As a critical interconnection technology in advanced packaging, Cu wire bonding has been widely adopted due to its high electrical conductivity, cost efficiency, and excellent thermal stability. This review systematically summarizes the material systems of Cu based bonding wires, the formation behavior of free air ball (FAB) and their influence on bond quality, as well as the dominant failure mechanisms of Cu wire bonding and corresponding approaches for reliability enhancement. First, the development trends of mainstream Cu based bonding wires are reviewed, including bare Cu wires, coated Cu wires, and microalloyed Cu wires. Second, the underlying mechanisms of key factors in the FAB formation process，such as Electronic Flame Off (EFO) energy, shielding atmosphere, coating architecture, and ultrasonic and thermal inputs are systematically analyzed, and the decisive influence of FAB morphology on first-bond quality is elucidated. Subsequently, the reliability of Cu wire bonding is discussed in a classified manner, covering several common failure mechanisms in wire bonding, and the commonly employed reliability evaluation methodologies are summarized. On this basis, Cu wire alloying and surface modification, optimization of bonding process parameters, and the design of wire loops and loop geometries are identified as three key technological pathways for enhancing the reliability of Cu wire bonding. Finally, the current progress of Cu wire bonding technology is summarized, and future research directions are discussed, with the aim of providing useful references for the further development and application of Cu wire bonding.

Metallic materials are widely used in modern engineering owing to their excellent mechanical properties and broad processing adaptability. At macroscopic scales, their mechanical behavior is generally regarded as size-independent and can be described by classical continuum plasticity theories. However, with the rapid development of micro- and nano-manufacturing technologies, metallic components are increasingly fabricated at reduced length scales, where pronounced size effects emerge. These effects are manifested by enhanced strength, altered plastic deformation behavior, increased property scatter, and distinct fracture modes. Although extensive experimental and theoretical studies have investigated size-dependent mechanical behavior, existing reviews mainly focus on isolated phenomena or specific material systems. A systematic and mechanism-based understanding of how size effects govern the entire mechanical response, from yielding and plastic flow to fracture, remains insufficient. Therefore, this review provides a comprehensive overview of size effects in metallic materials, with emphasis on their influence on yielding behavior, plastic deformation evolution, and fracture mechanisms. Representative theoretical models are critically assessed, and the implications of size effects for micro-manufacturing and engineering applications are discussed.

With the trend towards high-density microelectronic packaging, palladium-coated copper (PCC) wire is increasingly replacing gold wire due to its cost and performance advantages. However, key challenges in the looping process include stress concentration from the mechanical property mismatch between Pd and Cu, and the characteristics of the heat-affected zone (HAZ). This study employs a HAZ gradient synergistic optimization method, integrating orthogonal experiments with mechanical tests and microstructural characterization. The results demonstrate that the HAZ gradient significantly mitigates stress concentration and establishes reverse distance (RD) as the dominant factor influencing bonding strength. The optimal parameter combination (ultrasonic power: 110 mW; RD: 110 mu m; reverse height: 110 mu m) increases pull strength to 16 gf and reduces the stress concentration factor (SCF) to 1.125, effectively transferring the critical fracture interface to the neck of the first-bond. This study clarifies the stress-microstructure-fracture correlation mechanism, providing a theoretical basis for reliable bonding in advanced packaging.

W-La2O3 alloys and their composites exhibit high density, high melting point, good mechanical properties, excellent corrosion resistance, and oxidation resistance, making them widely used in national defense, aerospace, medical equipment, photovoltaic industry, and nuclear fusion fields. Due to its superior comprehensive properties and relatively low cost, La2O3 has become a representative strengthening phase. This paper systematically reviews the preparation techniques, microstructures, and strengthening mechanisms of W-La2O3 alloys and their composites. It summarizes the strengthening mechanisms of their properties at room temperature, and calls for future research to focus on a systematic evaluation of their properties at high temperatures. As a dispersion strengthening phase, La2O3 significantly refines tungsten grains and enhances the physical and mechanical properties of tungsten alloys, primarily through the synergistic effects of grain boundary strengthening and oxide dispersion strengthening. Furthermore, the application of La2O3 in composite systems such as W-Cu and W-Ni-Fe, along with their multi-mechanism synergistic strengthening effects, is discussed. Advances in microstructure control and properties of ultrafine tungsten alloy wires under advanced drawing processes are also summarized. Finally, current challenges in low-cost scalable preparation, performance in extreme service environments, and precise microstructure regulation are outlined, followed by prospects for the future development of W-La2O3 alloys and their composites. This review may provide valuable references for the rational design and application of high-performance tungsten-based materials in the future.

