B-Power electronic substrate-Direct bonded
Direct bonded copper substrate
Ceramic material used in DBC include:
Alumina (Al2O3), which is widely used because of its low cost. It is however not a really good thermal conductor (24-28 W/mK) and is brittle.
Aluminium nitride (AlN), which is more expensive, but has far better thermal performance (> 150 W/mK).
Beryllium oxide (BeO), which has good thermal performance, but is often avoided because of its toxicity when the powder is ingested or inhaled.
One of the main advantages of the DBC substrates is their low coefficient of thermal expansion, which is close to that of silicon (compared to pure copper). This ensures good thermal cycling performances (up to 50,000 cycles). The DBC substrates also have excellent electrical insulation and good heat spreading characteristics.
A related technique uses a seed layer, photoimaging, and then additional copper plating to allow for fine lines (as small as 50 micrometres) and through-vias to connect front and back sides. This can be combined with polymer-based circuits to create high density substrates that eliminate the need for direct connection of power devices to heat sinks.