LED is characterized by its small size, low power consumption, environmental protection, durability and rich color of light source.
It is highly favored by the majority of users.
However, one of the bottlenecks in the development of LED lighting is heat dissipation. In this paper, the importance of heat dissipation technology in LED lighting is derived by analyzing the influence of the heating problem in the lighting process on LED, and the current and future heat dissipation technology is summarized and analyzed.
1. Existing heating problems and effects in LED lighting
LED lighting problem
In the process of using LED lighting, as with traditional lighting methods, electrical energy needs to be converted to light energy.
However, in neither of these two ways, the electric energy can be completely converted into light energy, and only a small part of it can be converted into light energy. The rest of the electric energy (60% to 70%) is converted into heat energy in the process of LED light and illumination.
Especially for high-power LED devices and lighting lamps, as the power increases, the temperature of the internal LED chip will gradually rise, and the performance of the internal LED chip and other devices will decline or even fail as the temperature rises.
Eventually, the LED device fails to work.
Basically, the increase of junction temperature reduces the probability of light - emitting composite of PN junction.
The performance on the light source is the brightness of the luminescence drop, resulting in saturation phenomenon.
Therefore, the heating problem is an urgent problem to be solved in the development of LED.
Influence of heating problem on LED
As mentioned above, the heating problem not only affects the life of LED devices, but also affects the luminosity.
Experience shows that the life of LED, especially high-power LED, mainly depends on the junction temperature of the chip.
The lower the reliability, the shorter the service life.
Therefore, it is not only necessary to design LED devices comprehensively from the aspects of LED materials, manufacturing method, packaging structure and luminous principle, but more importantly, to solve the problem of heat dissipation in existing LED devices and lamps, select appropriate packaging structure and reasonable heat dissipation mode, and apply them to LED lighting.
Ii. Current status of LED lighting heat dissipation technology
Aiming at the limitation of LED devices and lamps in converting electrical energy into light energy, the concept of heat dissipation technology is proposed.
Heat dissipation aims to solve the problem of the effect of the heat generated by electrical energy on the internal LED chip (making the performance of the chip decline, aging or even failure) in the LED lighting process.
1. Main factors affecting LED heat dissipation
The main factors influencing heat dissipation include material properties (thermal conductivity), packaging structure, packaging material, chip size, chip material, current density on chip, etc.
Generally, LED lighting devices and lamps are made up of chips, substrates, external radiators and drivers.
Therefore, there are currently two design schemes for heat dissipation: one is to reduce the conversion of LED devices from electrical energy to thermal energy, and the realization process needs to improve the internal quantum efficiency of LED internal devices, so as to improve the efficiency of LED output, and then solve the heat dissipation problem of LED in lighting (use) from the inside.
On the second side, from the perspective of external design, the packaging materials or packaging methods of LED devices and lamps are changed to reduce the packaging thermal resistance. Sometimes, a suitable radiator is needed to solve the problem of high junction temperature, so as to extend the service life of LED devices.
2. Existing heat dissipation mode
Due to the limitations in technology, the external design of LED lighting device or the use of radiators are often adopted to solve the heat dissipation problem.
At present, there are many ways of heat dissipation of LED lighting devices, which can be divided into encapsulation-level heat dissipation and luminaire level heat dissipation.
Encapsulation-level heat dissipation mode, as the name implies, is to achieve the effect of reducing the encapsulation thermal resistance by optimizing the LED internal packaging structure and materials, which is mainly divided into silicon substrate chip (fban) structure, metal circuit board structure, and the selection principle of material based on substrate material and adhesive material.
And the cooling way to lamps and lanterns class mainly refers to the heat from the packaging substrate to transfer in the process of implementation of the external radiator cooling way, mainly divided into passive and active cooling heat dissipation, active cooling refer to energy through the system drive, LED internal chip and the heat out of the device itself, mainly including adding fans forced cooling, surface heat dissipation, semiconductor refrigeration and heat dissipation, ion wind cooling and synthetic jet cooling, etc.;
Passive heat dissipation refers to that the heat generated in the LED lighting process is dispersed only through the radiator itself to achieve the effect of reducing the junction temperature, which mainly includes direct natural convection heat dissipation and heat pipe (flat heat pipe, loop heat pipe and finned heat pipe) technology.
3. Examples of several heat dissipation modes
(1) principle of material selection
The premise of adopting this heat dissipation method is that the packaging structure has been determined, and the most suitable packaging materials can be selected according to the determined packaging structure to improve the thermal conductivity of the system, so as to reduce the encapsulated thermal resistance of LED lighting devices, and finally achieve the heat dissipation effect of the system.
Packaging materials can be roughly divided into three types: substrate materials, paste materials and packaging materials.
As far as the substrate material is concerned, the heat dissipation technology involved in LED lighting devices requires the substrate material to have high electrical insulation, high stability, high thermal conductivity and the heat expansion coefficient matched by the chip.
Common substrate materials include silicon, metals (aluminum, copper, etc.), ceramics (A1N, SiC) and composites.
(2) liquid cooling
Liquid cooling is a kind of heat dissipation technology which USES the liquid to flow through the radiator surface under the forced driving of the pump.
Us manufacturer Etemaleds has introduced a "water-cooled" LED lamp - Etemaleds HydraLux one.
By adopting the liquid-cooled heat dissipation method, it not only saves the heat dissipation pipe, radiator fin and fan used to cool the inside of the bulb, but also does not cover the heat dissipation material in the upper part of the bulb. Its radiation Angle is expanded to 360 degrees, as shown in figure 1-1.
It can be seen from the above introduction that the liquid cooling method is an active cooling method. However, the process of making the liquid cooling method is complex and difficult to realize, and the high price is not suitable for the harsh environment such as high temperature and vibration.
Moreover, in the application of liquid cooling and heat dissipation mode in LED lighting device, the liquid circulation refrigeration device with high seal is required. If it is not properly manufactured, LED device will be damaged.
Progress in LED lighting cooling technology
With the increasing maturity of LED lighting technology and the popularization of LED lighting application, the existing heat dissipation technology is not only based on packaging structure and material, but also based on energy transfer process.
In recent years, there have been new development of base plate materials in packaging materials, and the latest trend points to the research and development of GaN - on - Silicon.
Compared with existing sapphire substrate, gallium silicon-based nitride has the following characteristics: it can reduce the difference coefficient of thermal expansion, strengthen LED luminous intensity, low manufacturing cost and remarkable heat dissipation effect.
Gallium silicon-based nitride is thus favored by LED manufacturers.
Compared with the traditional lighting technology, LED does not completely replace the traditional light source. This is because there are still many key problems in LED lighting technology, and one of the main bottlenecks is heat dissipation.
Although there are many existing ways of heat dissipation, there are still some limitations, such as difficult implementation, high cost, poor thermal conductivity, high environmental requirements and immature technology.
Therefore, the research and development of LED lighting heat dissipation technology is still needed to lay a foundation for the mature development of LED related technologies and the wide application of LED.