10 ways to dissipate heat from PCB!

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10 ways to dissipate heat from PCB! [Copy link]

For electronic devices, a certain amount of heat will be generated when working, causing 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 do a good job of heat dissipation on the circuit board. The heat dissipation of the PCB circuit board is a very important link, so what are the heat dissipation techniques of the PCB circuit board? Let's discuss it together.

The PCB materials currently widely used for heat dissipation through the PCB board itself are copper-clad/epoxy glass cloth substrate or phenolic resin glass cloth substrate, and there are also a small amount 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-generating components, it is almost impossible to expect the PCB resin to conduct heat. Instead, the 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 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 extensive use of surface-mount 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 components, and conduct or dissipate it through the PCB board.

PCB Layout

Heat-sensitive devices are placed in the cold wind area .

The temperature sensing device is placed at the hottest location .

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 (inlet) 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.

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.

The heat dissipation of the printed circuit boards 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.

Air always tends to flow to places with less resistance, so when placing components on a printed circuit board, avoid leaving a large airspace in a certain area. The same considerations apply to the placement of multiple printed circuit boards in a complete machine.

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. Multiple devices are best arranged in a staggered manner on a horizontal plane.

Place the devices with the highest power consumption and the highest heat generation near the best heat dissipation position. Do not place the devices with higher heat generation in the corners and around the edges of the printed circuit board unless there is a heat sink nearby.

When designing power resistors, choose larger devices as much as possible, and adjust the printed circuit board layout to allow enough heat dissipation space.

Component spacing recommendations:

Add heat sinks and heat conducting plates to high-heat generating devices. When there are a few devices in the PCB that generate a lot of heat (less than 3), you can add a heat sink or heat pipe to the heat generating devices . If the temperature still cannot be lowered, you can use a heat sink with a fan to enhance the heat dissipation effect.

When there are many heat generating devices (more than 3), a large heat dissipation cover (plate) can be used . It is a special heat sink customized according to the position and height of the heat generating devices on the PCB board, 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 .

For equipment using free convection air cooling, it is best to arrange the integrated circuits (or other devices) in a vertical or horizontal arrangement.

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

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.

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.

07

The heat dissipation of the printed circuit boards 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 a printed circuit board, avoid leaving large airspace in a certain area.

The same considerations should also be taken into account when configuring multiple printed circuit boards in a complete machine.

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. Multiple devices are best arranged in a staggered manner on a horizontal plane.

Place 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 nearby. When designing power resistors, choose larger devices as much as possible, and adjust the printed circuit board layout to allow enough heat dissipation space.

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.

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It is often difficult to achieve strict uniform distribution during the design process, but areas with too high power density must be avoided to prevent hot spots from affecting the normal operation of the entire circuit.

If conditions permit, it is necessary to conduct thermal performance analysis of printed circuits. For example, the thermal performance index analysis software module added to some professional PCB design software can help designers optimize circuit design.