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ELECTRIC insulators & insulation, FLIP chip technology, SEMICONDUCTORS, VACUUM chambers, PACKAGING, NUMERICAL calculations, and ELECTRIC fields

Delamination between the molding compound and the die surface is a common failure pattern in the semiconductor package industry. Plasma treatment is a standard process to clean and activate the die surface to enhance the bonding force between the molding compound and the die surface in the packing procedure. However, the unexpected delamination still happens and results in a huge commercial loss for the packaged products. This study adopts experimental and numerical approaches to systematically investigate the delamination risk for plasma treatment before compound molding. A vacuum chamber is established to visualize the plasma distribution and the oxidation condition of the lead frames placed on the metal and the insulator rails. Moreover, a numerical calculation is used to systematically predict the plasma distribution over the lead frame and die surface. Results show that the lead frame placed on the metal rail exhibited a higher electric field gradient than that placed on the insulation rail. Moreover, the copper lead frame placed on the insulation rail exhibits a lower electric field gradient and less metal oxidation on the die surface. The delamination risk for semiconductor packaging can be systematically predicted and efficiently reduced before the packing process with the results obtained in the present study. [ABSTRACT FROM AUTHOR]

VACUUM, ELECTRON density, FIELD emission, ION bombardment, ELECTRONS, and GRAPHENE

This work reviews the progress in the area of high current density electron emitters, specifically for use in high frequency and high-power microwave vacuum electron devices. The review is divided into two subsections: 1) thermionic cathodes and 2) field emission cathodes. The thermionic cathode section includes the discussion on the M-type, MM-type, Scandate and the CPD cathodes. CPD cathode promises better usability in a practical device as compared to the Scandate cathodes which are limited by emission nonuniformity, poor resistance to poisoning/ion bombardment and low life. With the increasing demand for miniaturized and high power VEDs in the near future, the development of high current density field emission cathodes is of immediate interest to the VED community. The Spindt, CNT, and graphene-based emitters are the potential candidates in the field emitters section. Graphene-based film cathodes, when compared to the Mo/Si FEAs and the CNTs, offer larger emission area as well as high current carrying capability. This review includes the evolution of the emission capabilities of the emitters, state-of-the-art performances, and possible future developments. [ABSTRACT FROM AUTHOR]

ATMOSPHERIC pressure, METHYL methacrylate, ULTRAHIGH molecular weight polyethylene, FLASHOVER, PLASMA immersion ion implantation, POLYMETHYLMETHACRYLATE, PLASTICS, and POWER resources

Polymers are plastic materials used as insulators in power supplies, pulsers, transformers, etc., because of their low cost and excellent insulating properties. However, in several applications, the insulating performance of these materials is limited by the surface flashover instead of the dielectric bulk breakdown (BD). On the other hand, many works have demonstrated that the material hydrophobicity has a huge effect on the increase of resistance to surface flashover in polymers. In this article, to change this material property, the plasma immersion ion implantation (PIII) technique has been used for the treatment of sample surfaces of two important polymers: ultrahigh molecular weight polyethylene (UHMWPE) and poly-methyl-methacrylate (PMMA) used in medical and industrial applications, respectively. By means of the PIII treatment, it was shown that the surface BD voltage of such polymers has increased, improving the resistance to surface flashover. Contact angle diagnostic and atomic force microscopy (AFM) were measured, respectively, for the surface hydrophobicity and roughness to correlate with the increase of the surface BD voltage. Moreover, a special BD testing pulser is employed to assess the polymer resistance to surface flashover by measuring the corresponding BD voltage under atmospheric pressure. [ABSTRACT FROM AUTHOR]

GERMINATION, SEEDLINGS, LOW temperature plasmas, SCANNING electron microscopes, HORDEUM, and BARLEY

The experimental results of dielectric barrier discharge (DBD) plasma treatment on barley (Hordeum Valgare L cv. Yusef) seed germination and seedling growth are analyzed and presented. The seeds were exposed to DBD plasma with 40-, 80-, and 120-W powers for 15 s. All treatments showed positive effects on seed germination, seedling growth, and vigor index. The scanning electron microscope (SEM) images and water imbibition evaluations of plasma-treated seeds revealed that the treatments improved water absorption in the seeds. Similar positive improvements were observed for the plasma-treated seeds in the seedling stage. The best germination characteristics were obtained in 80-W DBD plasma, which included an 18.28% increment in total germination percentage, and 13.35%, 66.83%, 38.55%, and 31.93% increment on the seed germination potential, vigor index, shoot height, and root length, respectively. Moreover, the seed germination of the plasma-treated barley was studied after 2, 7, 14, and 30 days of storage, which indicated the desirable effect of plasma over the storage time. It is concluded that the use of cold plasma can significantly improve the germination and seedling growth of barley seeds. [ABSTRACT FROM AUTHOR]