Compared with bare copper wire, palladium-coated copper (PCC) wire is widely used in microelectronic packaging due to its improved oxidation resistance and enhanced reliability. However, the formation mechanism of free air balls (FABs) and the redistribution behavior of Pd during the electronic flame-off (EFO) process, particularly under different Pd coating thicknesses and processing conditions, have not yet been fully understood. In this work, four types of 1 mil PCC wires with Pd coating thicknesses of 60, 80, 100, and 120 nm were systematically investigated to study the influence of EFO parameters on FAB morphology and Pd redistribution behavior. SEM, FIB, and EDS analyses were employed to provide experimental insights into the coupled relationship between transient thermal input, internal pore distribution and elemental segregation evolution, and Pd redistribution behavior. The results show that the preferred FAB morphology is obtained at 54 mA and 580 μs, with a diameter-to-wire ratio of approximately 2. With increasing Pd coating thickness, the exposed copper area on the FAB surface decreases from 13% to 6%, while the Pd-deficient region gradually shifts toward the bottom of the FAB. This study provides experimental insights into the Pd redistribution behavior during FAB formation under different EFO conditions, which may contribute to the optimization of Pd-coated Cu bonding wires.

The evolution of electronic devices toward higher integration and power densities has exposed the limitations of conventional copper conductors. In particular, resistive heating and reliability issues now pose significant obstacles to further technological advancement. Graphene, with its extraordinary carrier mobility and superior electrical properties, has emerged as a promising material to enhance copper conductivity. However, practical applications are hindered by weak interfacial bonding and high resistance between graphene and copper. In this study, a surface coating process is employed to introduce a strategically optimized titanium interlayer at the copper/graphene interface, achieving a synergistic enhancement of interfacial structural stability and electronic transport properties. The rational incorporation of titanium effectively reduces interfacial voids, mitigates delamination, and decreases interfacial resistance, enabling the Ti/Gr-Cu composite wire to achieve a remarkable conductivity of 107.2% IACS. Theoretical calculations reveal that titanium strengthens orbital hybridization and facilitates charge transfer between copper and graphene, further enhancing electron transport efficiency. This work provides critical insights into interfacial engineering strategies for copper-based high-conductivity composite conductors.

The characteristics of palladium layer on the surface of copper wire are important factors affecting the quality of free air ball （FAB） and bonding during chip packaging. In this paper， palladium-coated copper wires with different coating speeds and coating temperatures are prepared by halogen-free direct coating process. The effects of coating speed on the morphology of the coating and the characteristics of FAB are studied. The results show that with the increase of coating speed， the coating time decreases， and the uniformity of the distribution of palladium particles on the surface of the copper wire becomes worse. The agglomeration of palladium particles with uneven local distribution causes the concentration of palladium particles to be too high， and the agglomeration area of palladium particles on the surface of the coating increases. Under the plating speed of 50 m/min， the distribution of palladium on the surface of the coating is more uniform. With the increase of coating speed， the diameter of FAB decreases gradually. The difference of palladium content between the agglomeration area and the non-agglomeration area of Pd particles on the surface of Pd-coated copper wire increases， and the consistency of FAB sphere size gradually decreases. At a lower coating speed of 50 m/min， the distribution of palladium content on the surface of FAB is relatively uniform. At a higher coating speed of 100 m/min， a large number of agglomerated palladium particles on the surface of the coating are remelted to form a large area of continuous palladium-rich area on the surface of the FAB， and the uniformity of palladium redistribution is poor. Considering the uniformity of FAB size and surface palladium redistribution， the coating speed of 50 m/min and the coating temperature of 400 ℃ are the better process parameters for the coating of palladium-coated copper wire.

