Design News for Mechanical and Design Engineers

Inherently conductive thermoplastics may soon be able to replace some of the metals and coated plastics that currently go into enclosures for telecom equipment and other electronics. XTech, a supplier of mechanical systems for circuit boards, has come up with developmental faceplate panels injection molded from a new stainless-steel-filled thermoplastic.

According to Steve Richardson, the applications engineer responsible for XTech’s conductive plastics program, the company began investigating engineered polymers for enclosure components as part of its on-going cost reduction plans. “In general, plastics can offer a cost advantage over metals at high production volumes and as design complexity and feature integration increase,” he says.

And now, thanks to the availability of conductive grades, plastics can offer inherent shielding capabilities too – that is, without the need for expensive conductive coatings. XTech has been working with a Faradex DS-1003 FR HI compound from GE Advanced Materials. Richardson says the material can provide EMI attenuation between 20-60 dB, a range that satisfies most electronics and telecommunications applications. Based on GE’s Lexan EXL polycarbonate, the Faradex offers an impact strength of 9 KJ/m2 at -45 C. It has been formulated with a halogen-free flame retardant and offers a UL 94 V0 flammability listing at thicknesses of 2.1 mm.

Working closely with injection molder Fielding Manufacturing, XTech has initially applied this conductive plastic to enclosure faceplates – in part because each one has so many variants. As Richardson explains, a faceplate family can include five to 10 or more different cutout geometries to accommodate different circuit board assemblies. "One of the challenges was to make a single mold with different inserts that would allow the customization of hole patterns," Richardson says.

So far, the results on this plastic enclosures project has been promising. Richardson says contrary to conventional wisdom, the plastics have performed well at higher frequencies during EMI testing – which typically runs up to 20 GHz. “The shielding effect actually improved with plastics as frequencies increased,” Richardson says. He believes molded plastics will offer other benefits too, among them improved corrosion resistance in outdoor settings and the ability to mold in features like fasteners.

Still, don’t look for conductive plastics to replace metal completely any time soon. “Metal has an inherent shielding and flame retardant advantages in thinner wall sections,” Richardson notes. And extruded and sheet metals in particular are tough to beat from a cost perspective – unless you have special design requirements or high volumes that favor plastics. “Moving forward, you’ll find that there’s a place for both metal and plastics,” Richardson says.

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