VACUUM arcs, ACETYLENE, ION energy, PLASMA density, and ENERGY density

Vacuum arc evaporation is a prospective technique to fabricate hard and wear material due to its high ion energy and plasma density. Nevertheless, target tends to be poisoned by the compound layer in common reactive gases such as acetylene. Then the coating deposition rate and the properties of the coatings would be strongly influenced. Thus, the formation of the compound layer has to be inhibited. Previous studies pointed out the potential of pulse-enhanced vacuum arc evaporation mode for inhibiting the formation of the compound layer. Within the presented study, motion of group spots (GSs), optical emission spectra, and substrate current based on PEVAE mode were examined entirely. The result shows that the area ratio of the compound layer in the target was decreased from about 75% to 42%. The ionization degree of titanium and mean substrate current could be substantially increased by up to 40% and 100%, respectively, in a mixture gas of nitrogen and acetylene due to larger plasma density indicated by higher spectra intensity of plasmas. All of the above made PEVAE prospective candidate to inhibit the formation of the compound layer. Beyond this PEVAE would lead to higher coating rate and denser coating in nitrogen plus acetylene atmosphere. [ABSTRACT FROM AUTHOR]

GAS flow, ELECTRODE potential, ATMOSPHERIC pressure, SEED treatment, FACTORY design & construction, and IONS

An experimental study of the velocity field in a three-electrode arrangement of a plasma-chemical surface dielectric barrier discharge (SDBD) reactor designed for plant seed’s treatment was carried out. The effect of polarity and magnitude of the extraction voltage (potential of the third electrode), configuration of the SDBD system (5- and 10-mm distances between the strips were observed) and the permeability for gas flow of the third electrode (in the form of a plate or a grid) on the magnitude of the extraction ion current, and induced gas flow structure were analyzed. It is shown that the most uniform flow in the direction of the third electrode, necessary for uniform seed treatment, is achieved in the case of a permeable third electrode under positive displacement potential, opposing a surface discharge electrodes with a distance between the strips much less than the gap dimensions (5 mm between the strips with 10 mm between the third electrode and the barrier surface). [ABSTRACT FROM AUTHOR]

SURFACE conductivity, FLASHOVER, SURFACE morphology, MEASUREMENT errors, ELECTRIC potential measurement, and SAMPLING errors

The blowback caused by the separation of rail and armature at muzzle is an important factor for the degradation of bore insulator. A small caliber launcher was modified by the transparent material of polycarbonate for capturing the process of blowback in inner bore with a high-speed camera. Three groups of experiments with the same peak linear current density and various muzzle currents were carried out. Nesting insulator samples were used to reduce the measurement error in cutting samples after experiments. Insulation performance of postshot samples was conducted from surface morphology, surface flashover voltage, and partial surface conductivity. Results show that the effects of blowback are related to muzzle current. With the increases of muzzle current, the average flashover voltage of samples in the region of 300–600 mm (600–900 mm) decreases from 9.98 kV/cm (5.37 kV/cm) to 3.59 kV/cm (3.01 kV/cm). Moreover, the number of samples that the flashover voltage is less than 9 kV/cm (half value of the original samples) increases from 7 to 12, which indicates that the damage area caused by blowback is gradually expanding with the muzzle current. Correspondingly, the partial surface conductivity of samples in 300–900 mm region increases with muzzle current. The increase of surface conductivity should be the main reason for the sharply decrease of surface flashover voltage. [ABSTRACT FROM AUTHOR]

OPTICAL materials, METAL coating, OPTICAL measurements, OPTICAL elements, OPTICAL mirrors, and WAVEFRONTS (Optics)

The need for a steam ingress environmental experiment is very significant to understand the impact of accidental in-vessel coolant leaks at ITER and to study the exposure of optical diagnostics to steam and humid conditions. This could happen as a result of the damage to the cooling pipes due to runaway electrons generated during plasma disruptions in ITER. In order to know the scope of this potential impact, an assessment was carried out to simulate and to study the exposure of optical elements to strong and hostile moisture conditions. After test, different measurements on optical mirrors were performed to characterize the reflectance properties, observed both in the visible and infrared spectral ranges, as well as the analysis of wavefront error, coating adherence test, and X-ray spectroscopy. Modification of properties and fluctuations in the physical behavior of optical materials and components were observed. Substrates and coatings were affected at different levels due to corrosion and oxidative depositions that modify their optical performances. In general, there are large differences in the results obtained for the same material manufactured by different manufacturing processes. Steam and humidity affected, especially substrates and metal coatings. Substrates made of silicon carbide and stainless steel were the least affected by corrosion. Rhodium coating suffered less damage than the molybdenum coating. [ABSTRACT FROM AUTHOR]

