At present, the theoretical life of LED has been 1.0 X 106h, and it is difficult to give a correct evaluation of its life and reliability by life test under normal stress conditions. The experiment of LED reliability is usually an accelerated life test, that is, the stress is increased without changing the stress failure mechanism to accelerate the change of the physical chemistry of the LED and shorten the test time. Through the accelerated life test, you can understand the product's life characteristics, failure law, failure rate, average life and various failure modes that may occur during the test. The following is a brief introduction to "the meaning of LED product life" and "introduction to accelerated life test methods" and "general steps to accelerate life."
First, the meaning of product life
1.1 What is the life of the product?
Product life is the period from the start of the operation to the failure of the product.
1.2 Definition of life
Life is generally defined by Mean Time Between Failure (MTBF) or MeanTime To Failure (MTTF).
1.3 What is MTTF?
What is the average time from the start of the product to the failure?
For example, the number of hours an engineer measured the life of five LEDs is as follows:
10000, 12000, 10500, 11200, 11000, then MTTF = (10000 + 12000 + 10500 + 11200 + 11000) / 5 = 10,940 hours.
1.4 What is the meaning of MTBF?
In addition to the life expectancy, MTBF generally refers to the average time of two failures in the “Repair Systemâ€, as shown in the figure below, MTBF=(100+80+120)/3=100 days.
1.5 Reasons for MTTF to assess life expectancy?
A: In practice, the MTBF is applicable to the reference of the Renew timing before the failure of the “repair system†to ensure that the system can operate normally.
B: Since the LED products are not part of the “repair systemâ€, the life expectancy of the MTTF is more in line with the LED product attributes.
Second, the introduction of life test
2.1 What is a life test?
A: Whether the life of the product meets the requirements must be determined by the “Test†procedure, which is called “Life Test†in reliability engineering.
B: Precautions for life test:
a) The failure rate of the same test conditions must be constant b) the early period product must be rejected
2.2 Planning of life test
a) Determine the method of product testing b) Determine the sampling plan c) Determine the number of samples n
d) setting the criteria C
2.3 Sampling plan method for life test
The life test has the following three sampling plans:
a) Fixed sampling plan b) Timed sampling plan c) Sampling plan
Unfinished
For more information, please refer to the September issue of "High-tech LED-Technology and Applications"
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