Screen-Printing of Yellow Phosphor Powder on Blue Light Emitting Diode (LED) Arrays for White Light Illumination

In current technology, white light generation from a light emitting diode (LED) can be achieved by combining the lights from three fundamental colors, namely, red, green and blue (RGB), of LEDs or by coating a phosphor layer onto the surface of a LED chip. The first method involving the RGB color mixing technique requires a complicated electrical circuit design for the control of light intensity and uniformity on the three different colors of LEDs and hence increases the costs of manufacturing. The second method is implemented by coating a layer of yellow phosphor on a blue LED chip for white light illumination. The quality of generated white light heavily depends on the packing density, the thickness and the uniformity of the phosphor coating. There have been some coating methods available in the industry. Each one of them has its own pros-n-cons. In the present study, a new yellow phosphor coating method by screen-printing on blue LED arrays is developed. Compared with conventional coating methods, this screen-printing method is considered relatively simple and rather effective. The newly developed method and the results of prototyping are introduced in this paper in detail.