In this study, based on the synergistic strategy of sustained release reduction and in-situ surface nanostructuring, oxidation-resistant and rapid sintering of submicron copper (Cu) paste in an air atmosphere was achieved. First, the critical temperature points at which Cu undergoes severe oxidation were identified. Based on this, the reductant system, composed of ascorbic acid and polyethylene glycol (PEG30 0), was specially designed to match the oxidation threshold of Cu. Notably, due to the sustained release effect of the reductant system, reduction activity was sustained throughout the entire sintering process. During sintering, both CuO and Cu2O were ultimately reduced to ultrafine Cu nanoparticles. Simultaneously, in-situ surface nanostructuring occurred on submicron Cu particles, enabling oxidation-resistant and rapid sintering in air. At a sintering temperature of 250 degrees C for 5 min, the resulting joints exhibited a shear strength of 38.1 MPa, meeting the requirements for power device packaging. This work provides a novel strategy for oxidation-resistant Cu sintering and its industrial application. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Abstract Precise small-strain detection is critical for various applications, yet most existing technologies lack conformability, environmental robustness, high performance, and fabrication simplicity. Here, we introduce a material-independent design strategy to prepare ultrasensitive stretchable sensors that leverage two cracking mechanisms: cut-through cracks abruptly rupture dominant conductive pathways, while mesh-like cracks drive the progressive degradation of auxiliary conductive pathways, collectively leading to a rapid and stable resistance increase under small strains. The resulting sensor possesses an ultrahigh gauge factor (~430), an ultralow detection limit (0.0003365% strain), and high durability (> 5,000 tensile cycles). Through conformal, in situ, and real-time structural monitoring with a high signal-to-noise ratio (> 50 dB), the sensor reliably captured a small compressive strain signal for deep-sea equipment under extreme hydrostatic pressure (50 MPa). Our design offers a general, scalable route for ultrasensitive sensing in aerospace, ocean engineering, and precision manufacturing.

Directed self-assembly (DSA) using wettability contrast guides functional inks into hydrophilic regions through interfacial tension. Herein, we report a charge-tunable DSA strategy using parallel-beam vacuum ultraviolet (PVUV) irradiation and alkaline activation to selectively modulate the dispersive (sigma sD) and polar (sigma sP) fractions of the surface free energy (SFE) of polymer substrates. sigma sD-rich regions repel polar inks, while sigma sP-rich regions attract them, enabling a controllable transition between attractive and repulsive patterning. In polydimethylsiloxane (PDMS), short PVUV exposure induces a higher negative surface charge, leading to electrostatic repulsion that expels ink from the modified regions. In contrast, prolonged PVUV exposure reduces the surface charge density while increasing the polarity, enabling van der Waals attraction to dominate and promote ink deposition. The mechanism is elucidated using a modified Derjaguin-Landau-Verwey-Overbeek framework. Utilizing this platform, silver nanowire (AgNW) inks are patterned into stretchable conductive networks with resolutions down to 50 & micro;m. The resulting AgNW traces exhibit low resistivity (8.19 & times; 10-8 Omega m) and reliable electromechanical responses under 60% tensile strain. This lithography-free, charge-tunable DSA approach provides a scalable route for fabricating high-resolution stretchable electronics with potential for use in wearable sensors and electrotactile haptic interfaces.

In fields such as industrial production, medical diagnosis, and aerospace, temperature monitoring is essential for indicating the dynamic balance of heat generation and dissipation in the measured objects. Traditional thermocouple temperature sensors are limited in their ability to conform to complex curved surfaces or irregularly shaped objects, making high-precision measurements difficult. Thin-film thermocouples, thanks to their slim design and flexibility, offer better conformity and faster response. However, current manufacturing methods for thin-film thermocouples face issues such as low efficiency, high costs, and environmental concerns. This study used screen-printing technology to successfully create a high-performance flexible Cu-Ni thin-film thermocouple with a sensitivity of 9.05 +/- 0.15 mu V degrees C-1. The fabricated thermocouples exhibited an excellent linear response from room temperature to 150 degrees C, responded in less than 1 s, and maintained good mechanical stability, with resistance remaining stable after 1000 bending cycles. Based on this, the study further developed a flexible sensor array with a shared-electrode design, which was successfully applied to curved-surface temperature detection and human-machine interaction, demonstrating its potential for high-precision measurement in complex environments. This work presents a cost-effective and efficient method for fabricating flexible thermocouples, paving the way for the scalable production and application of flexible electronic devices.

