This paper focuses on thermal analysis of the thermal performance of LEDs from a packaging perspective and thermal design. COB technology is used to directly package the LED chip on the aluminum substrate, shortening the distance between the hot channel and the heat conduction, thereby reducing the junction temperature of the LED, and designing an LED based on the COB technology. The equivalent thermal resistance network is analyzed, and the influence of different packaging methods on the heat dissipation performance of the whole LED device is compared, and the infrared thermal image analysis is performed.
introduction
The power loss of the LED device in operation is usually expressed in the form of thermal energy dissipation. Any part with resistance becomes an internal heat source, causing the heat density to rise sharply, so the temperature of the device itself also rises, and the surrounding ambient temperature will also increase. Affects internal temperature, which affects the reliability, performance and longevity of the LED. Studies have shown that as the temperature increases, the chip failure rate tends to increase. Therefore, reliable thermal design for LED packaging and implementation of effective thermal control measures are the key to improving its reliability.
In the electronics industry, for every 10 °C increase in the ambient temperature of the device, the failure rate is often increased by an order of magnitude. This is called the "10 °C rule." Most of the methods currently used are based on the material of the circuit board, and some materials with high thermal conductivity and stability, such as copper, aluminum, ceramics, etc., are selected. However, it is not enough to improve the heat dissipation problem only through the circuit board. It is also necessary to improve the heat dissipation performance of the LED through other thermal design methods.
Heat dissipation technology
Any electronic device and circuit is inevitably accompanied by heat generation. To improve its reliability and performance, heat must be minimized, and proper heat dissipation technology is the key.
When the substance itself or when it comes into contact with matter, the transfer of energy is called heat conduction. This is the most common form of heat transfer. Light is transmitted by direct contact between particles with lower energy and particles with higher energy. In contrast, the heat transfer mode is limited to solids and liquids because the molecular composition of the gas is not very tight, and the transfer of energy between them is called thermal diffusion.
The basic formula for heat transfer is:
Q=K×A×ΔT/ΔL (1)
Where Q is heat, which is the heat generated or conducted by heat conduction; K is the heat transfer coefficient of the material, the heat transfer coefficient is similar to specific heat, but it is different from the specific heat, the heat transfer coefficient is inversely proportional to the specific heat, and the heat transfer coefficient is higher. The lower the value of the specific heat. For example, the thermal conductivity of pure copper is 396.4, and its specific heat is 0.39; in the formula, A represents the heat transfer area (or the contact area of ​​two objects), ΔT represents the temperature difference between the two ends; ΔL is the distance between the two ends. . Therefore, we can find from the formula that the heat transfer is proportional to the heat transfer coefficient and heat transfer area, and inversely proportional to the distance. The higher the heat transfer coefficient, the larger the heat transfer area, and the shorter the distance traveled, the higher the energy of heat transfer, and the easier it is to carry away heat.
LED thermal performance and packaging
As a new generation of light source, LED is gradually applied to general illumination. The most basic optical requirement is luminous flux. At present, there are two ways to increase the luminous flux of LED, which are to increase the brightness of the chip and multiple dense arrays. These methods need to be input. Higher power energy, and only a small part of the input LED energy will be converted into a light source, most of which will be converted into heat energy, and the multiplied current will be sent in a single package, and the heat will naturally double, so in such a small heat dissipation Under the area, the heat dissipation problem will gradually deteriorate.
Like traditional light sources, LEDs generate heat during operation, depending on the overall luminous efficiency. Under the action of electrical energy is applied, the radiative recombination of electrons and holes electroluminescence occurs, in the vicinity of the PN junction of the light radiated from the chip itself needs led through a semiconductor package media and the media to reach the outside world. Comprehensive current injection efficiency, radiation luminescence quantum efficiency, external light extraction efficiency, etc., finally only 30%~40% of the input electrical energy is converted into light energy, and the remaining 60%~70% of the energy is mainly caused by non-radiative recombination lattice vibration. The form is transformed into heat. The increase in the temperature of the LED chip enhances the non-radiative recombination, further weakens the luminous efficiency, and shortens the lifetime. The heat dissipation technology adopted by the led lamp must be able to effectively reduce the thermal resistance of the light-emitting diode PN junction to the environment, in order to reduce the PN junction temperature of the LED as much as possible to improve the life of the LED lamp.
Figure 1 shows the relationship between the light decay and junction temperature of Lumidleds 1w led under constant operating current. It can be seen that the higher the junction temperature, the faster the luminous flux decays and the shorter the lifetime.
Our substantial chair comes with well-sewn PU cover and solid sponge padding. The relaxing backrest offers you good back support and reduces pains resulted from long time seating. Skin-friendly stylish armrests help release stress on your shoulders and give you added comfort. Every corner of this fine chair is good to touch and designed with sleek curves to avoid accidental protrusion hurt/damages.
Leather Master Chair, Beauty Master Chair, Design Master Chairs, Master Office Chairs
TOM SPA BEAUTY SALON EQUIPMENT CO.,LTD , https://www.tomspabeauty.com