Design Workable Thermal Management Solutions Into Your Next Product

DISCRETE MODULES AND THERMAL BARRIER
We can address hotspots on printedcircuit boards (PCBs) using discrete modules, strategically placing them near the source of heat. Metal traces, which can be several microns thick, can be stacked or interdigitated to provide highly conductive pathways for collecting heat from the underlying circuit and funneling that heat to the thermal bump. Additionally, adding thermal vias, i.e., copper filled vias, will be necessary to provide pathways for the dissipating heat.

Managing the heat flow in systems is also a problem for many manufacturers of mobile devices. Unlike electromagnetic energy, which designers can isolate and/or confine, heat is mechanical in nature and hence can flow in any direction. This may include flowing toward sensitive components such as LCDs and other delicate parts. One solution is to employ thermoelectrics to create a thermal barrier against the flow of this energy.

A thermal barrier creates a small temperature inversion that channels thermal energy away from the barrier and in a more desirable direction. Construction of a thermal barrier may consist of several discrete thermoelectric devices, however loosely spaced and powered only at a very low level (Fig. 5).

The overall design, the number of modules, their spacing, and the heat spreader materials and dimensions determine the characteristics of the thermal barrier. In most cases, a 3°C to 5°C temperature inversion is all that is necessary to cause the heat to flow away from a surface, in essence creating a mirror or thermal reflector. The thermal barrier can activate when the temperature of the board reaches a critical point, creating an on-demand thermal management solution.

SUMMARY
The use of thermal bumps and discrete devices to provide a thermal management solution does not obviate the need for system- level cooling or for a reasonable means of rejecting heat out of the system. Rather, it offers system design engineers a new set of tools with which to shape and enhance the performance of their system. Ultimately, the focus should be on cooling what you need to cool and nothing else and then managing the removal of this heat in a controlled fashion.