at an ambient environment of 22-900 °C and 0-700 kPa, and the pressure sensitivity of this sensor at room temperature is 14.52 kHz/kPa. In addition, the sensor with a simple fabrication process shows high potential for practical engineering applications in harsh environments.

Effect of Direct versus Indirect Bonding Technique on the Failure Rate of Mandibular Fixed Retainer-A Systematic Review and Meta-Analysis.

INTRODUCTION: Fixed retainer failure is a common cause of relapse and may require additional orthodontic treatment. The two main methods for bonding the mandibular fixed retainer include direct and indirect techniques. This topic has not been explored previously in a systematic review. Therefore, the objective of this systematic review was to evaluate the effect of direct versus indirect bonding technique on the failure rate of mandibular fixed retainer. METHODS: Online databases (PubMed, Dental and Oral Science, CINAHL, and Cochrane Central Register of Controlled Trials, Scopus) were systematically searched electronically for articles up until April 2021. Google Scholar and clinicaltrials.gov databases were utilized for hand searching. Randomized, non-randomized clinical trials and cohort studies on human subjects were considered regardless of language or year of publication. Orthodontic patients in their retention phase (mandibular 3×3 fixed retainer), in which the retainer was bonded using direct bonding technique as control and indirect as intervention were included. The outcome assessed was retainer failure rate. Two authors independently examined and extracted the data from the studies that satisfied the inclusion criteria. Risk of bias in clinical trials was assessed using the Cochrane Collaboration's tool, whereas risk of bias in cohort studies was assessed using the Newcastle-Ottawa Scale. The meta-analysis was conducted using the RevMan software V.5.3.5.22. The outcome was estimated using weighted average difference and 95% confidence intervals (CIs). The studies' heterogeneity was assessed using Cochrane's heterogeneity test (I2 Test). RESULTS: Four articles fulfilling the inclusion criteria were included in qualitative and quantitative synthesis. Retainer failure rates were analysed in a total number of 266 patients bonded with mandibular 3×3 retainers after orthodontic therapy. Direct bonding technique of fixed retainer on 131 patients was compared with indirect technique on 135 patients. There was no statistically significant difference in the rate of retainer failure between the two methods (95% CI, 0.67, 1.40). CONCLUSIONS: Within the limitations of insufficient evidence this systematic review and meta-analysis concluded that there is no difference in the failure rate of mandibular fixed retainers between direct and indirect bonding techniques. Due to the scarcity of available data, further studies are needed to establish definitively one's clinical benefit over the other.

Failure Mechanisms of Cu-Cu Bumps under Thermal Cycling.

The failure mechanisms of Cu-Cu bumps under thermal cycling test (TCT) were investigated. The resistance change of Cu-Cu bumps in chip corners was less than 20% after 1000 thermal cycles. Many cracks were found at the center of the bonding interface, assumed to be a result of weak grain boundaries. Finite element analysis (FEA) was performed to simulate the stress distribution under thermal cycling. The results show that the maximum stress was located close to the Cu redistribution lines (RDLs). With the TiW adhesion layer between the Cu-Cu bumps and RDLs, the bonding strength was strong enough to sustain the thermal stress. Additionally, the middle of the Cu-Cu bumps was subjected to tension. Some triple junctions with zig-zag grain boundaries after TCT were observed. From the pre-existing tiny voids at the bonding interface, cracks might initiate and propagate along the weak bonding interface. In order to avoid such failures, a postannealing bonding process was adopted to completely eliminate the bonding interface of Cu-Cu bumps. This study delivers a deep understanding of the thermal cycling reliability of Cu-Cu hybrid joints.