Views: 0 Author: Site Editor Publish Time: 2021-06-05 Origin: Site
The LED light source is powered on, and the P-N junction area inside the chip starts to work, where heat is generated and accumulated, and the temperature when the state reaches a stable state is called the junction temperature. In the actual measurement process, because the chip has been encapsulated, the temperature of the material cannot be directly tested. Therefore, the temperature of the pin electrode is usually used to indirectly indicate the junction temperature of the light source. The lower the junction temperature of the light source, the better the heat dissipation.
Usually, what directly affects the junction temperature of the LED light source is the material selected for the light source chip and the packaging form it adopts. The materials involved in the LED light source have a certain resistance value from the inside to the outside, and the size of these resistance values reflects the heat dissipation capacity of the light source to a certain extent. The larger the resistance value, the stronger the hindering effect of this material on heat transfer, the lower the transfer efficiency, and the heat will accumulate in the chip part as the working time goes by.
The LED light source is a more complex optical component, and its packaging structure design is interlocked layer by layer, the purpose is to make the light emitted by the chip output as much as possible to the outside of the packaging material. However, because the material itself has a certain refractive index, that is, the internal light cannot be completely transmitted to the outside, and the remaining part is continuously reflected inside the package, and finally converted into heat energy that is dissipated to the outside through heat conduction and heat convection to maintain energy conservation.
Because high-power LED light sources generate serious heat, it is usually necessary to add a heat sink to assist in heat dissipation, and the heat dissipation capacity of the heat sink directly affects the temperature of the light source chip. If the radiator has good heat dissipation performance and strong heat dissipation capacity, the more heat exchange between the heat and the surrounding environment, the faster the heat transfer to the outside world and the lower the temperature. Most of the packaging materials on the upper part of the chip are epoxy resins with extremely low thermal conductivity, so it can act as an insulator. The temperature of the chip cannot be dissipated into the air through the epoxy resin. Therefore, when heat is generated in the chip part, the heat will flow to the chip. The subsequent heat transfer medium transfers to the external heat sink and is emitted into the outside air. Obviously, the thermal conductivity of related packaging materials is a key factor affecting the heat dissipation performance of the heat sink.
In order for the UV-LED light source to work for a long time at room temperature, it is necessary to implement safe and reliable thermal management for the UV-LED light source to ensure that the maximum temperature of the UV-LED light source is below the critical value of the chip. The thermal management of UV-LED light source can be roughly divided into two links. In the production link of the light source, the chip packaging materials and packaging methods are innovated to improve the heat dissipation efficiency.
However, in engineering applications, adding external radiators can effectively enhance the heat dissipation performance. The structure of the radiator is diverse, such as fin type, heat pipe type, current sharing plate type and micro groove type, etc., which can effectively improve the heat dissipation efficiency of the UV-LED light source.
UV-LED radiator mechanism design and heat dissipation performance analysis:
UV-LED Three-Dimensional Model of Curing Light Source
In order for the UV-LED light source to work for a long time at room temperature, it is necessary to implement safe and reliable thermal management for the UV-LED light source to ensure that the maximum temperature of the UV-LED light source is below the critical value of the chip.
The heat dissipation design of UV-LED light source can be subdivided into chip level, package level and system level. The first two are determined by the light source in the production process. The research focus of this article is on the system-level heat dissipation problem, that is, to optimize the structure of the auxiliary heat sink of the UV-LED light source.
UV-LED radiator structure design:
The light source is composed of 60 UV-LED lamp beads with a power of 1W in series and installed on the PCB board. Connecting the PCB board and the aluminum substrate is thermal conductive silicone grease, which has good thermal conductivity and can conduct the heat generated by the UV-LED light source through the aluminum fins. The radiator is inside the curing light source, and its initial model is shown in the figure below:
Three Dimensional Model of Radiator Foundation
The radiator materials copper and aluminum have good thermal conductivity at room temperature, but considering the cost factor, the unit mass price of copper is three times that of aluminum, and the copper material has a high density, which is the material consumed to produce radiators of the same size. More. In terms of processing technology, the molding of copper under high temperature conditions is limited, and it cannot be extruded like aluminum. Based on the above factors, the UV-LED light source radiators designed in this paper are all made of aluminum, and the influence of other materials on the heat dissipation effect is not considered.
The use of forced heat exchange of low-temperature air-conditioning can effectively reduce the ambient temperature, which has greatly improved the heat dissipation efficiency of the radiator. Secondly, since the air-conditioning is introduced from the outside, the gas flow rate will be greater than the air flow rate under natural convection conditions. , can improve the convective heat transfer coefficient of the system. The structure of the radiator is optimized by combining the flow characteristics of the cold air and the total thermal resistance of the system.