How to design PCB circuit board for heat dissipation
Summary of content: For electronic devices, a certain amount of heat is generated during work, which causes the internal temperature of the device to rise rapidly. If the heat is not released in time, the device will continue to heat up and the device will fail due to overheating. The reliable performance of the equipment will decrease. Therefore, it is very important to perform a good heat dissipation process on the circuit board. The heat dissipation of PCB circuit board is a very important part, so what is the heat dissipation technique of PCB circuit board, let's discuss it together.
1. Heat dissipation through the PCB itself The currently widely used PCB materials 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 properties and processing properties, they have poor heat dissipation properties. As a heat dissipation method for highly heat-generating components, it is almost impossible to rely on the PCB resin to conduct heat, but to dissipate heat from the surface of the components to the surrounding air. However, as electronic products have entered the era of component miniaturization, high-density mounting, and high-heat assembly, it is not enough to dissipate heat only on the surface of components with very small surface areas. At the same time, due to the large use of surface mount components such as QFP and BGA, the heat generated by the components is transferred to the PCB board. Therefore, the best way to solve the heat dissipation is to improve the heat dissipation capability of the PCB itself that is in direct contact with the heating element. Conducted or emitted.
2. High heat-generating device plus heat sink and heat-conducting plate When a few devices in the PCB generate a large amount of heat (less than 3), a heat sink or heat-conducting tube can be added to the heat-generating device. A radiator with a fan can be used to enhance the cooling effect. When there are a large number of heating devices (more than 3), a large heat shield (board) can be used. It is a dedicated heat sink customized according to the position and height of the heating device on the PCB board or a large flat heat sink. Cut out different component height positions. The heat sink is buckled on the surface of the component as a whole, and contacts 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. Generally, a soft thermal phase change thermal pad is added on the component surface to improve the heat dissipation effect.
3. For equipment using free convection air cooling, it is best to arrange integrated circuits (or other devices) in a vertical or horizontal manner.
4. Use a reasonable wiring design to achieve heat dissipation. Due to the poor thermal conductivity of the resin in the sheet, copper foil lines and holes are good conductors of heat. Therefore, increasing the copper foil residual rate and increasing the heat conduction holes are the main means of heat dissipation. To evaluate the heat dissipation capability 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, one by one for an insulating substrate for a PCB.
5. The devices on the same printed board should be arranged as much as possible according to the amount of heat generated and the degree of heat dissipation. Devices with low heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) At the top of the cooling airflow (at the entrance), devices with high heat generation or 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 should be 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 should be arranged as close to the top of the printed board as possible to reduce the temperature of these devices on other devices Impact.
7. The heat dissipation of the printed board in the device mainly depends on the air flow, so the air flow path should be researched in the design, and the device or printed circuit board should be reasonably configured. When air flows, it tends to flow in a place with low resistance, so when configuring the device 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. It is better to place the temperature sensitive devices in the lowest temperature area (such as the bottom of the device). Do not place it directly above the heating device. It is better to stagger the multiple devices on the horizontal plane.
9. Place the device with the highest power consumption and heat generation near the best position for heat dissipation. Do not place devices with high heat generation at the corners and peripheral edges of the printed board, unless a heat sink is arranged near it. When designing the power resistor, select a larger device as much as possible, and make sure that there is enough space for heat dissipation when adjusting the layout of the printed board.
10. Avoid the concentration of hot spots on the PCB, and distribute the power as evenly as possible on the PCB to maintain uniform and consistent temperature performance on the PCB surface. It is often difficult to achieve strict uniform distribution during the design process, but it is necessary to avoid areas with too high power density to avoid excessive hot spots that affect 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 added in some professional PCB design software can help designers optimize circuit design.