Introduction To PCB Board Heat Dissipation Mode

The heat generated during the operation of the electronic equipment makes the internal temperature of the equipment rise rapidly. If the heat is not released in time, the equipment will continue to heat up, and the device will fail due to overheating, and the reliability of the electronic equipment will decline. Therefore, it is very important to cooling (heat dissipation) the circuit board.

Circuit board heat dissipation mode

1. High heating element with heat sink and heat conduction plate

When a few components in THE PCB have high heat (less than 3), heat sink or heat conduction tube can be added to the heating element. When the temperature cannot be lowered, the radiator with fan can be used to enhance the heat dissipation effect. When the number of heating elements is large (more than 3), a large heat sink (panel) can be used. It is a special radiator customized according to the position and height of heating elements on the PCB or a large flat radiator with different height and height of components cut out. The heat dissipation hood shall be fastened on the element surface and contact with each element for heat dissipation. However, the heat dissipation effect is not good due to the poor consistency of components during installation and welding. Soft thermal pads are usually added to the surface of components to improve heat dissipation.

2. Heat dissipation through PCB board itself

At present, PCB is widely used as copper clad/epoxy or phenolic resin clad glass, and a small amount of paper clad copper. Although these substrates have excellent electrical properties and machining properties, they have poor heat dissipation. As the heat dissipation way of high heating elements, it is almost impossible to rely on the resin of PCB to conduct heat, but to dissipate heat from the surface of components to the surrounding air. However, as electronic products have entered the era of component miniaturization, high-density installation and high-thermal-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, the heat generated by components is transferred to THE PCB in large quantities. Therefore, the best way to solve the heat dissipation problem is to improve the heat dissipation ability of the PCB in direct contact with the heating element and conduct or send out through the PCB.

3. Adopt reasonable wiring design to realize heat dissipation

Due to the poor thermal conductivity of the resin in the plate, and copper foil lines and holes are good conductors of heat, so increasing the residual rate of copper foil and increasing thermal conductivity 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 the insulating substrate for the composite material consisting of various materials with different thermal conductivity.

4. For devices using free convection air cooling, it is preferable to arrange the integrated circuits (or other devices) in a longitudinal or transverse manner.
5. On the same piece of PCB device should as far as possible according to its size and degree of heat partition of calorific value, calorific value is small or poor heat resistance devices (e.g., small signal transistor, small-scale integrated circuit, electrolytic capacitors, etc.) on the cooling airflow of the best () at the entrance, calorific value big or good heat resistance devices (such as power transistor, large scale integrated circuit, etc.) in the most downstream cooling airflow.
6. In the horizontal direction, the high-power device should be arranged as close to the edge of the printed board as possible, so as to shorten the heat transfer path; In the vertical direction, the high-power components are arranged as close as possible to the top of the printed board, so as to reduce the influence of these components on the temperature of other components when they work.
7. More sensitive to the temperature of the device is best placed in the lowest temperature area (such as the bottom of the device), do not put it on the heating device directly above, multiple devices are best in horizontal staggered layout.
8. The heat dissipation of printed board 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 reasonably configured. Air flow tends to flow where resistance is low, so avoid leaving a large space in an area when configuring devices on a printed circuit board. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
9. 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 a strict uniform distribution in the design process, but it is necessary to avoid areas with too high-power density, so as not to appear hot spots affecting the normal operation of the whole circuit. If possible, it is necessary to carry out thermal performance analysis of printed circuit. For example, the thermal performance index analysis software module added to some professional PCB design software can help designers to optimize circuit design.
10. The device with the highest power consumption and maximum heat is arranged near the optimal heat dissipation position. Do not place high heating devices at corners and edges of the printed board unless there is a heat sink nearby. In the design of power resistance as much as possible to choose a larger device, and adjust the PCB layout so that it has enough space for heat dissipation.
11. High heat dissipation devices should minimize the thermal resistance between them when connected to the substrate. In order to better meet the requirements of thermal characteristics, some thermal conductivity materials (such as applying a layer of thermal silica gel) can be used on the bottom surface of the chip, and a certain contact area can be maintained for the device to dissipate heat.
12. Connection between device and substrate:

(1) Shorten the lead length of the device as much as possible;

(2) When selecting a high-power device, the thermal conductivity of the lead material should be considered. If possible, the lead horizontal section should be selected to maximize;

(3) Select devices with more pins.

13. Package selection of devices:

(1) When considering thermal design, attention should be paid to the package description of the device and its thermal conductivity;

(2) Consideration should be given to providing a good heat conduction path between the substrate and the device package;

(3) In the heat conduction path should avoid the air partition, if there is such a situation can be filled with heat conduction materials.