Water-Triggered Self-Healing of Ti3C2Tx MXene Standalone Electrodes: Systematic Examination of Factors Affecting the Healing Process.

MXenes, with their remarkable attributes, stand at the forefront of diverse applications. However, the challenge remains in sustaining their performance, especially concerning Ti3C2Tx MXene electrodes. Current self-healing techniques, although promising, often rely heavily on adjacent organic materials. This study illuminates a pioneering water-initiated self-healing mechanism tailored specifically for standalone MXene electrodes. Here, both water and select organic solvents seamlessly mend impaired regions. Comprehensive evaluations around solvent types, thermal conditions, and substrate nuances underline water's unmatched healing efficacy, attributed to its innate ability to forge enduring hydrogen bonds with MXenes. Optimal healing environments range from ambient conditions to a modest 50 °C. Notably, on substrates rich in hydroxyl groups, the healing efficiency remains consistently high. The proposed healing mechanism encompasses hydrogen bonding formation, capillary action-induced expansion of interlayer spacing, solvent lubrication, Gibbs free energy minimizing MXene nanosheet rearrangement, and solvent evaporation-triggered MXene layer recombination. MXenes' resilience is further showcased by their electrical revival from profound damages, culminating in the crafting of Joule-heated circuits and heaters.

Effects of Cu Opening Size on the Mechanical Properties of Epoxy-Contained Sn-58Bi Solder Joints.

The effects of Cu opening size on the mechanical properties of epoxy-contained Sn-58Bi solder joints were investigated by a low-speed shear test. Eight sample types were fabricated with various Cu opening sizes and solder pastes. The Cu opening sizes of the component and substrate were 200 µm or 380 µm, respectively, and the component formed a Sn-3.0Ag-0.5Cu (SAC305) solder bump which was placed on the Sn-58Bi solder paste or epoxy Sn-58Bi solder paste printed on the substrate and then reflowed. The microstructures of the solder joints were observed using scanning electron microscopy (SEM), and the chemical compositions were analyzed by energy-dispersive X-ray spectroscopy (EDS) and electron probe X-ray micro-analyzer (EPMA). Epoxy was formed around the solder joints after the reflow process, improving the bonding strength of the epoxy-contained solder joints. Specifically, the bonding strength of the epoxy Sn-58Bi solder joints increased about 2.9 times in the 200 µm (opening size of component)/380 µm (opening size of substrate) sample. When the opening size of the component and substrate differed, a fracture occurred at the smaller opening size. On the other hand, a fracture occurred at the substrate side for the SAC305 (solder paste of component)/Sn-58Bi (solder paste of substrate) solder joints, while a fracture occurred at the interface between SAC305 and Sn-58Bi at the SAC305/epoxy Sn-58Bi solder joints for samples with the same opening size between the component and substrate.

Mechanical Property of SAC305 Ball-Grid Array and Epoxy Sn-58Bi Solder Joints with 85 °C/85% Relative Humidity Environmental Conditions.

The ball-grid array (BGA) is widely used to reduce component size and it had advantages such as high I/O pins and fine pitch. Typical Sn-Ag-Cu (SAC) solder alloys are used for formation of BGA because SAC solder has excellent characteristics among lead-free solders. However, the electronic components assembled by SAC solder were easily damaged by heat during manufacture process because SAC solder had high melting point of 220 °C. To prevent these thermal damages, SAC305 BGA component assembled by Sn-58Bi solder paste has been studied because Sn-58Bi solder had low melting point of 139 °C. In generally, Sn-58Bi solder was improved by additional elements or polymer such as epoxy because Sn-58Bi had a brittle property. However, the epoxy Sn-58Bi solder did not guaranteed high environmental reliability such as high-temperature high-humidity (HTHH) test. Thus, we evaluated the shear strength of solder joints assembled by SAC305 BGA components with Sn-58Bi solder paste and epoxy Sn-58Bi solder paste. The shear strength of solder joints was evaluated by die shear test after HTHH test at the 85 °C/85% RH conditions. The Cu6Sn5 intermetallic-compound (IMC) at the interface of solder joints was observed by scanning electron microscope (SEM). The IMC thickness of Sn-58Bi solder joints was smaller than that of epoxy Sn-58Bi solder. The shear strength was improved up to 20% by epoxy addition. The shear strength of epoxy Sn-58Bi solder joints dramatically decreased after HTHH test for 100 h.

Effect of Epoxy on Mechanical Property of SAC305 Solder Joint with Various Surface Finishes Under 3-Point Bend Test.

Microstructures and mechanical property of Sn-3.0Ag-0.5Cu (SAC305) and epoxy Sn-3.0Ag-0.5Cu (epoxy SAC) solder joints were investigated with various surface finishes; organic solderability preservative (OSP), electroless nickel immersion gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG). Bending property of solder joints was evaluated by 3-point bend test method. Microstructure and chemical composition of solder joints was characterized by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. Epoxy did not effect on intermetallic compound (IMC) morphology. Scalloped shaped Cu6Sn5 IMC was observed at OSP surface finish. Chunky-like shaped and needle-like shaped (Ni,Cu)6Sn5 IMC were observed at the solder/ENIG joint and solder/ENEPIG joint, respectively. The bending cycles of SAC305/OSP joint, SAC305/ENIG joints and SAC305/ENEPIG joints were 720, 440 and 481 cycle numbers. The bending cycles of epoxy SAC and three types surface finished solder joints were over 1000 bending cycles. Under OSP surface finish, bending cycles of epoxy SAC solder was approximately 1.5 times higher than those of SAC305 solder joint. Bending cycles of epoxy SAC solder was over twice times higher than those of SAC305 solder with ENIG and ENEPIG surface finishes. The bending property of epoxy solder joint was enhanced due to epoxy fillet held the solder joint.

Facet-controlled anatase TiO2 nanoparticles through various fluorine sources for superior photocatalytic activity.

Reactive surface-exposed anatase TiO2 (a-TiO2) is highly desirable for applications requiring superior photocatalytic activity. In order to obtain a favorable surface, morphology control of the a-TiO2 using capping agents has been widely investigated. Herein, we systematically study the effects of different F sources (HF, TiF4, and NH4F) as the capping agent on the morphology control and photocatalytic activities of a-TiO2 in a hydrothermal process. When either HF or TiF4 was added, large truncated bipyramids formed with the photocatalytically active {001} facet, whereas the NH4F was not effective for facet control, yielding nanospheres similar to the pure a-TiO2. The morphology changes were related to the decomposition behaviors of the F sources in the solvent material: HF and TiF4 decomposed and supplied F(-) ions before a-TiO2 nucleation, which changed the nucleation rate and growth direction, leading to the resultant a-TiO2 morphology. On the other hand, NH4F supplied F(-) ions after a-TiO2 nucleation and could not change the growth behavior. In terms of the photocatalytic effect, the HF- and TiF4-treated a-TiO2 effectively decomposed ∼90% and ∼80% of methylene blue, respectively, in 1 h, while ∼60% was decomposed for the NH4F-treated a-TiO2. Note that pure a-TiO2 photocatalytically decomposed only ∼10% of methylene blue over the same time. These results pave the way to precise control of the facet of TiO2 through using different capping agents.

Microwave Sintering of Silver Nanoink for Radio Frequency Applications.

Microwave sintering is a promising method for low-temperature processes, as it provides advantages such as uniform, fast, and volumetric heating. In this study, we investigated the electrical characteristics of inkjet-printed silver (Ag) circuits sintered by microwaves. The microstructural evolutions of inkjet-printed Ag circuits sintered at various temperatures for different durations were observed with a field emission scanning electron microscope. The electrical properties of the inkjet-printed Ag circuits were analysed by electrical resistivity measurements and radio frequency properties including scattering-parameters in the frequency range of 20 MHz to 20 GHz. The experimental results show that the signal losses of the Ag circuits sintered by microwave heating were lower than those sintered by conventional heating as microwave heating led to granular films which were nearly fully sintered without pores on the surfaces. When the inkjet-printed Ag circuits were sintered by microwaves at 300 °C for 4 min, their electrical resistivity was 5.1 µΩ cm, which is 3.2 times larger than that of bulk Ag. Furthermore, microwave sintering at 150 °C for 4 min achieved much lower signal losses (1.1 dB at 20 GHz) than conventional sintering under the same conditions.

Characterization of reliability of printed indium tin oxide thin films.

Recently, decreasing the amount of indium (In) element in the indium tin oxide (ITO) used for transparent conductive oxide (TCO) thin film has become necessary for cost reduction. One possible approach to this problem is using printed ITO thin film instead of sputtered. Previous studies showed potential for printed ITO thin films as the TCO layer. However, nothing has been reported on the reliability of printed ITO thin films. Therefore, in this study, the reliability of printed ITO thin films was characterized. ITO nanoparticle ink was fabricated and printed onto a glass substrate followed by heating at 400 degrees C. After measurement of the initial values of sheet resistance and optical transmittance of the printed ITO thin films, their reliabilities were characterized with an isothermal-isohumidity test for 500 hours at 85 degrees C and 85% RH, a thermal shock test for 1,000 cycles between 125 degrees C and -40 degrees C, and a high temperature storage test for 500 hours at 125 degrees C. The same properties were investigated after the tests. Printed ITO thin films showed stable properties despite extremely thermal and humid conditions. Sheet resistances of the printed ITO thin films changed slightly from 435 omega/square to 735 omega/square 507 omega/square and 442 omega/square after the tests, respectively. Optical transmittances of the printed ITO thin films were slightly changed from 84.74% to 81.86%, 88.03% and 88.26% after the tests, respectively. These test results suggest the stability of printed ITO thin film despite extreme environments.

Characterization of Ag-Pd nanocomposite paste for electrochemical migration resistance.

Direct printing such as inkjet, gravure, and screen printing is an attractive approach for achieving low-cost circuitry in the printed circuit board industry. One of the challenges for direct printing technology, however, is the poor resistance to electrochemical migration (ECM), especially for silver (Ag) which has been widely used in printed electronics. We demonstrate improved resistance to Ag electrochemical migration by adding palladium (Pd) nanoparticles to the Ag nanopaste. Conductive comb-type patterns were fabricated on a bismaleimide-triazine substrate via screen printing. Their ECM characteristics were assessed by water drop test with deionized water. These results showed that the ECM time required for dendritic growth from cathode to anode to cause short-circuit failure was affected by the Pd content and applied voltages: the ECM time of Ag-15wt.% Pd nanopaste was nearly threefold that of Ag nanopaste, and the ECM time decreased by 94.22%, on average, while the applied voltage increased from 3 V to 9 V.

Synthesis of Ag nanowires for the fabrication of transparent conductive electrode.

Recently, advances in nano-materials research have opened the door for various transparent conductive materials, which include CNTs, graphene, Ag and Cu nanowires, and printable metal grids. Among them, Ag nanowires are particularly interesting to synthesize because bulk Ag exhibits the highest electrical conductivity among all metals. We tried to synthesize the Ag nanowires with a small diameter and long length, resulting in large aspect ratios. For the synthesis of the Ag nanowires, effects of various experimental parameters, i.e., the reaction time for synthesis, molar ratio of Ag source to surfactant, and molar weight of the surfactant were investigated with the physical shape of synthesized products. The Ag nanowire suspensions were formulated with the synthesized Ag nanowires, and a bar coating method with a Meyer rod was used to fabricate the transparent and conductive film on a glass substrate. For the thinnest wet coating, the transparent conductive layer of 90.6% transmittance at 550 nm of light wavelength and 66 ohm/sq sheet resistance could be obtained, while 13 ohm/sq was achieved at the transmittance of 76%.

Self-Repairing and Energy-Harvesting Triboelectric Sensor for Tracking Limb Motion and Identifying Breathing Patterns.

