PCB circuit board heat dissipation skills

PCB circuit board heat dissipation skills

1. Circuit board heat dissipation method

1 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, as well as paper-based copper-clad boards that are used in a small amount. 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. 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 PCB 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. Conducted or radiated.

2 High heat-generating device plus radiator and heat conducting plate

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 heating device. When the temperature cannot be lowered, a heat sink with a fan can be used to enhance 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 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 wiring design to realize heat dissipation

Because the resin in the sheet has poor thermal conductivity, and the copper foil lines and holes are good conductors of heat, increasing the remaining rate of 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 (nine eq) of a composite material composed of various materials with different thermal conductivity-an insulating substrate for PCB.

5 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 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 flow (at the entrance) of the airflow, and the devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream of the cooling airflow.

6 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 are arranged as close as possible to the top of the printed board to reduce the temperature of other devices when these devices are working. influences.

7 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.

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 place multiple devices on the horizontal plane in a staggered layout.