Flexible metalized polyimide nonwoven fabrics for efficient electromagnetic interference shielding

Designing and preparing a compatible electromagnetic interference (EMI) shielding, radar and infrared stealth material exhibits significant prospect in the military field. Hence, a novel conductive/magnetic polyimide-based nonwoven fabric (PFNy) is prepared by alkali treatment, Fe3+ ion exchange, thermal reduction, and electroless nickel (Ni) plating process. Its impedance/insulation characteristics can be easily adjusted by controlling the in situ growth of Fe3O4 and electroless nickel plating. Subsequently, a new strategy of constructing hierarchical dual-gradient impedance/insulation structure is implemented to achieve EMI shielding, radar and infrared stealth via stacking PFNy with gradually decreased impedance/insulation characteristics from top to bottom. The formation of impedance matching gradient structure promotes effective introduction and dissipation of electromagnetic waves, endowing the composite with outstanding EMI shielding and radar stealth performance. Meanwhile, the construction of thermal insulation gradient structure can effectively inhibit thermal radiation from target, bringing an excellent infrared stealth performance. Importantly, the strong interfacial interactions between Fe3O4, Ni and polyimide fiber accelerate PFNy to resist the stresses originated from high-temperature heat source, achieving a compatible high-temperature resistant radar/infrared stealth performance. Such excellent comprehensive properties endow it with a great potential in high-temperature military camouflage applications against enemy radar and infrared detection.

One of the most preferable types of switched-mode power supplies (SMPS) is the flyback converter, due to its wide range of application areas. Properties such as low cost, provision of multiple output voltage terminals, and higher efficiencies make it important, and hence its usage in technologies including cell phone chargers, personal computers, set-top boxes, and televisions is increasing. Special attention should be paid to the design of this type of converter due to its working principles and electromagnetic interference (EMI) performance. Rapid switching of high current and high voltage during the operation of SMPS causes an EMI problem. The level of the EMI noise should be reduced in order to not interfere with the operation of other equipment. One of the methods for mitigating EMI emissions is the frequency modulation (FM) technique. In this paper, the FM technique, which has been increasingly used as an EMI-reduction method in SMPS, is investigated. The modulation technique that was applied to the switching frequency of the flyback converter is analyzed and its effect on the EMI performance is discussed. The FM technique was tested on an AC-DC flyback converter prototype that was built with an L6566B integrated circuit. Conducted emission noises from the SMPS were measured using an EMI receiver. Experimental results showed that EMI levels were reduced after the application of the FM method.

In the face of the increasingly polluted electromagnetic environment, materials with efficient absorption of electromagnetic waves have been paid more and more attention. The structure regulation of electromagnetic interference (EMI) shielding materials with could enhance their EMI performance. In this work, multilayered single‐walled carbon nanotubes (SWCNTs)/silver nanowires (AgNWs) composite film was fabricated via a facile vacuum‐assisted filtration. With the increasing number of layers from 3 to 7, 7‐layered composite film with introduced inner pores and gaps exhibited an excellent shielding performance more than 70 dB in X‐band. This excellent performance is attributed to the alternately stacked and porous AgNWs/SWCNTs structure, which effectively constructed the interboundary polarization of AgNWs/SWCNTs and provided space to enhance multiple absorption and reflection, thus greatly improving the material's ability to absorb electromagnetic waves. In addition, the EMI SE T value of Ag/C‐7L films in the X‐band decreases by an average of only 4% after 1000 bends, 15% at 100% humidity and 100 °C, and 10% at −196 °C, which has excellent mechanical properties and stability. In this study, multilayer Ag/C‐xL films show great potential in applications such as wearable materials, EMI protection in complex working environments, and green shielding.

Electroless nickel plating has been extensively applied on copper circuits as an under-layer deposition for solder joints, since it is possible to deposit on the isolated patterns without an outer electrode. A palladium catalyst is generally used for the electroless nickel plating reaction on the copper patterns, because copper has a lack of catalytic activity for initiation of the deposition reaction. The electroless nickel plating is applied on the condensed copper patterns by using the palladium catalyst ; however, nickel deposits tend to occur on the resin surface due to the adsorption of palladium ions on it.Dimethylamine-borane (DMAB) has a feature of catalytic activation power on the copper. Therefore we applied dilute nickel plating solution containing DMAB as an initiator for electroless nickel deposition on the copper surface instead of applying the palladium catalyst. Selective nickel plating on the copper patterns without deposition on the resin substrate was achieved using a dilute nickel plating bath containing DMAB. In addition, the strength of solder joints was improved by introducing this process. In this way, nodules on the nickel surface were greatly suppressed, and strong joints between the solder and deposited nickel were achieved.

