Improving the reliability of power LEDs with diamond boards

High power light emitting diodes (LEDs) are much more efficient than conventional light sources like filament bulbs. Nevertheless, heat is still generated, and this directly affects the reliability of these solid-state light (SSL) devices. In order to decrease the operating temperature, these LEDs can be assembled on metal core printed circuit boards (MCPCBs). However, in applications where stability/lifetime is a critical parameter, such as space applications, diamond plates may be considered. These plates are available from manufacturers with metallized tracks for direct assemblage of surface mount devices (SMD). In order to evaluate the impact of the board on SSL reliability, high power Cree LEDs were assembled on MCPCB and diamond plates. The case temperature was measured for different current ratings and the life-time increase induced by the diamond plate was estimated based on the calculation of the acceleration factor (AF). Diamond plates were shown to have a big impact on the life-time; for nominal current level, and depending on the activetion energy of the aging processes, the LED assembled on the MCPCB will age 2.5-8.8 times faster than the one assembled on the diamond plate. For high current ratings the spectrum radiated by the LED assembled on the diamond plate was also shown to be more stable than the one on the MCPCB.