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Cooling is the main content of PCB thermal design. The purpose of heat dissipation in the component temperature exceeds the reliability guarantee temperature, take appropriate cooling measures, so that the temperature dropped to the reliability of the working range. PCB heat dissipation mainly from the thermal conductivity, convection, radiation to carry out three aspects. This article describes the PCB circuit board cooling design techniques
First, the components arranged heat.
1, the components arranged to meet the cooling requirements
Staggered arrangement. In layout design components layout, should be heating components and general devices and temperature-sensitive devices to distinguish between the heat around the device should be left adequate cooling gas flow channel, heating elements should be staggered distribution. This is usually the same arrangement of the normal arrangement of the opposite, help to improve the cooling effect. In this case,
When the thermal performance of different components of the mixed installation, it is best to heat the components installed in the wind, the heat exothermic components installed in the wind, or heat-resistant components will be in the path of heat dissipation, its The result is a higher temperature at the part where the heat resistance is poor. When the heat-resistant elements are arranged at the same level, the order of arrangement is that the power consumption is high, and the components having poor heat dissipation are placed in the upwind. In this case,
2, the high heat devices heat
When a small number of components in the PCB when the heat is large, can be added in the heating device on the radiator or heat pipe, when the temperature can not come down, you can use a fan with a radiator to enhance the cooling effect. When the amount of heating device is large, you can use a large heat shield, which is based on the PCB board heating device location and level of custom heat sink or in a large flat radiator to cut out the different components of high and low position. Place the heat sink over the component surface, and contact each component to dissipate heat. But because of the high and low consistency of components when welding poor, heat dissipation is not good. Usually in the component surface plus a soft thermal phase change thermal pad to improve the cooling effect.
Second, PCB circuit board cooling
PCB board is copper / epoxy glass cloth substrate or phenolic resin glass cloth substrate, there are a small amount of paper-based copper clad sheet. Although these substrates have excellent electrical properties and processability, they have poor heat dissipation, and the heat dissipation path of the high heat generating element is to dissipate heat from the surface of the element to the ambient air. But only very small surface area of the component surface to heat is not enough. At the same time as the heat generated by a large number of components passed to the PCB board, so the best way to solve heat dissipation is to increase direct contact with the heating element of the PCB's own cooling capacity, through the PCB board out or distributed out. In this case,
1, the choice of good heat dissipation plate
Epoxy glass cloth sheet thermal conductivity of a 0.2W / m ℃. Ordinary electronic circuit due to heat a small, usually epoxy glass cloth substrate production, the heat generated by a small amount of heat through the alignment of the general design and components themselves distributed out. With the miniaturization of components, high integration, high frequency, the heat density increased significantly, especially the use of power devices, in order to meet this high heat requirements later developed a number of new thermal conductivity sheet.
2, the use of reasonable alignment cooling
Because of the poor thermal conductivity of the resin in the sheet metal, copper foil and the hole is a good conductor of heat, so to improve the copper foil remaining rate and increase the thermal hole is the main means of cooling. PCB heat dissipation capacity, the need for thermal conductivity of different PCB insulation substrate with the equivalent thermal conductivity calculation. The thicker the copper foil, the higher the residual rate of copper foil, the more the number of layers, the greater the equivalent thermal conductivity, P C B board, the better the cooling effect.
PCB thickness direction of the thermal conductivity coefficient of thermal conductivity than the surface is much smaller. In order to improve the thermal conductivity in the thickness direction, a heat conduction hole may be used. The thermal vias are through: the metallized holes of the PCB. The effect is equivalent to a thin copper tube along the PCB thickness direction from its surface through the PCB is the back of the heat conduction, heat the heat back to the PCB quickly escape or conduction to other thermal layer. Such as IC mounted on the bare chip in the PCB, PCB board in the bottom of the set of numerous thermal holes of the design program is gaining popularity. Therefore, in the PCB alignment to improve the cooling capacity, should be thick, thick copper foil, thin, multi-layer, large area of copper, plus thermal hole design