Revolution Control: AlN ceramic discs between 15 and 60 millimetres in diameter are used to insulate diodes, thyristors and small GTOs. The discs are pressed, sprayed with separators to stop them sticking together during sintering, and placed on firing bases. They are then sintered under very pure protective atmosphere at temperatures of up to 1840 degrees Celsius. After lapping, the surface of the disks are parallel and extremely even. Typically, an insulating disk of 32mm diameter is flat to within 1 micrometer over its whole width! In Europe, AlN pressure contacts have now completely replaced Beryllium oxide, which is known to carry health risks.