Cooling electronic boards can be a huge challenge, especially where powerful systems need to be ready for fanless operation. Dissipating heat using a purely mechanical coupling is expensive and consumes valuable space, not to mention that the boards need to be specially designed for this cooling concept from the start. How to choose the right cooling method? These questions could help to find the answer.

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February 8, 2018
5 Things to Know about
Thermal Management for Embedded Computing

2. 2
Thermal Management for Embedded Computing
Cooling electronic boards can be a huge challenge, especially where powerful
systems need to be ready for fanless operation. Dissipating heat using a purely
mechanical coupling is expensive and consumes valuable space, not to mention
that the boards need to be specially designed for this cooling concept from the
start.
How to choose the right cooling method? These questions could help to find the
answer.
1: How much heat can be transferred from my device?
2: What is convection cooling?
3: What is conduction cooling?
4: How to integrate appropriate cooling into 19”-systems?
5: Is conduction cooling for existing boards possible?

3. How much Heat can be Transferred from my Device?
The heat flow that results from a temperature difference is responsible for the
transfer of any heat. The bigger the temperature difference and the space
available, the bigger the heat flow. Additionally, it depends on the thermal
conductivity, a constant that depends on the material, it’s surface, and thickness.
Every layer of material of a finite thickness adds to the total thermal resistance
depending on its material and surface. For an IC, for instance, this is the package
filling, the heat conducting film, and the heat sink. Obviously, the higher the
thermal conductivity of the layers involved in the transfer is, the more efficient is
the cooling.

4. What is Convection Cooling?
This type of heat transfer is the easiest method to cool board assemblies. It is done
by guiding an air flow along the surface to be cooled.
While the mechanical set-up is simple, there are some facts that may turn out to
be serious drawbacks, depending on the application. With flowing air, impurities
and liquids can find their way into the device, and can do damage. Complex
filtering equipment can reduce this risk, but on the other hand they create the
need for maintenance during the device's lifecycle. Cooling fans are also
components that have a limited lifetime, and their failure may lead to a total loss of
some electronic components.

5. lhhWhat is Conduction Cooling?
This technology optimizes the thermal contact to conduct the heat from the
source to the outer wall of the enclosure. This makes the enclosure itself a heat
radiator. Suitable measures must be taken to minimize the thermal transfer
resistance from the electronic component to be cooled to the enclosure wall.
On the one hand, this is ensured by choosing the right materials. Aluminum
and copper are proven materials here.
On the other hand, the boards inside the enclosure need to be placed in the
right way, and the heat-conducting cooling blocks need to have such masses
that optimum heat transport is guaranteed.
The gradient between the inner and outer
temperature follows the rules already
described: the cooler the outer enclosure
surface, and the larger it is, the smaller the
total thermal resistance of the
arrangement.

6. How to Integrate Appropriate Cooling into 19”-
Systems?
While conventional conduction cooling is useful for individual PCBs, 19” racks
with multiple boards preclude the cards’ surfaces to connect directly to the
enclosure wall.
System designers need to find alternative methods to get the heat out of the
system, such as building upon the principles of conduction cooling.
One implementation of this design is an aluminum board assembly that fits over
the critical heat areas, essentially extending the overall conduction-cooling
principles. Another way is using the actual component contact surfaces on the
PCB to transfer heat through additional copper layers inside the PCB.
Of course, both impact the available surface for component placement, and
determine the number of copper layers, so these methods need to be
undertaken at the onset of PCB design.

7. Is Conduction Cooling for Existing Boards Possible?
If we accommodate for slightly more rack space than required for traditional
boards, it can be done. By using the guide rail area as an extension of the
conduction-cooling method, the designer can clamp the PCB to an aluminum
frame, which totally encloses the card. Even components at the bottom side can
be thermally coupled to the frame, resulting in exceptional heat management.
Standard 3U cPCI boards can be installed in a special rack system and operate
without convection cooling. This way, a card can host more functionality because
the cooling infrastructure does not take away precious space.
➢ Learn more about rugged
computing at MEN

8. www.men.de/competencies/rugged-computing/
www.menmicro.com/competencies/rugged-computing/
www.men-france.fr/competencies/rugged-computing/