1, the thermal performance of the device parameters Device manufacturers will provide the device's soldering temperature, package form, operating temperature range, device junction temperature limits, internal thermal resistance and other information, which is the parameters of the thermal design basis and premise. The following describes some of the commonly used thermal parameters one by one:
TDP—The device's thermal dissipation power, in W (Watts), represents the actual heat output of the device
Tc - device housing temperature in °C
Tj - junction temperature, in °C. As the junction temperature increases, the semiconductor device performance will decrease. When the junction temperature exceeds the maximum limit, the device lifetime is extremely reduced or even burned. This is the focus of thermal design.
Ta--ambient temperature in °C
Rja - Thermal resistance from junction to ambient, in °C/W
Rjc - Thermal resistance from junction to device case in °C/W
In the final analysis, the main task of thermal design is to satisfy: Tj<Tj(max) and leave an appropriate margin (usually guaranteed to have more than 10% margin).
Tj(max)=P* Rjc+ Tc(max)
Tc (max) is the maximum temperature of the device surface, it is clear that the more successful the thermal design, the lower the Tc(max).
2, the choice of cooling method
The choice of system cooling method should fully consider the system's thermal power consumption, temperature / volume / weight requirements, protection class, the operability of the heat sink, the price and many other factors, and ultimately choose the most suitable for their products, effective cooling method. Heat dissipation is mainly divided into natural heat dissipation and forced air cooling. Liquid cooling and so on. At present, the commonly used cooling method is still air cooling. The following table reflects the relationship between heat flux and temperature rise under different heat dissipation conditions.
Natural heat dissipation: The natural convection of air brings heat to the surrounding space. This heat dissipation method can be used in occasions where the heating power is low, weight, temperature, etc. are not required. Advantages: simple structure, no noise, low price.
Forced Air Cooling: For devices with large power dissipation, it is necessary to use forced air cooling, especially with some high-efficiency heat sinks to achieve the desired cooling effect. Because of the high efficiency of forced air-cooled heat exchange, it is generally several times that of natural heat dissipation. Advantages: high heat dissipation, product weight can be greatly reduced.
3, fan selection and air duct design
If the system uses forced air-cooled heat dissipation, choosing a suitable cooling fan directly determines the system cooling conditions. To perform fan selection, first determine the amount of cooling air required by the system and calculate it by the following formula:
Where ∆T represents the temperature difference between the system inlet/outlet.
The selection of the fan system must be combined with system air volume requirements, system resistance, fan characteristics, and other requirements for comprehensive assessment and confirmation.
Forced air cooling system is the key to the actual wind tunnel, the air duct is generally divided into two ways: air supply and air extraction. The advantages and disadvantages of these two methods are:
Air way:
A. The airflow near the fan outlet is mainly turbulent and the local heat exchange is strong. It should be used when the heating device is relatively concentrated. At this time, the main air outlet of the fan must be aligned with the centralized heating element.
B. When the air blows, a positive pressure will be formed in the device to prevent the dust in the gap from entering the device.
C. Fans will not be affected by the amount of heat dissipated by the system. They will work at lower air temperatures and have a longer fan life.
Ventilation method:
A. Uniform air supply, suitable for uniform distribution of heating devices and complicated air ducts
B. The flow entering the fan is mainly laminar
C. The fan will work under the high temperature air outlet and the life will be affected
D. Negative pressure is formed in the system. Dust in the gap will enter the cabinet/box.
4. Heatsink Optimization The heatsink optimization for high-power devices is mainly to optimize the design of the heatsink substrate thickness, tooth plate thickness, spacing, height, and surface treatment methods. With the continuous advancement of computer simulation technology, we can rely on electronic thermal simulation analysis software to optimize the radiator, and the optimized results are accurate and intuitive.
5, the correct installation
Correct and reasonable installation can ensure that the heat-dissipation products play a good role and enhance the overall reliability of the product. We know that in the process of installing heat-dissipation products, it is mainly to ensure that the device and the heat sink have a good and sufficient surface contact - so that the thermal contact resistance between the device and the heat sink is as low as possible.
The main factors that affect the thermal contact resistance are the following:
1, the contact surface flatness
2, heat dissipation products and heat source contact pressure
3. Selection and application of thermal interface materials It is recommended to use special fixtures for correct smearing of interface materials. You can refer to the pictures below to ensure that the thermal interface materials are uniform. Generally, the thickness needs to be controlled between 0.12-0.18mm.