Useful Tips | How to use PCB design to improve heat dissipation

Latest update time：2020-10-23

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For electronic devices, a certain amount of heat will be generated when working, which will cause the internal temperature of the device to rise rapidly. If the heat is not dissipated in time, the device will continue to heat up, the device will fail due to overheating, and the reliability of the electronic equipment will decrease. Therefore, it is very important to perform good heat dissipation on the circuit board.

1. Add heat dissipation copper foil and use large area power ground copper foil.

According to the above figure, we can see that the larger the area of the copper connection, the lower the junction temperature

According to the above figure, it can be seen that the larger the copper area, the lower the junction temperature.

2. Thermal vias

Thermal vias can effectively reduce the junction temperature of devices and improve the temperature uniformity in the thickness direction of the single board, making it possible to adopt other heat dissipation methods on the back of the PCB. Through simulation, it is found that compared with no thermal vias, the thermal vias with a device thermal power consumption of 2.5W, a spacing of 1mm, and a center design of 6x6 can reduce the junction temperature by about 4.8°C, and the temperature difference between the top and bottom surfaces of the PCB is reduced from the original 21°C to 5°C. After the thermal via array is changed to 4x4, the junction temperature of the device increases by 2.2°C compared with 6x6, which is worthy of attention.

3. Exposing copper on the back of the IC reduces the thermal resistance between the copper and the air

4. PCB layout

Requirements for high power, heat sensitive devices.

a. Heat-sensitive devices are placed in the cold air area.

b. Place the temperature detection device in the hottest location.

c. The devices on the same printed circuit board should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with low heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed at the uppermost stream (entrance) of the cooling airflow, and devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) should be placed at the lowermost stream of the cooling airflow.

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

e. The heat dissipation of the printed circuit board in the equipment mainly depends on air flow, so when designing, it is necessary to study the air flow path and reasonably configure the components or printed circuit boards. When air flows, it always tends to flow to places with less resistance, so when configuring components on the printed circuit board, it is necessary to avoid leaving a large airspace in a certain area. The same problem should also be paid attention to when configuring multiple printed circuit boards in the whole machine.

f. Temperature-sensitive devices are best placed in the area with the lowest temperature (such as the bottom of the device). Never place them directly above heat-generating devices. It is best to stagger multiple devices on a horizontal plane.

g. Arrange the devices with the highest power consumption and the highest heat generation near the best heat dissipation position. Do not place devices with high heat generation in the corners and edges of the printed circuit board unless there is a heat dissipation device near it. When designing power resistors, choose larger devices as much as possible, and adjust the layout of the printed circuit board to ensure that there is enough heat dissipation space.

h. Component spacing recommendations:

Reference document: PCB heat dissipation technology analysis Jishifu

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