Temperature is a major design constraint for any system that generates heat. Even a system that is 90% efficient still has to dissipate 10% of its power as heat. Excessive heat can substantially reduce the operating life of lithium batteries and LEDs, and thermal runaway can require a system to be powered down or even cause it to fail.
A common approach to managing heat is through active cooling. The heat is transferred through the air in the system and mechanical measures such as fans dissipate the heat.
Fans, however, generate noise, consume power, increase cost, and lower reliability. Passive thermal management reduces heat by conducting it out of the system, typically by spreading it over part of a metal enclosure. Effective passive thermal management can eliminate the need for active cooling.
Too often, thermal management is left as a design for manufacturing consideration. The electrical design team’s primary focus is on functionality. They make sure the processor has enough performance and sufficient memory to meet real-time application requirements. With the current emphasis on small form factors and energy efficiency, size and power are part of their considerations. The design is then passed to the PCB designer, who lays out the board and takes into account issues like signal integrity, noise, and EMI.
Once the PCB is done, this “finished” design is passed to the mechanical engineer whose job it is to fit the board into a physical enclosure. In many designs, this is the first time that thermal management is seriously considered. With tight space constraints, time-to-market pressures, and limited budget remaining, mechanical engineers can find themselves with a real challenge to overcome.
