The heat generated by electronic equipment during operation causes the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, the device will fail due to overheating, and the reliability of the electronic equipment will decrease. Therefore, it is very important to heat dissipate the circuit board.

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  1. Analysis of temperature rise factors of printed circuit boards
    The direct cause of the temperature rise of the printed board is the presence of power-consuming devices in the circuit. Electronic devices all consume power to varying degrees, and the intensity of heat generation changes with the amount of power consumption.
    Two phenomena of temperature rise in printed boards:
    (1) Local temperature rise or large area temperature rise;
    (2) Short-term temperature rise or long-term temperature rise.
    When analyzing PCB thermal power consumption, it is generally analyzed from the following aspects. ​
    1Electrical power consumption
    (1) Analyze the power consumption per unit area;
    (2) Analyze the distribution of power consumption on the PCB board. ​
  2. Structure of printed board
    (1) Size of printed board;
    (2) Printed board material.
  3. How to install printed circuit boards
    (1) Installation method (such as vertical installation, horizontal installation);
    (2) Sealing condition and distance from the casing. ​
  4. Thermal radiation
    (1) Radiation coefficient of printed board surface;
    (2) The temperature difference between the printed board and adjacent surfaces and their absolute temperatures;
  5. Heat conduction
    (1) Install the radiator;
    (2) Conduction from other installation structural parts. ​
    Thermal convection
    (1) Natural convection;
    (2) Forced cooling convection.
    Analysis of the above factors from PCB is an effective way to solve the temperature rise of printed boards. Often these factors are interrelated and dependent on each other in a product and system. Most factors should be analyzed according to the actual situation. Only for a specific Parameters such as temperature rise and power consumption can be more accurately calculated or estimated based on actual conditions. ​
  6. Circuit board heat dissipation method
    1 High-heating devices plus radiators and heat conduction plates
    When there are a few devices in the PCB that generate a large amount of heat (less than 3), a radiator or heat pipe can be added to the heating device. When the temperature cannot be lowered, a radiator with a fan can be used to enhance heat dissipation. Effect. When there are a large number of heating devices (more than 3), a large heat dissipation cover (board) can be used. It is a special radiator customized according to the position and height of the heating device on the PCB board or a large flat-panel radiator. Cut out the high and low positions of different components. Attach the heat dissipation cover to the component surface and make contact with each component to dissipate heat. However, due to the poor consistency of the components during assembly and soldering, the heat dissipation effect is not good. Usually, a soft thermal phase change thermal pad is added to the component surface to improve the heat dissipation effect.
  7. Dissipate heat 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 there are also a small amount of paper-based copper-clad boards. 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 the PCB resin 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 component miniaturization, high-density installation, and high-heat assembly, it is not enough to rely solely on the surface of components with very small surface areas to dissipate heat. At the same time, due to the extensive use of surface-mounted components such as QFP and BGA, the heat generated by the components is transferred to the PCB board in large quantities. Therefore, the best way to solve the problem of heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating components, through the PCB board Conduct or radiate out.
  8. Use reasonable wiring design to achieve heat dissipation
    Since the resin in the board has poor thermal conductivity, and copper foil lines and holes are good conductors of heat, increasing the remaining rate of copper foil and adding thermal holes are the main means of heat dissipation.
    To evaluate the heat dissipation capability of PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the insulating substrate for PCB, a composite material composed of various materials with different thermal conductivity.
    4 For equipment using free convection air cooling, it is best to arrange the integrated circuits (or other devices) lengthwise or horizontally.
  9. Devices on the same printed board should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed in cooling areas. In the uppermost part of the airflow (at the inlet), devices with high calorific value or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream part of the cooling airflow.
    6 In the horizontal direction, high-power devices should be placed 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 placed as close to the top of the printed board as possible to reduce the impact of these devices on the temperature of other devices when they are working. Influence.
  10. Devices that are sensitive to temperature are best placed in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heating device. It is best to arrange multiple devices staggered on the horizontal plane.
    The heat dissipation of the printed circuit board in the equipment mainly relies on air flow, so the air flow path must be studied during design and the devices or printed circuit boards 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 air space in a certain area. The same issue should also be paid attention to in the configuration of multiple printed circuit boards in the whole machine.
  11. Avoid the concentration of hot spots on the PCB, distribute the power evenly on the PCB 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 avoid hot spots that may affect the normal operation of the entire circuit. If possible, it is necessary to conduct thermal efficiency analysis of printed circuits. For example, the thermal efficiency index analysis software module added to some professional PCB design software can help designers optimize circuit design.
    Place the devices that consume the most power and generate the most heat near the best locations for heat dissipation. Do not place high-heat components in the corners and edges of the printed board unless a heat sink is arranged nearby. When designing the power resistor, choose a larger device as much as possible, and make sure there is enough space for heat dissipation when adjusting the printed board layout.
    High heat dissipation devices should be connected to the substrate with as little thermal resistance as possible between them. In order to better meet the thermal characteristics requirements, some thermally conductive materials (such as applying a layer of thermally conductive silicone) can be used on the bottom surface of the chip, and a certain contact area can be maintained for device heat dissipation.
    Connection between device and substrate:
    (1) Minimize the length of device leads;
    (2) When selecting high-power devices, the thermal conductivity of the lead material should be considered. If possible, try to select the lead with the largest cross section;
    (3) Choose a device with a larger number of pins.
  12. Device package selection:
    (1) When considering thermal design, attention should be paid to the packaging instructions of the device and its thermal conductivity;
    (2) Consideration should be given to providing a good thermal conduction path between the substrate and the device package;
    (3) Air partitions should be avoided on the heat conduction path. If this is the case, thermal conductive materials can be used for filling.

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