CeramCool® principle and function

The higher the Power Density, the more efficient the ceramic Cooling System

Chip-on-heat-sink on the metalized surface of CeramCool® heat-sinks makes it possible to achieve an extremely compact design for the entire cooling system. Using ceramic as the material for the heat-sink ensures outstanding thermal conductivity and electrical insulation; the closer it is used to a source of heat, the greater the cooling advantage it offers.

Heat-sensitive semi-conductor components are often mounted onto standard substrates. They need to offer suitable thermal conductivity in addition to electrical insulation. The result is often a “sandwich component” with multiple layers made of different materials. Each layer introduces its own set of risks, thereby restricting thermal conductivity. With CeramCool®, however, the substrate is the heat-sink because this solution uses advanced ceramics such as alumina or aluminum nitride.

Chip-on-Heatsink Technology

Powermodule with Chip-on-Heatsink
Zth = 0.268 k/W*

* Examination done by Fraunhofer IISB, Nuremberg


Conventional structure of a Powermodule:
Zth = 0.55 k/W*

* Examination done by Fraunhofer IISB, Nuremberg

Ceramics combine two essential properties: electrical insulation and thermal conductivity. They offer good electromagnetic compatibility and have a thermal expansion coefficient close to that of semiconductor materials. Unlike other materials, ceramics feature the same thermal expansion coefficient and thermal conductivity in all directions. Moreover, ceramics are watertight and UV and corrosion-resistant.

The simplified design combined with the direct, permanent bonding between heat-sensitive electronic components and the CeramCool® surface – chip-on-heat-sink – create the ideal operating conditions.

Worth knowing:

CeramCool® Chip-on-Heat-Sink

CeramTec developed chip-on-heat-sink as a revolutionary process for mounting a heat source such as an LED or power semi-conductor directly onto a metalized heat-sink via soldering or Ag sintering. This achieves an optimum thermal connection with the coolant (air or liquid).

CeramCool® Materials

CeramTec has two materials at its disposal for manufacturing CeramCool® heat-sinks that have had a proven track record in the electronics industry for many years: Rubalit® aluminum oxide (Al2O3) and Alunit® aluminum nitride (AlN).

CeramCool® Rubalit® Al2O3 Alunit® AlN
Honeycomb Cooler
Box Cooler
Cell Cooler
Fin Cooler
Material Properties Unit Rubalit® 708S Rubalit® 710 Alunit®
Material class
DIN VDE 0335
C795 96% Al2O3 C799 99,6% Al2O3 AlN
Surface roughness Ra μm ≤ 0.8 ≤ 0.1 ≤ 0.6
Water absorption capacity % ≤ 0.1 ≤ 0.1 ≤ 0.1
Flexural strength [S0]
Dual-ring method
0,63 mm
Substrate thickness
MPa ≥ 450 ≥ 420 ≥ 320
Thermal conductivity 20°C W/mK ≥ 22 ≥ 26 ≥ 170
Breakthrough voltage KV/mm ≥ 15 ≥ 15 ≥ 15
Volume resistivity 20°C Ohm x cm ≥ 1013 ≥ 1013 ≥ 1012
Density g/cm3 ≥ 3.73 ≥ 3.86 ≥ 3.23

CeramCool® Liquid Cooling Performance Comparison

To prove the performance capability of the CeramCool® principle in liquid-cooled systems, a directly metalized heat-sink (chip-on-heat-sink) went head to head with a conventional liquid cooler with a soldered-on DCB. During an exhibition, identical load current was applied to both cooling solutions’ IGBTs until a constant temperature was reached. Then the cool down curve was measured. The result: With the same power supplied, ΔT – and thus the thermal resistance – in the CeramCool® system design was only half that of a conventionally designed system.

Comparison: Chip-on-Heatsink/Conventional structure of a Powermodule (Pin = 100 W)

This makes CeramCool® Liquid Cooling one of the most efficient and reliable liquid cooling systems on the market. No other design can achieve this and still assure such a long lifetime. The ceramic heat-sink is perfectly electrically insulated and inert. It can be populated with electrical circuits and advanced components without creating any thermal barriers This ceramic system’s efficiency grows with the power density.

CeramCool® Air Cooling Performance Comparison

A fin heat-sink was optimized for 4W cooling and used as a basis for comparison in order to prove the performance capability of the CeramCool® principle in air-cooled systems. The result: The total thermal resistance of the ceramic Rubalit® design is at least 13% better than that of an aluminum assembly with an identical design. Using Alunit® even helped CeramCool® achieve a minimum improvement of 31%.

CeramCool® geometry for 4W cooling. Rubalit® improves the total thermal resistance Rtt for the assembly by at least 13% compared to aluminum, and Alunit® can even deliver an improvement of 31%!

13% better performance
Rtt= 11.0 K/W
Max. temp. heat slug 59,7°C

31% better performance
Rtt= 8.7 K/W
Max. temp. heat slug 51,3°C

Aluminium and PCB
Rtt= 12.7 K/W
Max. temp. heat slug 65,9°C

Air-cooled CeramCool® fin heat-sinks have a proven track record in applications with less extreme power densities, such as LED modules or in CPV photovoltaics with low concentration factors.

Recommended Contacts

Please click on the button “Contacts” to the right, to get a list with the personal and direct responsible contacts within the CeramTec Group.