As an electronic component, LED has been used for more than 40 years, but it has been limited by luminous efficiency and brightness for a long time. It is only used by the indicator light. It broke through the technical bottleneck until the end of the last century, producing high-brightness and high-efficiency LED and blue light. LEDs extend the range of applications to signal lights, urban nightscape projects, full color screens, etc., providing the possibility of being an illumination source. As the range of LED applications increases, improving LED reliability is of even greater significance. LED has the advantages of high reliability and long life. In the actual production and development process, the reliability level of the LED chip needs to be priced through the life test, and the reliability level of the LED chip is improved by quality feedback to ensure the LED chip. For this reason, in order to realize the industrialization of full-color LEDs, the conditions, methods, means and devices for the life test of LED chips have been developed to improve the scientificity of the life test and the accuracy of the results.
Determination of life test conditions
The work test performed by an electronic product under specified working and environmental conditions is called a life test, also known as a durability test. With the improvement of LED production technology, the life and reliability of the product are greatly improved. The theoretical life of LED is 100,000 hours. If the life test under normal normal stress is still used, it is difficult to maintain the life and reliability of the product. A more objective price is made, and the main purpose of our experiment is to grasp the light output attenuation of the LED chip through the life test, and then infer its life. According to the characteristics of the LED device, after comparative test and statistical analysis, the life test conditions of the chip below 0.3×~0.3mm2 are finally specified:
[1]. The samples were randomly selected and the number was 8-10 chips, which were made into Ñ„5 single lamps;
[2]. Working current is 30mA;
[3]. The environmental conditions are room temperature (25 ° C ± 5 ° C);
[4]. The test period is three hours of 96 hours, 1000 hours and 5000 hours;
The working current is 30 mA, which is 1.5 times of the rated value. It is a life test to increase the electrical stress. Although the result does not represent the real life condition, it has great reference value. The life test uses the epitaxial wafer production batch as the mother sample and is random. 8 to 10 chips in one of the epitaxial wafers were taken and packaged into a Ñ„5 single-lamp device for a 96-hour life test, and the results represent all epitaxial wafers of the production batch. It is generally considered that a test period of 1000 hours or more is called a long-term life test. When the production process is stable, the 1000-hour life test frequency is lower, and the 5000-hour life test frequency can be lower.
Process and precautions
For the LED chip life test sample, a chip, generally referred to as a bare crystal, or a packaged device may be used. Adopting the bare crystal form, the external stress is small, and it is easy to dissipate heat. Therefore, the light decay is small and the service life is long. The difference from the actual application is large. Although it can be adjusted by increasing the current, it is better to use the single-lamp device directly. The life test is carried out in the form of a single lamp device, which causes the factors of the light decay aging of the device to be complicated, and may have chip factors as well as packaging factors. During the test, various measures are taken to reduce the influence of packaging factors, and the details that may affect the accuracy of the life test results are improved one by one, ensuring the objectivity and accuracy of the life test results.
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