Polymers offer improved EMI shielding and design freedom

Two new thermoplastic shielding materials have been developed that achieve new levels of EMI shielding and electrical conductivity.

The ability to include design features on a part made from the materials, such as internal compartments, also means customers can accommodate multiple logic and RF components in a single shield.

Chomerics' 'Premier' range of conductive plastic shielding materials now includes two new compounds - 'A230-HTHF' and 'A240-HTHF' - with properties that, the company said "enhance design freedom" and make them suitable for use in the most demanding applications. The materials conform to RoHS, WEEE and EPA standards.

The new compounds achieve impressive shielding performance of around 85dB. They use high aspect ratio, nickel-plated carbon fibres, which are treated with a proprietary sizing agent to give superior processing and dispersion.

The fibres are then augmented with nickel-based fillers with a lower aspect ratio. The careful control of this process results in a high melt flow. This in turn allows the manufacture of parts with walls down to 0.8mm, with localised areas between 0.5mm and 0.8mm thick, without loss of shielding effectiveness or electrical conductivity.

The reduction of long fibres also produces a smoother, more even surface on finished parts. Chomerics said this was particularly useful "where aesthetics are an important design consideration". A good example of this is where parts, once assembled into a finished product, are visible to the equipment user.

Premier shields offer space, cost and weight savings (they are up to 75% lighter), plus greater design freedom compared to most other shielding approaches. By having shielding functionality integrated, Premier materials alleviate the need for expensive secondary operations such as machining, plating, painting or vacuum coating. This, said Chomerics, can reduce costs by up to 50% with comparable die castings, bent or formed metal, or machined extrusions.

The materials are abrasion- and corrosion-resistant and exhibit high tensile and flexural strength characteristics. The ability to include design features such as internal compartments also means that a single part can accommodate multiple logic and RF components in a single shield. The material can be ordered in pellet form or as finished custom parts.

Tom Shelley

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