LED lighting cooling failure reasons
The PN junction heating of the LED is first conducted to the surface of the wafer by the wafer semiconductor material itself, which has a certain thermal resistance. From the perspective of the LED component, depending on the structure of the package, there is also a thermal resistance of different sizes between the wafer and the holder. The sum of these two thermal resistances constitutes the thermal resistance Rj-a of the LED. From the user's point of view, the Rj-a parameter of a specific LED cannot be changed. This is a problem that LED packaging companies need to study, but it is possible to reduce the Rj-a value by selecting products or models from different manufacturers. .
In LED luminaires, the heat transfer path of LED is quite complicated. The main way is LED-PCB-heatsink-fluid. As a designer of luminaires, the really meaningful work is to optimize the luminaire material and heat dissipation structure to reduce LED components as much as possible. Thermal resistance between fluids.
As a carrier for mounting electronic components, the LED components are mainly connected to the circuit board by soldering. The overall thermal resistance of the metal-based circuit board is relatively small. Commonly used are copper substrates and aluminum substrates, and the aluminum substrates are relatively low in price. It has been widely adopted by the industry. The thermal resistance of the aluminum substrate varies depending on the process of different manufacturers. The approximate thermal resistance is 0.6-4.0 ° C / W, and the price difference is relatively large. The aluminum substrate generally has three physical layers, a wiring layer, an insulating layer, and a substrate layer. The thermal conductivity of general electrical insulating materials is also very poor, so the thermal resistance mainly comes from the insulating layer, and the insulating materials used are quite different. Among them, the ceramic-based insulating medium has the smallest thermal resistance. A relatively inexpensive aluminum substrate is generally a glass fiber insulating layer or a resin insulating layer. The thermal resistance is also positively related to the thickness of the insulation layer.
Under the condition of both cost and performance, the aluminum substrate type and the aluminum substrate area are reasonably selected. In contrast, the correct design of the heat sink shape and the best connection between the heat sink and the aluminum substrate is the key to the success of the luminaire design. The real factor in determining the amount of heat dissipation is the contact area of the heat sink with the fluid and the flow rate of the fluid. General LED lamps are passively dissipated by natural convection, and thermal radiation is also one of the main methods of heat dissipation.
Therefore, we can analyze the reasons for the failure of LED lamps to dissipate heat:
1. The LED light source has a large thermal resistance, and the light source cannot be dissipated. The use of the thermal paste will cause the heat dissipation movement to fail.
2. The aluminum substrate is used as the PCB connection light source. Because the aluminum substrate has multiple thermal resistances, the heat source of the light source cannot be transmitted, and the use of the thermal grease will cause the heat dissipation motion to fail.
3. There is no space for thermal buffering of the light-emitting surface, which will cause the heat dissipation of the LED light source to fail, and the light decay is advanced. The above three reasons are the main reasons for the failure of LED lighting equipment in the industry, and there is no more thorough solution. Some large companies use a ceramic substrate for heat dissipation in a lamp-integrated package, but they cannot be widely used due to their high cost.
Therefore, some improvements have been proposed:
1. The surface roughening of the heat sink of the LED lamp is one of the ways to effectively improve the heat dissipation capability.
Surface roughening means that no smooth surface is used, which can be achieved by physical and chemical methods. Generally, it is a method of sand blasting and oxidation. Coloring is also a chemical method, which can be completed together with oxidation. When designing the profile grinding tool, it is possible to add some ribs to the surface to increase the surface area to improve the heat dissipation capability of the LED lamp.
2. A common way to improve the heat radiation capability is to use a black colored surface treatment.