Enhancing the electrical conductivity of copper (Cu), the most widely used electrical conductor, is crucial for advancing energy-efficient technologies and industrial innovation. The integration of graphene (Gr), a two-dimensional material with exceptional carrier mobility, into Cu has emerged as a promising route to next-generation composite conductors. However, the practical realization of high-performance Cu-Gr composites (CGC) is hindered by critical challenges, including weak interfacial bonding, nonuniform Gr dispersion, and processing-induced structural defects, which can limit conductivity gains. A detailed understanding of the interfacial interaction mechanisms between Cu and Gr, coupled with the optimization of processing methodologies, is essential to overcome these barriers. In this review, we examine the intrinsic physical properties of Cu and Gr, clarify their interfacial interaction mechanisms, summarize design strategies and processing techniques for improving CGC conductors, and evaluate the electrical performance of state-of-the-art CGC. We further identify current knowledge gaps and outline future research directions, including advanced interfacial engineering, scalable fabrication, and predictive modeling for optimizing CGC properties.

In this paper, ball-burning and bonding tests were conducted using Ag-Au-Pd alloy wires with a diameter of phi 0.025 mm, and the performance of free air ball (FAB) morphology and bonding strength under various bonding parameters was investigated. The results showed that when the electronic flame off (EFO) current is 20 mA, the FAB of Ag-Au-Pd bonding alloy wire appears small ellipsoid, whereas increasing the EFO current to 40 mA resulted in a golf club-shaped FAB. Similarly, when the EFO time was 0.4 ms, the FAB appears as a small spherical, but extending the EFO time to 1.2 ms caused the FAB to enlarge and exhibit a golf club phenomenon. The addition of Pd element reduced the FAB heat affected zone length of Ag-Au-Pd alloy wire by 19.4% compared to Ag-Au wire. Insufficient ultrasonic power and bonding pressure lead to weak bonding at the bonded interface, thereby reducing the bonding strength, while excessive ultrasonic power and bonding pressure can cause short circuits and pad damage. The optimized bonding parameters for the Ag-Au-Pd alloy wire determined to be: an ultrasonic power of 65 mW and a bonding pressure of 45 g for the ball bond, and an ultrasonic power of 95 mW and a bonding pressure is 75 g for the wedge bond.

With the rapid advancement of microelectronic packaging technology, copper wire bonding has emerged as a promising alternative to traditional gold wire bonding, owing to its excellent mechanical and electrical properties and significant cost advantages. However, copper wire bonding still faces several practical challenges, including oxidation, corrosion, and instability at the bonding interface, which adversely affect the long-term reliability and lifespan of bonded copper wires. This paper presents a comprehensive review of recent developments in copper wire bonding for microelectronics, focusing on the optimization of copper wire materials, control of free air ball (FAB) morphology, the influence of palladium distribution on the FAB surfaces, and strategies to mitigate halogen ion-induced corrosion. In addition, this paper analyzes the growth mechanisms of intermetallic compounds at bonded interfaces and highlights the indispensable role of palladium in enhancing interfacial strength and corrosion resistance. Finally, the review summarizes the current research progress and proposes future research directions of copper wires, aiming to provide a reference for further optimization and wider application of copper wire bonding technology.

The effects of different deformation processing routes (rolling and rotary forging) and temperature conditions on the microstructure and mechanical properties of W-1%La2O3 alloy wire were investigated. The results indicate that with increasing cumulative deformation (from ø22 mm to ø5.2 mm), the grain refinement efficiency of the “rolling + rotary forging” sequence is significantly superior to that of the “rotary forging + rotary forging” process. For the as-deformed ø5.2 mm W-La alloy bars, the material processed by “rolling + rotary forging” exhibited a higher Vickers hardness of 544.9 HV compared to that processed solely by rotary forging. Following annealing treatment, the hardness values of ø9.0 mm and ø5.2 mm bars produced via the “rolling + rotary forging” route were 467.2 HV and 460.4 HV, respectively. These values are notably higher than those obtained from the “rotary forging + rotary forging” process, which measured 446.1 HV and 433.5 HV for the corresponding diameters. In summary, this study systematically compares the effects of rolling and rotary forging processes on the microstructure and properties of W-La alloy, providing a valuable foundation for the future development of high-strength tungsten alloy wires.

