Compare ceramic materials using values at the same test temperature, for identified grades, with compatible measurement directions and methods. Keep measured values separate from interpolated estimates, and leave unsupported temperatures blank. A room-temperature conductivity figure cannot establish which substrate performs better at the temperature reached by your ceramic PCB.
Have candidate datasheets but inconsistent conditions? Discuss your ceramic material requirements with the grade names, target temperature range and assembly constraints.
Start with a comparison question you can actually answer
“Which ceramic is best?” is too broad for a property table. A usable question is: “Which of these two named grades has the better-supported through-thickness thermal conductivity between 25 and 150 °C?” That defines the property, direction and temperature range. Electrical isolation, manufacturability and mechanical reliability still need separate decisions.
Use the ceramic PCB materials guide to shortlist families, then compare grade-specific evidence. For an alumina PCB, a purity percentage alone is not enough to identify a conductivity curve. KYOCERA explains that porosity, grain boundaries and impurities affect ceramic thermal conductivity. Its thermal-conductivity material reference is a useful starting point for understanding why a family name does not define one universal value.
Separate test temperature from the other temperatures on the drawing
The temperature attached to a property measurement is not automatically the ambient temperature, semiconductor junction temperature, process firing temperature or maximum service rating. A material may have a conductivity measured at 100 °C while the assembly experiences a range of local temperatures. Write down which temperature your model needs before selecting data.
- Measurement temperature: the specimen temperature associated with the reported property, including how the method defines it.
- Operating temperature field: the temperatures the ceramic reaches under the specified load and cooling conditions. A temperature-dependent model may require several property points.
- Temperature difference: a rise of 20 K is also a rise of 20 °C. An absolute temperature of 400 K, however, is 126.85 °C, not 400 °C.
- Service limit: a separate suitability or qualification statement. It does not supply missing conductivity measurements.
Temperature dependence is documented in primary research: Xu and colleagues measured crystalline AlN using the 3ω method across 100–400 K and studied the influence of defects. Their AlN thermal-conductivity study supports treating temperature and material condition as explicit variables. Its crystalline specimens do not establish the curve of an unnamed commercial sintered substrate.
Build a common temperature grid before ranking candidates
Choose the grid from the thermal design envelope. For each target temperature, retain the original source point and mark how the comparison value was obtained. Do not quietly relabel “room temperature” as 25 °C when the source does not define it. Ask for the missing condition or record it as unknown.
On small screens, scroll the table sideways to read all columns.
| Available evidence | Treatment in the comparison | Remaining check |
|---|---|---|
| Same grade measured at 100 °C | Use the reported point, with its uncertainty and value type. | Direction, method and specimen condition must still match the question. |
| Same grade measured at 75 and 125 °C | An interpolation may support screening if the behavior between points justifies it. | Label the estimate; do not call it a measurement or guaranteed minimum. |
| Only an undefined “room-temperature” value | Leave the 100 °C entry unavailable. | Request a curve or a measurement near the required temperature. |
| A 100 °C value for another grade or crystal orientation | Keep it outside the direct ranking. | Establish whether that material or direction represents the proposed part. |
| Finished-stack conductance instead of bare-ceramic conductivity | Compare it in an assembly model, not the same property column. | Record layer geometry, interfaces, units and test boundary conditions. |
Methods need to be compatible, not merely carry similar labels. Different valid methods can agree, but that agreement needs evidence and an uncertainty assessment. A shared method name alone also does not prove that different specimens or directions are comparable.
Illustrative example: a ranking can depend on the comparison temperature
The following values are invented teaching data for fictional ceramic candidates A and B. They are not supplier specifications, typical values for alumina or AlN, or AluminaPCB test results. Assume compatible methods, through-thickness direction and unchanged specimen condition throughout. The purpose is to show how to organize a comparison, not to predict a real material pair.
Compare at 25 °C
A has the larger assumed value.
Compare at 150 °C
B has the larger assumed value.
On small screens, scroll the table sideways to read all columns.
| Temperature | Candidate A | Candidate B | What the assumed numbers show |
|---|---|---|---|
| 25 °C | 30 | 28 | A is numerically higher. |
| 100 °C | 24 | 25 | B is numerically higher. |
| 150 °C | 20 | 22 | B is numerically higher. |
| 200 °C | Unavailable | Unavailable | No supported comparison; missing does not mean zero. |
Comparing A at 25 °C with B at 150 °C would produce a misleading margin. Even a correctly aligned numerical ranking is not a statistical conclusion without measurement uncertainty, nor a complete board-performance ranking. The ceramic conductivity and thermal-resistance guide explains why geometry and interfaces must enter the next stage of analysis.
