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Technical Article

PCB Heat Dissipation Skills

Time:2021-03-16 11:35:18 Click:

Speaking of the electronic equipment, as we all know, a certain amount of heat will be generated during operation, and which usually cause the internal temperature of the equipment rises rapidly. However, 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 the electronic equipment will definitely decline. Therefore, it is very important to conduct a good heat dissipation treatment on the circuit board. Since the heat dissipation of the circuit board is a vital part, so what is the heat dissipation technique of the printed circuit board? Let's discuss the heat dissipation method of the circuit board together.






1. Heat dissipation through the PCB itself


At present, the widely used PCB boards are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, and a small amount of paper-based copper-clad boards are used. Although these substrates have excellent electrical properties and processing properties, they have still poor in the terms of heat dissipation. As a heat dissipation path for high-heating components, it is almost impossible to expect heat from the resin of the PCB itself to conduct heat; Instead, those heat will dissipate from the surface of the component to the surrounding air. However, as electronic products have entered the era of miniaturization of components, high-density mounting, and high-heating assembly, it is not enough to rely on the surface of a component with a very small surface area to dissipate heat. At the same time, due to the extensive use of surface mount components such as QFP and BGA, a large amount of heat generated by the components is transferred to the circuit board. Therefore, the best way to solve the problem of heat dissipation is to improve the heat dissipation capacity of the PCB itself, which is in direct contact with the heating element, through the PCB board to conduct or radiate.



2. High heat-generating components plus radiator and thermal board


When a small number of components in the PCB generate a large amount of heat (less than 3pcs), a radiator or heat pipe can be added to the heating component. When the temperature cannot be lowered, a radiator with a fan can be used to enhance heat dissipation effect; While the number of heating devices is large (more than 3pcs), a large heat dissipation cover (board) can be used, which is a special heat sink customized according to the position and height of the heating device on the PCB or a large flat heat sink cut out different component height positions. The heat dissipation cover is integrally buckled on the surface of the component, and it contacts each component to dissipate heat. However, the heat dissipation effect is not good due to the poor consistency of height during assembly and welding of components. Usually, a soft thermal phase change thermal pad is added on the surface of the component to improve the heat dissipation effect.



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







4. Use reasonable routing design to realize heat dissipation


Due to the resin in the plate has poor thermal conductivity, and the copper foil lines and holes are good conductors of heat, increasing the residual rate of the copper foil and increasing the heat conduction holes are the main means of heat dissipation.


To evaluate the heat dissipation capacity of a PCB, it is necessary to calculate the equivalent thermal conductivity of a composite material composed of various materials with different thermal conductivity-an insulating substrate for PCB.


5. The devices on the same circuit board should be arranged as far as possible according to their calorific value and heat dissipation degree. Devices with small calorific value or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed in cooling the uppermost part of the airflow (at the entrance), and the devices with large heat or heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the lowermost part of the cooling airflow.


6. In the horizontal direction, high-power devices should be placed as close to the edge of the circuit board as possible to shorten the heat transfer path; In the vertical direction, high-power devices should be placed as close as possible to the top of the circuit board to reduce the impact of these devices on the temperature of other devices. .







7. The heat dissipation of the circuit board in the equipment mainly relies on air flow, so the air flow path should be studied during the design, and the device or printed circuit board 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 airspace in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.


8. The temperature-sensitive device is best placed in the lowest temperature area (such as the bottom of the device). Never place it directly above the heating device. It is best to stagger multiple devices on the horizontal plane.


9. Arrange the devices with the highest power consumption and the highest heat generation near the best position for heat dissipation. Do not place high-heating devices on the corners and peripheral edges of the circuit board, unless a heat sink is arranged near it. When designing the power resistor, choose a larger device as much as possible, and make it have enough space for heat dissipation when adjusting the layout of the circuit board.


10. Avoid the concentration of hot spots on the PCB, distribute the power evenly on the PCB board 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 prevent hot spots from affecting the normal operation of the entire circuit. If possible, it is also necessary to analyze the thermal efficiency of the printed circuit. For example, the thermal efficiency index analysis software module added in some professional PCB design software can help designers optimize the circuit design.

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