1 Introduction
With the rising awareness of global environmental protection, energy saving has become the trend. The LED lights industry is one of the industries most attention in recent years. Now, LED products are energy saving, energy-saving, high efficiency, fast response time, long life cycle, and does not contain mercury, with environmental benefits and advantages. General, however, LED high power input power of approximately 20% can be converted into light, and the remaining 80% of electrical energy is converted into heat.
In general, the heat generated by LED light can not export, will make the LED junction surface temperature, thereby affecting the product life cycle, luminous efficiency, stability, and the LED junction surface temperature, luminous efficiency and life relationship, the following diagram for further instructions.
2, the LED thermal path
Depending on the packaging technology, the cooling method also is different from the LED variety of thermal path method can approximate Figure III indicate the:
In general, the LED grain (Die) to fight the golden thread, eutectic or flip chip way to link its substrate (Substrate of LED Die) and the formation of an LED chip (chip), then then the LED chip is fixed on the system circuit board (System circuit board). LED possible thermal path for heat directly from the air (shown in three ways 1), or by the LED die substrate to the system board to the atmospheric environment. Heat from the system board to the rate of the atmospheric environment depends on the entire LED lighting system design.
However, at this stage of the cooling of the entire system bottlenecks, mostly dominated in the heat conduction from the LED die to the substrate to the system board. Possible in this part of the cooling channels: one for direct by grains substrate cooling to the system board (Figure 3 ways 2), this thermal path, heat dissipation capability of the LED die and the substrate materials is quite important parameters. On the other hand, the LED generated by the heat will be through the electrode metal wire to the system board, in general, the use of gold thread to do the cooling by the metal wire electrode junction, more slender geometry limited (such as three way 3); Therefore, the eutectic (Eutectic) or flip chip (Flip chip) bonding recently, this design significantly reduce wire length, and a substantial increase in wire cross-sectional area, this way, by the LED electrode the cooling efficiency of the wires to the system board will effectively improve (Figure 3 way and 4 below).
Explained through the thermal path above, learned that the choice of the heat the substrate material and its LED die packages accounted for a very important part in the management of LED street lights heat dissipation, and back outline for LED heat dissipation substrate.