Knowledge

For electronic equipment, a certain amount of heat will be generated during operation, causing the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, and the device will fail due to overheating. The reliability of electronic equipment Performance will decrease.
Therefore, it is very important to handle the heat dissipation of the circuit board well. The heat dissipation of PCB circuit board is a very important link. So what are the heat dissipation techniques of PCB circuit board? Let’s discuss it together.

01

Heat dissipation through the PCB board itself. The currently widely used PCB boards are copper-clad/epoxy glass cloth base materials or phenolic resin glass cloth base materials, and there are also a small amount of paper-based copper-clad sheets.
Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation. As a heat dissipation path for high-heating 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 component 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 extensive 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 problem of heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating components, through the PCB board Conduct or radiate out.

▼Add heat dissipation copper foil and use large-area power supply ground copper foil

▼Thermal vias

▼The copper is exposed on the back of the IC to reduce the thermal resistance between the copper and the air

PCB layout
Heat-sensitive devices are placed in the cold air area.
The temperature detection device is placed in the hottest location.
Devices on the same printed board should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed in the cooling air flow. At the top of the cooling air flow (at the entrance), devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the bottom of the cooling air flow.
In the horizontal direction, high-power devices should be placed as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, high-power devices should be placed as close to the top of the printed board as possible to reduce the impact of these devices on the temperature of other devices when they are working. .
The heat dissipation of printed boards in equipment mainly relies on air flow, so the air flow path must be studied during design and the devices or printed circuit boards should be reasonably configured.
When air flows, it always tends to flow in places with low resistance, so when configuring devices on a printed circuit board, avoid leaving a large air space in a certain area. The same issue should also be paid attention to in the configuration of multiple printed circuit boards in the whole machine.
Devices that are more sensitive to temperature are best placed in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heating device. It is best to arrange multiple devices staggered on the horizontal plane.
Place the devices that consume the most power and generate the most heat near the best locations for heat dissipation. Do not place high-heat components in the corners and edges of the printed board unless a heat sink is arranged nearby.
When designing the power resistor, choose a larger device as much as possible, and make sure there is enough space for heat dissipation when adjusting the printed board layout.

Component spacing recommendations:

02

Add radiators and heat conduction plates to high-heating devices. When there are a few devices in the PCB that generate a large amount of heat (less than 3), you can add radiators or heat pipes to the heating devices. When the temperature cannot be lowered, you can use Radiator with fan to enhance cooling effect.
When there are a large number of heating devices (more than 3), a large heat dissipation cover (board) can be used. It is a special radiator customized according to the position and height of the heating device on the PCB board or placed on a large flat-panel radiator. Cut out the high and low positions of different components. Attach the heat dissipation cover to the component surface and make contact with each component to dissipate heat.
However, due to the poor consistency of the components during assembly and soldering, the heat dissipation effect is not good. Usually, a soft thermal phase change thermal pad is added to the component surface to improve the heat dissipation effect.

03

For equipment that uses free convection air cooling, it is best to arrange the integrated circuits (or other devices) vertically or horizontally.

04

Use reasonable wiring design to achieve heat dissipation. Since the resin in the board has poor thermal conductivity, and copper foil lines and holes are good conductors of heat, increasing the remaining rate of copper foil and adding thermal holes are the main means of heat dissipation. To evaluate the heat dissipation capability of PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the insulating substrate for PCB, which is a composite material composed of various materials with different thermal conductivity.

05

Devices on the same printed board should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed in the cooling air flow. At the top of the cooling air flow (at the entrance), devices with high heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the bottom of the cooling air flow.

06

In the horizontal direction, high-power devices should be placed as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, high-power devices should be placed as close to the top of the printed 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 printed boards in equipment mainly relies on air flow, so the air flow path must be studied during design and the devices or printed circuit boards should be reasonably configured.
When air flows, it always tends to flow in places with low resistance, so when configuring devices on a printed circuit board, avoid leaving a large air space in a certain area.
The same issue should also be paid attention to in the configuration of multiple printed circuit boards in the whole machine.

08

Devices that are more sensitive to temperature are best placed in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heating device. It is best to arrange multiple devices staggered on the horizontal plane.

09

Place the devices that consume the most power and generate the most heat near the best locations for heat dissipation. Do not place high-heat components in the corners and edges of the printed board unless a heat sink is arranged nearby. When designing the power resistor, choose a larger device as much as possible, and make sure there is enough space for heat dissipation when adjusting the printed board layout.

10

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 areas with too high power density must be avoided to avoid hot spots that may affect the normal operation of the entire circuit.
If possible, it is necessary to conduct thermal efficiency analysis of printed circuits. For example, the thermal efficiency index analysis software module added to some professional PCB design software can help designers optimize circuit design.