Apalis Carrier Board Design Guide
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4.3 Thermal Solution
In the datasheet of the according Apalis module, the operating temperature range can be found.
The actual maximum operation temperature depends on the cooling solution of the system and the
system work load. The numbers found in the datasheet are only a reference under ideal
conditions. The number that matters at the end is the SoC junction temperature, which can also be
found in the datasheet. The cooling solution needs to make sure that junction temperature remains
within its allowed boundaries over the required operation temperature range of the system.
The location and height of the SoC is not guaranteed to be the same between different Apalis
modules. Therefore, cooling solution may need to be optimized for the different modules.
Figure 68: Bottom Side of Heat Sink
For every type of Toradex Apalis module, an optimized heats sink is available. The heat sink can be
used as passive or active cooling solution. Passive means that the natural convection is used to
transport the heat from the surface to the air. The efficiency of the natural convection is dependent
on the housings and the environment, but it has no moving parts and does not produce additional
noise. If the passive cooling is not sufficient, a fan can be mounted on top of the heat sink. This
increases the efficiency dramatically. In order to reduce the noise of the fan, the speed of the fan
might be regulated according to the SoC temperature by using one of the free PWM signals.
Figure 69: Mounted Heat Sink
In order to guarantee good thermal conductivity between SoC and the heat sink required for
effective heat dissipation, pressure needs to be applied to the thermal interface material between
SoC and spreader. As the Apalis module PCB is only 1.2mm thick, adding pressure in the middle of
the board would cause undesired bending and flex, which could damage the module. To prevent
such bending, every Apalis module features a pad on the bottom side of the module. This pad
allows the addition of a support standoff between module and carrier board.
If a cooling system is used that applies force to the center area of the module PCB, it is strongly
recommended that the additional spacer be added under the module.