A Comprehensive Analysis and Future Trends of LED Heat Dissipation Technology
With the continuous development of LED materials and packaging technology, the brightness of LED products has been continuously improved, and their application scope has become increasingly extensive. In recent years, the application of LED as a backlight for display screens has become a hot topic, mainly due to the advantages of various LED backlight technologies. Compared with traditional cold cathode fluorescent lamps (CCFL), LEDs have significant advantages in terms of color, brightness, lifespan, power consumption, and environmental protection requirements, which has attracted active investment in the LED manufacturing equipment industry.
The Evolution of LED Packaging Technology and Heat Dissipation Challenges
The initial single-chip LEDs had relatively low power and generated limited heat, so the packaging method was relatively simple. However, with the breakthroughs in LED material technology, LED packaging technology has also undergone tremendous changes, evolving from the early single-chip bullet-shaped packaging to planar, large-area multi-chip packaging modules. The operating current has gradually increased from 20mA low-power LEDs to high-power LEDs of 1/3A to 1A. The input power of a single LED has reached over 1W, and even developed to 3W and 5W.
The heat dissipation problem of high-brightness, high-power LED systems has become a key factor affecting product functionality. In order to quickly transfer the heat generated by LED components to the surrounding environment, thermal management must start from the packaging level (L1 and L2). Currently, the commonly adopted method in the industry is to connect the LED chip to the heat diffuser through solder or thermal paste, and reduce the thermal resistance of the packaging module through the heat diffuser. This method is the most common LED packaging module solution in the market, mainly provided by internationally renowned manufacturers such as Lumileds, OSRAM, Cree, and Nichia.
The Importance of Thermal Management
In many end application products (such as mini projectors, automotive lighting, and other light sources), it is often necessary to achieve a light output of thousands or even tens of thousands of lumens in a specific area. Obviously, relying solely on single-chip packaging modules is no longer sufficient, and multi-chip packaging and direct chip bonding to the substrate will be the future development trend.
The heat dissipation problem is the main obstacle to the development of LEDs as lighting devices. Using ceramics or heat pipes is an effective way to prevent overheating, but thermal management solutions will increase material costs. The goal of high-power LED heat dissipation management design is to effectively reduce the thermal resistance between chip heat dissipation and the final product. “R junction to the housing” is a method that directly transfers heat from the chip to the outside of the package through materials with low thermal resistance but high thermal conductivity.
Common Heat Dissipation Methods and Materials
Active Heat Dissipation and Passive Heat Dissipation
According to the way the heat sink takes away heat, heat dissipation can be divided into active heat dissipation and passive heat dissipation:
・Passive Heat Dissipation
Heat is dissipated naturally through the heat sink, and the heat of the LED light source is dissipated into the air. Its heat dissipation effect is proportional to the size of the heat sink, but due to natural heat dissipation, the effect is limited, and it is suitable for devices that generate less heat.
・Active Heat Dissipation
Forced heat dissipation is carried out with the help of heat dissipation devices such as fans, which is more efficient and the device is smaller in size, and it is widely used in scenarios with high heat dissipation requirements. Active heat dissipation includes methods such as air cooling, liquid cooling, heat pipe heat dissipation, semiconductor refrigeration, and chemical refrigeration.
Specific Heat Dissipation Technologies
Air Cooling
The most common and relatively inexpensive heat dissipation method, using a fan to take away the heat absorbed by the heat sink, but it is sensitive to the ambient temperature.
Liquid Cooling
The cooling liquid is forced to circulate through a pump. The advantages are quiet operation, stable cooling, and low dependence on the environment, but it is relatively expensive and complex to install.
Semiconductor Refrigeration
The semiconductor refrigeration sheet is used to generate a temperature difference to cool down when powered on, and the temperature of the cold end can be lower than -10°C, but the cost is high and the technology is not yet mature.
Chemical Refrigeration
Heat is absorbed and cooled by using ultra-low temperature chemical substances such as dry ice or liquid nitrogen, which is commonly seen in laboratory or extreme overclocking scenarios.
Commonly Used Heat Dissipation Materials
The heat sink material needs to have high specific heat and high thermal conductivity. Silver and copper have the best thermal conductivity, but due to cost issues, aluminum and copper are mainly used in the market.
・Pure Aluminum Heat Sink
It has a low cost and simple process, and occupied the early market, but its thermal conductivity is worse than that of copper.
・Pure Copper Heat Sink
Its thermal conductivity is 1.69 times higher than that of aluminum, but it has a high cost, large mass, and high processing difficulty.
・Copper-Aluminum Bonding Technology
The heat sink that combines a copper base with aluminum fins has both the thermal conductivity of copper and the lightness of aluminum, and is the mainstream choice for high-end heat sinks currently.
Future Trend: Fanless Heat Dissipation
With the increase in the power of LED backlight modules (for example, the backlight powers of 40-inch and 46-inch LEDs are 470W and 550W respectively), 80% of the energy will be converted into heat. Currently, the industry mainly adopts heat dissipation methods that combine water cooling and heat pipes with fans, but there are problems such as high cost and noise. In the future, fanless heat dissipation technology may become the key to determining the winners in the market.
