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Advantech SOM-ETX Design Guide
8.2 Thermal Interface Material
It is important to understand and consider the impact the interface between the
processor and heatsink base has on the overall thermal solution. Specifically, the
bond line thickness, interface material area, and interface material thermal
conductivity must be selected to optimize the thermal solution. It is important to
minimize the thickness of the thermal interface material, commonly referred to as the
bond line thickness. A large gap between the heatsink base and processor die yields
a greater thermal resistance. The thickness of the gap is determined by the flatness
of both the heatsink base and the die, plus the thickness of the thermal interface
material (i.e., thermal grease), and the clamping force applied by the heatsink
attachment method. To ensure proper and consistent thermal performance, the
thermal interface material (TIM) and application process must be properly designed.
Alternative material can be used at the users' discretion. The entire heatsink
assembly, including the heatsink, attachment method, and thermal interface material,
must be validated together for specific applications.
8.3 Attachment Method of Thermal Solution
The thermal solution can be attached to the motherboard in a number of ways. The
thermal solutions have been designed with mounting holes in the heatsink base. A
plastic rivet is currently in development that can be used to fasten smaller heatsinks.
For larger and heavier heatsinks, a fastening system consisting of screws, springs,
and secured with a nut should be used. The entire heatsink assembly must be
validated together for specific applications, including the heatsink, attach method,
and thermal interface material.
8.4 Grounding Issues
The mounting holes on all Advantech SOM-ETX CPU modules are connected to
digital circuit ground (GND) for improved EMC performance. Using conductive
screws and distance keepers will also connect the heat spreader and attached heat
sink to GND. In some applications the heat sink or heat spreader will be directly
screwed with the inner surface of the chassis. In some cases, however, it may not be
desirable to have a direct connection of circuit ground (GND) and chassis ground
through the heat sink and / or heat spreader. System designers should take this into
account when defining system grounding.
8.5 Air intake clearance and Airflow of Heatsink
The heatsink were designed to maximize the available space within the volumetric
keep-out zone. These heatsinks must be oriented in a specific direction relative to the
processor keep-out zone and airflow. In order to use this design, the processor must
be placed on the PCB in an orientation so the heatsink fins will be parallel to the
airflow.
Chapter 8 Heat Sink Recommended Design
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