What are the factors affecting led reliability and service life?

Date：2022-05-27 14:41:00Views：682

With the continuous improvement of LED lighting efficiency in recent years, the service life and reliability of LED have been paid more and more attention by the industry. It is one of the most important performances of LED products. LED product reliability test standard project. LED products are very common in our life, such as LED displays, LED lights and a series of products. However, if these products want to be successfully put on the market, they must be tested for reliability.

Life is the ultimate performance of reliability. Therefore, it is necessary to adopt accelerated aging life test for LED products. At the same time, the thermal characteristics, environmental weatherability, electromagnetic compatibility immunity and other performances closely related to life and reliability should also be tested to comprehensively analyze the life of LED.

Key indicators related to LED reliability and life

Every element and link in the manufacturing of LED products will have an impact on its reliability and service life, for example, the faulty soldering of LED junction and substrate, the thermal quenching and degradation of LED phosphor, the degradation of packaging materials and the failure of drivers, etc. the semiconductor (PN junction) itself may be the final degradation. These factors lead to LED product failure (degradation) in different ways, which can be generally divided into gradualdegradation and transient degradation.

The indicators of slow degradation (failure) of LED mainly include:

The lumen maintenance rate decreases, i.e. light failure. Generally, the initial luminous flux is 100%. When the lumen maintenance rate of LED products decreases to 70% or 50% of the initial value, it is considered that the LED is invalid, and the lumen maintenance life is correspondingly recorded as L50 or L70;

Color drift: due to the change of phosphor or packaging material, the color of LED will drift within the service life. The drift should be within the specified range (e.g. △ u'v '≤ 0.007). If it exceeds the range, it will be deemed as LED failure;

The change of electrical performance can be monitored more intuitively;

Switching times, the switching may have a certain impact on the driving circuit;

The change of thermal resistance and other thermal characteristic parameters are closely related to the service life. The measurement and analysis of thermal characteristics are helpful to find out the weak links of LED reliability;

The transient degradation (failure) of LED, that is, the light output of LED suddenly drops to 0. Its main degradation includes: anti electromagnetic interference ability: electrostatic discharge, lightning surge, fast group pulse, cycle drop; High and low temperature impact resistance characteristics; Salt spray, humidity resistance, vibration, etc.

The purpose of reliability test usually includes several aspects:

1. In the development stage, it is used to expose the defects in all aspects of the trial product and evaluate the reliability of the product to reach the predetermined indicators;

2. The production stage provides information for monitoring the production process;

3. Carry out reliability appraisal or acceptance for finalized products;

4. Expose and analyze the failure rules, relevant failure modes and failure mechanisms of products under different environments and stress conditions;

5. To improve product reliability, formulate and improve reliability test scheme, and provide basis for users to select products.

For different products, in order to achieve different purposes, different reliability test methods can be selected.

There are many classification methods for LED product reliability testing:

1. If divided by environmental conditions, it can be divided into simulation test and field test under various stress conditions;

2. According to the test items, it can be divided into environmental test, life test, accelerated test and various special tests;

3. If it is divided according to the test purpose, it can be divided into screening test, identification test and acceptance test;

4. If divided according to the nature of the test, it can also be divided into destructive test and non-destructive test.

5. However, the usual classification method is to classify it into five categories:Environmental test, life test, screening test, field service test and identification test.

Executive standard for reliability test of LED products

1. Low temperature: IEC 60068-2-1, gb/t 2423.1;

2. High temperature: IEC 60068-2-2, gb/t 2423.2;

3. Constant damp heat: IEC 60068-2-78, gb/t 2423.3;

4. Alternating damp heat: IEC 60068-2-30, gb/t 2423.4;

5. Impact: IEC 60068-2-27, gb/t 2423.5;

6. Impact caused by rough operation: IEC 60068-2-31, gb/t 2423.7;

7. Vibration: IEC 60068-2-6, gb/t 2423.10;

8. CTB salt spray test: IEC 60068-2-11, gb/t 2423.17, IEC 60068-2-52, gb/t 2423.18.

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