Cu nanoparticle sintering technology, known for its low electromigration rate, superior electrical and thermal properties, and cost efficiency, is a promising method for high-power device packaging. Despite limited research on substrate conditions, this study uses molecular dynamics (MD) simulations to investigate how substrate surface roughness affects the quality of Cu nanoparticle sintered joints. Various surface roughness levels were simulated by arraying bumps of different heights on the Cu substrate. The findings indicate that a smaller roughness on the substrate enhances sintering quality, whereas a larger roughness detrimentally affects sintering quality. The effects of varying sintering temperatures, Cu nanoparticles and pressures were examined to address the challenge of improving sintering quality under conditions of greater roughness. Computational results reveal that an appropriate particle size can effectively fill surface defects. Additionally, increasing the sintering temperature and pressure significantly mitigates the negative impact of roughness on sintering quality. These results address substrate surface roughness and provide insights for optimizing the Cu nanoparticle sintering process.

The redistribution of the palladium coating on the surface of palladium-coated copper wires during the bonding process is a critical factor influencing the bond connections of chips and wires. In this paper, a micro-area coating technique was used to obtain palladium-coated copper wires with varying characteristics by controlling the heating temperature. Ball formation and ball bonding experiments were conducted to investigate the evolution process of the palladium coating and its impact on bonding strength. The results indicate that at 400 degrees C, the thickness distribution of the palladium coating on the coated copper wire is uniform, with larger nanocrystal sizes and narrower amorphous band widths, forming larger free air ball (FAB) sizes and thicker redistribution coatings. The bonding interface exhibits a continuous and uniformly distributed palladium coating, with higher bond connection strength. For copper wires subjected to secondary heating at 300 degrees C, there is a significant fluctuation in coating thickness with a wider range of nanocrystal sizes and a broader width of the amorphous band. At this juncture, thinner and discontinuous coatings form at the bonding interface alongside Al2Cu intermetallic compounds emerging, which leads to reduced bonding connection strength. The distribution of nanocrystals and amorphous regions within the coating influences the melting behavior and redistribution dynamics of coatings by changing thermal transfer behavior. The strength of the bonding interface is modified by the palladium coating at the interface due to blocking the diffusion between copper and aluminum.

Highly conductive single-crystal copper processing wire is a critical material in the fields of audio-video, new energy, and other conductor transmission applications. Enhancing its electrical conductivity has emerged as a research hotspot. In this study, single-crystal copper processing wires with varying diameters were produced through continuous deformation of Y micro-alloyed single-crystal copper rod billets. XRD, EBSD, and TEM were employed to characterize and analyze the materials. The influence of Y on the impurity elements and microstructural features of single-crystal copper processing wire under high-strain deformation was investigated, revealing the mechanism behind the changes in electrical conductivity. The results demonstrate that the electrical conductivity of Cu-0.03Y, with a diameter of 0.18 mm, reached 98.01% IACS, representing a 1.15% improvement over that of single-crystal copper processing wire. This enhancement is attributed to the presence of nanoscale precipitates (YP, Y2S3), which reduce electron scattering caused by solute atoms. In the undeformed stage, rare earth microalloying reduces the grain size and electrical conductivity of single-crystal copper processing wire, increases the deformation dislocation accumulation capacity, and promotes recrystallization and twinning. When the deformation reaches Phi 0.18 mm, the grain size of the single-crystal copper processing wire exhibits a multiscale microband structure. Nanoscale microbands (<200 nm) possess lower dislocation densities and serve as effective channels for electron mobility. Consequently, the enhancement in electrical conductivity can be attributed to the reduced electron scattering effect facilitated by the precipitated phases, nanoscale microbands, and twins, which promote free electron movement.

