What are the detailed methods of PCB circuit board heat dissipation?
For electronic equipment, a certain amount of heat is generated during operation, which causes the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, the device will fail due to overheating, and the reliability of electronic equipment Performance will decrease. Therefore, it is very important to perform a good heat dissipation treatment on the circuit board. The heat dissipation of the PCB circuit board is a very important link, so what are the heat dissipation techniques of the PCB circuit board? Let's discuss it together.
1.Heat dissipation through the PCB board itself The currently widely used PCB sheet is copper-clad/epoxy glass cloth substrate or phenolic resin glass cloth substrate, and a small amount of paper-based copper-clad sheet is used. Although these substrates have excellent electrical performance and processing performance, they have poor heat dissipation. As a heat dissipation route for high heat-generating components, the PCB itself can hardly be expected to conduct heat from the resin of the PCB, but to dissipate heat from the surface of the component to the surrounding air. However, as electronic products have entered the era of miniaturization of components, high-density installation, and high-heat assembly, it is not enough to rely on the surface of components with very small surface area to dissipate heat. At the same time, due to the heavy 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 heat dissipation is to improve the heat dissipation capacity of the PCB itself in direct contact with the heating element. Conduct or emit.
2.High heat-generating devices plus heat sinks and heat-conducting plates. When a few devices in the PCB generate a large amount of heat (less than 3), heat sinks or heat-conducting tubes can be added to the heat-generating devices. When the temperature cannot be lowered, A radiator with a fan can be used to enhance the cooling effect. When there are more 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 in a large flat radiator Cut out the height of different components. Fasten the heat dissipation cover to the component surface, and contact each component to dissipate heat. However, due to the poor consistency of the components during assembly and welding, the heat dissipation effect is not good. Usually a soft thermal phase change thermal pad is added on the component surface to improve the heat dissipation effect.
3. For equipment that uses free convection air cooling, it is best to arrange the integrated circuits (or other devices) in a vertically long manner, or in a horizontally long manner.
4. Adopt reasonable wiring design to achieve heat dissipation. Because the resin in the plate has poor thermal conductivity, and the copper foil lines and holes are good conductors of heat, improving the copper foil residual rate and increasing the thermal conduction holes are the main means of heat dissipation. To evaluate the heat dissipation capacity of the PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the composite material composed of various materials with different thermal conductivity coefficients—the insulating substrate for PCB.
5. The devices on the same printed board should be arranged according to their heat generation and heat dissipation 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.) are placed in The uppermost stream of the cooling airflow (at the entrance), devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream of the cooling airflow.
6. In the horizontal direction, the high-power devices should be placed 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 should be placed as close as possible to the top of the printed board to reduce the temperature of these devices to other devices when working Impact.
7. The heat dissipation of the printed board in the device mainly depends on the air flow, so the air flow path should be studied in the design, and the device or the printed circuit board should be reasonably configured. When the air flows, it always tends to flow where the resistance is small, so when configuring devices on the printed circuit board, it is necessary to avoid leaving a large air space in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
8. The temperature-sensitive device is best placed in the lowest temperature area (such as the bottom of the device). Never place it directly above the heating device. Multiple devices are preferably staggered on the horizontal plane.
9. Arrange the device with the highest power consumption and the highest heat generation near the optimal heat dissipation position. Do not place devices with high heat generation at the corners and surrounding edges of the printed board unless heat dissipation devices are arranged near it. When designing the power resistor, choose a larger device as much as possible, and adjust the layout of the printed circuit board to make it have sufficient 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 temperature performance of the PCB surface uniform and consistent. It is often difficult to achieve strict uniform distribution in the design process, but it is necessary to avoid areas with too high power density to avoid hot spots that affect the normal operation of the entire circuit. If conditions permit, thermal efficiency analysis of printed circuits is necessary. For example, thermal efficiency index analysis software modules added in some professional PCB design software can help designers optimize circuit design.