Electronic devices generate heat during operation, causing the internal temperature to rise rapidly. If this heat is not dissipated in time, the device will continue to heat up, causing components to fail due to overheating and reducing the reliability of the electronic device.
Therefore, effective heat dissipation for circuit boards is crucial. Heat dissipation is a very important aspect of PCB circuit boards, so let's discuss some PCB circuit board heat dissipation techniques.
01
Currently, the most widely used PCB materials for heat dissipation through the PCB board itself are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, with a small amount of paper-based copper-clad boards also used.
Although these substrates have excellent electrical and processing properties, they have poor heat dissipation. As a heat dissipation path for high-heat-generating components, it is almost impossible to rely on the PCB resin itself to conduct heat. Instead, heat is dissipated from the surface of the component to the surrounding air.
However, as electronic products have entered an era of miniaturized components, high-density assembly, and high-heat-generating assembly, relying solely on the surface of components with very small surface areas for heat dissipation is far from sufficient.
Meanwhile, due to the extensive use of surface mount components such as QFP and BGA, a large amount of heat generated by these components is transferred to the PCB board. Therefore, the best way to solve the heat dissipation problem is to improve the heat dissipation capacity of the PCB itself, which is in direct contact with the heat-generating components, so that the heat can be conducted away or dissipated through the PCB board.
▼Add heat dissipation copper foil and use large area power ground copper foil
▼Hot via
▼Exposing copper on the back of the IC reduces thermal resistance between the copper foil and the air.
Heat-sensitive components are placed in the cool air zone in the PCB layout.
The temperature sensing device is placed in the hottest position.
Devices on the same printed circuit board should be arranged in zones 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.) should be placed at the top of the cooling airflow (at the inlet), while devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) should be placed at the bottom of the cooling airflow.
In the horizontal direction, high-power devices are placed as close as possible to the edge of the printed circuit board to shorten the heat transfer path; in the vertical direction, high-power devices are placed as close as possible to the top of the printed circuit board to reduce the impact of these devices on the temperature of other devices when they are operating.
The heat dissipation of printed circuit boards inside the equipment mainly relies on airflow, so the airflow path should be studied during the design process, and the components or printed circuit boards should be configured reasonably.
Air always flows along the path of least resistance, so when placing components on a printed circuit board, it's important to avoid leaving large empty spaces in any one area. The same principle applies to the placement of multiple printed circuit boards in a complete machine.
Temperature-sensitive components should be placed in the coolest area (such as the bottom of the device). Never place them directly above heat-generating components. Multiple components should ideally be arranged in a staggered manner on a horizontal plane.
Place the components with the highest power consumption and heat generation near the best heat dissipation locations. Do not place high-heat-generating components in the corners or edges of the printed circuit board unless heat dissipation devices are arranged nearby.
When designing power resistors, choose larger components whenever possible, and ensure sufficient heat dissipation space when adjusting the printed circuit board layout.
Recommended component spacing:
02
When there are a few components on the PCB that generate a lot of heat (less than 3), a heat sink or heat pipe can be added to the heat-generating components. If the temperature still cannot be reduced, a heat sink with a fan can be used to enhance the heat dissipation effect.
When there are many heat-generating components (more than 3), a large heat sink (plate) can be used. This is a custom-made heat sink based on the position and height of the heat-generating components on the PCB, or it can be a large flat heat sink with different component heights cut out. The heat sink is placed over the component surface, making contact with each component to dissipate heat.
However, due to poor uniformity in component placement during soldering, heat dissipation is not ideal. A soft, phase-change thermal pad is typically added to the component surface to improve heat dissipation.
03
For equipment that uses free convection air cooling, it is best to arrange integrated circuits (or other devices) in a vertical or horizontal manner.
04
Achieving heat dissipation through reasonable trace design is crucial. Since the resin in the board material has poor thermal conductivity, while copper foil traces and holes are excellent conductors of heat, increasing the copper foil surplus and adding thermal vias are the main methods for heat dissipation. Evaluating the heat dissipation capacity of a PCB requires calculating the equivalent thermal conductivity (neq) of the insulating substrate for PCBs—a composite material composed of various materials with different thermal conductivityes.
05
Devices on the same printed circuit board should be arranged in zones 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.) should be placed at the top of the cooling airflow (at the inlet), while devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) should be placed at the bottom of the cooling airflow.
06
In the horizontal direction, high-power devices are placed as close as possible to the edge of the printed circuit board to shorten the heat transfer path; in the vertical direction, high-power devices are placed as close as possible to the top of the printed circuit board to reduce the impact of these devices on the temperature of other devices when they are operating.
07
The heat dissipation of printed circuit boards inside the equipment mainly relies on airflow, so the airflow path should be studied during the design process, and the components or printed circuit boards should be configured reasonably.
Air always tends to flow where there is less resistance, so when placing components on a printed circuit board, it is important to avoid leaving large empty spaces in any area.
The same issue should be considered when configuring multiple printed circuit boards in the whole machine.
08
Temperature-sensitive components should be placed in the coolest area (such as the bottom of the device). Never place them directly above heat-generating components. Multiple components should ideally be arranged in a staggered manner on a horizontal plane.
09
Place the components with the highest power consumption and heat generation near the best heat dissipation locations. Avoid placing high-heat-generating components in the corners and edges of the printed circuit board unless heat dissipation devices are provided nearby. When designing power resistors, choose larger components whenever possible, and ensure sufficient space for heat dissipation when adjusting the printed circuit board layout.
10
To avoid the concentration of hot spots on the PCB, power should be distributed as evenly as possible on the PCB board to maintain uniform and consistent surface temperature performance.
Achieving a strictly uniform power distribution during the design process is often quite difficult, but it is essential to avoid areas with excessively high power density to prevent hot spots from affecting the normal operation of the entire circuit.
If possible, it is essential to perform thermal performance analysis on printed circuit boards. For example, some professional PCB design software now includes thermal performance analysis modules, which can help designers optimize circuit designs.
