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Electronic Assemblies
Published in Michael Pecht, Handbook of Electronic Package Design, 2018
Chip components can also be mounted using solder paste or solder wire. The solders used for these applications are not always eutectic, although they can be. These solders are normally lead/tin alloys, rather than the gold alloys used for die attaching. These solders reflow at lower temperatures and are not necessarily eutectic (i.e., do not have a single reflow temperature). To get good uniform adhesion, or “wetting,” of the solder to the surface metal, oxides must be removed. Removal of oxides can be accomplished in two ways. In one method the solder is reflowed in a reducing atmosphere in a furnace filled with forming gas. Forming gas is a mixture of inert nitrogen and approximately 5% hydrogen. The nitrogen prevents the introduction of any new oxides and the hydrogen, at the reflow temperature, reduces the oxides that have formed on the solder. This method is normally used for higher-temperature or eutectic solders. The other method is to utilize flux to increase the wetting of the material. The flux chemically reduces any oxides on the metal surface or in the solder. Flux can be applied to the metal surface or on the component prior to mounting. For example, flux can be printed on a board that has been pretinned or has been thick solder plated. The flux can then act as the tacky substance that temporarily holds the components in place prior to solder reflow. Another means of introducing the flux is to dip the already pretinned components into flux before placing them down on the board surface This method, however, is labor intensive and not frequently used.
F
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
forward converter the processing of the fork subroutine commences. The parent handler is called after the processing of the fork subroutine completes in the parent process. The child handler is called after the processing of the fork subroutine completes in the child process. form term used to indicate the structure and dimensions of a multiterm equation without details within component terms. formants the main frequencies that result from typical short-time spectral analysis of vowels. Depending on the application, two or three formants are commonly extracted. forming gas a mixture of hydrogen and nitrogen (typically 5% hydrogen and 95% nitrogen),
Impact of High-Power Heat Load and W Surface Carbidization on Its Structural-Phase Composition and Properties
Published in Fusion Science and Technology, 2021
Mazhyn Skakov, Gainiya Zhanbolatova, Arman Miniyazov, Timur Tulenbergenov, Igor Sokolov, Yerzhan Sapatayev, Yernat Kozhakhmetov, Olga Bukina
Recrystallized annealing of the W samples was carried out on PBI in the electron beam regime in accordance with Ref. 14. The temperature of the samples upon annealing was 1300°С ± 20°С. The samples were annealed for 3600 s. The plasma-forming gas methane (CH4) was fed into the PBI interaction chamber after annealing to obtain a carbidized layer on the prepared W samples’ surface according to a previously developed method.16–20 Experiments on the formation of layers in the form of tungsten semicarbide (W2C) and tungsten monocarbide (WC) were carried out under various exposure times, which were chosen based on the data presented in Refs. 21, 22, and 23. Table I presents the test conditions of the samples studied. The surfaces of the HP-1 and HP-2 samples were not exposed to plasma irradiation. They are initial samples used to analyze the impact of the carbidized layer on the physical-mechanical and structural-phase properties of the W surface after exposure to high-power heat loads.
Numerical evaluation on the performance of CO₂ plasma in material processing applications
Published in Materials and Manufacturing Processes, 2019
K. Sowmiya, K. Ramachandran, R. Abiyazhini, V.R. Barath
Pershin et al.[9] developed and tested the high-power plasma torch operated with carbondioxide–hydrocarbon gas mixture. They found that the use of CO2/CH4 gas mixtures as plasma forming gas is favorable for metal spraying due to lower level of oxygen and presence of CO.[10] Also, it was observed that the plasma torch can be operated with lower current and higher voltage as well as has higher electro-thermal efficiency while comparing the plasma torch operated with Ar.[11] Pershin et al.[12] studied the influence of CO2 and CH4 gas mixture on thermal efficiency of the plasma torch and in-flight YSZ particle’s behavior while spraying. They also examined the effect of CO2–CH4 mixture ratio on the spheriodization of tungsten carbide and alumina powders.[13] Xu et al.[14] used a mixture of CO2-Ar-CH4 as plasma gas to fabricate ZrO₂ coatings. To dissociate CO2 gas, Kobayashi et al.[15] introduced CO2 with argon plasma in a gas tunnel type plasma torch. They found that the plasma arc voltage is increased by increasing the mixing ratio of CO2 with argon and their values are greater when compared to N2 with argon. The thermal efficiency of torch was found to be increased by the addition of CO2 with argon compared to N2 with Ar. The CO2 decomposition rate was estimated to be about 30%.[16]
Optimization and surface modification of silk fabric using DBD air plasma for improving wicking properties
Published in The Journal of The Textile Institute, 2018
K. Vinisha Rani, Nisha Chandwani, Purvi Kikani, S. K. Nema, Arun Kumar Sarma, Bornali Sarma
In the present investigations, non-thermal atmospheric pressure DBD plasma is used for surface modification of silk fabrics without feeding any gasses. For economical reasons, air is used as the plasma forming gas due to the reactivity of oxygen molecules in the air can convert into reactive atomic oxygen radicals and produce reactive hydroxyl radicals. The DBD plasma system used here does not require any vacuum pump. Therefore, it can be easily scaled up for treating larger samples and for continuous processing. This work is mainly focusing on wetting and wicking properties of the silk fabrics. In DBD plasma treatment, the effect of plasma variables such as discharge power and exposure time on silk fabrics has been investigated. The wicking and wettability have been characterized by contact angle, vertical wicking test and Wet-out time test. The functional groups have been detected by Attenuated Total Reflection Fourier Transforms Infrared spectrometer (ATR-FTIR). Scanning electron microscope (SEM) provides information about morphological changes that took place after plasma exposure.