Case Study: Form in Place EMI Gasket Eliminates Shielding Cans

Cover with Form-in-Place EMI Gasket Eliminates Shielding Cans

In a digital satellite telephone system, a noisy PCB was shielded using 12 metal cans. These were mounted into “fences” soldered onto ground traces. To reduce costs, save board space, and shorten maintenance times, the manufacturer changed from this shielding solution to a conductive cover with a form-in-place EMI gasket.

The cover is an injection molded PC/ABS plastic with a conductive coating on its inner surface.CHO_FRM

The shielded cover’s internal ribs provide more than 70 dB of EMI isolation between the 12 separate compartments or circuits on the PCB. Due to flatness and dimensional tolerances, the cover ribs did not mate perfectly against the PCB surface. Since the width of each rib was only about 3 mm, attaching groove-fit or adhesive-mounted EMI gaskets was impractical.

The solution was a Cho-Form 3.0 robotically dispensed form-in-place conductive elastomer. By programming the EMI gasket configuration on a three-axis dispensing machine, an accurately positioned “D”-profile gasket bead was formed and cured directly onto the cover ribs. The plastic easily withstood the 85°C (185°F) in-line oven cure required for the elastomer material selected. Self-tapping screws provided sufficient closure force to achieve 20-25% gasket deflection.

Cho-Form technology permits rapid prototyping, design changes and scale-up at nominal cost, accommodating batch runs or continuous high-speed production, from ten to ten million parts. Room temperature cure materials are also available.CHO-FORM4

For more information, see Chomerics’Cho-Form automated form-in-place gasket system.