Based on the five raw materials and five major processes of LED packaging , this paper analyzes the main factors affecting the life of LED . Taking high temperature and high current as test conditions, the rapid aging test is used to quickly analyze and identify LEDs. For the rapid introduction of LED manufacturers to do the basis.
With the continuous development of LED products , the LED industry has presented a pattern of blooming from upstream wafers, midstream packaging or downstream applications. However, nowadays, from the state of blossoming to the mode of big shuffling, how to survive in the LED shuffling, the biggest factor is to improve the cost performance of its own products. Therefore, the current LED industry, whether it is Philips, OSRAM and other LED giants or some small domestic companies are carrying out a brutal price war. For LED lighting products, LED granules account for the highest proportion of cost, so LED application plants will continue to look for low-cost LED granule suppliers, and LED granule suppliers must make their products more cost-effective and must be reduced. Therefore, the raw materials such as LED chips , gold wires, and brackets are the first to be replaced.
At present, the cost reduction rate of LED pellets has been increased from the previous quarterly cost reduction to monthly cost reduction, so how to control the LED reliability is very important. If the test method using LM80/LM79 obviously cannot meet the requirements of the application factory, the test cycle of LM80 is generally normal at 6000 hr. The price of LED granules has been updated several times after verification in this way. Therefore, for LED application plants, it is necessary to judge the reliability of an LED in the shortest time, that is, to explore a low-cost, fast and effective method for screening LED particles.
LED package material introduction
As shown in Figure (1) above, the main raw materials of LED are five parts: encapsulant, gold wire, wafer, solid crystal glue and bracket. Each material directly affects LED performance. For example, poor encapsulation not only leads to low light extraction efficiency, but also causes the material to be easily damp and the risk of vulcanization increases.
With the increasing number of LED packaging companies and the pressure of cost and competition elimination, the wire used in packaging plants has evolved from the original 99.99% pure gold wire to K gold wire, palladium-plated copper wire, and these wires are thermally conductive. The rate will decrease, and the ductility will be reduced. This will be sensitive to the stress generated by the outside world, and it is easy to cause disconnection. For example, because the LED is a moisture sensitive device, if there is moisture in the LED, when the patch is completed, During reflow soldering, stress is generated due to thermal expansion. If the ductility of the wire is not good, the wire may be broken due to stress, which may cause serious death after reflow.
In addition, due to the pressure of cost, many packaging factories are reducing the size of the wafer, and the overcurrent operation, for example, the early 10*30mil chip will only achieve 0.1W, drive to 30mA, and now some manufacturers will overload to 100mA, so The maximum withstand current of this wafer has been exceeded, and the risk of light decay is too great.
Another important material that has a major impact on LED life is the stent. For the same LED, in order to obtain more luminous flux under the premise of constant cost, the most effective method is to drive over current, but this operation will cause the current density to be too large, resulting in a very large increase in heat, as follows Figure 2 shows the same 28351W LED used as a candle light to push the temperature corresponding to different currents.
Figure 2 LED different drive current corresponding temperature (test instrument: infrared camera)
As can be seen from the above figure, the LED drive current drops by 20%, and the corresponding LED chip surface temperature drops by 17%. In addition, 130° has exceeded the maximum withstand temperature of the LED chip (typically 115° for medium and small power chips and 125° for better points). Excessive temperature not only causes damage to the LED chip, but also reduces the efficiency of phosphor excitation. It also causes the reflective cover on the holder to yellow, which will eventually lead to serious LED light decay.
At present, the small and medium power (below 0.5W) is still used by PA9T. Some manufacturers even use PA6T for cost considerations and are not resistant to high temperatures. The best performance for high temperature resistance is EMC, followed by PCT, then PA9T, and PT6T is the worst performer.
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