BRAZING, PHASED array antennas, WELDING, CRYSTAL grain boundaries, LASER welding, and ELECTRON beams

Recent advances in selective laser melting 3-D printing technology allow additive manufacturing of lower hybrid current drive (LHCD) RF launchers from a new material, Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, in configurations unachievable by conventional machining. Cr2Nb crystals pin grain boundaries within the copper matrix resulting in high tensile strength and resistance to annealing at elevated temperatures. Brazing, laser, and electron-beam welding (EBW) techniques are explored for joining a thin-walled GRCop-84 waveguide with zero porosity and minimal internal surface roughness. GRCop-84 wets well with the silver solder, CuSil, and Cusil-ABA brazes, once the durable surface oxide is mechanically removed. GRCop-84 melt pool size and flow during EBW is reduced compared to oxygen-free copper (OFC). Pulsed laser and e-beam welding maintains the Cr2Nb precipitate size; precipitate coarsening occurs in conduction mode e-beam welding. [ABSTRACT FROM AUTHOR]

PLASMA instabilities, MATERIAL erosion, EROSION, ENERGY consumption, PLASMA sources, and FUSION reactors

Deposition of plasma energy during off-normal fusion reactor operational events delivers a transient heat flux of up to 100 MJ/m2 to the plasma-facing materials (PFMs). Understanding the exact material response to the extreme energy loading conditions plays a key role in establishing a realistic computational tool that simulates the fusion plasma–material interaction. Surface damage can occur due to vaporization, melting, spallation, and liquid splatter. However, splashing mechanisms such as boiling and splattering, which result from various liquid instabilities, appear to be the main mechanism contributing to the melt layer erosion. The primary focus of this article is melting and resolidification and the effect of redeposition of the eroded material on surface erosion. A set of selected PFMs was exposed to a plasma heat flux of up to 40 GW/m2 over a deposition duration of $200~\mu \text{s}$. The source of the high energy plasma used in this article is the Surface InteRaction Experiment at North Carolina State (SIRENS) plasma source, which used to simulate disrupted plasma conditions. The underlying erosion mechanisms involved in the formation, ejection, and solidification of molten droplets are investigated using the basic plasma equations and a plasma fluid model implemented in the simulation code. The net erosion and redeposition thickness due to erosion of the vapor and melt layer have been evaluated post-plasma exposure and compared to the experimental measurements. [ABSTRACT FROM AUTHOR]

AUSTRIAN pine, PLASMA flow, GERMINATION, NON-thermal plasma, PLANT ecology, and PHANEROGAMS

We studied the effects of nonthermal plasma (NTP) treatment on various parameters of early germination stages of Pinus nigra seeds. In the experiment, the diffuse coplanar surface barrier discharge (DCSBD) with treatment time periods of 0, 1, 3, 5, 10, 30, and 60 s was used. Changes on the plasma-treated seed surface were studied by attenuated total reflectance-Fourier transform infrared spectroscopy. Seed germination, germination rate, germination index, length of seedling, dry seedling weight, and seedling vigor index I and II were determined in a growth test under laboratory conditions. Various statistically significant effects of seed exposure to DCSBD plasma treatment were recorded. A positive reaction was observed in the germinated seeds after exposure for 1- and 5-s. Longer exposure time periods had a rather inhibitory effect. The performance of forest nurseries of NTP modification of seeds should be evaluated in order to measure the durability of the observed growth characteristics. The potential of NTP treatment on seeds in plant ecology in future is highlighted. [ABSTRACT FROM AUTHOR]

FUSED silica, ATMOSPHERIC pressure, PLASMA pressure, X-ray photoelectron spectroscopy, ATOMIC force microscopy, and QUARTZ

In this article, experimental study of a device combining the advantages of dielectric barrier discharge (DBD) and atmospheric pressure plasma jet (APPJ) has been presented. This device with a total length of 500 mm was capable of generating stable uniform atmospheric pressure plasma (APP) with a length of 400 mm, which was operated using a 12-kV HV supply and the air flow rate of 20–30 L/min. The plasma spectra were obtained by optical emission spectroscopy (OES), in which N2(C-B) and N2+ can be observed, and the rotational temperature was calculated to be 360 K. The macroscopic temperature was measured by an infrared camera. The result showed that the central temperature was room temperature. In addition, quartz glass substrates were treated by this device. The surface properties of quartz glass were investigated by water contact angle (WCA), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results revealed that hydrophilicity and surface roughness of the quartz substrates were gradually increased with increasing treatment time. However, the results of XPS indicated that the content of hydrophilic groups at the surface had a slight change. Therefore, hydrophilicity of quartz glass improved effectively after APP treatment, which was due to the change in surface morphology and the increase in roughness. [ABSTRACT FROM AUTHOR]

