Process and considerations
Process and considerations
For LED chip life test samples, chips can be used, usually called bare crystal, or packaged devices can be used. The use of bare crystal form, the external stress is small, easy to heat, so the light decline is small, long life, and the actual application of a big gap, although can be adjusted by increasing the current, but not directly using a single lamp device form intuitive.
Using single lamp device for life test, the factors that cause the photoaging of the device are complex, including chip and package. In the process of the test, a variety of measures were taken to reduce the influence of packaging factors and to improve the details that might affect the accuracy of the life test results one by one, thus ensuring the objectivity and accuracy of the life test results.
Life test can only be evaluated by sampling test, which has certain risk.
First of all, the product quality has a certain degree of uniformity and stability is the premise of the sampling evaluation, only if the product quality is considered to be uniform, the sampling is representative;
Secondly, due to the discreteness of the actual product quality, we adopted the method of partition random sampling to improve the accuracy of the life test results. We by looking for related information and a lot of contrast test, and put forward a more scientific way of sample extraction, the chip according to its position in the epitaxial wafer is divided into four area, were 2 ~ 3 chip, a total of 8 ~ 10 chips, for different device life test results of six to one, and even contradictory situation, we stipulated the strict life test method, namely were 4 ~ 6 chip, a total of 16 ~ 20 grains chips, according to the normal conditions of life test, just number add yan, rather than add strict test conditions;
Thirdly, generally speaking, the more samples, the less risks and the more accurate the results of the life test will be. However, the more samples, the more samples, the more waste of manpower, material resources and time will be caused, and the test cost will rise. How to deal with the relationship between risk and cost has always been the content of our research. Our goal is to minimize the risk under the same test cost by adopting scientific sampling method.
In LED life test, the test samples are firstly tested and screened for photoelectric parameters, and the devices with abnormal photoelectric parameters are eliminated. The qualified ones are numbered one by one and put into life test. After the continuous test is completed, re-test is conducted to obtain the life test results.
In order to make the life test results objective and accurate, in addition to the measurement of the test instrument, it is also stipulated that in principle the same test instrument is used before and after the test, so as to reduce unnecessary error factors. This is particularly important for optical parameters. Early we use measuring device to judge light failure condition, the change of light intensity the general test device of the axial intensity, half Angle smaller devices for light distribution curve, the size of the intensity values along with the geometric position and a sharp change, repeatability is poor, affect the life test result of the objectivity and accuracy, in order to avoid this kind of situation, take the form of encapsulation large Angle, and choose no reflection cup holder, eliminate reflection cup light distribution, eliminate the influence of device packaging format with optical performance and improve the accuracy of the optical parameters testing, follow-up have been verified by means of luminous flux measurement.
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