With the deceleration of Moore's Law, the improvement of chip performance is transitioning from pure transistor scaling to the parallel advancement of device miniaturization and advanced packaging technologies, aiming to achieve higher levels of system integration and interconnect density. Following this trend, copper pillar bumps, owing to their miniature dimensions, fine pitch, and outstanding electrical and thermal properties, have emerged as essential interconnect structures in 2.5D and 3D packaging technologies. However, copper pillar bump technology continues to encounter issues, including elevated interconnection temperatures, inadequate thermo-electric reliability, and constrained performance under ultra-high-density conditions. This review provides an overview of the research background, current progress, and prospective trends in copper pillar bump technology. Beginning with the basic fabrication processes, this paper elaborates on the evolution of material systems for copper pillar bumps and the most recent advancements in novel fabrication techniques. Next, the underlying mechanisms and suitability of different interconnection approaches are examined. Moreover, advances in reliability testing, failure mechanisms, and optimization strategies for interconnections are summarized, providing theoretical guidance for extending their service life and enhancing long-term reliability. Finally, the prospects and research directions of copper pillar bump technology are discussed.

Flexible sensors are attracting a significant amount of attention due to their potential applications in e-skin, healthcare, Human-Machine Interaction (HMI). However, the reliability of the sensor signal is still a challenge. Machine learning (ML) has been employed to enhance the accuracy of flexible sensors through data- related production and analysis. In this review, we summarize the ML methods and performances for a wide range of flexible sensors. Firstly, how ML-assisted data interpretation improves the performances of flexible sensors is elaborated. Then the applications of ML in flexible sensors are exhibited covering materials science, healthcare, HMI, and soft robots. Finally, the advantages, challenges, and future perspectives associated with the integration of flexible sensing technology and ML algorithms are discussed. These will give significant insights to the further application of ML in flexible sensing systems.

This paper presents two studies based on low-temperature Cu sinter-joining technology: a bimodal Cu sphere/flake paste optimized via simulation achieved a shear strength of 45.6 MPa and resistivity below 7 μΩ•cm under pressureless sintering at 280 °C; a screen-printed flexible Cu-Ni thin-film thermocouple achieved a sensitivity of 9.05 ± 0.15 μV/°C, response time below 1 s, and stable performance after 1000 bending cycles, with a 3×3 array demonstrated for curved-surface temperature monitoring and human-machine interaction. Both works validate their practical potential for high-power and intelligent electronics.

In recent years, in addition to the pursuit of miniaturization and integration, electronic devices have exhibited an increasingly prominent demand for high power and intelligent functions, which has become a...

This paper reviews large-area metal paste sinter joining, focusing on the progress and challenges related to delamination, warpage, and reliability—findings that are crucial for the development of highly reliable power electronics.

Copper (Cu) pastes have emerged as highly promising bonding materials in the field of power electronics packaging due to their low cost, high thermal conductivity, and outstanding mechanical reliability. However, the high-temperature and high-pressure sinter-joining processes significantly limit their practical application. This study proposes a multi-solvent collaborative engineering strategy to effectively promote the activation, rearrangement, and densification of Cu particles during sintering. By modulating the reducing property, wettability, and evaporation property of the solvent, Cu joints with shear strength of up to 50.67 f 4.19 MPa are achieved under low-temperature (200 degrees C) and pressureless conditions. Even when the temperature decreases to 160 degrees C, the shear strength maintains 46.10 f 2.56 MPa. Additionally, the developed Cu paste exhibits outstanding compatibility with Au and Ag metallized surfaces. The high performance of this Cu paste offers potential applications and commercial value in the packaging of high-power electronic devices.

Electrochromic devices (ECDs) hold great promise for applications in displays and smart military camouflage. However, achieving different electrochromic colored states with compatible integration into a monolithic device remains a significant challenge. In this study, we realized effective color modulation of ECDs by tuning the solvent composition, leveraging the effects of solvent polarity. The resulting ECDs exhibited tunable absorption peaks and color switching behaviors across various solvent systems. The ECDs achieved a high optical contrast of 74%, while maintaining a coloration efficiency of 41.6 cm2 C-1.

Flexible temperature sensors, which are celebrated for their outstanding bendability, display an elevated level of compatibility with diverse surfaces. Owing to their remarkable comfort and biocompatibility, they have emerged as the prime option for portable and wearable medical monitoring apparatuses. Printed electronics technology, an innovative methodology, integrates traditional printing techniques with functional inks, providing an economical, scalable, and high-throughput strategy for manufacturing flexible temperature sensors. This paper reviews recent research on flexible temperature sensors based on printed electronics technology, detailing the temperature sensing mechanisms, essential materials for preparing thermosensitive layers, various printed electronics techniques used in sensor production, and the applications of these sensors in different fields. Moreover, the paper profoundly analyzes the challenges of flexible temperature sensors and proposes targeted improvement strategies and future directions.

