Trends of LED heat sink in 2010

1, preface

With the increasing awareness of global environmental protection, energy saving has become a trend. LED industry is one of the most attractive industries in recent years. Up to now, LED products have the advantages of energy saving, energy saving, high efficiency, fast reaction time, long life cycle, and mercury free... Other advantages. Usually, however, the input power of the LED high power product is about 20% which can be converted into light, and the remaining 80% of the energy is converted into heat energy.

In general, the heat generated by the LED light-emitting if you can not export, it will make the LED junction temperature is too high, thereby affecting the product life cycle, luminous efficiency, stability, and the LED junction temperature, the relationship between the luminous efficiency and service life, the following relationship will be further explained by map.

Figure 75% shows the relationship between the junction temperature and the luminous efficiency of the LED. When the junction temperature rises from 25 DEG C to a temperature of 100 DEG C, the luminous efficiency will be reduced by between the ages of 20% and over, which is the most serious one. In addition, the higher the operating temperature of the LED, the lower the life of the product (as shown in Figure two), when the operating temperature from 63 LED to 74 DEG C, the average life expectancy will be reduced by 3/4. Therefore, to improve the luminous efficiency of LED, LED system of heat management and design has become a important topic, before we know the LED radiation problem, we must first understand the heat way, so as to improve heat dissipation bottleneck.

2, LED cooling way

According to different packaging technology, the cooling method is different, and the LED method can approach a variety of heat to figure three:

Figure three schematic diagram of LED heat dissipation.

Heat dissipation: 1 from the air cooling

2 heat energy directly derived from System circuit board 3 through the gold wire to export energy

4 if the eutectic and Flip chip process, the heat will be through the hole to the system circuit board and export

In general, LED chip (Die) to gold, eutectic or mode of flip chip connected to the substrate (Substrate of LED Die) and the formation of a LED chip (chip), and then the circuit board is fixed on the LED chip system (System circuit board). Therefore, LED may be the way to direct heat dissipation from the air (as shown in Figure three, figure 1), or through the LED chip substrate to the system board and then to the atmospheric environment. The rate of heat dissipation from the system board to the atmosphere depends on the design of the entire luminaire or system.

However, at this stage of the entire system, most of the heat leak occurs in the heat transfer from the LED chip to the substrate and then to the system circuit board. May the heat way this part: one is directly by the chip substrate cooling to system circuit board (Figure 2 shows three ways), this way in the heat, LED chip substrate material heat dissipation ability for important parameters. On the other hand, the heat generated by the LED will be through the electrode wire to the system board, in general, by way of gold electrode bonding, heat dissipation by wire geometry itself more slender and Limited (Figure 3 shows three ways); therefore, recently the eutectic (Eutectic) or cover crystal (Flip chip) joint, this design greatly reduced the length of the wire, and greatly increase the conductor cross-sectional area, thus, by cooling the LED electrode wire to the circuit board of the system will effectively enhance the efficiency (Figure 4 shows three ways).

Through the above approach to explain the heat dissipation, can be informed that the choice of cooling substrate material and its LED chip packaging methods in the LED heat dispersion management accounted for a very important part, the latter section will be made on the basis of LED heat sink.

3, LED heat sink substrate

LED heat sink substrate is mainly based on its heat sink material itself has a better thermal conductivity, the heat source from the LED chip export. Therefore, we describe the heat from the LED pathway, the LED substrate segments of two categories, respectively (1) LED (2) substrate and the chip circuit board system, the two kinds of substrates were carrying the LED chip and the LED chip will be the heat generated by the LED chip light, via LED chip radiating substrate to system circuit board, and then absorbed by the atmosphere, in order to achieve the effect of heat.

3.1 system circuit board

The system circuit board is mainly used as the LED heat dissipation system, and finally the heat energy is transferred to the radiating fin, the shell or the air. In recent years, the printed circuit board (PCB) production technology has been quite mature. The system circuit board of early LED products based on PCB, but with the increasing demand of high power LED, PCB cooling capacity of material is limited, it can not be used in the high power products, in order to improve the high power LED heat dissipation problem, recent development high thermal conductivity aluminum substrate (MCPCB), the heat dissipation characteristics of metallic materials with good characteristics, has reached the purpose of heat dissipation of high power products. However, with the continuous development of LED brightness and efficiency, while the system circuit board of LED can be generated by the chip thermal effective heat dissipation to the atmospheric environment, but the heat generated by the LED chip are unable to transfer to the system from the perspective of chip circuit board, when the LED power to more efficient promotion, radiating the bottleneck LED will appear in the LED chip heat dissipation substrate, the passage will make further exploration on LED chip substrate.

3.2 LED chip substrate

LED chip substrate is mainly used as the medium between the LED chip and the system circuit board, through the process of wire bonding, eutectic or flip chip bonding with LED chip. Based on thermal considerations, the current market LED chip substrate is mainly based on Tao Ciji