Meaning
Physical area allocated on a printed circuit board facilitates the transfer of heat from high power components to the surrounding environment or a cooling structure. A thermal dissipation footprint includes the copper pads, thermal vias, secondary planes and surface finishes that act as a heat sink for an integrated circuit. Effective management of this area prevents component overheating and ensures long term reliability of the assembly.
The size and shape of the footprint depend on the power rating of the device and the available airflow.
Heat Transfer
Conduction through the board material is the primary method of moving heat away from surface mount components. The thermal dissipation footprint utilizes large areas of copper to spread the heat laterally before it is transferred to the air or an external chassis. Adding thermal vias connects the surface pad to internal ground planes, which increases the effective volume of the heat sink.
This vertical path reduces the thermal resistance between the component and the board.
Layout Constraint
Competing requirements for signal routing and power delivery often limit the space available for cooling on a high density design. A thermal dissipation footprint must be large enough to keep the junction temperature within the manufacturer limits while not interfering with adjacent high speed traces. Designers use thermal simulation tools to predict the temperature distribution across the board under various load conditions.
If the footprint is too small, the component may throttle its performance or fail prematurely. Calculations must account for the worst case ambient temperature and the maximum power consumption of the device.
Material Selection
Thermal conductivity of the dielectric material and the thickness of the copper layers influence the efficiency of the cooling path. Using a thermal dissipation footprint on a board with heavy copper or a metal core provides superior heat management for power electronics. The choice of solder and thermal interface materials also impacts the total thermal resistance of the assembly.
Engineers specify these parameters to meet the thermal budget.
