ALUMINUM NITRIDE CERAMIC: THERMALLY CONDUCTIVE AND ELECTRICALLY INSULATING

As a high-performance ceramic, aluminum nitride (AlN) is one of the few materials that combines thermal conductivity comparable to metals with excellent electrical insulation. Chemically, it is a non-oxide ceramic composed of aluminum (Al) and nitrogen (N). This unique combination of high thermal conductivity and reliable electrical insulation distinguishes aluminum nitride ceramics from conventional engineering ceramics, making it the ideal material for components that must efficiently dissipate heat while protecting sensitive electronic systems through effective electrical isolation.

OVERVIEW OF MATERIAL PROPERTIES

The key properties of aluminum nitride at a glance:

Thermal conductivity: typically 140–180 W/(m·K), depending on purity and sintering process
Electrical insulation: resistivity > 10¹⁴ Ω·cm, dielectric strength approx. 14 kV/mm and low dielectric losses
Coefficient of thermal expansion: approx. 4.5·10⁻⁶/K, close to silicon and therefore ideal for semiconductor substrates
Density: approx. 3.26 g/cm³
Hardness: approx. 1,100 HV
Flexural strength: approx. 320 MPa, stable even at high temperatures
Modulus of elasticity: approx. 220 GPa
Maximum operating temperature: up to approx. 1,800–2,000 °C under inert or nitrogen atmospheres, depending on load and environment
Chemically: corrosion-resistant against molten aluminum, selected non-ferrous metal melts and gallium arsenide, and resistant to plasma erosion; sensitive to prolonged exposure to moisture
Health and safety: non-toxic and safe for use

EXCEPTIONAL THERMAL CONDUCTIVITY OF ALUMINUM NITRIDE

The hight thermal conductivity of aluminum nitride is its most distinctive property: at around 170 W/(m·K), it is many times higher than that of aluminum oxide, reaching values that are exceptional for an electrically insulating ceramic. It is determined by the non-oxide crystal lattice and the additives added during sintering: a low-oxygen microstructure is crucial, as dissolved oxygen disrupts heat transfer within the crystal lattice. Sintering additives such as yttrium oxide bind this oxygen and significantly increase the thermal conductivity of aluminum nitride. Precisely for this reason, it is highly sensitive to powder purity and process control, and these two parameters can be precisely tailored to its properties.

In practice, this means that AlN components efficiently dissipate waste heat from sensitive electronic and semiconductor devices, helping to maintain safe operating temperatures even under demanding conditions.

Vergleich zu Aluminiumoxid

A direct comparison of the two materials clearly shows why aluminum nitride ceramic is primarily chosen for its thermal management properties, while aluminum oxide (Al₂O₃) scores points for hardness, wear resistance, and cost-effectiveness:

CHARACTERISTIC	ALUMINIUM NITRIDE (AlN)	ALUMINUM OXIDE (Al₂O₃)
Thermal conductivity	approximately 170 W/(m·K)	25–35 W/(m·K)
Electrical insulation	excellent	excellent
Thermal expansion	approximately 4.5·10⁻⁶/K, close to silicon	approx. 7–8·10⁻⁶/K
Flexural strength	approx. 320 MPa	360–600 MPa
Hardness	approx. 1’100 HV	approx. 1’500–1’900 HV
Density	approx. 3,26 g/cm³	3,75–3,95 g/cm³
Moisture resistance	sensitive (slow hydrolysis)	Highly resistant
Key strength	Heat dissipation with electrical insulation	Hardness, wear resistance, and cost-effectiveness

DESIGN CONSIDERATIONS

Zwei quadratische Platten aus AlN Keramik

To ensure that aluminium nitride performs reliably in service, it is worth taking a look at some of the material’s limitations beforehand:

Caution is required in humid environments and when exposed to water: AlN reacts with humid atmospheres over extended periods, especially at higher temperatures. Protective coatings or suitable metallization can remedy this.
Mechanically, the flexural strength is lower than that of zirconia, which is why an early material comparison is worthwhile for components subjected to high tensile or bending stress.
In oxidizing atmospheres, an oxide layer forms on air above approximately 900 °C, which is usually tolerable, but should be taken into account for continuous use.
Depending on the medium, a different technical ceramic or a cemented carbide such as tungsten carbide is the better choice for resistance to aggressive acids and alkalis.

APPLICATIONS OF ALUMINUM NITRIDE CERAMICS: TYPICAL COMPONENTS AND INDUSTRIES

The areas of use and applications of aluminium nitride are centred on heat-critical components across a range of industries:

In the semiconductor industry, AlN ceramic is used as a heat dissipation substrate and heat sink.
In the automotive industry, it is used in power electronics, inverter modules, and thermal management systems.
Specific functions in high-temperature technology as well as specialised components in aerospace industry.
Microwave communication uses substrates and packaging for microwave circuits.
High-temperature reaction vessels and furnace linings are used in metal smelting.

In many of these applications, aluminum nitride ceramic replaces aluminum oxide: because the components remain cooler, the entire assembly operates more stably and lasts longer.

MANUFACTURED FROM POWDER UNDER A PROTECTIVE ATMOSPHERE

Aluminum nitride is produced using powder metallurgy : Fine AlN powder is mixed with sintering additives such as yttrium oxide and shaped in its unsintered state, for example by dry pressing or, for thin substrates, by foil casting. The structure is then densified under a nitrogen protective atmosphere at approximately 1,700 to 1,900 °C to form the finished material, during which the part shrinks by about 15–20%. The protective atmosphere is crucial, as it prevents the material from oxidizing and losing its high thermal conductivity.

Depending on the powder quality, additive content and sintering regime, different grades are produced:

Standard-Grade AlN

Economical option for insulating components and substrates requiring high, but not maximum, heat dissipation.

HIGH THERMAL CONDUCTIVITY ALN QUALITY

Purer powder and optimized sintering for power electronics with the highest heat flux densities.

ALN HARD MACHINING: FROM BLANK TO COMPONENT

Komplexes Bauteil aus Aluminiumnitrid-Keramik auf weissem Hintergrund

Components only acquire their final shape after sintering through hard machining with diamond tools and lasers. The necessary steps depend on the type of component:

Flat substrates are produced as thin plates during film casting; after sintering, they are ground flat and lapped, cut to size and drilled by laser, and finally metallized so that they can be used in power electronics.
Complex structural components are first pressed and, after sintering, ground to their final contour using diamond tools until even three-dimensional shapes achieve the required tight tolerances.

PURCHASE ALUMINUM NITRIDE CERAMIC COMPONENTS FROM GRAF HARTMETALL

Are you looking to buy aluminum nitride , but aren’t sure whether another technical ceramic or a cemented carbide like tungsten carbide would be best suited for your component? Whether its for a prototype, a small batch, or ongoing production: We support you in selecting the right material for your application and manufacture your precision parts and ceramic components according to your specifications. Tell us about your project. We’d be happy to advise you in detail!