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Military Microwaves Supplement
Brush Ceramic Products Inc., a wholly owned subsidiary of Brush Wellman Inc. and a leading supplier of beryllium oxide (BeO), announced the achievement of a significant increase in thermal conductivity over standard BeO.
Beryllium oxide is used as an insulating material in high power RF and microwave power transistor packages and electron devices such as inductive output tubes that power broadcast transmitters and radar systems. BW3250, as the new material is called, now delivers thermal conductivity (TC) of greater than 325 W/mK at room temperature, an increase of over 15 percent from the 285 W/mK that was previously obtainable. The benefits in heat dissipation afforded by the advancement will allow devices employing BeO to deliver higher RF outputs.
BeO has been a core component of many high power microwave devices for decades. Among insulating materials, it exceeds all but diamond, since its nearest competitor -- aluminum nitride (AlN) -- has a thermal conductivity of only 185 W/mK, while alumina (Al2O3) can only achieve a TC of 25. In addition to TC, BeO’s coefficient of thermal expansion (CTE) at 9.0 ppm/°C is close to that of gallium arsenide (6.9), which makes it much easier to match to the devices with which it is used, and it also well matched to metal matrix composites as Cu/W, Cu/Mo, Al/SiC and E-materials.
The electrical resistivity and dielectric strength of BeO is better than AlN and is similar to alumina. It has a low dielectric constant of 6.7 and a low loss index of 0.0012 at 1 MHz, which addresses the increase in losses that occur as frequency increases. In addition to these characteristics, BeO is also inherently stable in oxidizing environments, in contrast to nitrides such as AlN that decompose over time to their oxide equivalent. Finally, as an oxide ceramic, BeO is very stable in oxygen and moisture-containing environments. Ceramic-to-metal joints and metalization coatings are generally very strong and reliable, which is important in the design of high-reliability military systems. In addition, BeO is also about 11 times more resistant to thermal shock than alumina.
“The performance increases we have achieved with BW3250 are very gratifying,” said Brush Ceramic products general manager John Scheatzle. “They are the result of many years of development and will deliver benefits in virtually all of our current material applications including those in microwave and photonics. Many of our key customers are currently evaluating the advanced BeO, and the results have been overwhelmingly positive.”
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