PCB Tech - Heat dissipation skills of PCB circuit board

For electronic equipment, certain heat will be generated during operation, so that the internal temperature of the equipment will rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, the devices will fail due to overheating, and the reliability of electronic equipment will decline.

Therefore, it is very important to heat the circuit board well. The heat dissipation of PCB circuit board is a very important link. What are the heat dissipation skills of PCB circuit board? Let's discuss it together.

one

Heat is dissipated through the PCB itself. At present, the widely used PCB plates are copper-clad / epoxy glass cloth substrate or phenolic resin glass cloth substrate, and a small amount of paper-based copper-clad plates are used.

Although these substrates have excellent electrical and processing properties, they have poor heat dissipation. As the heat dissipation path of high heating elements, it is almost impossible to expect the resin of PCB itself to conduct heat, but to dissipate heat from the surface of the elements to the surrounding air.

However, as electronic products have entered the era of component miniaturization, high-density installation and high heating assembly, it is not enough to dissipate heat only on the surface of components with very small surface area.

At the same time, due to the extensive use of surface mounted components such as QFP and BGA, a large amount of heat generated by components is transmitted to the PCB board. Therefore, a Zui good way to solve the heat dissipation is to improve the heat dissipation capacity of the PCB in direct contact with the heating element and transmit or emit it through the PCB board.

Add heat dissipation copper foil and copper foil with large area power supply

Thermal via

Copper is exposed on the back of IC to reduce the thermal resistance between copper sheet and air

PCB layout

a. The thermal sensing device is placed in the cold air area.

b. The temperature detection device is placed in a Zui hot position.

c. The devices on the same printed board shall be arranged in zones according to their calorific value and heat dissipation degree as far as possible. Devices with low calorific value or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) shall be placed on the Zui upstream (inlet) of the cooling air flow, and devices with high calorific value or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) Placed Zui downstream of the cooling air stream.

d. In the horizontal direction, high-power devices are arranged as close to the edge of the printed board as possible to shorten the heat transfer path; In the vertical direction, high-power devices shall be arranged as close as possible to the top of the printed board, so as to reduce the impact of these devices on the temperature of other devices.

e. The heat dissipation of printed boards in the equipment mainly depends on air flow, so the air flow path should be studied in the design, and the devices or printed circuit boards should be configured reasonably. When air flows, it always tends to flow where the resistance is small, so when configuring devices on the 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.

f. The temperature sensitive device Zui should be placed in the area with low temperature Zui (such as the bottom of the equipment). Never put it directly above the heating device. Multiple devices Zui should be staggered on the horizontal plane.

g. Devices with high power consumption Zui and large heat generation Zui are arranged near a good heat dissipation Zui position. Do not place the device with high heat on the corner and surrounding edge of the printed board unless a heat sink is arranged near it. When designing the power resistance, select a larger device as much as possible, and make it have enough heat dissipation space when adjusting the layout of the printed board.

h. Component spacing recommendations:

two

Heat sink and heat conduction board are added to high heating devices. When a few devices in PCB have large heating capacity (less than 3), heat sink or heat conduction pipe can be added to the heating devices. When the temperature cannot be reduced, heat sink with fan can be used to enhance the heat dissipation effect.

When the quantity of heating components is large (more than 3), a large heat dissipation cover (plate) can be used. It is a special radiator customized according to the position and height of heating components on PCB board, or different component high and low positions can be pulled out on a large flat radiator.

The whole heat dissipation cover is buckled on the element surface to contact with each element to dissipate heat. However, due to the poor consistency in the assembly and welding of components, the heat dissipation effect is not good. Usually, a soft thermal phase change heat conduction pad is added on the surface of components to improve the heat dissipation effect.

three

For equipment cooled by free convection air, Zui it is better to arrange the integrated circuits (or other devices) in a longitudinal or transverse manner.

four

Reasonable wiring design is adopted to realize heat dissipation. Because the resin in the plate has poor thermal conductivity, and the copper foil lines and holes are good conductors of heat, improving the residual rate of copper foil and increasing heat conduction holes are the main means of heat dissipation.

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

five

The devices on the same printed board shall be arranged in zones according to their calorific value and heat dissipation degree as far as possible. Devices with low calorific value or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) shall be placed on the Zui upstream (inlet) of the cooling air flow, and devices with high calorific value or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) Placed Zui downstream of the cooling air stream.

six

In the horizontal direction, high-power devices are arranged as close to the edge of the printed board as possible to shorten the heat transfer path; In the vertical direction, high-power devices shall be arranged as close as possible to the top of the printed board, so as to reduce the impact of these devices on the temperature of other devices.

seven

The heat dissipation of printed boards in the equipment mainly depends on air flow, so the air flow path should be studied in the design, and the devices or printed circuit boards should be configured reasonably.

When air flows, it always tends to flow where the resistance is small, so when configuring devices on the 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.

eight

The temperature sensitive device Zui should be placed in the area with low temperature Zui (such as the bottom of the equipment). Never put it directly above the heating device. Multiple devices Zui should be staggered on the horizontal plane.

nine

Devices with high power consumption Zui and large heat generation Zui are arranged near a good heat dissipation Zui position. Do not place the device with high heat on the corner and surrounding edge of the printed board unless a heat sink is arranged near it.

When designing the power resistance, select a larger device as much as possible, and make it have enough heat dissipation space when adjusting the layout of the printed board.

ten

Avoid the concentration of hot spots on the PCB, distribute the power evenly on the PCB as much as possible, and maintain the uniformity and consistency of PCB surface temperature performance.

It is often difficult to achieve strict uniform distribution in the design process, but we must avoid areas with too high power density, so as to avoid excessive hot spots affecting the normal operation of the whole circuit.

If possible, it is necessary to analyze the thermal efficiency of printed circuits. For example, the thermal efficiency index analysis software module added in some PCB design software of Zhuan industry can help designers optimize circuit design.