Due to its advantages of energy saving, environmental protection and safety, LED has been widely used in the general lighting and backlight market, and penetrates into the automotive field with higher quality and performance requirements. Currently, LED related products can be applied to headlights, daytime lights, directions. Lights, taillights, interior lights, etc. The headlights and daytime lights are white, while the turn signals are amber. Generally, the amber LED package is protected by a transparent organic material such as epoxy or silica gel on the AlGalnP chip. This structure faces the common problem of the conventional package: the organic material is deteriorated due to heat aging. In addition, the AlGalnP chip will suffer from color point drift and reduced luminous efficiency due to heat, which is the most prominent two challenges faced by amber LED packaging technology.
In response to the above problems, researchers from South Korea's Samsung and National University of Gongju proposed a new solution. They mixed Ca-α-SiAlON:Eu phosphor and SiO2–B2O3–RO (R=Ba,Zn) glass powder and sintered it into a dense glass phosphor sheet, which was then packaged into amber with this sheet combined with a blue chip. The full conversion LED (PiG Amber) avoids the thorny problem of AlGalnP chip color point drift and low efficiency, and the inorganic glass medium replaces the organic packaging material to achieve higher reliability in high temperature and high humidity environment.
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New Automotive Packaging Technology: Glass Phosphors for Enhancing Amber LED Reliability
The researchers first prepared a Ca-α-SiAlON:Eu powder with a particle size of about 11 μm. This phosphor can be excited by blue light of about 450 nm, with a peak wavelength of 591 nm, and maintains the initial level of luminescence at a high temperature of 800 °C. . The glass transition temperature of SiO2–B2O3–RO (R=Ba, Zn) glass is 590 °C, which means that the mixed powder of the two can be sintered at a temperature of about 700 °C without affecting the phosphorescence. performance. By optimizing the gas-sintering (GPS-Gas Pressed Sintering) process and formulation, a glass phosphor powder with a phosphor content of 40% and a thickness of 180 μm was obtained. After being packaged by a blue chip, the color purity was up to 96.2% and the brightness was 88 lm.
Automotive LEDs are subject to more stringent reliability tests due to driver safety and higher quality requirements. The researchers compared the lumen maintenance of the conventional silica gel package and the glass phosphor package at 85 ° C / 85% temperature and humidity according to the AEC-Q101 test standard. The results show that at a junction temperature of about 150 ° C and 1 A current operating conditions, the brightness of the silicone packaged LED is reduced by 10% at 250 hours, and only 40% of the initial luminous flux at 500 hours, while the brightness of the glass phosphor packaged LED is maintained at 1000 hours. More than 97% level.
The package form of the blue-light-excited glass phosphor sheet provides a new idea for solving the thermal bottleneck of the common amber LED, and has great commercial potential. The results of the study were published in full text on the latest issue of Optics Express on March 29, 2016.
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