The increasing prevalence of health problems stemming from sedentary lifestyles and evolving workplace cultures has placed a substantial burden on healthcare systems. Consequently, remote health wearable monitoring systems have emerged as essential tools to track individuals' health and well-being. Self-powered triboelectric nanogenerators (TENGs) have exhibited significant potential for use as emerging detection devices capable of recognizing body movements and monitoring breathing patterns. However, several challenges remain to be addressed in order to fulfill the requirements for self-healing ability, air permeability, energy harvesting, and suitable sensing materials. These materials must possess high flexibility, be lightweight, and have excellent triboelectric charging effects in both electropositive and electronegative layers. In this work, we investigated self-healable electrospun polybutadiene-based urethane (PBU) as a positive triboelectric layer and titanium carbide (Ti3C2Tx) MXene as a negative triboelectric layer for the fabrication of an energy-harvesting TENG device. PBU consists of maleimide and furfuryl components as well as hydrogen bonds that trigger the Diels-Alder reaction, contributing to its self-healing properties. Moreover, this urethane incorporates a multitude of carbonyl and amine groups, which create dipole moments in both the stiff and the flexible segments of the polymer. This characteristic positively influences the triboelectric qualities of PBU by facilitating electron transfer between contacting materials, ultimately resulting in high output performance. We employed this device for sensing applications to monitor human motion and breathing pattern recognition. The soft and fibrous-structured TENG generates a high and stable open-circuit voltage of up to 30 V and a short-circuit current of 4 µA at an operation frequency of 4.0 Hz, demonstrating remarkable cyclic stability. A significant feature of our TENG is its self-healing ability, which allows for the restoration of its functionality and performance after sustaining damage. This characteristic has been achieved through the utilization of the self-healable PBU fibers, which can be repaired via a simple vapor solvent method. This innovative approach enables the TENG device to maintain optimal performance and continue functioning effectively even after multiple uses. After integration with a rectifier, the TENG can charge various capacitors and power 120 LEDs. Moreover, we employed the TENG as a self-powered active motion sensor, attaching it to the human body to monitor various body movements for energy-harvesting and sensing purposes. Additionally, the device demonstrates the capability to recognize breathing patterns in real time, offering valuable insights into an individual's respiratory health.

Electronic textiles: New age of wearable technology for healthcare and fitness solutions.

Sedentary lifestyles and evolving work environments have created challenges for global health and cause huge burdens on healthcare and fitness systems. Physical immobility and functional losses due to aging are two main reasons for noncommunicable disease mortality. Smart electronic textiles (e-textiles) have attracted considerable attention because of their potential uses in health monitoring, rehabilitation, and training assessment applications. Interactive textiles integrated with electronic devices and algorithms can be used to gather, process, and digitize data on human body motion in real time for purposes such as electrotherapy, improving blood circulation, and promoting wound healing. This review summarizes research advances on e-textiles designed for wearable healthcare and fitness systems. The significance of e-textiles, key applications, and future demand expectations are addressed in this review. Various health conditions and fitness problems and possible solutions involving the use of multifunctional interactive garments are discussed. A brief discussion of essential materials and basic procedures used to fabricate wearable e-textiles are included. Finally, the current challenges, possible solutions, opportunities, and future perspectives in the area of smart textiles are discussed.

Role of Oxygen in the Ti3AlC2 MAX Phase in the Oxide Formation and Conductivity of Ti3C2-Based MXene Nanosheets.

Ti3C2Tx MXene, a two-dimensional transition metal carbide, has attracted substantial interest due to its unique physical properties and a wide range of potential applications. Although the properties of devices using MXene have been substantially enhanced in recent years, it is not fully understood how the oxygen concentration in Ti3AlC2 MAX affects oxide formation in Ti3C2-based MXene nanosheets and their fundamental properties. To this end, we compared two types of MAX phases: MAX with low oxygen content (LO-MAX) and MAX synthesized by a conventional process. Since the conventional MAX synthesis employs metal (Ti) as a primary material, it is referred to as metal-based MAX (MB-MAX) from here. The oxygen content of the LO-MAX was only 0.56 wt %, which was about 20% compared to that of MAX synthesized using conventional methods. We compared the properties of MXene nanosheets prepared from the LO-MAX with MXene nanosheets obtained from the MB-MAX. Microscopic and chemical analyses revealed smooth and wrinkle-free morphology and small amounts of oxygen in MXene nanosheets prepared from LO-MAX (LO-MXene). The LO-MXene nanosheet film exhibited an exceptionally high conductivity of 10,540 S/cm and an ultralow surface roughness of 1.7 nm, which originated from inhibited surface oxide formation. Moreover, the inhibition of oxide formation strengthened the function of -O or -OH groups on the surface of MXene, thereby facilitating strong hydrogen bonding to the polymer with hydroxyl groups. To clearly reveal these properties, we prepared a pressure sensor by coating these MXene nanosheets on nylon/polyester fibers. The fabricated sensor exhibited a high sensitivity of up to 85.6/kPa and excellent stretch stability and reliability. These results clearly revealed that lowering the oxygen content in MAX can make a decisive contribution to improving the fundamental properties of MXene nanosheets prepared therefrom.

