PCB News - PCB board heat dissipation skills

For electronic equipment, there will be a certain amount of heat when working, so that the internal temperature of the equipment rises rapidly. If the heat is not emitted in time, the equipment will continue to heat up, the device will fail because of overheating, and the reliable performance of electronic equipment will decline.

Therefore, it is very important to conduct a good heat dissipation treatment for 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. Heat dissipation through PCB board itself At present, PCB board widely used is copper/epoxy glass cloth base material or phenolic resin glass cloth base material, and a small amount of paper copper coated board.

Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation. As a way of heat dissipation for high-heating components, heat can hardly be expected to be transmitted by the RESIN of the PCB itself, but heat dissipation from the surface of the components to the surrounding air.

However, as electronic products have entered the era of component miniaturization, high-density installation and high thermal assembly, it is not enough to dissipate heat only by the surface of components with very small surface area.

At the same time, due to the large use of surface mounted components such as QFP and BGA, the heat generated by 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 directly in contact with the heating element, and conduct or emit out through the PCB board.

PCB layout

a. Heat sensitive devices should be placed in the cold wind zone.

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 heat and heat dissipation partition, small heat or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) on the cooling air flow of the highest (entrance), High heat or heat resistant devices (such as power transistors, large-scale integrated circuits, etc.) are placed in the most downstream of the cooling airflow.

d. In the horizontal direction, the high-power devices should be arranged as close as possible to the edge of the printed board to shorten the heat transfer path; In the vertical direction, high-power devices are 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.

e. The heat dissipation of the printed board in the equipment mainly depends on air flow, so it is necessary to study the air flow path and reasonably configure devices or printed circuit boards in the design. Air flow always tends to flow where resistance is small, so when configuring devices on printed circuit boards, avoid having a large airspace in a certain area. The configuration of multiple printed circuit boards in the whole machine should pay attention to the same problem.

f. the temperature sensitive device is best placed in the lowest temperature area (such as the bottom of the device), do not put it on the heating device is above, the best multiple devices are staggered layout on the horizontal plane.

g. Place the device with the highest power consumption and the highest heat dissipation near the best heat dissipation position. Do not place hot components in the corners and edges of the printed board unless there is a cooling device near it. In the design of the power resistance as large as possible to choose a larger device, and in the adjustment of the printed board layout so that there is enough space for heat dissipation.

h. Recommended spacing of components:

2. When a few components in the PCB have high heat (less than three), heat sink or heat conduction tube can be added to the heating device. When the temperature cannot be lowered, a heat sink with a fan can be used to enhance the heat dissipation effect. When the number of heating devices is large (more than 3), a large heat sink (plate) can be used. It 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 different component height position. The heat dissipation cover is buckled on the component surface as a whole, and the heat dissipation is in contact with each component. However, the heat dissipation effect is not good because of the poor consistency of components. Soft thermal phase change pad is usually added on the surface of the component to improve the heat dissipation effect.

3. For equipment cooled by free convection air, it is best to arrange the integrated circuits (or other devices) longitudiously or longitudiously.

4. Due to the poor thermal conductivity of the resin in the plate, and copper foil lines and holes are good heat conductors, so improving the residual rate of copper foil and increasing heat conduction holes is the main means of heat dissipation.

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

5. Devices on the same printed board should be arranged as far as possible according to the size of heat and heat dissipation partition, small heat or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) on the cooling air flow of the highest (entrance), High heat or heat resistant devices (such as power transistors, large-scale integrated circuits, etc.) are placed in the most downstream of the cooling airflow.

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, high-power devices are 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.

7. The heat dissipation of the printed board in the equipment mainly depends on air flow, so it is necessary to study the air flow path and reasonably configure the device or printed circuit board during the design.

Air flow always tends to flow where resistance is small, so when configuring devices on printed circuit boards, avoid having a large airspace in a certain area. The configuration of multiple printed circuit boards in the whole machine should 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), do not put it on the heating device is directly above, the best multiple devices are staggered layout on the horizontal plane.

9. The device with the highest power consumption and the highest heat is arranged near the best heat dissipation position. Do not place hot components in the corners and edges of the printed board unless there is a cooling device near it.

In the design of the power resistance as large as possible to choose a larger device, and in the adjustment of the printed board layout so that there is enough space for heat dissipation.

10. Avoid concentration of hot spots on PCB, distribute power evenly on PCB board as much as possible, and keep PCB surface temperature performance 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, so as not to affect the normal operation of the whole circuit.

If possible, it is necessary to analyze the thermal performance of printed circuit boards, such as the thermal performance index analysis software module added to some Zhuan PCB design software, which can help designers optimize the circuit design.