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Three ways for power module heat dissipation

Article Source：Kinri Energy | Author：Kinri Energy | Issuing Time：2024.05.21
There are three ways for power module heat dissipation: convection, conduction, and radiation. In practical applications, convection is mostly used as the main heat dissipation method. If the design is appropriate and combined with two heat dissipation methods, conduction and radiation, the effect will be maximized. But if not designed properly, it can cause a backlash. Therefore, when designing power modules, designing a cooling system has become an important aspect.


AC DC POWER MODULE


1. Convective heat dissipation method

Convective heat dissipation refers to the transfer of heat through the fluid medium air to achieve heat dissipation, which is a commonly used heat dissipation method. There are generally two types of convection methods, forced convection and natural convection. Forced convection refers to the transfer of heat from the surface of a heating object to the flowing air, while natural convection refers to the transfer of heat from the surface of a heating object to the cooler surrounding air. The advantages of using natural convection are simple implementation, low cost, no need for external cooling fans, and high reliability. Forced convection requires a larger volume of heat sink to reach the normal substrate temperature, which takes up usage space.

When designing a natural convection heat sink, attention should be paid. If the horizontal heat sink has poor heat dissipation effect, the area of the heat sink should be appropriately increased or forced convection heat dissipation should be used when installing horizontally.

2. Conduction heat dissipation method

During the use of the power module, the heat on the substrate needs to be transmitted to a distant heat dissipation surface through the thermal conductive element. In this way, the temperature of the substrate will be equal to the temperature of the heat dissipation surface, the temperature rise of the thermal conductive element, and the sum of the temperature rises of the two contact surfaces. This method can evaporate thermal energy in an effective space, ensuring that the components can work properly. The thermal resistance of thermal conductive components is proportional to their length and inversely proportional to their cross-sectional area and thermal conductivity. If the installation space size and cost are not considered, the heat sink with the lowest thermal resistance value should be used. Because every time the substrate temperature of the power supply drops, the average time between failures will be significantly improved, the stability of the power supply will also be improved, and the service life will be longer.

Temperature is an important factor affecting power supply performance, so when choosing a heat sink, it is important to focus on its manufacturing materials. In practical applications, the heat generated by the module is transmitted from the substrate to the heat sink or thermal conductive element. However, there will be a temperature difference on the contact surface between the power substrate and the thermal conductive element, which must be controlled. The temperature of the substrate should be the sum of the temperature rise of the contact surface and the temperature of the thermal conductive element. If not controlled, the temperature rise of the contact surface will be particularly significant. So the contact surface area should be as large as possible, and the smoothness of the contact surface should be within 5 mils, which is within 0.005 inches.

In order to eliminate surface unevenness, thermal conductive adhesive or pad should be filled on the contact surface. After taking appropriate measures, the thermal resistance of the contact surface can be reduced to below 0.1 ℃/W. Only by reducing the heat dissipation resistance or power consumption can the temperature rise be reduced. The maximum output power of the power supply is related to the application environment temperature, and the influencing parameters generally include loss power, thermal resistance, and the maximum power supply shell temperature. Power supplies with high efficiency and good heat dissipation will have a lower temperature rise, and there will be a margin for their available temperature at rated power output. Power supplies with lower efficiency or poor heat dissipation will have a higher temperature rise because they require air cooling or need to be downgraded for use.

3. Radiation heat dissipation method

Radiative heat dissipation is the continuous radiative transfer of heat that occurs when two interfaces with different temperatures are facing each other. The effect of radiation on the temperature of a single object depends on many factors, such as the temperature difference of various components, the external environment of the components, the position of the components, and the influence of distance between them. In practical applications, these factors are difficult to quantify, and coupled with the influence of radiative energy exchange in the surrounding environment, it is difficult to accurately calculate the chaotic impact of radiation on temperature.

In practical applications, it is not possible to use radiation cooling alone for power supply, as this method can generally only dissipate 10% or less of the total heat. It is usually used as an auxiliary means of the main cooling method, and its impact on temperature is generally not considered in thermal design. When the power supply is in operation, its temperature is generally higher than the ambient temperature, and radiation transfer helps with overall heat dissipation. But in special circumstances, the radiation from heat sources near the power supply, such as high-power resistors, device boards, etc., can cause the temperature of the power module to rise.
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