Effect of bath pH and stabilizer on electroless nickel plating of magnesium alloys

In this study, we use the standard TSMC 0.35 μm 2P4M process to design CMOS-MEMS probe chip. MEMS technology involves the following steps such as lithography process, electroless nickel (EN) plating process, grinding process and dry etching process. The probe chip has through silicon via (TSV) package structure, and the combination of CMOS process within the multi-layer interconnections, which could assist the connection between the probes head the external devices, and reduce the difficulty of wiring layout. In addition, passive components or circuits could be integrated with the CMOS chip to improve the frequency bandwidth and measuring quality. So far, MEMS probe exist a shortcomings that are not able to be integrated with the CMOS process, and the testing cost. The finite element method was adapted to design of probe shapes and sizes. The LIGA-like thick photoresist process and EN plating technique was used in this study, Ni-P alloy to increase the thickness of the cantilever probe to strengthen its support strength were also applied. When the probe cantilever through the EN plating of deposition time, the uneven surface was appeared, each layer structure is used by polishing process to achieve the surface coplanarity. Finally, the probes structure were suspended by the dry etching process (RIE, ICP-RIE), and this study successfully fabricated chips forming one of the probe.

Studies were conducted on several fundamental aspects of electroless nickel/solder metallization for silicon solar cells. A process proposed by Motorola, which precedes the electroless nickel plating with several steps of palladium plating and heat treatment, was compared directly with single step electroless nickel plating. Work has directed toward answering specific questions concerning the effect of silicon surface oxide on nickel plating, effects of thermal stresses on the metallization, sintering of nickel plated on silicon, and effects of exposure to the plating solution on solar cell characteristics. The Motorola process was compared with simple electroless nickel plating in a series of parallel experiments. Results are presented. (WHK)

Effects of fluoride ions as electrolyte additives for a PEO/Ni-P composite coating onto Mg alloy AZ31B

Taking four kinds of imperfect ground planes as examples, the effect of the imperfect ground plane on the signal integrity (SI) and electromagnetic interference (EMI) for high-speed digital transmission line on the printed circuit boards (PCB) are investigated both by FDTD simulation and experimental measurement. It is found that good signal quality does not guarantee good EMI performance and ill signal integrity does not imply severe radiated emission. The dominant factor that affects the EMI performance of the signal trace on the reference plane is the path of return current. All simulated S-parameter and EMI behavior of the signal traces are compared with the measurement results. The agreement between them is good.

Recommended EMI (electromagnetic interference) tests were developed which can be performed early in the MMIC (monolithic microwave integrated circuit) development cycle. These tests can aid the designer in developing EMI-tolerant devices and systems. Recommended tests are described for microwave input and output pins, digital and analog control pins, and power and ground pins. Measurements at wafer, packaged chip, and system levels of fabrication are addressed as well. It is pointed out that conducted interference measurements should be performed early in the design cycle as part of design proof and qualification tests. Redesigns of devices should be requalified for EMI performance to verify that the redesigns have not adversely affected EMI performance. >

In this paper, electroless nickel plating is explored for the protection of binder-jetting-based additively manufactured (AM) composite materials. Electroless nickel plating was attempted on binder-jetted composites composed of stainless steel and bronze, resulting in differences in the physicochemical properties. We investigated the impact of surface finishing, plating solution chemistry, and plating parameters to attain a wide range of surface morphologies and roughness levels. We employed the Keyence microscope to quantitatively evaluate dramatically different surface properties before and after the coating of AM composites. Scanning electron microscopy revealed a wide range of microstructural properties in relation to each combination of surface finishing and coating parameters. We studied chempolishing, plasma cleaning, and organic cleaning as the surface preparation methods prior to coating. We found that surface preparation dictated the surface roughness. Taguchi statistical analysis was performed to investigate the relative strength of experimental factors and interconnectedness among process parameters to attain optimum coating qualities. The quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the roughness of the nickel-plated surface were 17.95%, 8.2%, 50.02%, and 13.21%, respectively. On the other hand, the quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the thickness of nickel plating were 35.12%, 41.40%, 3.87%, and 18.24%, respectively. The optimum combination of the factors’ level projected the lowest roughness of Ra at 7.76 µm. The optimum combination of the factors’ level projected the maximum achievable thickness of ~149 µm. This paper provides insights into coating process for overcoming the sensitivity of AM composites in hazardous application spaces via robust coating.

