When you are looking for substrates for electronic circuits with a high thermal conductivity and a low expansion coefficient (CTE), ceramic PCB will be your preferred choice of material. Today ceramics are already widely used as substrates in many microelectronic components and power LED packages and more and more they are replacing entire printed circuit boards reducing complexity in design and manufacturing while increasing performance. Examples are Chip-on-board (COB) modules, High power circuits, proximity sensors, battery drivers for EVs, … .
Ceramics advantages over other printed circuit boards:
- Higher operating temperature up to 350ºC
- Lower expansion coefficient
- Good thermal properties
- Superior high frequency performance
- Lower system cost: reduces test, insertion, assembly
- Smaller package size due to integration
- Cost effective for dense package due to parallel processing of layers
- Hermetic packages possible, 0% water absorption
DK Thermal specializes in Alumina Oxide (Al2O3) and Aluminium Nitride boards (AlN) using thick film as well as direct bonded copper (DBC) and direct plated copper Technologies (DPC) to print the circuits.
- Alumina (Al2O3) is widely used because of its low cost. It is, however, a less good thermal conductor (24-28 W/mK) but still outperforms most IMS (metal core) PCB since it does not require a dielectric layer between circuits and core. If needed, thermal performance can be still enhanced using silver (Ag) filled vias. Boards are usually thicker (0.5mm-1.5mm). AluminumOxide can also be made transparent, click here for more info on transparent PCB.
- Aluminum Nitride (AlN) has far better thermal performance (>170 W/mK) but is also more expensive. Also here thermal performance can be further improved by Ag or Au traces and vias.
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. We advise copper in 1-2 layer applications from low to high volume applications. Silver is advised when going to multi-layer and only in medium to high volume due to the higher tooling costs. In case you are unsure what material to specify, please to not hesitate to contact us.
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.
Thanks to its dielectric and thermal conductive characteristics, components can be placed directly on ceramic boards allowing heat to flow through easier compared to FR4 and metal core boards. Furthermore, since (buried) vias are possible, multilayer boards can also be made making ceramic PCBs a true alternative for FR4/CEM3 and metal core PCBs.
For a full comparison with FR4/CEM3 and metal core boards, we refer to the table below.
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%||%||96% (more is possible)|
|Electrical||Dielectric Constant (1MHz)||-||9.8||9.0|
|Dielectric strenght||MV/m or KV/mm||>14||>19|
|Mechanical||Density after Sintering (Bulk density)||g/cm3||3.72||3.30|
|Flexural Strength (3 point)||Mpa||400||300|
|Thermal||Coefficient of Thermal Expansion (CTE)||ppm/°C||5.95||3.16|
|Coefficient of Thermal Expansion (CTE) RT~500 °C||ppm/°C||6.82||4.02|
|Thermal Conductivity (25°C)||W/m‧K||22||170|
* Reflectivity test reference thickness of 1mm * 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.
Why do you claim ceramic PCBs in AluminaOxide (Al2O3) have a good thermal conductivity compared metal core PCB (IMS) when you know Al (160 W/mK) and Cu (>200 W/mK) have a much higher thermal conductivity compared to Al2O3 (22 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 (<10 W/mK) the thermal conductivity of the board can be reduced by 70-90%!
Alumina 96% (Al2O3), 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 ceramic PCBs expensive?
While ceramic boards are usually more expensive then FR4 & CEM3 boards, the cost of thick film Al2O3 is in line with Al metal core PCBs and even below Cu metal core PCBs.
Can ceramic PCBs pass reflow and be used in SMT & pick-and-place machines?
Yes, both are possible.
Can ceramic PCBs be multi-layer?
Yes and we have experience in making ceramic circuits up to 10 layers
How big can ceramic boards be?
Our maximum standard size is 125mmx125mm or 5″x 5″ panels. Upon request, we can accommodate boards up to 180mm x 180mm (7″x 7″) or even larger.
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 in the top menu.
What is the difference between Thick film ceramics and LTCC?
Thick film ceramic boards are post fired which means vias, traces, stacking, etc… are only done after the board has been ‘baked’ already and is in its sturdy and hard form. On the other hand, LTCC or Low-Temperature Co-fired Ceramics are still in a relatively soft state when cavities, vias & holes are punched and traces are printed. This way, it is still possible to smooth & round inclinations so multi-shape and angled designs are possible. Only after this process, the board will be co-fired at a temperature of 900°C.