Second, the circuit board cooling method
1, high fever devices plus radiator, thermal plate
When the PCB has a small number of devices when the heat is relatively large (less than 3), the heat sink can be added to the radiator or heat pipe, when the temperature can not be lowered, you can use a fan with a fan to enhance the heat effect. When the amount of heat generating device is more (more than 3), a large heat sink (plate) can be used. It is a special heat sink customized by the position and height of the heating device on the PCB board or in a large plate radiator On the different elements out of the high and low position. The whole heat sink on the element surface, with each component in contact with the heat. But because of the high and low consistency of components installed welding, cooling effect is not good. Usually in the component surface plus a soft thermal change thermal insulation pad to improve the cooling effect.
2, through the PCB board itself heat
Currently widely used PCB sheet is copper / epoxy glass cloth substrate or phenolic resin glass cloth substrate, there are a small amount of paper-based CCL. Although these substrates have excellent electrical properties and processability, they are poor in heat dissipation and can hardly be expected to heat heat from the PCB itself, but from the surface of the component to the surrounding air. But with the electronic products have entered the miniaturization of components, high-density installation, high fever assembly era, if only the surface area is very small component surface to heat is not enough. At the same time due to QFP, BGA and other surface-mounted components of the extensive use of components generated by the heat generated by a large number of PCB board, so the best way to solve heat dissipation is to improve the thermal contact with the heating element PCB itself, Pass out or emit out.
3, the use of reasonable alignment design to achieve heat
As the resin in the plate is poor in thermal conductivity, and copper foil lines and holes are hot conductor, so to improve the copper foil residual rate and increase the heat conduction hole is the main means of heat dissipation.
Evaluating the heat dissipation capacity of the PCB requires calculation of the equivalent thermal conductivity (Nine eq) of the composite substrate consisting of a variety of materials with different thermal conductivity.
4. For equipment with free convection air cooling, it is advisable to arrange the integrated circuits (or other devices) in an elongated manner or in a horizontally long way.
5. The devices on the same printed circuit board should be arranged as far as possible according to the size of the heat and the degree of heat dissipation. The devices with small heat or poor heat resistance (such as small signal transistors, small scale integrated circuits, electrolytic capacitors, etc.) In the most upstream (inlet) of the cooling airflow, devices with high 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, the high-power devices are arranged as close as possible to the edge of the printed circuit board in order to shorten the heat transfer path; in the vertical direction, the high-power devices are arranged as close as possible to the printed circuit board in order to reduce the operation of these devices to other devices The effect of temperature.
7, the temperature sensitive devices are best placed in the lowest temperature areas (such as the bottom of the device), do not put it directly on the heating device, multiple devices are best in the horizontal plane staggered layout.
8, the equipment within the printed circuit board cooling mainly rely on air flow, so in the design to study the air flow path, a reasonable configuration device or printed circuit board. Air flow always tends to flow where the resistance is small, so when configuring the device on a printed circuit board, avoid having a larger airspace in a certain area. Machine in the multi-block printed circuit board configuration should also pay attention to the same problem.
9. To avoid the concentration of hot spots on the PCB, as far as possible the power evenly distributed on the PCB board to maintain the PCB surface temperature performance uniformity and consistency. Often in the design process to achieve a strict uniform distribution is more difficult, but must avoid the power density is too high in the area, so as to avoid overheating the normal operation of the entire circuit. If conditions permit, the thermal performance analysis of the printed circuit is necessary, such as some of the professional PCB design software to increase the thermal performance index analysis software module, you can help designers optimize the circuit design.
10, the highest power consumption and heat the largest device arranged in the vicinity of the best heat dissipation. Do not place higher heaters on the corners of the printed circuit board and the surrounding edges unless a heat sink is arranged near it. In the design of power resistors as much as possible to choose a large number of devices, and in the adjustment of printed circuit board layout so that it has enough cooling space.
11, high heat dissipation devices should be connected with the substrate should be able to reduce the thermal resistance between them. In order to better meet the thermal characteristics of the requirements, in the bottom of the chip can use some thermal conductivity materials (such as applying a layer of thermal silica gel), and maintain a certain contact area for the device heat.
12, the device and the substrate connection:
(1) to minimize the device lead length;
(2) When selecting high-power devices, consider the thermal conductivity of the lead material, if possible, try to select the maximum cross-section;
(3) select the pin count more devices.
13, the device package selection:
(1) in considering the thermal design should pay attention to the device package description and its thermal conductivity;
(2) Consideration should be given to providing a good heat transfer path between the substrate and the device package;
(3) in the heat conduction path should be avoided with air partition, if there is such a situation can be used to fill the thermal material.