Updated February 15, 2007

BeO is a toxic material, but its combination of high thermal conductivity and low expansion coefficient make it seem like a magical solution to a lot of semiconductor heat problems. At Microwaves101.com we advise you against using this compound in any design. Exposure can cause a severe allergic reaction in some people, and breathing dust containing beryllia will kill you faster than asbestos. Because it is so toxic, it is required by law that you label all parts containing beryllium with handling instructions, you can't perform any type of rework to it, and disposal of scrap may be a crime depending on where you live and your local regulations. Consider aluminum nitride as safe alternative, or take you design back to the drawing board and figure out a better way to dump the heat! Why put your employees and customers through potential a health risk and your company at a legal risk?

Here's a link to Brush Wellman's instructions on handling BeO which is one of their main products.

Some of the data came from an old MIC Technology databook.

Formula or Composition:	BeO
Dielectric Constant ():	6.7
Dissipation Factor (a.k.a. loss tangent, or tan):	0.003
Temperature Coefficient of :	ppm/°C
Bulk Resistivity:	-cm
Temperature Coefficient of Resistivity (TCR):	ppm/°C
Mass Density:	3.01 gr/cc
Specific Heat:	J/g/°C
Thermal Conductivity (k):	290 W/m°C
Temperature Coefficient of Expansion (TCE):	7.6 ppm/°C
Melting Point, °C:	2200 °C 3992 °F