Magnetorheological finishing (MRF) is one of the key technologies for the efficient and precise planarization of surfaces. While maintaining magnetic properties, improving the corrosion resistance of magnetic particles and their synergy with abrasives plays an important role in improving the efficiency and quality of magnetorheological finishing. In this work, TiO2 and TiH2 powders were used as titanium sources to prepare two Fe-Ti-O magnetorheological composite powders, labelled as A and B, through an in-situ oxidation-reduction process. Subsequently, diamond grits (0.5 mu m, 5 wt%) were added into the Fe-Ti-O magnetorheological composite powders and spherical magnetorheological composite abrasives (SAs) with particle size ranged from 2 to 12 mu m were prepared by a spray granulation process. The effects of TiO2/TiH2 addition on the microscopic morphology, phase composition, microhardness, density, magnetic properties, particle sizes, specific surface areas and corrosion resistance of A, B and SAs were investigated. The results indicate that A and B are composed of two phases, Fe and Fe2TiO4, which have a unique "Ferrero" structure. The microhardness, density, saturation magnetization and corrosion potential of B were 525 HV, 5.125 g/cm3, 131 emu/g and -0.841 VSCE respectively, which were higher than those of A. The results of the magnetorheological finishing of single crystal silicon wafers demonstrate that the efficiency of the magnetorheological slurry (MRS-B) is approximately 6.3 times that of MRS-A. It has been demonstrated that B is a more suitable base material for SAs, which possess a high degree of sphericity and a high degree of particle size concentration. The Raman spectra of SAs demonstrated that the preparation process did not result in the carbonization of the diamond grits. The magnetic properties (Ms = 104.1 emu/g, Hc = 133.12 Oe, Mr = 5.88 emu/g) of SAs meets the requirements for magnetorheological finishing and positions them as ideal candidates for the magnetorheological finishing of third-generation semiconductor SiC wafers.

The characteristics of the free air balls (FABs) are important factors affecting the reliability of bonding connection and the quality of chips. In this paper, palladium-coated copper wires with different palladium coating structures were obtained by changing the heating temperature of the micro-area coating process and then obtaining corresponding FABs. The intrinsic relationship between the palladium coating structure and the FAB characteristics was studied. Results show that with the increase in heating temperature, the rate of palladium particle aggregation on the surface coating accelerated. Secondary heating resulted in reduced uniformity in the distribution of palladium and thickness of the coating and increased the range of nanocrystal sizes within the coating. The uniformity of the thickness of the coating affected the surface tension at different positions on the surface of the FABs after remelting. A more uniform thickness distribution was conducive to the formation of FABs with better roundness. The narrower nanocrystal size width could be remelted in a smaller temperature range, which was beneficial to the flow of palladium coating and increased uniformity of palladium redistribution on the surface of FABs. The FABs formed with palladium-coated copper wire at 400 degrees C had better morphology and more uniform palladium redistribution.

Single-crystal copper processing wire as a critical conductive material for transmission wires in integrated circuits, plays an essential role in ultra-fine processing due to its superior plastic deformation capability. This study investigates the evolution of plastic deformation and microstructural changes in single-crystal copper processing wire under high strain conditions with the addition of the rare earth element Y. Furthermore, the influence of the rare earth element Y on the mechanical properties, microstructure development, and texture composition of single-crystal copper processing wire is systematically examined. The study employed scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), three-dimensional atom probe tomography (3D-APT), and transmission electron microscopy (TEM) for material analysis and characterization. A Y-O atomic mutual attraction model was developed to analyze the nanoscale precipitated phases. The results indicate that a "Y-O '' phase forms at epsilon >= 3.68, accompanied by a "self-annealing" phenomenon. Specifically, during room temperature plastic deformation, the tensile strength of Cu-0.03Y processing wire (291.73 MPa) decreases by 35.4 %, while its elongation(5.75 %) increases by 751 % compared to that of single-crystal copper processing wire (0.675 %). The presence of multi-scale precipitates, including nanoscale Y2O3 and micron-scale Cu5Y precipitates, in micro-alloyed single-crystal copper processing wires induces significant lattice distortion and enhances the cumulative dislocation density. The high dislocation density facilitates dislocation reorganization, subgrain rotation, and the transition from LAGBs to HAGBs, thereby increasing the volume fraction of <100> and <110> fiber textures and promoting recrystallization.

