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Analysis and Improvement of Main Failure Mode of LED(II)
- Jun 06, 2017 -

  Hsu et al. Conducted accelerated life experiments on LED samples provided by different manufacturers. The samples were placed at 80, 100, 120 ° C at 3.2 V, and the optical power of the sample was reduced to the starting value Of the 50%, that is judged to be invalid. The experimental results show that the life of the high power LED decreases with the increase of the experimental temperature of the accelerated life and the increase of the acceleration time. In the accelerated life experiment, LED junction temperature will make the epoxy resin material mutation, thereby increasing the thermal resistance of the system, making the chip and the heating surface between the package degradation, eventually leading to packaging failure.

(4) Over-stress failure

If the LED in the case of over-current (EOS) or electrostatic shock damage (ESD) of the chip, will cause the chip open circuit, the formation of electrical stress failure. For example, GaN is a wide bandgap material. If the use of such chips, in the production process due to static electricity generated by the induced charge is not easy to disappear, when it is accumulated to a considerable extent, can produce a high electrostatic voltage, the voltage once the material beyond the affordability, it will happen Break the phenomenon and discharge, making the device failure.

Second, improve measures

By analyzing the main failure modes of the LEDs described above, it is possible to learn from the technical methods of improving the actual service life of the LEDs.

(1) Cooling technology

Cooling technology has always been an important part of the impact of LED applications, if the LED device can not be timely cooling, it will lead to a serious increase in the chip junction temperature, and then a sharp decline in luminous efficiency, reliability (such as life, color shift, etc.) will deteriorate; At the same time, high temperature and high heat will make the LED package structure internal mechanical stress, may further lead to a series of reliability problems [5]. Therefore, in the manufacturing process, you can choose a good thermal conductivity of the base, and make the LED cooling area as large as possible, thereby increasing the device's thermal performance.

(2) Anti-static technology

With GaN as a chip LED, in use there is a big problem is the electrostatic effect, if you do not deal with this problem, it will seriously affect the life of the device. Therefore, in the LED design, to fully take into account the anti-static design, in order to avoid the device due to high voltage caused by breakdown voltage failure phenomenon.

(3) Packaging technology

Epoxy resin used in packaging materials, because of light and temperature rise caused by its light transmittance degradation, in use, the performance of the original transparent epoxy resin material browning, affecting the original spectral power distribution of the device. Therefore, in the LED package, we have to strictly control the curing temperature, to avoid the time in the package, it has caused the aging of the epoxy resin in advance.

On the other hand, in order to prevent corrosion of the device, in the choice of transparent packaging materials at the same time, pay attention to the injection process, as far as possible to clean the inside of the material to reduce the residual water vapor, reducing the device corrosion probability.

(4) Optimize the manufacturing process

LED manufacturing process requires the appropriate bonding conditions, if the bonding will be too large will crush the chip, otherwise the device will result in insufficient bonding strength, making the device easy to loose. Therefore, while ensuring the bonding strength of the device at the same time, you need to minimize the bonding process caused by the damage to the chip in order to achieve the purpose of optimizing the bonding process.

In the chip bonding, the requirements of the control temperature and time within the appropriate range, making the solder to achieve dense, no voids, residual stress and other small technical requirements.

(5) Reasonable screening

In the LED factory, you can add a screening process, which is some of these samples for reasonable aging and screening test, remove some of the equipment may occur in advance to reduce the actual use of LED in the early failure phenomenon.

Conclusion

In summary, although the LED has a high theoretical life, but in the actual use of the process, by the chip, packaging, stress and other factors, the use of time is far from the expected theoretical value. In order to really improve the life of LED, both in the manufacturing process, or in the application level, need to further research, exploration and practice. With the continuous development of LED technology, there must be new problems continue to emerge. But as long as the root cause of the failure to grasp the LED can be in practice to improve the performance of LED devices, this new light source will be extended to the front end of the application areas, and better serve the production and life.

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