PLASMA flow, PLASMA frequencies, PLASMA torch, LOW temperature plasmas, CULTURAL property, and HYDROFLUORIC acid

This article presents five alternative plasma equipments patented by the author, designed for specific applications like activation, cleaning, decontamination, or monomer polymerization on surfaces. Two equipments perform HF cold plasma treatment of highly adherent powdery materials (pigments, plastics, drugs, and so on), that are used to modify the physical-chemical characteristics of surfaces. Another HF plasma equipment is employed for the treatment of nonwoven stratified materials used as filters for gaseous media. A specially designed afterglow plasma equipment is used for decontamination and cleaning of highly fragile flat or 3-D cultural heritage items. An equipment for producing HF torch plasma is also described. [ABSTRACT FROM AUTHOR]

MATERIAL erosion, ELECTRODES, EROSION, GAS mixtures, CHEMICAL reactions, and COMPACTING

The electrode erosion and lifetime performance of a compact and repetitively triggered field distortion spark gap switch were studied at a repetitive frequency rate of 30 Hz, a peak current of 8.5 kA, and a working voltage of ±35 kV when the switch was filled with a gas mixture of 30% SF6 and 70% N2 at a pressure of 0.3 MPa. The variations of the time-delay jitter and the self-breakdown voltage were both studied for the whole service lifetime of the spark gap switch. The morphology of both the electrodes and the plate insulator, before and after the service lifetime tests, is also analyzed. The results show that during these tests, the time-delay jitter is basically synchronized with the self-breakdown voltage jitter, and both undergo firstly a process of rapidly decreasing their values, then remaining stable, and finally and gradually increasing after 70 000 pulses. The change in the electrode surface roughness (i.e., surface profile) is caused by erosion and chemical deposits in the switch cavity, which are mainly the two factors that affect the time-delay jitter of the switch. Tip protrusions on the electrode surface, due to electrode erosion, contribute to reducing the time-delay jitter. However, due to chemical reactions, fluorides and sulfides are deposited on the switch components, as well as metal particles caused by electrode erosion sputtering. Slowly, after a large number of shots, all these phenomena affect the self-breakdown performance resulting in an increased self-breakdown voltage jitter, which also causes the time-delay jitter to increase. Although there are a number of reasons that contribute to the deterioration of the performance of the switch, it is fortunate that if a switch suffering a degraded performance is reassembled, with the electrodes mechanically polished and all the components cleaned, the optimal performance of the switch can be restored. If maintenance work is carried out regularly to preserve the condition of the switch’s inner components, the service lifetime of the switch can be prolonged. [ABSTRACT FROM AUTHOR]

PLASMA sheaths, ELECTRIC charge, ELECTRIC propulsion, SURFACE charges, PLASMA oscillations, SURFACE potential, and SHIP propulsion

When designing spacecraft with electric propulsion (EP) devices, it is important to assess spacecraft integration to ensure that the important components are not subject to significant sputtering by high-energy ions. In addition to the EP device and its plume, surface charging of spacecraft has to be modeled properly, as surface potential can directly affect the sputtering rate. Three surface charging models are incorporated into the spacecraft module of the numerical simulation framework–Thermophysics Universal Research Framework (TURF), and these include: 1) dielectric; 2) conductive; and 3) charge propagation models. The charge propagation model has been upgraded to solve the surface charge distribution implicitly, allowing a wide range of electrical conductivity values without causing the simulation to become unstable. Each of the charging models is verified against a simple problem where an analytical solution can be determined. Then, the coupling of the surface charging model and a hybrid particle/fluid model is tested in a more complex problem, where the floating potential on a sphere immersed in plasma is to be obtained. Finally, the surface charging model in an EP plume simulation is demonstrated. These problems are multiscale in that the charging model has to resolve an electron timescale (i.e., plasma oscillation) while the particle time step has to be orders of magnitude larger than the electron timescale in order to maintain a long enough sampling window for the ion current to effectively reduce the statistical noise. Therefore, two separate time steps are introduced for a stable convergence of the coupled models. [ABSTRACT FROM AUTHOR]