Electromagnetic interference (EMI) is one of the main issues in Brushless Direct Current (BLDC) motors, which harms efficiency, reliability, and international EMI regulations. Traditional methods of suppression are not always flexible and deteriorate performance, which requires solutions of high quality. To solve this, a new system, Enhanced EMI Resilience Optimization System (EEROS), is proposed, which combines three new methods: Active Common Mode Swarm-Enhanced EMI Mitigation System (ACS-EMS), Adaptive Power Management EMI Control System (APM-ECS), and Adaptive Spread Spectrum-Filtered Genetic EMI Suppression (ASSF-GES). These techniques use Spread Spectrum Modulation (SSM), Active EMI Filters (AEF), Genetic Algorithms (GA), Particle Swarm Optimization (PSO), and Dynamic Frequency Modulation (DFM) to create dynamic suppression of high-frequency EMI and motor efficiency of 98%, thermal stability of 59℃, and responsiveness of 98%. The paper also analyses how the variations of control parameters affect the EMI suppression and performance trade-offs and proves the existence of a strong and high-efficiency mitigation framework. The proposed system offers a scalable solution to automotive, industrial and aerospace applications and has better EMI resilience, regulatory compliance and operational reliability.

We observed the effects of nickel plating temperatures for controlling the surface morphologies of the deposited nickel layers on the alumina nano-pores. The alumina nano-channels were filled with nickel at various processing temperatures of 60-90 degrees C. The electrical properties of the alumina film capacitors were changed with processing temperatures. The electroless nickel plating (ENP) at 60 degrees C improved the nickel penetration into the alumina nano-channels due to the reduced reaction rate. Nickel layers are uniformly formed on the high aspect ratio alumina pores. Due to the uniform nickel electrode, the capacitance density of the alumina film capacitors is improved by the low leakage current, dissipation factor and equivalent series resistance. Alumina film capacitors made by ENP at 60 degrees C had a high capacitance density of 160 nF/cm2.

Neutral Point Clamped (NPC) converter configuration is suitable for operation at Medium Voltage DC (MVDC) level as it allows the use of a higher DC bus voltage than the blocking capability of individual switching devices. The Active NPC (ANPC) configuration offers more flexibility than NPC in terms of control and power loss distribution. NPC/ANPC phase leg aspires to be an ideal candidate for the MVDC side of a Dual Active Bridge (DAB) converter which is used in a wide range of applications requiring bidirectional power flow, voltage matching and soft-switching. Operation under Zero Voltage Switching (ZVS) and the conducted Electromagnetic Interference (EMI) performance of the ANPC converter phase leg is being analyzed in this paper. Based on the analysis, a Printed Circuit Board (PCB) bus-bar has been designed to suppress the high frequency conducted EMI of the system. Minimization of parasitic capacitance from drain to heat sink has also been discussed.

MXene-based layered films featuring a "brick-and-mortar" architecture show significant potential for electromagnetic interference (EMI) shielding applications; however, the insulating polymer "mortar" disrupts the connectivity of the MXene network, ultimately compromising both electrical conductivity and shielding effectiveness (SE). To address this limitation, this study introduces an innovative interpenetrating layered structure, comprising independent aramid nanofiber (ANF) layers and MXene layers, fabricated through a directional freeze-thaw intercalation-gel-film formation strategy. Unlike traditional homogeneous layered films, this unique layered structure features mutually embedded conductive and insulating layers, facilitating efficient electron transport, generating numerous heterogeneous interfaces for multiple reflections and scattering, and enhancing oxidation resistance. The interpenetrating ANF/MXene film exhibits exceptional electrical conductivity (5630.8 S/m) and EMI SE (43.3dB) at ∼40 wt.% MXene loading, significantly outperforming the homogeneous ANF/MXene film (26.9dB). Importantly, the interpenetrating ANF layers fully encapsulate the MXene layers, providing remarkable long-term stability with only a 10% decline in EMI performance after 80 days of aging. Furthermore, the interpenetrating ANF layers form a resilient mechanical framework, resulting in the A@M film boasting outstanding mechanical properties (tensile strength of 121.0MPa, fracture strain of 13%). Consequently, this work presents a novel design and approach for fabricating high-performance MXene-based layered EMI shielding films.