| abstract |
In an aluminum nitride substrate for a circuit board having aluminum nitride crystal particles having an average particle diameter of 2 to 5 μm and having a thermal conductivity of 170 W / m · K or more, the dielectric breakdown voltage at 400 ° C. does not contain a dendritic grain boundary phase. An aluminum nitride substrate for a circuit board of 30 kV / mm or more is disclosed. Further, a raw material containing aluminum nitride powder is heated to a temperature of 150 Pa or lower at a temperature of 150 Pa or lower, and then heated and maintained at 1700 to 1900 ° C with a non-oxidizing gas as a pressurized atmosphere of 0.4 MPa or more, and then 10 ° C to 1600 ° C. Provided is a method for producing an aluminum nitride substrate for a circuit board, which includes a step of cooling at a cooling rate of less than / min. |