Guides / Materials

The Insulator That Moves Heat: When AlN Is Worth Five Times the Price

May 4, 2026

Most technical ceramics make a choice for you: conduct electricity or conduct heat, rarely neither and never both. Aluminium nitride refuses that trade. It is a dielectric that moves heat at roughly half the rate of aluminium metal, and that single property is why it costs what it costs.

The comparison that matters

	Alumina 99.5%	Aluminium nitride
Thermal conductivity	Around 30 W/mK	170 to 200 W/mK
Electrical resistivity	Insulator	Insulator
Thermal expansion	Around 8 ppm/K	Around 4.5 ppm/K
Flexural strength	300 to 400 MPa	300 to 350 MPa
Relative blank price	Baseline	Several times higher
Water and humidity	Stable	Slowly hydrolyses

The expansion number is the quiet second reason engineers choose AlN. Silicon sits near 3 to 4 ppm/K. Mounting a die or a wafer on alumina means living with a mismatch that stresses the joint every cycle. On AlN the mismatch is small enough to stop being the design problem.

Where AlN earns its price

• Power electronics substrates. Heat has to leave the device without the substrate becoming a conductor.
• Electrostatic chucks and heaters in semiconductor tools. The part holds a wafer, insulates an electrode and pulls heat evenly. Alumina cannot do the third job well enough at the flatness these tools demand.
• Laser and RF component mounts. Small devices, high power density, tight positional stability.
• Heat spreaders under a sensor that must stay electrically floating.

If your part is not doing one of these, alumina is almost certainly the right material. Paying an AlN premium for a bracket that never sees a thermal gradient is a common and expensive habit.

What is different about machining it

AlN grinds reasonably, sitting between alumina and the harder grades in difficulty. Two things do change.

Water. AlN reacts slowly with water and humid air, producing aluminium hydroxide and ammonia. A shop that grinds it regularly manages coolant chemistry, rinses and drying for that reason. A shop that has never run it may hand you a part that looks fine and develops a hazy surface weeks later. Ask directly whether they have run AlN before.

Surface metallisation. Many AlN parts end up plated or brazed. Thick film and thin film metallisation on AlN is mature but it is not the same process as moly-manganese on alumina. Say on the RFQ if the part is going to be metallised, because that can change which blank the shop buys. See metallising and brazing ceramic to metal.

The machinable alternative for prototypes

Shapal Hi M Soft is an aluminium nitride and boron nitride composite. It cuts with ordinary carbide tooling, holds tolerances near those of Macor and still conducts heat at around 90 W/mK, which is three times dense alumina.

That makes it useful when:

• You need a thermally conductive insulator this week, not in three months
• The part is a fixture or a test rig that may change
• The quantity is one to five and grinding a dense AlN part is not worth it

It is weaker and rougher than sintered AlN, so it is a prototype and fixture material, not a production substrate. The same logic applies to Macor and other machinable ceramics.

Specifying an AlN part

1. State the thermal conductivity you need as a minimum, because grades vary widely
2. State flatness and finish separately from the general tolerance, since these parts usually sit against something
3. Say whether the part will be metallised, plated or brazed
4. Say whether it will see water, steam or long term humidity
5. Ask about stock plate thickness, because grinding a thick AlN blank down is expensive material to throw away

For the wider selection question, see pick a ceramic by property.

For alumina against silicon carbide as a heat path, see alumina vs silicon carbide.

See also: the aluminium nitride reference page.

Send your drawing and we match you with up to 3 shops that have actually run aluminium nitride. Reply within 24 business hours.

Frequently asked questions

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