For electronic devices, a certain amount of heat will be generated during operation, so that the internal temperature of the device will rise rapidly. If the heat is not dissipated in time, the device will continue to heat up, and the device will fail due to overheating. Performance will drop.
Therefore, it is very important to have a good heat dissipation treatment of the circuit board. The heat dissipation of the PCB circuit board is a very important link, so what are the heat dissipation skills of the PCB circuit board, let’s discuss it together.
01
Heat dissipation through the PCB board itself is currently widely used PCB boards are copper clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, as well as 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 heat to be conducted by the resin of the PCB itself, but to dissipate heat from the surface of the component to the surrounding air.
However, as electronic products have entered the era of miniaturization of components, high-density installation, and high-heat-generation assembly, it is not enough to rely on the surface of components with very small surface area 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 a large amount. Therefore, the best way to solve the heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating element. conduct or emanate.
PCB layout
Thermally sensitive devices are placed in the cold air area.
Place the temperature sensing device in the hottest location.
We should arrange devices on the same printed board according to their calorific value and degree of heat dissipation as much as possible. Place low calorific value or poor heat resistance device in the uppermost stream of the cooling airflow. Place the high heat generation or good heat resistance device at the most downstream of the cooling airflow.
In the horizontal direction, we arrange the high-power devices close to the edge of the printed board; in the vertical direction, we arrange the high-power devices close to the top of the printed board to reduce the temperature impact of these devices on other devices.
The heat dissipation of the printed board in the equipment mainly depends on the air flow, so the air flow path should be studied in the design, and the device or printed circuit board should be reasonably configured.
When air flows, it always tends to flow where the resistance is small, so when configuring components on a printed circuit board, it is necessary to avoid leaving a large airspace in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
We best place the Devices that are more sensitive to temperature in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heat-generating device. Stagger multiple devices on a horizontal plane.
Place the devices that consume the most power and generate the most heat near the best heat dissipation locations. Do not place high-heat components on the corners and edges of the printed board unless you arrange a heat sink near it.
When designing the power resistor, choose a larger device as much as possible, and adjust the layout of the printed board so that there is enough space for heat dissipation.
Component spacing recommendations:
02
High-heat-generating devices plus radiator and heat-conducting plate. When there are a few devices in the PCB that generate a large amount of heat (less than 3), we can add a heat-sink or heat-conducting pipe to the heat-generating device. If we cannot lower the temperature, use Radiator with a fan for enhanced cooling.
Then the number of heating devices is large (more than 3), we can use a large heat dissipation cover (board), we customize a special radiator according to the position and height of the heating device on the PCB or a large flat radiator. Cut out the high and low positions of different components. Fasten the heat dissipation cover on the component surface as a whole, and contact with each component to dissipate heat.
However, the heat dissipation effect is not good due to the poor consistency of the components during assembly and welding. Usually, we add a soft thermal phase change thermal pad to the component surface. In order to improve the heat dissipation effect.
03
For equipment cooled by free convection air, it is best to arrange the integrated circuits (or other devices) in a vertical arrangement or a horizontal arrangement.
04
Use reasonable trace design to achieve heat dissipation. Because of poor thermal conductivity, improving the residual rate and thermal vias are the main means of heat dissipation. To evaluate the heat dissipation capability of the PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the composite material composed of various materials with different thermal conductivity—the insulating substrate for PCB.
05
We should arrange devices on the same printed board as far as possible. According to their calorific value and degree of heat dissipation. Place devices with low calorific value or poor heat resistance in the uppermost stream of the cooling airflow. Place the devices with high heat generation or good heat resistance at the most downstream of the cooling airflow.
06
In the horizontal direction, we arrange the high-power devices as close to the edge of the printed board as possible. In order to shorten the heat transfer path. However in the vertical direction, we set that close to the top of the printed board as possible. So as to reduce the temperature impact of these devices on other devices.
07
The heat dissipation of the PCB in the equipment mainly depends on the airflow. So we should study the airflow path, and configure the device or PCB reasonably.
When air flows, it always tends to flow where the resistance is small. So when configuring components on PCB, it is necessary to avoid leaving large airspace in a certain area.
The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
08
We best place more sensitive to temperature devices in the area with the lowest temperature. Never place it directly above the heat-generating device. Stagger the multiple devices on a horizontal plane are best.
09
Place the devices that consume the most power and generate the most heat near the best heat dissipation locations. Do not place high-heat components on the corners and edges unless we arrange a heat sink near it. When designing the power resistor, choose a larger device as much as possible. Also, adjust the layout so that there is enough space for heat dissipation.
10
Avoid the concentration, distribute the power evenly as much as possible, and keep the temperature performance uniform and consistent.
It is often difficult to achieve strict uniform distribution in the design process. But it is necessary to avoid areas with too high power density. So as to avoid hot spots affecting the normal operation of the entire circuit.
If possible, it is necessary to analyze the thermal efficiency of printed circuits. For example, the thermal efficiency index analysis software module can optimize circuit design.
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