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Coating, Encapsulating, and Marking
Published in Fred W. Kear, Hybrid Assemblies and Multichip Modules, 2020
The physical properties of the conformal coating material should be studied to ensure that it will do the job properly. The coefficient of expansion of the material and its adhesive properties are both important in affecting total surface coating. Outgassing and degradation of the material over time are also important considerations. The role of the conformal coating material is to seal the surfaces of the hybrid assembly completely against the outside environment and to maintain this seal throughout the life of the product. In order to meet these objectives, the surface of the assembly must be clean and dry before the coating process begins. The coating material must be correctly formulated and applied. All materials do not exhibit the same properties and may not be suitable for specific applications. Some materials may need to be degassed in a vacuum chamber before application in order to minimize gas bubbles in the coating. Conformal coating materials harden by different methods such as ultraviolet curing, evaporation of volatile materials, and polymerization. Most of these curing methods are accelerated by the application of heat, which may also accelerate the outgassing of the material.
Reactive Hot Melt Conformal Coating Materials
Published in Ralph D. Hermansen, Polymeric Thermosetting Compounds, 2017
Conformal coatings are commonly used to protect electronic assemblies from contamination, moisture, corrosive chemicals, and shock and vibra-tion. The automotive industry and the defense/aerospace industry espe-cially need conformal coatings to protect circuitry from hostile environ-ments. Conformal coatings are most often composed of the following polymers: silicones, acrylics, polyurethanes, and epoxies. One problem with several commercially available conformal coatings is that they con-tain an organic solvent, which evaporates into the air during coating appli-cation. Environmental regulations outlaw many solvents and impose strict controls on the others. In addition to the solvent problem, conformal coat-ings require some kind of special processing be it metering and mixing of two component systems, dispensing, and curing the polymers in ovens, etc. It would be desirable to eliminate solvents and the need for special equipment and processing entirely.
Coating Application and Curing Techniques
Published in Richard J. LaPorte, Hydrophilic Polymer Coatings for Medical Devices, 2017
A recently developed process for depositing thin polymer films onto various substrates is plasma polymerization. Just as in the corresponding surface treatment technique, the method involves generating a plasma through electron excitation, but the gas mixture used as the plasma source includes an organic monomer. The conformal coatings that result range in thickness from a few hundred angstroms up to a micrometer. Cross-linking density is usually greater than in conventionally applied coatings, and thin films exhibiting good adhesion can be laid down on virtually any type of substrate, such as polymers, metals, glass, and ceramics.
Design of Low Profile Cylindrical Conformed Microstrip Patch Antenna for Wideband Operation
Published in IETE Journal of Research, 2021
Sandeep Kohar, Surinder Singh, Asok De
The polar plots of the cylindrical case show that although it does not match the planar case, still it is able to attain acceptable radiation pattern. This is probably due to the high curvature of the conformal case (taken approximately as 3λ). As the curvature is decreased (radius of curvature increased) the results will tend to approach more or less towards the planar one. The curvature effect of the cylindrical host body is clearly evident on the gain characteristics of the antenna. It is seen from Figure 7 that the gain is almost constant over the pass band for the planar antenna with a slight dip at around 9 GHz. However, it is evident from the graph that the gain is acceptable at the two resonant frequencies. The variation of gain is more in the cylindrical case with a comparatively higher gradient relative to the planar case beyond 14 GHz. The gain of the planar and cylindrical antenna is comparable at the corresponding lower resonance while the gain at higher resonance in case of cylinder is lower than the planar counterpart. This is probably due to the fact that the corresponding curvature in terms of the wavelength becomes less at higher frequencies.
A novel implementation of IEDG-based DDM for solving electromagnetic scattering from large and complex PEC objects
Published in Electromagnetics, 2018
Kui Han, Zaiping Nie, Ming Jiang, Yongpin Chen, Jun Hu
To approximate the unknown electric current , the sub-domain surface is first meshed so that the trial functions can be defined. In a conformal discretization, the div-conformal vector basis function, such as the RWG basis function, is usually employed to expand the surface current. However, in nonconformal discretizations, such a basis function is difficult to be defined on a nonconformal mesh. A common practice to expand the surface current across sub-domain interfaces is to employ the mono-polar RWG basis function defined on a single mesh cell (Ubeda and Rius 2006). For simplicity, the current inside each sub-domain is still modeled by the conventional RWG basis function. Denote both the RWG and the mono-polar RWG basis functions on sub-domain as . The unknown electric current can be approximated as
Assessing 40 years of spatial dynamics and patterns in megacities along the Belt and Road region using satellite imagery
Published in International Journal of Digital Earth, 2021
Zhongchang Sun, Sisi Yu, Huadong Guo, Cuizhen Wang, ZengXiang Zhang, Ru Xu
Megacities in the B&R region were observed to exhibit various spatial differences over a 40-year period. In a conformal projection, the shapes of these megacities are preserved in the UTM coordinate system. For better visualization, Figure 3 outlines each map by keeping the urban lands in the center of the subset. This was exemplified by the spatial distribution and growth of urban land areas. From 1975 to 2015, megacities in developing countries (i.e. Manila, Shanghai) had undergone more dramatic urban expansion, while those in developed countries (i.e. London, Osaka) had grown relatively slowly (Figure 3). For instance, urban expansion in London nearly halted during the observed time period (Figure 3(a)).