10 ways to dissipate heat from PCB!

For electronic equipment, work will produce a certain amount of heat, so that the internal temperature of the device rises rapidly, if not in a timely manner the heat will be emitted, the device will continue to heat up, the device will fail due to overheating, the reliability of the electronic equipment will decline.

Therefore, it is very important to carry out a dissipate heat from PCB, PCB circuit board cooling is a very important part of the PCB circuit board cooling skills is how, let’s discuss.

1.Through the PCB board itself heat dissipation is currently widely used PCB boards are copper/epoxy glass cloth substrate or phenolic resin glass cloth substrate, and a small number of paper-based copper-clad boards.

Although these substrates have excellent electrical properties and processing performance, but poor heat dissipation, as a high heat component cooling path, almost can not be expected by the PCB itself resin conduction of heat, but from the surface of the component to the surrounding air heat dissipation.

However, as electronic products have entered the era of miniaturization of components, high-density installation, high heat generation assembly, if you rely only on the surface area of the component surface is very small to dissipate heat is very insufficient.

At the same time, due to the large number of QFP, BGA and other surface-mounted components, components generated by a large number of heat to the PCB board, therefore, the best way to solve the problem of heat dissipation is to improve the direct contact with the heating components of the PCB’s own heat dissipation capabilities, through the PCB board to conduct or disseminate out.

Adding heat dissipation copper foil and adopting large-area power ground copper foil.

Thermal cross-hole

Expose copper on the back of IC to reduce the thermal resistance between copper skin and air.

PCB Layout

Heat sensitive devices are placed in the cold air area.

Temperature detecting devices are placed in the hottest position.

The devices on the same printed circuit board should be arranged as far as possible according to the size of their heat generation and the degree of heat dissipation zoning, heat generation of small or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) placed in the cooling airflow of the most upstream (inlet), the heat generation of large or heat-resistant device (eg, power transistors, large-scale integrated circuits, etc.) placed in the most downstream of the cooling airflow.

In the horizontal direction, high-power devices as close as possible to the printed board edge arrangement, in order to shorten the heat transfer path; in the vertical direction, high-power devices as close as possible to the printed board above the arrangement, in order to reduce the work of these devices on the temperature of other devices.

Equipment within the printed circuit board heat mainly rely on air flow, so the design should study the air flow path, a reasonable configuration of the device or printed circuit board.

Air flow always tends to flow in places of low resistance, so the configuration of the device on the printed circuit board, to avoid leaving a large airspace in a region. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.

More sensitive to the temperature of the device is best placed in the region of the lowest temperature (such as the bottom of the device), never put it in the heat device is directly above the multiple devices is best in the horizontal plane staggered layout.

Arrange the devices with the highest power consumption and the highest heat generation near the best location for heat dissipation. Do not place a device that generates high heat in the corners and around the edges of the printed board unless a heat sink is arranged near it.

When designing power resistors, choose larger devices when possible and adjust the board layout to allow for adequate heat dissipation.

Component spacing recommendations:

2.High heat device with heat sinks, thermal conductors when there are a few devices in the PCB when the amount of heat (less than 3), you can add heat sinks or thermal conductors in the heat device, when the temperature can not be reduced, you can use a heat sink with a fan to enhance the heat dissipation effect.

When the amount of heat-generating device is more (more than 3), you can use a large heat shield (plate), which is customized according to the location of the heat-generating device on the PCB board and the height of the special radiator or in a large flat radiator keyed to the different components of the high and low positions. The heat sink cover will be fastened to the component surface as a whole, and each component contact and heat dissipation.

However, due to the poor consistency of the height of the components when soldering, the heat dissipation effect is not good. Usually in the component surface with a soft thermal phase change thermal pad to improve heat dissipation.

3.For the use of free convection air-cooled equipment, it is best to be integrated circuits (or other devices) in accordance with the longitudinal arrangement, or in accordance with the cross-length arrangement.

4.Adopt reasonable alignment design to realize heat dissipation due to the poor thermal conductivity of the resin in the board, while the copper foil lines and holes are good conductors of heat, so improve the copper foil residual rate and increase the thermal conductivity of the holes is the main means of heat dissipation. To evaluate the heat dissipation capability of a PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of a composite material consisting of various materials with different thermal conductivity, i.e., an insulating substrate for PCBs.

5.The same printed circuit board devices should be arranged as far as possible according to the size of its heat generation and heat dissipation degree of partitioning, heat generation of small or poor heat resistance devices (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) in the cooling airflow of the most upstream (at the entrance), heat generation of large or heat-resistant device (eg, power transistors, large-scale integrated circuits, etc.) placed in the cooling airflow in the downstream.

6.In the horizontal direction, high-power devices as close as possible to the edge of the printed board layout, in order to shorten the heat transfer path; in the vertical direction, high-power devices as close as possible to the printed board above the layout in order to reduce the work of these devices on the temperature of other devices.

7.The heat dissipation of the printed circuit board within the device mainly relies on air flow, so the design should study the air flow path, reasonable configuration of the device or printed circuit board.

Air flow always tends to flow in the place of low resistance, so the configuration of the device on the printed circuit board, to avoid leaving a large airspace in a region.

The whole machine in the configuration of multiple printed circuit boards should also pay attention to the same problem.

8.More sensitive to the temperature of the device is best placed in the lowest temperature region (such as the bottom of the device), do not put it in the heat device is directly above the multiple devices is best in the horizontal plane staggered layout.

9.Arrange the devices with the highest power consumption and the greatest heat generation near the best location for heat dissipation. Do not place the device with higher heat generation in the corners and around the edges of the printed board, unless there is a heat sink arranged in its vicinity. In the design of the power resistor as far as possible to choose a larger device, and in adjusting the layout of the printed circuit board so that it has enough space for heat dissipation.

10.Avoid the concentration of hot spots on the PCB, as far as possible, the power is evenly distributed on the PCB board, to maintain the PCB surface temperature performance uniformity and consistency.

Often the design process to achieve a strict uniform distribution is more difficult, but be sure to avoid the power density is too high in the region, so as to avoid the emergence of excessive hot spots affect the normal operation of the entire circuit.

If there are conditions, the thermal efficiency of printed circuits is necessary, such as some of the professional PCB design software now increase the thermal efficiency index analysis software module, you can help designers optimize circuit design.