Uncover the Degradation Science of Silicone under the Combined Temperature and Humidity Conditions

In this paper, we report the mechanistic insights into thermal and humidity induced degradation of silicone employed in high power LEDs. High power blue and white light emitting diodes (LEDs) are used for experimentation. The silicone encapsulant of both the blue and white LEDs are degraded due to hydrolysis, likewise for the molding part of the blue LED. However, the molding part of the white LED is degraded via thermal oxidation. We find that lumen degradation is rapid for white LEDs, whereas material degradation is unexpectedly rapid for blue LEDs. The reasons for such differences in the degradation of the packaging materials are explained. We also found that the degradation of LEDs under high temperature alone is different from that under high temperature and humid condition, such as those used in the outdoor applications.