How to Dissipate Heat from PCB?

What are the methods for PCB heat dissipation?

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[^1] treatment on the circuit board. Heat dissipation of PCB circuit boards is a very important link.

So what are the PCB circuit board heat dissipation techniques? Let's discuss it together below.

Heat dissipation through the PCB board itself. The widely used PCB board materials are copper-clad/epoxy glass cloth substrates[^2] or phenolic resin glass cloth substrates, and there are also a small number 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-heat 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 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 large-scale 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 problem is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heat-generating component, and conduct or dissipate it through the PCB board.

Add heat dissipation copper foil[^3] and use large area power ground copper foil

Thermal vias

Copper is exposed on the back of the IC to reduce the thermal resistance[^4] between the copper and the air

What are the techniques for heat dissipation layout?

1. Heat-sensitive devices are placed in the cold air zone.

2. Temperature detection devices are placed in the hottest position.

3. Devices on the same printed circuit board should be arranged according to their heat generation and heat dissipation 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.) are placed at the uppermost (inlet) of the cooling airflow, and devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the downstream of the cooling airflow.

4. In the horizontal direction, high-power devices are 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 are 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.

5. The heat dissipation of the printed circuit board in the equipment mainly depends on air flow, so when designing, the air flow path[^5] should be studied and the devices or printed circuit boards should be reasonably configured. When air flows, it always tends to flow to places with low resistance, so when configuring devices on the printed circuit board, avoid leaving a large airspace in a certain area. The same problem should also be noted when configuring multiple printed circuit boards in the whole machine.

6. 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 them directly above the heating device. Multiple devices are best arranged in a staggered manner on the horizontal plane.

7. Place the devices with the highest power consumption and the highest heat generation near the best heat dissipation position. Do not place devices with higher 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 make sure there is enough heat dissipation space when adjusting the printed circuit board layout.

8. Component spacing recommendations:

Tips for preventing high-heating components

When there are a few devices on the PCB that generate a lot of heat (less than 3), you can add a heat sink or heat pipe to the heat-generating device. When the temperature cannot be lowered, you can use a heat sink with a fan to enhance the heat dissipation effect.

When there are a large number of heat-generating devices (more than 3), you can use a large heat dissipation cover (plate), which is a special heat sink customized according to the position and height of the heat-generating device on the PCB, or a large flat heat sink with different component heights cut out.

The heat dissipation cover is buckled on the component surface as a whole, and contacts each component to dissipate heat. However, due to the poor height consistency of components during soldering, 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.

How to efficiently dissipate heat from PCB boards?

1. For equipment that uses free convection air cooling, it is best to arrange the integrated circuits (or other devices) in a longitudinal or transverse manner.

2. Use reasonable routing design to achieve heat dissipation. Since the resin in the board has poor thermal conductivity, and the copper foil lines and holes are good conductors of heat, increasing the copper foil surplus rate and increasing the thermal conductive 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 (9eq) of the insulating substrate for PCB, a composite material composed of various materials with different thermal conductivities.

3. 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.) are 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.) are placed at the lowest downstream of the cooling airflow.

4. 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.

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

6. Devices that are sensitive to temperature are best placed in the lowest temperature area (such as the bottom of the equipment), and never place it directly above the heating device. Multiple devices are best arranged in a staggered layout on the horizontal plane.

7. Arrange the devices with the highest power consumption and the highest heat generation near the best heat dissipation position. Do not place devices with higher 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 PCB layout to allow for sufficient heat dissipation space.

8. 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 it is important to avoid areas with too high power density to prevent overheating from affecting the normal operation of the entire circuit.

Conclusion

Effective PCB heat dissipation methods include thermal vias, copper cladding, strategic component layout for airflow optimization[^6], heatsinks, exposed copper pads, phase-change materials, proper spacing, and distributing high-power components near edges to prevent hotspots and enhance thermal management.

[^1]: Understanding effective heat dissipation methods is crucial for maintaining device reliability and performance. Explore this link for in-depth techniques.
[^2]: Learn about the properties and benefits of copper-clad substrates in PCB design to optimize heat management in electronics.
[^3]: Understanding heat dissipation copper foil can enhance your PCB design for better thermal management and performance.
[^4]: Exploring thermal resistance will help you grasp its impact on component efficiency and longevity in electronic designs.
[^5]: Learning about air flow path design can significantly improve the cooling efficiency of your electronic devices, ensuring optimal performance.
[^6]: Discover how optimizing component layout can improve airflow and thermal performance in printed circuit boards.