Thermal Imaging
The following picture shows a thermogram of the top side of a Picolo U4 H.264 PCI-104 RH.
The board was operating in the following conditions:
- Full processing load
- Without forced airflow in an ambient temperature of 25°C
- Horizontal mount (natural air convection is perpendicular to the board plane)
- On top of PCI-104 stack composed of 2 items:
- A Eurotech ISIS CPU module with an Intel Atom processor
- A single Picolo U4 H.264 PCI-104 RH module
The position of U1, U3, U4 are the main power contributors, and the on-board temperature probe "t°" is added to the picture.
The right side of the picture shows the calibrated temperature scale in °C.
The thermogram shows that:
- The hottest components are reaching case temperatures as high as 80°C, namely 55°C above the ambient air temperature.
- Most of the heat is produced at the center of the module; the hottest components are U1, U3, and U4.
- The heat is spread around by conduction into the printed circuit board material. The temperature decreases progressively from the board center to the boundaries of the printed circuit board.
Heat Production
At full processing load, the board produces typically 6 Watts (6.8 Watts max) of heat power.
The following table shows the power contribution of each of the hottest components:
Reference |
Power dissipation (Watt) |
Relative contribution (% total power) |
U1 |
4,00 |
67% |
U3 |
0,63 |
10% |
U4 |
0,63 |
10% |
Other components |
0,75 |
12% |
Total power |
6,00 |
100% |
Note. U1, U3, and U4 contribute together for 88% of the total power.
Board Thermal Requirements
The fundamental thermal requirement is: "The junction temperature of all integrated circuits must be kept below the max limit".
With reference to thermogram, the most critical components are U1, U3, U4. The requirements for these components are:
- The maximum junction temperature of U1 may not exceed 125°C.
- The maximum junction temperature of U2, and U3 may not exceed 100°C.
Note that the junction temperatures cannot practically be measured, these requirements are replaced by the following requirements that are easily verified:
- The board temperature measured by the on-board temperature sensor may not exceed 95°C (203°F).
- The heatsink has to drain 4W of heat power, and its temperature measured at its hottest point may not exceed 90°C.
- The interface between the critical components and the heatsink uses a thermal pad with better or equal characteristic than the one specified hereafter in Using Off-The-Shelf Footprint Compatible Heatsinks.
