Effect of Packaging Architecture on the Optical and Thermal Performances of High-Power Light Emitting Diodes

The phosphor and die bonding configuration affect the optical efficiency and thermal performance in phosphor-coated white light emitting diodes (LEDs). In this paper, light emission studies reveal that the chromaticity shift and light extraction losses depend on the uniformity of phosphor particles deposited over the LED surface. A nonuniform and sparse phosphor layer affects the correlated color temperature (CCT) and the spectral Y–B ratio due to the disproportionate contribution of light emission between the LED device and the phosphor layer. Furthermore, the Y–B ratio was observed to reduce with temperature due to higher Stoke's energy and light extraction losses in the phosphor layer. As a result, the Y–B ratio exhibits an inverse relationship with the package's thermal resistance as a function of temperature. On the other hand, the thermal performance of a LED package is dependent on the die-bonding configurations (conventional and flip-chip). Due to the improved heat dissipation capabilities in flip-chip bonding, the temperature rise and thermal resistance of the package were observed to reduce with temperature. By alleviating the heat accumulation in the package, more stable colorimetric properties such as CCT and Y–B ratio can be achieved.