Study on influence of silicone encapsulant for ceramic LED package after HTOL test

To estimate influence of silicone encapsulant for ceramic LED package, we prepared silicone samples and ceramic LED packages used encapsulant as the same silicone with neither bonding adhesive nor phosphor. Also, a test jig was designed for high temperature operational life (HTOL) test on ceramic LED packages. The test jig made ceramic LED packages luminous, and was able to guide the light from ceramic LED packages to silicone samples. And then, thermal and optical stress tests on silicone samples were performed with HTOL test on ceramic LED packages in three different temperatures to compare the transmittance of the silicone samples according to the thermal and optical stress from ceramic LED packages. Transmittance of silicone sample and luminous flux of ceramic LED package were measured every 250 hours by UV-VIS spectrophotometer and integrating sphere, respectively. As results, more transmittance variations at 300~400 nm were inspected in silicone samples tested by thermal and optical stresses than by only thermal stress. And, the difference of transmittance characteristics was analyzed to find out how the silicone samples had changed during thermal and optical stress test with Raman analysis. In addition, the luminous flux of ceramic LED package was also changed during HTOL test according to transmittance variations in silicone samples.