Parylene是非常理想的塗佈塗料,用於鐵芯直徑小於 9.5mm (0.375.英吋) 之產品.Parylene極為一致的塗佈,有著均勻的厚度,即使在轉角和邊緣部份.它是利用氣相沉積的方法塗佈,避免小孔徑堵塞.其附著在鐵芯上的厚度,一般標準約1密爾,增加的厚度微乎其微,同時擁有高阻抗和低摩擦係數(接近鐵氟龍),以降低繞線時線傷.Parylene 其相對導電系數為 2.95,所增加的電容量也是些微.塗佈後的產品可耐1000伏特電壓測試,若要承受更高之電壓,其塗佈厚度相對要增加.

使用Epoxy 環氧樹脂塗佈是用在鐵芯直徑在9.5mm (0.375.英吋) 以上之產品.大部份利用噴撒的方式達成塗佈.塗佈尺寸約1020密爾高出Paryrlene許多.借塗佈層使鐵芯在繞線時摩擦減緩.及其黏結能力及耐腐蝕的性.,使得鐵芯在老化測試時,保持其功.塗佈後的鐵芯,可耐 1000伏特之電壓測試,若要耐得更高壓,其塗佈厚度相對需要增加.

Parylene Applications - Magnets & Ferrite Cores

A family of xylylene polymers originally developed as protective coatings for printed circuit boards are now finding new applications in areas where other traditional coating materials are unable to perform to desired specification.

Parylene is the generic name for members of a unique polymer series. The basic member of this series is poly-p-xylylene, a completely linear, highly crystalline material. The unique physical and electrical properties of Parylene, coupled with a stress free application process indicate that Parylene can be a viable alternative coating option for many types of material.

Pinhole Free Coating by Vapour Deposition

Coating is carried out under vacuum and is best described as Vapour Deposition Polymerisation (VDP). As a coating technique, VDP offers certain advantages over other coating techniques such as brushing, dipping, or spraying. These advantages stem principally from the fact that the solid coating is formed from the gaseous monomer directly, without an intermediate liquid stage. As a result, the forces of surface tension, which cause the pulling away from sharp edges and the filling in of troughs in conventional methods, are not operative. Coatings of Parylene grow from the substrate surface outward, producing a conformal layer of uniform thickness. Extensive tests demonstrate that the coating so farmed is pinhole-free at thicknesses well below one micrometer (1 µm).

Stress Free Application

The Parylene coating is formed spontaneously on components at or near room temperature; a cure cycle at elevated temperature is not necessary. The substrate need not be subjected to temperatures above ambient, and no further time is required beyond that needed for the growth of the film.

Because the polymerization is spontaneous, no catalyst is necessary. Catalysts that promote other polymerizations are often ionic or ionogenic, and, to the extent that they remain in the coating after cure, their residues are capable of participating in charge mobilisation mechanisms, with detrimental effects in electrical properties. Because the coating is formed at room temperature, stresses that might be induced by differential thermal expansion between the temperature of cure and room temperature are avoided.

Outstanding lnsulation Properties

In addition to these intrinsic properties Parylenes have excellent electrical properties, and provide a prime dielectric which has a low dissipation factor and high dielectric strength, coupled with excellent mechanical qualities. Such a combination makes Parylene uniquely suitable for insulation on miniature wire wound components.

The insulating varnish of fine copper wire may be damaged due to the rigors of the winding operation and particularly in the case of the smaller devices the toroid or bobbin requires the application of a coating to not only provide insulation but also to eliminate abrasion damage to the wire during winding. The high insulation strength of Parylene and its dry lubricity characteristics make it ideally suited for this application.

Maximising the Winding Window

The application of Nylon or PTFE coatings tend to reduce the winding window by build up of these coatings and abrasion protection is less effective due to surface tension causing thinning of the coating at edges and corners. Parylene coatings being thinner and evenly distributed maintain maximum winding window allowing a larger wire gauge to be used for better performance of the finished product.

Parylene can also be used to "impregnate" wound components and this is especially applicable to small ferrite transformers and inductors, since unlike conventional varnish impregnating methods, Parylene does not introduce the magnetostrictive or permeability problems sometimes encountered with conventional varnish impregnation. Maximum winding window is vital for small rotor and stator assemblies. Usually of bonded nickel iron laminates these components are difficult to coat with Epoxy or PTFE materials due to the complex shape and retention of coating material within the winding apertures. Also, due to surface tension, very little coating remains on the sharp outer corners; the very area where maximum abrasion to the winding wire occurs. The uniformity of Parylene retains the window aperture and the full coating thickness on the outer corners provides protection to the winding wire.

Coating for Miniature Components

The use of adhesive tape as insulation between winding and metal component is a well established process however as components get smaller, application of tape becomes difficult, in many instances resulting in a fall in yield of acceptable parts. A coating of Parylene can virtually eliminate faulty components plus improving electrical performance. An excellent example of this is the extremely small bobbins used as the "pick-up" coil fitted to some Hearing Aids.

Enhanced Strength and Corrosion Protection

Recent advances in magnetic materials such as sintered and plastic encapsulated neodymium-iron-boron components, the latter available in very complex shapes, has highlighted the advantages of the Parylene coating process. Moulded plastic NdFeB magnetic components are fragile and an additional advantage of a Parylene coating is increased strength. NdFeB material is also very susceptible to corrosion from atmospheric moisture. The extremely low water vapour transmission properties of Parylene provide excellent protection against corrosion.

Cost Effective Processing

Parylene coatings also offer a reduction in processing and labour costs since it is possible to coat many thousands of parts simultaneously using a tumble system during the VDP process which is analogous to barrel electro-plating. The development of new technologies as well as the proper utilisation of existing technologies serves to place new tools in the hands of the engineer and designer which will enable them to better address today's extremely complex problems.

Liquid Coating		Vacuum Deposition Parylene
Liquid Coatings do not provide even coverage across all surfaces of a coil form. Build-up of conventional coating material on a coil form can restrict windings capacity compared to an uncoated form or a form with a thin and uniform Parylene Coating.		Thin and uniform Parylene coating has little effect on the shape and capacity of a coil form.

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