For electronic equipment, the work will produce a certain amount of heat, so that the internal temperature of the equipment rises 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 reliable performance of the electronic equipment will decline. Therefore, it is very important to perform a good heat dissipation treatment on the circuit board. The heat dissipation of PCB circuit board is a very important link, so what is the heat dissipation skill of PCB circuit board, let's discuss it together.
1. through the PCB board itself heat dissipation is currently widely used PCB board is copper-coated/epoxy glass cloth substrate or phenolic resin glass cloth substrate, there is a small amount of paper-based copper-coated sheet.
Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation, and as a heat dissipation pathway for high-heating components, they can hardly be expected to conduct heat by the PCB itself, 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 only on the surface of a very small surface area to dissipate heat. At the same time, due to the large use of surface mounted components such as QFP and BGA, the heat generated by the components is transmitted 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, which is transmitted or distributed through the PCB board. The PCB layout is as follows:
a. the heat sensitive device is placed in the cold air area.
b. the temperature detection device is placed in the hottest position.
c. the devices on the same printed board should be arranged as far as possible according to the size of its heat and heat dissipation degree, small heat or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) placed in the most upstream of the cooling air flow (entrance), Devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the downstream of the cooling stream.
d. in the horizontal direction, the high-power devices are arranged as close as possible to the edge of the printed board in order to shorten the heat transfer path; In the vertical direction, the high-power devices are arranged as close as possible to the printed board, in order to reduce the impact of these devices on the temperature of other devices when they work.
e. the heat dissipation of the printed board in the equipment mainly depends on the air flow, so the air flow path should be studied in the design, and the device or printed circuit board should be reasonably configured. When the air flows, it always tends to flow where the resistance is low, so when configuring the device on the printed circuit board, it is necessary to avoid leaving a large airspace in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
f. more temperature-sensitive devices are best placed in the lowest temperature area (such as the bottom of the device), do not put it above the heating device, multiple devices are best staggered layout on the horizontal plane.
g. arrange the device with the highest power consumption and the largest heat dissipation near the best location for heat dissipation. Do not place devices with high heat in the corners and edges of the printed board, unless a cooling device is arranged near it. When designing the power resistance, choose a larger device as much as possible, and adjust the layout of the printed board so that it has enough space for heat dissipation.
h. component spacing suggestion:
2. high heating device with radiator, heat conduction plate when the PCB has a few devices with large heat (less than 3), you can add a radiator or heat conduction tube on the heating device, when the temperature can not be lowered, you can use a radiator with a fan to enhance the heat dissipation effect.
When the amount of heating devices is large (more than 3), a large heat shield (plate) can be used, which is a special radiator customized according to the position and height of the heating device on the PCB board, or a large flat radiator to cut out the height of different components. The heat shield is fastened on the component surface as a whole, and the heat is dissipated by contact with each component. However, due to the poor consistency of the components during installation and welding, the heat dissipation effect is not good. Usually add a soft thermal phase change thermal pad on the surface of the component to improve the heat dissipation effect.
3. for the use of free convection air cooling equipment, it is best to arrange the integrated circuit (or other devices) according to the longitudinal length, or according to the transverse length.
4. the use of reasonable wire design to achieve heat dissipation because the resin in the plate has poor thermal conductivity, and the copper foil line and hole are good conductors of heat, so improving the copper foil residual rate and increasing the heat conduction hole is the main means of heat dissipation. To evaluate the heat dissipation capacity of PCB, it is necessary to calculate the equivalent thermal conductivity (9 eq) of the PCB insulating substrate composed of various materials with different thermal conductivity.
5. the devices on the same printed board should be arranged as far as possible according to the size of its heat and the degree of heat dissipation, small heat or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) placed in the most upstream of the cooling air flow (entrance), Devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the downstream of the cooling stream.
6. In the horizontal direction, the high-power devices are arranged as close as possible to the edge of the printed board in order to shorten the heat transfer path; In the vertical direction, the high-power devices are arranged as close as possible to the printed board, in order to reduce the impact of these devices on the temperature of other devices when they work.
7. the heat dissipation of the printed board in the equipment mainly depends on the air flow, so the air flow path should be studied in the design, and the device or printed circuit board should be reasonably configured. When the air flows, it always tends to flow where the resistance is low, so when configuring the device on the printed circuit board, it is necessary to avoid leaving a large airspace 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 device is more sensitive to temperature is best placed in the lowest temperature area (such as the bottom of the device), do not put it above the heating device, multiple devices are best staggered layout on the horizontal plane.
9. the device with the highest power consumption and the largest heat is arranged near the best location for heat dissipation. Do not place devices with high heat in the corners and edges of the printed board, unless a cooling device is arranged near it. When designing the power resistance, choose a larger device as much as possible, and adjust the layout of the printed board so that it has enough space for heat dissipation.
10. Avoid the concentration of hot spots on the PCB, as far as possible to evenly distribute the power on the PCB board, and maintain the uniform and consistent PCB surface temperature performance. 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.
English
Chinese