Luminescence mechanism analysis on high power tunable color temperature Chip-on-Board white LED modules

Recently, with the increasing requirements on guaranteeing the color uniformity and improving the luminous efficacy and manufacturing efficiency, a wafer level chip scale packaging (WLCSP) technology has been developed by thermally impressing a thin multiple phosphor film on a LED wafer, then being segmented into individual LED chips. In this paper, a high power white LED Chip-on-Board (COB) module with high color rendering index (CRI, Ra>93) and tunable correlated color temperatures (CCTs) is prepared. In this COB module, the tunable color temperatures are achieved by using two types of white LED WLCSPs with different target CCTs of 3000K and 5000K, and twelve CSPs are mounted in series with the flip-chip soldering technology. The thermal dissipation effect and luminescence mechanism of this COB module are studied through the finite element analysis (FEA) and Monte-Carlo Ray-tracing simulations respectively. The results reveal that: firstly, the measured spectral power distribution (SPD) intensity of the prepared COB module are smaller than the arithmetic sum of SPD intensities of its each series connected CSPs, which may be attribute to the light absorption happened among CSPs. Secondly, the case temperature and driven current have the different effects on the optical and color performances of COB module (such as luminous flux, CCT and CRI).