Thermally Conductive Ceramics

The application of ceramics in high thermal conductivity scenarios represents a burgeoning niche market. Among these materials, oxide ceramics stand out as the most prevalent base materials. However, their thermal conductivity typically ranges from 26-30 W/mK. When compared to the thermal conductivity of copper at approximately 385 W/mK and aluminum at 150-185 W/mK, there exists a substantial disparity.

The objective is to enhance thermal conductance while preserving ceramics’ essential trait: electrical insulation. Recent advancements in alumina have pushed its thermal conductivity in certain grades to around 39 W/mK, although this still falls significantly short of the thermal conductivity offered by commonly used metals. Nevertheless, this marks a noteworthy improvement from its initial levels.

Identifying ceramic materials capable of achieving higher thermal conductance is a specialized endeavor. Each type possesses unique strengths and weaknesses, and not all of them provide the crucial property of electrical insulation.

Examining four potential candidates, including Boron Nitride, Aluminum Nitride (AlN) composites, Beryllium oxide, and pure Aluminum Nitride, provides valuable insights. The first contender, Shapal Hi-M Soft, combines Aluminum Nitride and Boron Nitride, yielding a substantial increase in thermal conductivity at over 92 W/mK, along with enhanced electrical insulation. This composite also offers the advantage of machinability without the need for diamond tools, though its production through hot pressing limits its size availability.

Boron Nitride, another hot-pressed material, is also machinable and comes in larger pieces, with multiple grades accessible. However, only the highest purity matches the machinable AlN/Boron Nitride composite in thermal conductance and, in certain cases, even surpasses it. Yet, these high purity grades are mechanically weaker and softer than the machinable Aluminum Nitride/Boron Nitride composite.

Beryllium Oxide has remained a preferred choice for high-end projects over the years. With a thermal conductivity of 285 W/mK, excellent electrical insulation, and lacking the specialized nitrogen furnacing requirements of Aluminum Nitride due to its oxide ceramic nature, it stands out. However, its utilization is limited due to health and safety concerns, making it suitable primarily for specialized applications, such as military requirements.

Aluminum Nitride (AlN) is primarily utilized in substrate form, often seen as the next level up from Alumina substrates. The majority of the global AlN production is in this substrate format. The thermal conductivity of AlN varies based on the grade and quality, with the industry standard ranging from 170-180 W/mK. Lower grades can be found at around 150 W/mK, while ultra-high purity grades can reach up to approximately 220 W/mK. AlN components in a 3D geometry are relatively uncommon. Many engineers opt for machinable Aluminum Nitride composites, especially during initial design phases, and sometimes even in production volumes, despite their lower thermal conductivity.

For those with substantial financial resources seeking the utmost thermal conductance, synthetic Diamond, boasting over 2000 W/mK, is an option. However, such a choice would necessitate an exceptionally high thermal conductance requirement.

Below is a table comparing the thermal conductivity of three electrical insulators (Aluminum Nitride, Shapal, and Alumina) and two electrical conductors (Aluminum and Copper).