| Decision | AlN | Si₃N₄ |
|---|---|---|
| Typical emphasis | High thermal conductivity | Toughness and cycling robustness |
| Named conductivity example | 170 W/m·K, curamik Thermal | 90 W/m·K, curamik Performance |
| Representative route | DBC or AMB, supplier-dependent | AMB power substrate |
| Critical comparison | Heat path and interfaces | Copper stress and failure mechanism |
Compare thickness as well as conductivity
A thinner qualified Si₃N₄ layer can offset part of the conductivity difference from AlN. Insulation and handling requirements constrain the permissible thickness. A thermal comparison does not establish equivalent working voltage or mechanical life.
Review the metallized construction
Copper thickness, braze, edge profile and pattern balance matter. Ask for evidence on structures resembling your design. Isolated bending-strength or toughness numbers do not directly predict the lifetime of an assembled module.
Choose around the limiting failure mode
If attachment resistance dominates temperature, higher ceramic conductivity may have limited value. If substrate cracking is the problem, tougher ceramic may help, but fixture loads and copper geometry still require correction.
Engineering example
At 100 mm² area, 0.32 mm Si₃N₄ with k = 90 gives about 0.0356 K/W; 0.635 mm AlN with k = 170 gives about 0.0374 K/W. This simple comparison excludes all interfaces.
Before you release the design
- Compare qualified thicknesses.
- Identify the expected failure location.
- Request construction-specific reliability evidence.
Sources and further technical reading
Manufacturer references support the material and process context. Worked examples and checklists are engineering guidance; they are not test results or supplier guarantees.