PCB Tech - Understand the various methods of PCB heat dissipation

Every PCB electronic device generates a certain amount of heat when it is working, so that the internal temperature of the device rises rapidly. If the heat is not dissipated in time, the device will continue to heat up, and the PCB device will fail due to overheating. Reliability performance will decrease.

Therefore, it is very important to conduct a good heat dissipation treatment on the circuit board. The heat dissipation of the PCB circuit board is a very important link, so what is the heat dissipation technique of the PCB circuit board, let's discuss it together below.

Heat dissipation through the PCB board itself The currently 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 poor 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, but to dissipate heat from the surface of the component to the surrounding air.

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 the 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, 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. Transmit or radiate

Add heat-dissipating copper foil and copper foil with large area power supply

Thermal via

Exposure of copper on the back of the IC reduces the thermal resistance between the copper skin and the air

PCB layout

a. Place the heat sensitive device in the cold wind area

b. Place the temperature detection device in the hottest position.

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

d. In the horizontal direction, high-power devices are arranged as close as possible to the edge of the printed board to shorten the heat transfer path; in the vertical direction, high-power devices are arranged as close as possible to the top of the printed board to reduce the temperature of other devices when these devices work. Impact.

e. The heat dissipation of the printed 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.

f. 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.

g. 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 printed 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 printed board.

h. Suggested component spacing:

High heat-generating components plus radiators and heat-conducting plates. When a small number of components in the PCB generate a large amount of heat (less than 3), a heat sink or heat pipe can be added to the heat-generating components. When the temperature cannot be lowered, it can be used A radiator with a fan to enhance the heat dissipation effect.

When the number of heating devices is large (more than 3), 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 is in contact with 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.

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

Adopt a reasonable wiring design to realize heat dissipation. Because the resin in the plate has poor thermal conductivity, and the copper foil lines and holes are good heat conductors, increasing the remaining rate of copper foil and increasing the heat conduction holes are the main means of heat dissipation.

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 printed board.

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 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.