Alumina (Al₂O₃)
The workhorse ceramic: good dielectric strength, moderate thermal conductivity, mature thick-film and direct-bonded-copper processes, and the lower cost of the two. It suits sensor substrates, LED boards and power circuits where the thermal load is moderate.
Aluminium nitride (AlN)
Higher thermal conductivity and a thermal expansion closer to silicon, which reduces stress on large dies. The price is a harder, more brittle substrate and a narrower process window, so it is reserved for high-power density work.
Design rules that differ from FR-4
- Feature sizes are set by the metallisation process, not by etched copper foil.
- Vias are laser-machined and filled or metallised, so the pad geometry changes.
- Boards are usually single or double sided; multilayer ceramic exists but costs jump sharply.
Send the thermal model and the die footprint; the substrate choice follows from the watts per square millimetre and the allowed junction temperature.