Thermal resistance of light emitting diode PCB with thermal vias.

Light emitting diodes (LEDs) are already familiar for use as lighting sources in various electronic devices and displays. LEDs have many advantages such as long life, low power consumption, and high reliability. In the future, as an alternative to fluorescent lighting, LEDs are certain to receive much attention. However, in components related to advanced LED packages or modules there has been an issue regarding the heat from the LED chip. The LED chip is still being developed for use in high-power devices which generate more heat. In this study, we investigate the variation of thermal resistance in LED modules embedded with thermal vias. Through the analysis of thermal resistance with various test vehicles, we obtained the concrete relationship between thermal resistance and the thermal via structure.

Ductile fracture mechanism of low-temperature In-48Sn alloy joint under high strain rate loading.

The failure behaviors of In-48Sn solder ball joints under various strain rate loadings were investigated with both experimental and finite element modeling study. The bonding force of In-48Sn solder on an Ni plated Cu pad increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. In contrast to the cases of Sn-based Pb-free solder joints, the transition of the fracture mode from a ductile mode to a brittle mode was not observed in this solder joint system due to the soft nature of the In-48Sn alloy. This result is discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect and the resulting stress concentration at the interfacial regions.

Effect of gold immersion time on the electrochemical migration property of electroless nickel/immersion gold surface finishing.

In this study, the electrochemical performance of an electroless nickel/immersion gold (ENIG) surface finish was evaluated as a function of the Au immersion time by the water immersion migration test. As the Au plating time increased, the electroless nickel phosphorous (EN-P) changed from amorphous to crystalline and then increased in crystallinity. X-ray diffraction (XRD) was used to evaluate the crystallinity of the plating layer. The electrical resistance of the electrodes was tracked as the sample was immersed in water with a 5 V bias. The microstructures of the electrodes after the electrochemical migration test were observed by using secondary electron microscopy (SEM) and energy dispersive spectroscopy (EDS). As the Au immersion time increased, the EN-P's crystallinity and Au thickness increased. This enhanced the electrochemical migration protection of the surface finish layer.

Adhesion characteristics of silver tracks screen-printed on polyimide with an environmental reliability test.

Printable and flexible electronics are increasingly being used in numerous applications that are miniaturized, multi-functional and lightweight. Simultaneously, reliability issues of the printed and flexible electronic devices are getting more attention. The adhesion of screen-printed silver (Ag) tracks on a polyimide (PI) film was investigated after two kinds of the environmental reliability test: a constant-temperature storage test, and a steady-state temperature and humidity storage test. Atmospheric-pressure plasma (APP) was adopted on the PI film surface to improve the poor adhesion derived from the inherent hydrophobicity. The Ag tracks constructed via screen printing were sintered at 250 degrees C for 30 min in air using a box-type muffle furnace. Some samples were exposed under 85 degrees C and 85% relative humidity (RH) for various durations (24, 72, 168 and 500 h), and others were aged at 85 degrees C with same durations to compare the influence of moisture on the adhesion. The adhesion of the screen-printed Ag tracks was evaluated by a roll-type 90 degrees peel test. The peel strength of the screen-printed Ag tracks decreased by 76.74% and 69.88% after 500 h run of the 85 degrees C/85% RH test, and the aging test, respectively. The weakest adhesion was 4.98 gf/mm after the 500 h run of the 85 degrees C/85% RH test. To demonstrate these experimental results, the microstructural evolution and chemical bonding states of the interfacial surfaces were characterized using a field emission scanning electron microscope (FE-SEM), and X-ray photoelectron spectroscope (XPS), respectively.

