STMicroelectronics has announced what it describes as innovative plastic air-cavity packages that enable high-power transistors for Radio-Frequency (RF) applications such as transceivers, broadcast equipment and MRI scanners to deliver performance and cost advantages over alternative devices in ceramic packages.

Air-cavity packages provide high electrical isolation for silicon die, and are well suited for high-frequency, high-power applications. According to the company, whereas the traditional package body is typically ceramic, to withstand high-temperature soldering during package assembly, this new air-cavity technology now enables lower thermal resistance, lower weight, and reduced cost compared to devices in ceramic packages.

ST's new STAC plastic packages achieve junction-to-case thermal resistance (RTH) of 0.28°C/W, which is some 20% better than comparable ceramic packages. This improves heat removal from the die during normal operation, allowing transistors to deliver increased gain and greater output power while simultaneously increasing reliability. In addition, the Mean Time To Failure (MTTF) for devices in the new packages is up to four-times longer than comparable devices in ceramic packages. In addition, 75% lighter weight delivers valuable savings for designers of equipment such as avionics systems or mobile devices. Two versions are available, matching the dimensions of industry-standard solder-down (flangeless) or bolt-down ceramic packages to enable direct replacement in existing designs.

ST has introduced three new devices for applications up to 250MHz using this new package technology, including the only 100V VHF MOSFET currently on the market. The 100V STAC3932B/F, in bolt-down or flangeless configurations, has 26dB linear gain and can sustain pulse-power output up to 900W. The STAC2932B/F and STAC2942B/F are 50V devices having linear gain and continuous rated output power of 20dB/400W and 21dB/450W respectively. The devices achieve nominal efficiency from 68% to 75%, compared to around 55% for the nearest ceramic alternatives.

The bolt-down version of the device is in full production; the flangeless variant is now sampling and will be in full production in Q2 2010. Prices for the power transistors in the new plastic air-cavity packaging start at $48 for the STAC2932B/F in quantities over 25,000 units.