PCB Blog - Thermal Design of Switching Power Supply on Metal PCB board

1. Natural air cooling and forced air cooling
In the actual PCB board design of switching power supply, two forms of natural air cooling and fan forced air cooling are usually used. When installing a natural air-cooled heat sink, the blades of the heat sink should be placed vertically upward. If possible, several ventilation holes can be drilled around the installation position of the heat sink on the PCB board to facilitate air convection. Forced ventilation cooling is to use a fan to force air convection, so the design of the air duct should also make the axial direction of the blades of the heat sink consistent with the exhaust direction of the fan. Close to the exhaust fan, in the case of an exhaust fan, the thermal resistance of the heat sink is shown in the table.

2. Metal PCB board
With the miniaturization of switching power supplies, surface-mount components are widely used in actual production of crystals, and it is difficult to install heat sinks on power devices at this time. At present, the main method to overcome this problem is to use metal PCB boards as the carrier of power devices. There are mainly aluminum-based copper-clad boards, iron-based copper-clad boards, and metal PCB boards. The heat dissipation performance is much better than that of traditional PCB boards, and SIVD can be mounted. element. There is also a copper core PCB board. The middle layer of the substrate is a copper plate insulation layer, which adopts a high thermal conductivity epoxy glass fiber cloth adhesive sheet or a high thermal conductivity epoxy resin. It can mount SMD components on both sides, and high-power SND components can be The heat sink of the SMD itself is directly welded on the metal PCB board, and the metal plate in the metal PCB board is used to dissipate heat.

3. Arrangement of heating elements
The main heating elements in the switching power supply are high-power semiconductor devices and their radiators, power conversion transformers, high-power resistors, etc. The basic requirement for the layout of heating elements is to arrange them from small to large according to the degree of heat generation. The smaller the calorific value, the higher the wind direction of the switching power supply air duct, the closer the device with the larger calorific value is to the exhaust fan. . In order to improve production efficiency, multiple power devices are often fixed on the same large heat sink. At this time, the heat sink should be placed as close to the edge of the PCB as possible. However, there should be at least a distance of more than 1cm from the shell or other parts of the switching power supply. If there are several large heat sinks on one circuit board, they should be parallel to each other and the wind direction of the air duct. In the vertical direction, devices that generate less heat are arranged in layers and devices that generate more heat are placed higher. Heat-generating components should be placed as far away as possible from temperature-sensitive components, such as electrolytic capacitors, on the PCB board layout.