Wide bandgap semiconductors, silicon carbide (SiC) and gallium nitride (GaN), hold significant importance in applications such as new energy vehicles, aerospace, and 5G technology due to their high breakdown voltage, excellent thermal conductivity, and outstanding radiation resistance. However, traditional lead-free solder has limitations in electrical and thermal performance, making it difficult to meet the demands of electronic packaging. Although silver (Ag) sinter-joining technology has high performance, its cost is relatively high and its resistance to electrochemical migration is weak, making high-cost-performance copper (Cu) sinter-joining technology a promising alternative. To overcome the oxidation risk and agglomeration tendency of nanoparticles in Cu pastes, this study introduces micron-Cu flakes, aiming to strike a balance between stability and sintering ability. We optimize the ratio of bimodal particles using a combination of computer simulations and experimental methods. The study shows that the optimal packing density and sintering performance are achieved when the ratio of submicron-Cu spheres to micron-Cu flakes is 7:3. On this basis, the solvent system of Cu paste is improved, enhancing its low-temperature sintering performance. At an ultra-low temperature of 160 degrees C, the shear strength is up to 46 MPa, providing significant application potential and commercial value in the field of high-power electronic device packaging.

SiC power devices represent a breakthrough in wide bandgap semiconductor technology, offering superior performance through high current density, extreme temperature operation, and fast switching capabilities that enable transformative improvements in power electronics, yet their full potential is constrained by the limitations of traditional soldering techniques in meeting stringent high-temperature stability and thermal management requirements. This chapter comprehensively examines low-temperature sintering technology as a transformative solution for SiC interconnects, showcasing material innovations including advanced Ag sintering formulations with nano/micro hybrid particles achieving robust connections at unprecedented low temperatures through particle engineering breakthroughs, alongside pioneering Cu sintering methods utilizing formic acid reduction and nanoscale surface treatments to provide cost-effective alternatives with exceptional mechanical strength exceeding 130 MPa. The implementation of this technology offers significant advantages across advanced packaging architectures, including DTS, Cu Clip, and double-sided cooling systems, as well as emerging embedded configurations. These developments firmly establish low-temperature sintering as an essential enabling technology for next-generation power electronics packaging solutions.

This study introduces a novel technology for direct bonding of bare aluminum (Al) to aluminum nitride (AlN) ceramics using Ag sinter paste under low-temperature conditions starting from 180 degrees C, and air environments. A robust interface shear strength of up to 40.5 MPa was achieved at a low sintering temperature of 300 degrees C under a pressure of 5 MPa, significantly lower than the melting point of Al (660 degrees C). Transmission Electron Microscopy (TEM) observations revealed that Ag particles attach to and inter-diffuse into the natural oxide layer of Al (Al2O3) and the AlN layers during the initial stages of sintering, forming a porous structure after sintering. Additionally, the interface bonding mechanism for Ag/Al and Ag/Al2O3 was analyzed using Molecular Dynamics (MD) simulations. The results indicated that the diffusion of Ag into Al2O3 occurs moderately faster than into Al, suggesting that the Al2O3 layer facilitates interface bonding for Ag during low-temperature, low-pressure sintering. The high-temperature reliability of the Al/AlN bonding structure was also examined by aging it at 300 degrees C for 500 h. Despite the microstructural evolution within the bonding layer, the shear strength remained above 20 MPa after aging, demonstrating excellent high-temperature stability.

Although adding binders could significantly improve the adhesion between metal pastes and polymer substrates, they also considerably decrease the conductivity of printed circuits, limiting their applications in printed electronics. This study innovatively adds a copper (Cu) precursor to the paste to solve this problem. Cu nanoparticles are formed on the surface of Cu flakes and within the binders due to their in situ decomposition characteristics. The decomposed Cu nanoparticles construct more conductive pathways that improve the conductivity of the printed circuits. Furthermore, this study employs an orthogonal test to investigate the relationship between the formulation of pastes and the performance of printed circuits, optimizing the proportion of the Cu precursor and binders based on these results. Compared to conventional pastes that consist solely of Cu fillers, binders, and solvents, the paste developed in this study exhibits high conductivity, which is approximately 2.6 times that of the pure Cu flake paste at low metal content around 40%. Thus, with more binders, the printed circuits not only met the 5B level according to ASTM D3359 standards but also showed excellent electrical properties after curing at 200 degrees C for 5 min, achieving a resistivity as low as 331 mu Omegacm. Additionally, the paste exhibited outstanding performance in the application of heaters and ultrabroadband (UWB) antennas, further confirming its considerable potential for commercial printed circuits.

