BeO Still A Force In RF Power Transistor Packaging

The excellent performance characteristics of beryllium oxide (BeO) continue to make it well suited for RF power transistors and other devices that operate at very high power levels. Typical applications include military and aerospace pulsed power applications, where its inherent advantages remain unchallenged. BeO's continued importance as an insulating material is a result of its superior thermal conductivity (TC) of about 325 W/mK at room temperature, which among insulating materials, exceeds all but diamond (up to 1800 W/mK). Its nearest competitor in this respect is aluminum nitride (AlN) at about 185 W/mK, with alumina (Al2O3) at a distant 25. As a result, when thermal management and electrical isolation are key considerations, RF power transistor packages based on BeO are the best choice.

In addition to thermal conductivity, BeO's coefficient of thermal expansion (CTE) at 9.0 ppm/ºC is close to that of gallium arsenide (6.9) and is also well matched to other metal matrix composites (MMCs) such as Cu/W, Cu/Mo, Al/SiC, and E-materials. In other relevant areas, such as electrical resistivity and dielectric strength, BeO has better electrical characteristics than AlN and is similar to alumina. With a low dielectric constant of 6.7 and low loss index of 0.0012 at 1 MHz, BeO is well suited for use at high frequencies as well. In addition to these characteristics, BeO also is inherently stable in oxidizing environments, in contrast to nitrides such as AlN that decompose over time to their oxide equivalent.

Since beryllium is an oxide ceramic, BeO is very stable in oxygen/moisture-containing environments. Ceramic-to-metal joints and metallization 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.