Combining phosphor with LED chip has become the most common method to realize white light output for white LED.Thermal conduction and phosphor coating are two key factors that influence on the quality of products.The spatial distributions of color temperature and chromaticity are the crucial parameters of power white LED used in lighting.The range of color temperature deviation within single white LED which can be distinguished by human eyes is from 50 K to 100 K.The uniformity of color temperature of white LED devices still cannot achieve the optimized standard

because the color temperature deviation of single product can even attain 800 K.This can be attributed on the nonuniformity of phosphor coating on the LED chip.Therefore

the uniformity of light output is of great importance as white LEDs found their way in the lighting application.The conventional dispensing method(or dipping method)for phosphor coating

which is much popular currently used in the LEDs industry

was introduced in this paper.Further

some modification had been made in the structure configuration of the phosphor layer to improve the uniformity of light output of white LEDs based on the dispensing process.Nine-point scheme had been adopted to measure the spatial distribution of brightness and chromaticity of light output of different LEDs samples with different process parameters.Although these modification has improved the uniformity of chromaticity of white light spot in a certain extent

as a whole the uniformity of white light output of devices made by employing conventional dispensing method of phosphor coating is still not good

and deviations of spatial coordinates of white light spots are larger than those of 0.01 that human eyes can distinguish.This can be ascribed to the cumber shape of phosphor coating.Since the process of phosphor coating is operated by handwork

the thickness of phosphor layer is not uniform which causes a big influence to the performance of products.In addition

the consistency of products of same batch is not good

and deviation of color temperature and chromaticity among different products is large.It can be explained that the process of phosphor dispensing cannot be well controlled among different products.All of these indicate that the conventional phosphor coating method-dispensing has lots of defects.To eliminate and overcome these defects

a novel phosphor coating method termed conformal coating

which can largely improves the uniformity of phosphor layer

should be emphasized.