Compared with soldering technology, metal particle sinter-joining technology can provide better thermodynamic performance and higher packaging reliability. It is considered one of the most promising technologies for achieving interconnects with high reliability and heat resistance for wide-band gap semiconductor devices. However, sinter-jointed layers are usually porous structures, and the porosity inevitably affects the sinter-joints' thermal and mechanical properties. Compared with traditional unimodal metal particle pastes, multimodal particle pastes can reduce the sinter-jointed layers' porosity and improve their performance effectively. In order to obtain the optimal ratio of multimodal micro/nanoparticle materials, a Monte Carlo simulation method was developed to achieve their random stacking. The results show that regardless of radius ratios between bimodal spherical particles, their stacking density gets the highest value when the mass of the small particles comprises similar to 30%. When the spherical particles with r1=0.5 and non-spherical (elliptical) particles with the principal axis 2a=10, 2b=8, thickness 2d=1.5 and theta(max)=10 degrees were used, the stacking density gets the highest value when the spherical particles account for similar to 70%. Overall, the computer simulation method for evaluating the stacking density of multimodal spherical or non-spherical particles is provided and proved useful.

Low-temperature copper (Cu) sinter-joining technology has attracted increasing attention in high-power electronic device packaging because of its low material cost, good electrical and thermal conductivity, low-temperature joining processes, and high-temperature service characteristics. However, due to the high oxidation risk and agglomeration tendency of Cu particles, the stability of Cu pastes is poor, the sinter-joining conditions become harsh, and the performances of sintered parts could be better. These defects heavily hinder the application of low-temperature Cu sinter-joining technology in power electronic packaging. In this review, the research of the low-temperature Cu sinter-joining technology is reviewed, including its background, development, challenges, and perspectives. Based on the sinter-joining mechanism, the advanced progress of Cu paste formulas and sintering processes are described in detail, and the mainstream strategies for improving Cu paste's stability and oxidation resistance are discussed, highlighting scientific issues and advocating for best practices in conducting low-temperature Cu sinter-joining technology. In addition, the reliability and failure mechanisms of sintered Cu joints are summarized, which provides theoretical support for further improving the performance and service life of the joint. Finally, the development trend and future research directions of low-temperature Cu sinter-joining technology are described.

Direct printing of flexible Cu traces is one of the most promising additive manufacturing technologies in advanced electronics because it is a cost-effective and environmentally friendly process. However, the low oxidation resistance of Cu is currently a critical issue for the preparation of high-performance metallic inks and the manufacturing of reliable printed traces. Herein, we propose a hybrid ink containing Cu/Ni complexes and Cu particles that can be directly printed onto polyimide substrates to generate high-performance Cu-Ni alloy traces by low-temperature preheating and intense pulsed-light irradiation. The nanoparticles in-situ formed by the decomposition of the complexes effectively bridge the interfaces among Cu particles, allowing the printed traces after subsequent intense pulsed-light irradiation to achieve a low resistivity of 29.4 mu omega & sdot;cm and excellent mechanical stability at a bending radius of 7 mm. Strikingly, the obtained Cu-Ni alloy traces achieve multiscale core-shell structures because of the heterogeneous nucleation and passivation of Ni, which enables the printed traces to maintain high conductivity and oxidation resistance even at 250 degrees C in the air, showing strong potential for use in advanced electronics manufacturing.

In this study, the thermal characteristics and structure reliability during power cycling for the four types of SiC power module fabricated using a SiC-heater chip, direct bonded aluminum (DBA) substrate, and aluminum (Al) heatsink were evaluated. Two die-attach materials, including a Sn-Ag-Cu (SAC 305) solder and an Ag paste sinter, were used to bond the SiC to DBA substrate. Furthermore, three types of substrates bonding layer, including SAC solder and Ag paste sinter, and Si grease, were used to bond the DBA substrate to Al heatsink. The large area bonding between the DBA substrate (30 x 30 mm2) and Al heatsink was achieved. In addition, comparing with the tradition SAC solder-Si grease joint structure, the SiC chip temperature decreased from 265.5 ℃ to 180.4 ℃ and the total thermal resistance of the joint structure decreased from 1.58 K/W to 0.85 K/W for the Ag-Ag sinter joint at the same input power. The heat dissipation improved by 1.86 times. The results were validated and fit well using 3D finite element analysis. The failure time was improved 14.5 times from 2340 cycles to 33926 cycles for the AgAg sinter joint during the power cycling test. This study will help us to create a SiC power device structure that is smaller, thinner, and possesses ultra-low thermal resistance, and high reliability.