Thermal analyses and measurements of low-cost COP package for high-power LED

The high-power Light Emitting Diode (LED), which features low-power consumption, longer life time and shorter response time, has a potential to replace the conventional general lighting, such as incandescent and fluorescent lamps. However, the LED issues, associated with high cost, high junction temperature, low luminous efficiency, and low reliability, have to be solved before gaining more market penetration. With special features of low-junctiontemperature and low-cost design, a novel package for highpower LED, so called COP (Chip on Plate) package, is proposed in this study. The thermal behaviors of the COP package with and without a heat sink are investigated by experimental measurements (with LED junction temperature tester and thermal couples), a thermal resistance circuit (TRC) method, a finite element method (FEM) and a computational fluid dynamics (CFD) approach. The junction temperature (Tj) of the COP package was measured by the junction temperature tester and found to be comparable with those from commercial products, such as Cree's, and Lumiled's packages. Furthermore, the TRC and FEM were used for addressing the thermal fields of the COP package with and without a heat sink. The results of the thermal fields including the Tj from the experiments, FEM and TRC were found to be reasonably consistent under various input powers for the COP package, but not for the package with a heat sink. Moreover, the under-estimated thermal fields of the package with a heat sink from both FEM and TRC analyses were evaluated again by the CFD approach. The results indicate that the heat convection coefficients on the heat sink used the FEM and TRC analyses are higher than those calculated from the CFD. Finally, the reasonable and validated FEM and TRC models were used for parametric studies and their results show that the thermal conductivities of the die attach, chip substrate and package substrate (rather than the heat sink, chip, thermal grease and encapsulant) have an obvious effect on the T_j. In addition, for reducing the Tj, increasing the radius of the heat sink was found to be more beneficial than increasing the height.