The intermetallic compound layer at the Cu/Al bonding interface is undergoing a dynamic evolution stage with the consumption of the Al pad during the continuous annealing process. This paper establishes a microstructure model of the Cu/Al bonding interface and analyses the crack extension behavior of the bonding interface through finite element simulation under three key aging states: initial bonding, moderately annealed and highly aged. The findings indicated that alterations in the annealed state would result in a modification of the damage mode of the bonding interface, leading to a deviation in the crack path. In the initial stages of the bonding process, crack initiation occurs at the edge of the Al pad and extends inward, resulting in fracture. The occurrence of cracks depends on the extent of annealing, with softer Al pad or Al-rich IMCs, such as CuAl2 layer, exhibiting these defects under moderately annealed conditions. Subsequently, the cracks gradually extend towards the harder and more brittle Cu9Al4 to fracture. In highly aged conditions, cracks initially emerge in the Al-rich CuAl2 layer and subsequently deflect into the CuAl layer. Finally, they deflect once more into the Cu9Al4 layer, eventually leading to fracture. In addition, cracks are affected by the grain orientation of IMCs and form at interfaces that are approximately perpendicular to the loading direction. The simulation results corroborate the fracture modes of the bonding interface in different aging processes from the micro grain perspective, which provides a technical reference for the study of the fracture mechanism of Cu/Al bonding.

The relationship and influencing mechanism among the reduction rate, the strengthening behavior and the microstructure evolution of rolled Cu strips were studied. It was found that with the increase of reduction rate, the uneven deformation behavior of the Cu strip was divided into three zones. The grain size in Zone I was refined accompanied by large-scale entangled dislocations, and a nanosheet layered texture was formed. The primary reason for the increase in the strength of the Cu strip is the combined strengthening effect of dislocation, grain boundary and texture, as well as the strengthening effect provided by some lattice friction. The grain orientation exhibited periodic transitions between <110> and <111>, <001>, which provides assistance for grain refinement and dislocation accumulation. The grains in the fracture zone of the Cu strip are elongated and refined during stretching, and flow towards the central axis of the cross-section. The fracture mechanism has shifted from cutting to a chip edge/point to a combined action of multiple mechanisms, which is also accompanied by a gradual increase in the "tearing angle".

To enhance the application of 8YSZ ceramics in high-temperature environments, ongoing efforts have focused on improving their thermal shock resistance. In this study, MgO was introduced as a second phase to modify the thermal shock resistance of 8YSZ ceramics, and the effect of MgO content on the microstructure, mechanical properties and thermal characteristics of 8YSZ ceramics was systematically investigated. With the addition of MgO, the solid solution reaction improved the sintering properties of 8YSZ, resulting in the relative density increased from 92.0 % of 8YSZ to 93.7 % of 12 wt% MgO doped 8YSZ ceramics. The presence of the second phase MgO and the microcracks caused by the mismatch in coefficients of thermal expansion between 8YSZ and MgO deflected the cracks generated in the samples during thermal shock. Consequently, the thermal damage resistance parameter of the samples was increased and the thermal shock fracture resistance parameter was not significantly reduced. Results from cooling at room temperature quenching experiments and the calculation of the thermal damage resistance parameter (R' ' ' ') demonstrated an improved thermal shock resistance in MgO doped 8YSZ ceramics, with an increase in the residual flexural strength ratio (RFSR) from 48.69 % of 8YSZ to 67.25 % of 12 wt% MgO doped 8YSZ ceramics.