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RF screen coating for moulded packages

MicroShield is a screening technology that integrates RF screening on the surface of a moulded package, saving space compared to an architecture that adds a screening can. The protected device might contain a single chip or a multi-chip module. RF Micro Devices developed the process to replace metal screening cans that designers must often mount on PCBs either to shield the enclosed circuitry from external interfering signals, or to prevent RF interference from leaking out. MicroShield takes the form of a sprayed-on conductive coating that makes conductive contact with a “skirt” contact band that runs around the bottom edge of the moulded package. When the assembly process solders the package to the PCB in the usual way, the “skirt” contacts a grounded ring that surrounds the package site. In this way, a five-side screen surrounds the contents of the moulded package; a ground-plane under the package, with vias for connections, will complete the six-sided screen. At the time of introduction, RFMD was not quoting figures for screening effectiveness in terms of decibels, but a spokesman indicated that results were competitive with those of metal cans while reducing height and volume for RF-circuit sections by 25 to 50%. RFMD will employ the process on its own product lines as an option, and it will also license it to other manufacturers, who can apply it to any over-moulded package technology.

RF Micro Devices, www.rfmd.com.