Ceramic substrate materials

Choose the ceramic grade for the complete assembly

Alumina, aluminum nitride and silicon nitride are different engineering ceramics. A material name or purity percentage narrows the search; it does not define the finished circuit board. Thermal conductivity, expansion, dielectric behavior and strength vary by grade, test conditions and part geometry. Compare a named supplier grade at the temperature and frequency that matter to the design, then check how the ceramic will be metallized, attached and cooled. Use the comparison questions above to identify the data needed from a current grade datasheet.

Kyocera’s material index separates these families and their grades. CoorsTek’s alumina catalog illustrates how properties differ among formulations. Those are supplier examples, not AluminaPCB certificates or guaranteed values.

Alumina: start with the specified grade

Alumina is an electrical insulator that can also conduct heat through a ceramic substrate. Purity labels such as 96% and 99.6% do not by themselves settle thermal, RF or assembly performance. Compare the actual grades for thermal conductivity at the relevant temperature, dielectric properties at the relevant frequency, substrate thickness, mechanical strength and available finish. The 96% alumina page and 99.6% alumina page provide separate entry points; request the source datasheet behind any property used in a design decision.

Aluminum nitride: evaluate the heat path, not just conductivity

Aluminum nitride is another electrically insulating ceramic often considered when the substrate portion of the thermal path is critical. Its material conductivity alone does not predict device temperature. Ceramic thickness, metal coverage, die attach, interface material and cooling boundary also matter. Compare named AlN grades and their conditions with the alumina candidate, then calculate or measure the full stack. See the AlN versus alumina guide and the focused AlN substrate page. Kyocera identifies AlN as a high-conductivity electrical insulator in its material description; that does not establish this site’s available grades.

Silicon nitride: examine mechanical and cycling requirements

Silicon nitride is commonly evaluated where mechanical loading or repeated temperature change is central to the application. A toughness figure from one supplier’s grade is not a guaranteed lifetime for an assembled power module. Metal thickness and pattern, joining interfaces, mounting and the actual temperature-cycle profile all affect reliability. Kyocera’s silicon-nitride material information illustrates why grade-specific mechanical and thermal properties must be read together. For a design review, specify the loading and the inspection or cycling evidence you need.

Beryllium oxide: handle feasibility and safety explicitly

Beryllium oxide is an electrically insulating ceramic with useful thermal properties in some specialized designs. It should not appear as a routine substitute for AlN or alumina. Fabrication or rework that releases beryllium-containing dust requires appropriate occupational controls; OSHA’s beryllium guidance identifies beryllium oxide ceramic manufacturing and machining among potential exposure settings. Before specifying BeO, confirm that the chosen supplier can actually provide it and that the intended processing, handling and downstream work are controlled. No BeO supply capability is asserted here.

Match the substrate to the conductor process

Material selection and metallization cannot be separated. Direct bonded copper, direct plated copper, thick film and thin film form different conductor structures and have different pattern, thickness and assembly implications. The same ceramic family may require a different grade or surface preparation for different processes. The DBC versus DPC comparison explains one important process choice. Request a feasibility review for the actual ceramic, conductor, finish and geometry before assuming a process combination is available.

A practical selection sequence

1. Define heat load, electrical isolation, operating temperature, attachment method and mechanical constraints.
2. Shortlist specific ceramic grades and record the source, units and test conditions for every property used.
3. Check substrate thickness and interfaces in the full heat path. A screening calculation for a uniform slab is R = t/(kA); real spreading and interfaces require further evaluation. The thermal guide explains the limits.
4. Choose a candidate conductor process and finish for the required current, feature geometry and assembly method.
5. Send the controlled drawing and acceptance criteria for a part-specific quotation.

If the design remains open, label the alternatives rather than asking for a single unspecified “ceramic PCB.” Send the drawing or requirements for review and ask that material and process assumptions be stated in the response. Availability, price and timing depend on the actual specification and must be confirmed separately.