High thermal stability and humidity resistance of phosphor-converted white-light-emitting diodes (PC-WLEDs) using Ce:YAG doped glass, instead of conventional Ce:YAG doped silicone, as a phosphor-converted layer is proposed and fabricated. The glass has five times higher glass transition temperature (Tg) of 750¢J compare with silicone of 150¢J, that could exhibited better performance than silicone, including lumen loss, chromaticity shift, transmittance loss, and peak emission intensity undergoing three industry-standard reliability tests at either high (8wt%) or low (2wt%) doping concentrations of Ce:YAG. The proposed glass phosphor possesses host stability as glass and retains desired fluorescence as Ce:YAG. In thermal aging, thermal shock, and damp heat reliability results, the thermal aging has the largest degradation of lumen loss, but the results showed better thermal stability that the glass phosphor with 22~30% lumen loss improvement for 2~8 wt% Ce:YAG doping than silicone phosphor. The damp heat test has the largest degradation of chromaticity shift, but the results showed excellent humidity resistance that the glass phosphor with highest 49~65% chromaticity shift improvement for 2~8 wt% Ce:YAG doping than silicone phosphor. But under thermal shock test, there isn¡¦t a large difference between glass and silicone phosphor. In this study, we demonstrate the feasibility of adapting glass as a phosphor-converted layer in PC-WLED module that can potentially provide higher reliability and better performance for high-power LEDs, particularly in the area where strict reliability is highly required and in the environment where silicone does not stand for long.

A Ce:YAG-doped glass phosphor layer instead of conventional Ce:YAG-doped silicone phosphor layer as phosphor-converted white-light emitting diodes (PC-WLEDs) is demonstrated. The advantage of employing doped glass encapsulation in high power PC-WLEDs could be explained the material property of glass transition temperature of 750¢J was higher than silicone of 150¢J. The lumen degradation, chromaticity shift, color temperature change, transmittance, and fluorescence spectrum in glass and silicone based high-power PC-WLEDs under thermal aging at 150¢J, 200¢J, and 250¢J is compared and presented. Under highest temperature of 250¢J, the glass and silicone encapsulation base d PC-WLEDs exhibited 8.15% and 38.85% in lumen loss, 1.07 and 7.32 in chromaticity shift, 856 K and 3666 K in color temperature change, 4.21% and 28.1% in transmittance loss, respectively. However, the excitation spectrum altered as slight as emission spectrum before and after experiments. After aging test, the mean-time-to-failure (MTTF) evaluation of glass and silicone encapsulation materials for PC-WLEDs in accelerated thermal tests is also compared and presented by the using of Weibull distribution and Arrhenius equation. The MTTF of PC-WLEDs is defined the lumen decayed to 90%. The results showed that the glass as encapsulation material of PC-WLEDs exhibited higher MTTF than the silicone encapsulation by about 4.81, 5.92, and 7.53 times in lumen loss at 150¢J, 200¢J, and 250¢J, respectively. The results of the lumen loss, chromaticity shift, and MTTF investigations demonstrated that the thermal-stability performance of the glass based PC-WLEDs were better than silicone based PC-WLEDs at 150¢J, 200¢J, and 250¢J. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.

The temperature and thermal stress distributions and variations of the high power LED module were studied in this work. The thermal-elastic-plastic 3D finite element models of MSC.marc software package are employed to simulate these performances for the high power LED module. Two high power white light LED module designs are investigated¡G one is the traditional phosphorescent silicone with blue LED module and the other is a phosphor glass lens with blue LED module. The distributions of temperature and thermal stress of in these two operating LED modules are compared and discussed. The effects of different packaging parameters¡Ge.g. bonding materials, substrate materials, lens materials on the temperature and thermal stress have also been studied in this work. The simulated results reveal that the serious thermal crack may occur for these two designs if the power of single die is over 10 watt. The simulated results also indicate that an attached fin cooler may improve these thermal crack disadvantaged significantly. The effect of fin design parameters on the peak temperature reduction has studied. A feasible fin design for the high power LED module has also been proposed.