On the technique of heat dissipation of circuit board

1、 Heat dissipation mode of circuit board

1. Heat dissipation through PCB board itself

At present, the widely used PCB board is copper-clad / epoxy glass cloth or phenolic resin glass cloth, and a small amount of paper-based copper-clad board. Although these substrates have excellent electrical performance and processing performance, they have poor heat dissipation. As the heat dissipation way of high heating elements, it is almost impossible to rely on PCB resin to conduct heat, but to dissipate heat from the surface of the elements to the surrounding air. However, as electronic products have entered the era of miniaturization, high-density installation and high thermal assembly, it is not enough to rely on the surface of components with very small surface area for heat dissipation. At the same time, due to the extensive use of QFP, BGA and other surface mounted components, the heat generated by the components is largely transferred to the PCB board. Therefore, the best way to solve the heat dissipation problem is to improve the heat dissipation capacity of the PCB itself, which is in direct contact with the heating elements, and transmit or emit it through the PCB board.

2 high heating device with radiator and heat conducting plate

When there are a few devices in PCB with large heating capacity (less than 3), heat sink or heat conduction pipe can be added to the heating device. When the temperature can not be lowered, heat sink with fan can be used to enhance the heat dissipation effect. When there are more than 3 heating elements, a large radiator cover (board) can be used, which is a special radiator customized according to the position and height of the heating elements on the PCB board, or a large flat radiator with different elements in high and low positions. The heat dissipation cover is buckled on the surface of the component as a whole and contacts with each component to dissipate heat. However, due to the poor consistency of component assembly and welding, the heat dissipation effect is not good. Soft thermal phase change thermal pad is usually added on the surface of components to improve the heat dissipation effect.

For the equipment cooled by free convection air, it is better to arrange the integrated circuits (or other devices) in longitudinal or transverse way.

4. Adopt reasonable routing design to realize heat dissipation

Because the resin in the plate has poor thermal conductivity, and copper foil circuit and hole are good conductors of heat, it is the main means to improve the residual rate and increase the heat conduction hole of copper foil.

To evaluate the thermal dissipation capacity of PCB, it is necessary to calculate the equivalent thermal conductivity (9eq) of the insulating substrate for PCB, which is composed of various materials with different thermal conductivity.

5 the devices on the same printed board shall be arranged according to the heat output and heat dissipation degree as far as possible. The devices with small heat or poor heat resistance (such as small signal transistors, small scale integrated circuits, electrolytic capacitors, etc.) shall be placed at the top flow (entrance) of cooling air flow. The devices with high heating capacity or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) shall be placed at the downstream of cooling air flow .

6 in the horizontal direction, the high-power devices shall be arranged as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, the high-power devices shall be arranged as close as possible to the printed board, so as to reduce the influence of these devices on the temperature of other devices when they work.

The heat dissipation of printed boards in equipment mainly depends on air flow. Therefore, the air flow path should be studied in design and devices or PCB should be reasonably configured. Air flow tends to flow in places with small resistance, so when the devices are configured on PCB, it is necessary to avoid leaving a larger airspace in a certain area. The same problems should be paid attention to in the configuration of multiple printed circuit boards in the whole machine.

8 the temperature sensitive devices should be placed in the lowest temperature area (such as the bottom of the equipment), and do not put it directly above the heating device. The multiple devices should be staggered on the horizontal plane.