MEMS microphones in plastic

11 July 2012 Analogue, Mixed Signal, LSI

STMicroelectronics has commenced mass production of MEMS microphones in plastic packages. The patented technology breakthrough saves space and increases durability in consumer and professional voice-input applications, from mobile phones and tablets to noise-level meters and noise-cancelling headphones.

While other MEMS microphone manufacturers still produce devices with metallic lids, ST’s novel microphone assembly process ensures high electrical and acoustic performance, mechanical robustness and slimmer form factors, while simultaneously advancing the microphone chip size reduction to 2 x 2 mm in devices that will soon arrive in the market. This technology development paves the way to introducing microphones embedded in silicon cavities as the ultimate step in device miniaturisation.

The microphones are suitable for assembly on flat-cable printed circuit boards that simplify design in space-constrained consumer devices. The patented package technology allows equipment manufacturers to place the ‘sound hole’ either on the top or the bottom of the package to ensure the slimmest possible design and shortest acoustic path from the environment to the microphone.

While the microphones with the sound hole on the top (top-port) suit the size and sound-inlet position requirements of laptops and tablets, the bottom-port microphones are mostly used in mobile phones.

Stringent compression and drop tests have shown that microphones in plastic packages also outperform traditional metallic-lid devices in durability. When subjected to a force of 40 N, microphones in metallic packages collapsed, whereas ST devices in plastic packages remained intact. Similar results were obtained when devices from both categories were exposed to 40 drops from a height of 1,5 m with a static force of 15 N applied on the package.

ST’s plastic-package microphones integrate an internal shielding cage for electromagnetic immunity and are compatible with standard surface-mount assembly machinery and conventional pick-and-place equipment.

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