High Color Uniformity of White Light-Emitting Diodes Using Chip-Scaled Package
Chip-scaled package light-emitting diodes (CSP LEDs) are promising for illumination applications because of their advantages of compact size and high luminous density. Contrary to traditional conformal package structures, the material and thickness of top and sides, respectively, are controllable, showing great potential to achieve high color uniformity. In this letter, different kinds of CSP LEDs were comprehensively compared, and the requirements to gain high color uniformity were further investigated with simulation and experiment. Results show that a top volume proportion of phosphor <inline-formula> <tex-math notation="LaTeX">${V}_{\mathrm {top}}$ </tex-math></inline-formula> between 75% and 85% contributes to high color uniformity for the universally used 35 and 45 mil flip chips. The fabricated CSP LEDs with <inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {top}}=77.8\% $ </tex-math></inline-formula> can gain an extra uniform color distribution with a <inline-formula> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>CCT of only 92 K at a CCT of approximately 6000 K, which is 82.1% lower than that of traditional conformal LEDs. These results indicate that the CSP structure is an important alternative for illumination applications requiring high color uniformity.