Heat Dissipation Technique Of PCB Circuit Board

Heat dissipation technique of PCB Circuit Board

The heat produced when the electronic equipment is working causes the internal temperature of the equipment to rise rapidly. If the heat is not released in time, the equipment will continue to heat up, the device will fail because of overheating, and the reliability of the electronic equipment will decline. It is very important to heat dissipation treatment the circuit board.

One,analysis of temperature rise factors of printed Circuit Board

The direct reason for the temperature rise of PCB is the existence of power dissipation devices, and the heat intensity varies with the power consumption. Two phenomena of temperature rise in printed boards:

1) local or large area temperature rise;

2) short or long time temperature rise.

In the analysis of PCB thermal power consumption, generally from the following aspects to analyze.

1. Electrical power consumption

   1) Analysis of power consumption per unit area;

   2) The distribution of power consumption on PCB circuit board is analyzed.

2. Structure of printed boards

   1)Size of printed boards;

   2)Materials for printed boards.

3. Mode of installation of printed boards

   1)Installation mode (such as vertical installation, horizontal installation);

   2)Sealing conditions and distance from the housing.

4. Thermal radiation

   1)Radiation coefficient of PCB surface;

   2)The temperature difference between printed boards and adjacent surfaces and their absolute temperature;

5. Conduction of heat

   1)Installation of radiators;

   2)Transmission of other mounting structures.

6. Heat convection

   1) Natural convection;

   2) Forced cooling convection

The analysis of the above factors from PCB is an effective way to solve the temperature rise of PCB. Often these factors are interrelated and dependent on each other in a product and system. Most of the factors should be analyzed according to the actual situation. The parameters such as temperature rise and power consumption can be calculated or estimated correctly only according to a specific situation.

Second, circuit board heat dissipation mode

1. High heating device plus radiator, heat conduction board

   A radiator or a heat conduction tube may be added to the heating device when there are a few devices in the PCB with a larger heat value (less than 3), and a radiator with a fan may be used when the temperature cannot be lowered. In order to enhance the heat dissipation effect. When the quantity of heating device is more than 3, a large heat sink can be used. It is a special radiator tailored to the position and height of the heating device on the PCB board or heat dissipation on a large plate. Pick out different high and low positions of components on the device. Buckle the heat sink on the surface of the element as a whole, However, the heat dissipation effect is not good due to the low and low consistency of component assembly and welding. A soft thermal phase change heat transfer pad is usually added to the component surface to improve the heat dissipation effect.

2. Heat dissipation through the PCB board itself

   At present, the widely used PCB sheets are copper clad / epoxy glass cloth substrates or phenolic resin glass cloth substrates, as well as a small amount of paper based copper clad laminates. Although these substrates have excellent electrical and processing properties, they have poor heat dissipation. As a heat dissipation channel for high heating elements, heat transfer from the surface of the element to the surrounding air can hardly be expected from the PCB resin itself. But as the electronic product has entered the miniaturization of the components, the high density is installed. In the era of high heating assembly, it is not enough to dissipate heat only by the surface of the element with very small surface area. At the same time, due to the extensive use of surface mounting elements, such as QFPGA-BGA, the heat produced by the components is transferred to the PCB board in large quantities. The best way to solve the heat dissipation is to improve the heat dissipation ability of PCB which is in direct contact with the heating element and transmit or emit through the PCB plate.

3. Using rational Line Design to realize Heat dissipation

4. For devices cooled by free convection air, it is best to arrange integrated circuits (or other devices) in a longitudinal or horizontal manner.

5. Devices on the same printed board shall be arranged as far as possible according to their calorific size and extent of heat dissipation. Devices with little heat or poor heat resistance (e.g., small signal transistors, small integrated circuits), Electrolytic capacitors are placed at the top of the cooling flow (inlet), and devices with high calorific or heat resistance (e.g. power transistors, large scale integrated circuits, etc.) are placed downstream of the cooling flow.

6. In the horizontal direction, the high-power devices are arranged as close as possible to the edge of the PCB in order to shorten the heat transfer path; in the vertical direction, the high-power devices are arranged as close as possible to the top of the PCB, In order to reduce the effect of these devices on the temperature of other devices.

7. Thermo-sensitive devices are best placed in the lowest temperature area (e.g., the bottom of the device, do not place it directly above the heating device, and multiple devices are preferably staggered on the horizontal plane.

8. The heat dissipation of printed circuit board in equipment mainly depends on air flow, so we should study the air flow path in design, reasonably configure the device or printed circuit board. The air flow always tends to flow in the place where the resistance is small. Therefore, when configuring devices on printed circuit boards, we should avoid leaving a larger airspace in a certain area. The same problem should be noticed in the configuration of multiple printed circuit boards in the whole machine.

9. To avoid the concentration of hot spots on PCB and distribute power evenly on PCB board as far as possible to keep the uniformity and uniformity of surface temperature performance of PCB, it is often difficult to achieve strict uniform distribution in the design process. However, it is necessary to avoid areas with high power density so as to avoid the occurrence of hot spots affecting the normal operation of the whole circuit.

10. Place the devices with the highest power consumption and the highest heating near the optimum position for heat dissipation. Do not place the high-heating devices in the corners and edges of the printed circuit board, Unless a heat dissipation device is arranged near it, select larger devices when designing power resistors, and allow sufficient heat dissipation space when adjusting the layout of the PCB.

11. The thermal resistance between high heat dissipation devices should be minimized when they are connected to the substrate. Some thermal conductive materials (such as coating a layer of thermal conductive silica gel) can be used on the bottom of the chip, and a certain contact area can be maintained for device heat dissipation.

12. Connection of device to substrate:

    1)Reduce the lead length of the device as much as possible

    2)When selecting high power device, the thermal conductivity of lead material should be considered, and if possible, the maximum cross section of lead wire should be chosen.

    3)Choose a device with more pins

13. Device package selection:

    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 packaging;

    3)Air cutoff should be avoided in the heat conduction path, if this is the case, it can be filled with heat conduction material.