We investigated the effect of selective coating of white silicone on the output and thermal performance of white LED packages for middle power lighting application. The LED package, where a Zener diode part was coated by TiO2 particles-mixed white silicone, exhibited lower surface temperature and heat flux than those with the uncoated Zener diode. The white silicone-coated packages resulted in lower thermal resistance (Rth) than the uncoated ones. For example, the Rth at 85 °C of the uncoated and coated white LED packages in the junction-PCB was 26.30 K W-1 and 21.98 K W-1, respectively. The coated blue and white LED packages yielded 6.5% and 4.5% higher luminous fluxes than the uncoated packages, respectively. Far-field emission patterns showed that the coated white LED packages had view angle of 118.06° and 118.10° along the two orthogonal directions, respectively, whilst the uncoated package gave 117.37° and 117.55°. After operation under 60 °C/80% relative humidity condition for 1000 h, the uncoated white LED package yielded maintenance rate of 96.85% whereas the coated packages gave 98.17%. At 85 °C under 200 mA, the thermal resistance of the white silicone-coated white LED packages was lowered by 17.7% than the uncoated packages.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials