Knowledge

For electronic equipment, a certain amount of heat will be generated during operation, causing the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, and the device will fail due to overheating. The reliability of electronic equipment Performance will decrease. Therefore, it is very important to handle the heat dissipation of the circuit board well. The heat dissipation of the circuit board is a very important link.

Optimized design techniques for circuit board heat dissipation

1. Dissipate heat through the PCB board itself

The currently widely used PCB boards are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, and there are also a small amount of paper-based copper-clad boards. Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation. As a heat dissipation path for high-heating components, it is almost impossible to expect the PCB resin itself to conduct heat, but to dissipate heat from the surface of the component to the surrounding air. However, as electronic products have entered the era of component miniaturization, high-density installation, and high-heat assembly, it is not enough to rely solely on the surface of components with very small surface areas to dissipate heat. At the same time, due to the extensive use of surface-mounted components such as QFP and BGA, the heat generated by the components is transferred to the PCB board in large quantities. Therefore, the best way to solve the problem of heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating component, through the PCB board Conduct or radiate out.

2. High-heating devices plus radiators and heat conduction plates

When there are a few devices in the PCB that generate a large amount of heat (less than 3), a radiator or heat pipe can be added to the heating device. When the temperature cannot be lowered, a radiator with a fan can be used to enhance heat dissipation. Effect. When there are a large number of heating devices (more than 3), a large heat dissipation cover (board) can be used. It is a special radiator customized according to the position and height of the heating device on the PCB board or placed on a large flat-panel radiator. Cut out the high and low positions of different components. Attach the entire heat dissipation cover to the component surface and make contact with each component to dissipate heat. However, due to the poor consistency of the components during assembly and soldering, the heat dissipation effect is not good. Usually, a soft thermal phase change thermal pad is added to the component surface to improve the heat dissipation effect.

3. For equipment using free convection air cooling, it is best to arrange the integrated circuits (or other devices) vertically or horizontally.

4. Use reasonable wiring design to achieve heat dissipation

Since the resin in the board has poor thermal conductivity, and copper foil lines and holes are good conductors of heat, increasing the remaining rate of copper foil and adding thermal holes are the main means of heat dissipation. To evaluate the heat dissipation capacity of PCB, it is necessary to calculate the equivalent thermal conductivity of the insulating substrate for PCB, which is a composite material composed of various materials with different thermal conductivity.

5. Devices on the same PCB should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed in cooling In the uppermost part of the airflow (at the entrance), devices with high calorific value or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream part of the cooling airflow.

6. In the horizontal direction, high-power devices should be placed as close to the edge of the PCB board as possible to shorten the heat transfer path; in the vertical direction, high-power devices should be placed as close to the top of the PCB board as possible to reduce the impact of these devices on the temperature of other devices when they are working. .

7. The heat dissipation of the PCB board in the equipment mainly relies on air flow, so the air flow path must be studied during design and the devices or printed circuit boards should be reasonably configured. When air flows, it always tends to flow in places with low resistance, so when configuring devices on a printed circuit board, avoid leaving a large air space in a certain area. The same issue should also be paid attention to in the configuration of multiple printed circuit boards in the whole machine.

8. Devices that are sensitive to temperature are best placed in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heating device. It is best to arrange multiple devices staggered on the horizontal plane.

9. Place the devices with the highest power consumption and heat generation near the best heat dissipation locations. Do not place high-heat components in the corners and edges of the PCB unless there is a heat sink arranged nearby. When designing the power resistor, choose a larger device as much as possible, and adjust the PCB board layout to allow enough heat dissipation space.

10. Avoid the concentration of hot spots on the PCB, distribute the power evenly on the PCB as much as possible, and keep the PCB surface temperature performance uniform and consistent. It is often difficult to achieve strict uniform distribution during the design process, but areas with too high power density must be avoided to avoid hot spots that may affect the normal operation of the entire circuit.
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