printed circuit boards make use of conductive and convective cooling as their primary methods. Radiated heat plays a much smaller role. Conduction is facilitated by the use of heat sinks, strategically placed metal parts and the use of thermally conductive adhesives to bond parts to the boards. In some cases, the boards are designed to also help dissipate heat.
Heat Sinks
Heat sinks are usually finned aluminum extrusions attached atop heat sensitive electronic devices such as microprocessors. Some power supply transistors may be attached to a heat sink with machine screws, with two leads projecting through holes. In this case, the heat sink is part of the circuit as it will be electrically isolated with insulators.
Metal Mounting Parts
Metal parts can be used for heat sinks. They may be part of the chassis, a sheet metal cover or a mounting bracket. One computer uses metal rails called wedgelocks to mount boards inside a welded aluminum chassis. Power supply transistors are attached to the circuit board with their metal heat dissipation tabs underneath the wedgelocks, supplying a thermal path to the chassis.
Thermally Conductive Adhesives
Metal parts used as heat sinks are electrically isolated from the surrounding circuitry and the unit's case, but they may use a thermally conductive adhesive to assist in heat transfer. This adhesive may be a paste or a tape. Maintaining parts within thermal limits is essential, so always check the manufacturer's specifications for the correct material when performing repairs.
Ground Planes
Some multi-layer printed circuit boards have a large ground plane -- a thick sheet of copper -- underlying thermally sensitive components. This is usually found inside the board rather than on the surface. It transfers heat very well, making soldering components through it a chore for technicians, but it also serves as a shield for radio frequency interference. A copper ground plane can handle large currents that would burn smaller traces.
