The PN junction of LED is mainly conductive to the chip through the semiconductor material itself, which has an inevitable thermal resistance. From the perspective of LED components, depending on the packaging structure, there will also be thermal resistance of different sizes between the chip and the bracket. The sum of these two thermal resistances constitutes the thermal resistance Rj-a of LED. From the user's point of view, the Rj-a parameter of a specific LED cannot be changed. This is a subject that LED packaging enterprises need to study. However, the Rj-a value can be minimized by selecting products or models from different manufacturers.
Among LED lamps, the heat transfer path of LED is quite complex, and the first way is LED PCB heatsink fluid. As a designer of lamps, it is the intention to optimize the materials and heat dissipation structure of lamps and reduce the thermal resistance between LED components and fluid as much as possible.
As the carrier for the installation of electronic components, LED components are still connected to the circuit board mainly by welding. The overall thermal resistance of the metal based circuit board is relatively small. Copper substrate and aluminum substrate are often used. Aluminum substrate is widely adopted in the industry because of its relatively low price. The thermal resistance of aluminum substrate is different due to different manufacturers' processes. The approximate thermal resistance is 0.6-4.0 ° C/W, and the price difference is also large. The aluminum substrate generally has 3 physical layers, including the circuit layer, insulation layer and substrate layer. The thermal conductivity of general electrical insulation materials is also very poor, so the thermal resistance mainly comes from the insulation layer, and the insulation materials used are different. In this case, the thermal resistance of ceramic based insulating medium is small. The relatively cheap aluminum substrate generally adopts glass fiber insulation layer or resin insulation layer. The thermal resistance is also positively related to the thickness of the insulating layer.
On the premise of coordinating the cost and function, the type and area of aluminum substrate should be reasonably selected. In contrast, accurate design of radiator shape and good connection between radiator and aluminum substrate are the key points for the success of lamp design. The factors determining the heat dissipation capacity are the area of the contact surface between the radiator and the fluid and the flow rate of the fluid. General LED lamps are passive heat dissipation by natural convection, and thermal radiation is also one of the primary heat dissipation methods.
Therefore, we can explain the reasons for the failure of LED wall washing lights:
1. The thermal resistance of LED light source is large, and the heat cannot be dissipated from the light source. The use of thermal conductive paste will lead to the failure of heat dissipation. Wall washing lamp lighting procurement
2. The aluminum substrate is used as the light source adjacent to the PCB. Because the aluminum substrate has multiple thermal resistances, the heat from the light source cannot be transmitted, and the use of thermal conductive paste will lead to the failure of heat dissipation activities.
3. There is no necessary space for thermal buffering of the light-emitting surface, which will cause heat dissipation failure of the LED light source and premature light failure. The above three reasons are the primary reasons for the heat dissipation failure of LED lighting equipment in the industry, and there is no complete solution. Some companies apply ceramic substrate for heat dissipation in integrated packaging of lamp beads, but they can not get widespread use because of high cost.
Therefore, some improvement methods are proposed:
Overview of LED wall washing light radiator Roughening is one of the ways to improve heat dissipation
Roughening is not to use slippery surface, but can be achieved by physical and chemical means, usually by sandblasting and oxidation. Coloring is also a chemical method, which can be completed together with oxidation. When designing profile abrasives, you can add some channels and add profile products to improve the heat dissipation capacity of LED lights.