Study On The Correlation Mechanism Between Degradation Mechanism Of LED Package Color Shift And Environmental Test Stress

As the fourth-generation lighting source,light-emitting diodes(LEDs)has the advantages of low-loss energy,high luminous efficiency and long service life.In recent years,LEDs are replacing traditional light sources and becoming the market leader gradually.However,like other electronic products,LED products have many reliability problems.As an important indicator for evaluating the reliability of LED products,the stability of color coordinates has become the focus of people's attention and research.Studying the degradation mechanism of color shift of LED products and determining the correlation mechanism between color shift and environmental test stress are of great significance for improving the reliability of LED products.In this article,the mechanism of color shift degradation of LED packages is studied,and the correlation mechanism between color shift and environmental test stress is analyzed.The specific research content and results are as follows:(1)Design and carry out accelerated tests of different stresses to study the relationship between light and color performance parameters of LED packages and environmental test stress.The results show that the luminous flux and color coordinates of the LED package have a strong sensitivity to moisture and thermal stress.In the accelerated test,humidity stress is helpful to improve the degradation rate of LED package.(2)Study on the degradation trajectory and statistical analysis model of LED packages.Under different acceleration conditions,the luminous flux of the LED package gradually decreases with time,and the attenuation trajectory conforms to the exponential model;The degradation trajectory of the color coordinate and color shift conforms to the linear model.The greater the test stress,the greater the degradation rate of color shift.Through data extrapolation,the life of the LED can be inferred.Relative to luminous flux attenuation,LED package require less time to achieve color shift failure.(3)Study on the degradation mechanism of color shift of LED packages.In the accelerated test,the direction of the color shift of the white LED packages are opposite to the blue LED packages,indicating that the aging of the phosphor has a great influence on the color shift.In the accelerated test of the silicone material,the silicone material gradually turned yellow,which in turn led to the degradation of the light and color parameters of the LED light source;The degradation of the silicone material makes the ratio of the peak of blue light to yellow light larger.Moreover,the reduction in the transmittance of blue light is more obvious than yellow light by the silicone lens material after aging,which is an important reason for the color shift of LEDs.(4)Study on the aging mechanism of LED packaging silicone lens material.The silicone lens material gradually yellowing after accelerated testing.Oxidation and hydrolysis reactions are the aging mechanism of silicone lens materials.Infrared spectroscopy shows that the vibration absorption frequency of different functional groups will change after the aging of silicone lens material,and new functional groups will appear.Combining the firstprinciples and molecular dynamics simulation analysis results,It can be found that the main chain of the silicone material is broken under hygrothermal stress and occur hydrolysis and oxidation reactions.