Electrochemical migration characteristics of screen-printed silver patterns on FR-4 substrate.

We evaluated the electrical reliability of screen-printed silver (Ag) patterns sintered at various temperatures under variable bias voltages. Comb-type patterns were screen-printed onto a flame resistance-4 substrate using a commercial Ag nanopaste (24 nm in diameter, 73 wt% of Ag nanoparticles). The printed patterns were then sintered for 30 min in air at various temperatures ranging from 100 degrees C to 200 degrees C. The microstructures and thickness profiles of the sintered conductive patterns were identified with a field emission scanning electron microscope and a 3-D surface profiler, respectively. In this study, the phenomenon of electrochemical migration was investigated with a water drop test with deionized water. These results showed that the time required by dendrites to bridge from a cathode to an anode was affected by the sintering temperature and applied voltage; when the sintering temperature was 200 degrees C, the time to achieve a short circuit was nearly four times that of the sample sintered at 100 degrees C, and while the applied voltage increased from 3 V to 9 V, the time to reach a short circuit decreased, on average, by 11%.

Flexibility of silver conductive circuits screen-printed on a polyimide substrate.

The microstructural evolution and mechanical characteristics, especially folding endurance, of screen-printed Ag circuits under various sintering conditions were investigated. The circuits were constructed on a polyimide (PI) film by a screen printing technique using a commercial Ag nanopaste. The sintering temperature and time were raised from 150 to 300 degrees C and from 15 min to 1 hour while the sintering time and temperature were fixed at 30 min and 200 degrees C, respectively. The Massachusetts Institute of Technology (MIT)-type folding endurance tester was used to measure the flexibility of the screen-printed Ag circuits. We observed the change of electrical resistance while the printed Ag patterns were being folded. The folding endurance was better at lower sintering temperature and time, which was explained by the microstructural evolution and macrostructural change of the screen-printed Ag circuits; however, the electrical characteristics were generally poor. Further research is therefore required to improve the electrical and mechanical properties of patterns using direct printing technologies simultaneously.

Evaluation of the flexibility of silver circuits screen-printed on polyimide with an environmental reliability test.

The flexibility of screen-printed silver (Ag) circuits on a polyimide (PI) substrate was investigated under a high temperature and relative humidity (RH). The conductive circuits were constructed on a PI film with a commercial Ag nanopaste via screen printing. The printed patterns were sintered at 200 degrees C for 30 min in a box-type furnace, after which they were placed in a chamber at 85 degrees C/85% RH for various durations: 100, 300, 500, and 1000 h. The Institute for Interconnecting and Packaging Electronic Circuits (IPC) flexural resistance endurance test was conducted to measure the flexibility of the conductive circuits, and the flexibility of the printed patterns was evaluated by detecting the variation of the electrical resistance. The flexibility of the screen-printed conductive circuits decreased as the duration of the 85 degrees C/85% RH test increased. After the 1000 h run of the 85 degrees C/85% RH test, the flexibility of the printed circuits was almost halved compared to that after the 100 h test. To demonstrate the decreased flexibility, the microstructural evolution and partial volume were investigated with a field emission scanning electron microscope (FE-SEM) and a 3D surface profiler, respectively.

High frequency characteristics of printed Cu conductive circuit.

The effects of sintering temperature on microstructural evolution and electrical characteristics of screen printed Cu patterns were observed. A commercial conducting paste containing Cu nanoparticles was screen printed onto a sodalime wafer sintered under a sintering temperature range of 300 degrees C to 450 degrees C. A network analyzer and Cascade's probe system in the frequency range of 10 MHz to 20 GHz were employed to measure the S-parameters of the sintered Cu conducting patterns. From the measured S-parameters, the insertion losses in high frequencies decreased with increasing sintering temperature due to the formation of an interparticle necking after heat treatment at high temperatures. However, oxidation of Cu nanoparticles during the sintering deteriorated the RF performance of the circuits, resulting large deviation of the S-parameters from the simulated curves.