Aluminum Nitride (AlN) is currently the best ceramic substrate material available. thanks to its high thermal conductivity (170 W/mK) combined with a high dielectric strength and low expansion (CTE) it is already widely used as a substrate or package for high power LEDs, IC’s, sensors and other components.
Ceramics advantages over other printed circuit boards:
- Superior thermal conductivity 170W/mK
- Strong dielectric
- High operating temperature >350ºC
- Low expansion coefficient <4 ppm/C
- Smaller package size due to integration
- Hermetic packages possible, 0% water absorption
- Limited to no outgassing
Circuits can either be printed using Copper (Cu) or Silver (Ag) depending on the application and the request. Copper is offered both in DBC/DPC as well as Thick film screen print processes while silver can only be done in using the second manufacturing option. Today we are only able to manufacture single or double layer designs.
Solder resist and surface finishes can be applied similarly to regular PCB when copper metallization is used. However, for silver thick film designs, we offer only a glass solder mask which is recommended for high-temperature designs. For high sulfur environments where silver corrosion can be an issue, we offer Gold plating as a solution to protect the exposed pads.
Material properties AlN
AluminaOxide or Al2O3 is the most widely used ceramic substrates thanks to its low cost and bright white color. AlN has better thermal capabilities but is also more expensive. Under is a full overview of both materials properties.
|Material - Aluminium%||%|
|Electrical||Dielectric Constant (1MHz)||-||9.0|
|Dielectric strenght||MV/m or KV/mm||>19|
|Mechanical||Density after Sintering (Bulk density)||g/cm3||3.30|
|Flexural Strength (3 point)||Mpa||300|
|Thermal||Coefficient of Thermal Expansion (CTE)||ppm/°C||3.16|
|Coefficient of Thermal Expansion (CTE) RT~500 °C||ppm/°C||4.02|
|Thermal Conductivity (25°C)||W/m‧K||170|
* Reflectivity test reference thickness of 0.5mm
The data shown is typical of commercially available material and is only offered for comparative purposes. The information shall not to be interpreted as absolute material properties nor does it constitute a representation or warranty for which we assume legal liability. User shall determine suitability of the material for the intended use and assumes all risk and liability whatsoever in connection therewith.
Frequently asked questions (faq)
Why do you claim aluminum nitride PCB have a superior thermal conductivity compared to metal core PCB (IMS) when you know Al (160 W/mK) and Cu (>200 W/mK) have an equal or even higher thermal conductivity compared to AlN (170 W/mK)?
Al & Cu have indeed high thermal performances but the dielectric layer which separates the metal core from the conductive traces will increase the thermal resistance significantly. Both the dielectric by itself (usually <3 W/mK thermal conductivity) as the interface resistance will reduce the total thermal performance. Depending on the thickness of this layer the thermal conductivity of the board can be reduced by 70-90%!
Aluminum Nitride (AlN), on the other hand, is a dielectric material and thus traces can be placed directly onto the board eliminating any loss in conductivity. Additionally, DK Thermal is using Copper (Cu – 396 W/mK) as well as Silver (Ag – 400 W/mK) metallization allowing the heat to spread even better over a large ceramic surface away from the sensitive component.
Are AlN PCBs expensive?
Yes and No. A simple PCB to PCB comparison will show that AlN circuits are for more expensive than standard or even metal core PCB. this is simply due to the high price of the material and higher processing cost. however, thanks to the better thermal properties, using AlN can lead to simplification of the full module (f.e. reduce the need for active cooling) and therefore decrease the total cost of the full electronics design.
Can AlN PCBs pass reflow and be used in SMT & pick-and-place machines?
Yes, both are possible
Can Aluminum Nitride PCBs be multi-layer?
At this moment we can only manufacture single and double layer designs.
How big can AlN boards be?
Our standard size is 110mmx110mm panels. Upon request, we can accommodate larger boards, please enquire.
Is there also a solder mask layer, surface finish and silkscreen possible?
Yes. The possibilities depend on the manufacturing process. Solder mask similar to other PCB can be applied in most cases, however, we do also offer a glass for high-temperature solutions which can be transparent or black.
Surface finish has a similar reasoning, however, for high-temperature applications, we offer only silver and gold plating.
Last but not least, applying silkscreen is no issue.
What should I take into account when designing circuits layouts for a ceramic board? What are your design rules?
You can download and see our complete design rules under Design & cost.