If your candidate documents leave cells empty, send the datasheets and required temperature range for discussion. Include the proposed ceramic thickness, conductor process and heat path so the data request relates to the actual part.
Interpolate only within a supported interval
A linear interpolation is a declared approximation between two points for the same property and grade. It is not a temperature correction that can be transferred between unrelated ceramics. Check for curvature, transitions and changes of test condition before using it.
k(T) = k₁ + (k₂ − k₁) × (T − T₁)/(T₂ − T₁)
Using the fictional 25 and 100 °C points at a target of 80 °C:
- A: 30 + (24 − 30) × (80 − 25)/(100 − 25) = 25.6 W/(m·K).
- B: 28 + (25 − 28) × (80 − 25)/(100 − 25) = 25.8 W/(m·K).
The 0.2 W/(m·K) difference is only a difference between assumed estimates. It cannot establish a robust winner without uncertainty and model-error information. For a real decision close to the margin, request better evidence near 80 °C. Extending these lines to 200 °C would be extrapolation; this example supplies no basis for doing so.
Check temperature and units when conductivity is calculated
NETZSCH describes flash analysis as measuring thermal diffusivity, with conductivity calculated using diffusivity, specific heat capacity and density. Write the relationship as k(T) = a(T) × cp(T) × ρ(T). The three inputs must represent compatible material conditions at the comparison temperature; document any approximation used for an input.
In a separate, hypothetical unit-check example at 100 °C, assume a = 7.5 mm²/s, cp = 800 J/(kg·K) and ρ = 3,800 kg/m³. Convert diffusivity to 7.5 × 10−6 m²/s. Then k = 7.5 × 10−6 × 800 × 3,800 = 22.8 W/(m·K). These are assumed inputs, not a named ceramic grade or measured result.
Multiplying a high-temperature diffusivity by unrelated room-temperature heat-capacity data can create an apparently precise number with mismatched assumptions. Ask which inputs were measured, which were taken from references, and how uncertainty was propagated.
Keep a comparison worksheet that survives a design review
For every accepted value, retain these fields together. The alumina datasheet-to-RFQ workflow covers document control and acceptance questions; the worksheet here focuses on aligning property data.
- Supplier, exact grade, source revision and specimen state: bare ceramic, coated material or assembled stack.
- Property, units, measurement direction and test method, including any relevant orientation.
- Original temperature points and the target temperature grid; preserve Kelvin-to-Celsius conversions explicitly.
- Value type: measured, supplier typical, guaranteed limit or interpolated screening estimate.
- Uncertainty or tolerance, missing inputs and the action needed to resolve each gap.
- Decision boundary: what the data can support, and which thermal, electrical or mechanical checks remain.
Then return to the broader ceramic PCB material and process comparisons with the evidence limits visible. A conductivity comparison is one input to selection; it does not establish available manufacturing capability or qualification of the finished assembly.
Frequently asked questions
Can I assume that “room temperature” always means 25 °C?
No. Preserve the source wording until its reference temperature is confirmed. If the difference could affect selection, ask the supplier for the defined condition and a point or curve near your target.
Can I apply one percentage reduction per degree to all ceramic grades?
No general reduction factor is established here. Use the actual grade’s data over the relevant interval. A curve from another formulation or specimen is background evidence, not an automatic correction rule.
Does a higher conductivity at every matched temperature guarantee a cooler device?
No. The ceramic’s contribution depends on thickness, area and heat spreading; attach layers, interfaces and cooling also matter. Compare the full assembly under the same power and boundary conditions.
Should I average two conflicting supplier values?
First resolve whether they describe the same grade, temperature, direction and value type. Averaging incompatible entries hides the discrepancy. For comparable measurements, use a justified uncertainty analysis rather than an unexplained arithmetic mean.
Can the same temperature grid be used for dielectric data?
It can organize temperatures, but temperature alignment alone is insufficient. Also align frequency, measurement method, direction and specimen condition. Keep dielectric constant and loss separate from thermal conductivity.
What should I do when only one candidate has data at operating temperature?
Mark the other candidate as unverified at that temperature and request the missing evidence. Do not fill the gap with zero, its room-temperature value or a different grade’s curve. Continue selection only within the evidence available.
Prepare the material discussion
Share the candidate grade names, temperature and frequency ranges, heat load, ceramic geometry, electrical and mechanical constraints, and intended assembly method. Attach the source datasheets and flag missing conditions. Discuss your ceramic material requirements so material and process assumptions can be made explicit before a quotation is finalized.