Study On Flip-chip LED Packaging Technology With High Color Rendering Index

LED package plays the key role in the process of turning LED chip into the LED light source.The LED flip chip packaging is superior to the traditional chip packaging with its advantages of no gold wire,high reliability and good heat dissipation effect.The existing white light LED with high color rendering index mainly uses a blue light LED chip to stimulate YAG phosphor powder.Therefore,the phosphor layer covering technology has become one of the key technologies of the white LED package.The traditional phosphor coating process is simple and cost saving,but it is difficult to produce high quality white LED light source with high color rendering index,high luminous efficacy and wide color temperature range by controlling the amount of phosphor glue and the size of light-emitting area.The key technology and performance of flip-chip LED packaging is studied.The flip-chip LED packaging process is optimized,including substrate designing,solder pasting,chip placing,reflow soldering and phosphor layer covering.By comparing the performance with the normal LED chip package,it is shown that the luminous flux,luminous efficacy and reliability of flip chip packaging is better under the high current.By comparing the different welding technology,it is proved that a slight pressure on the chip surface and the welding method of reflow soldering is greatly helpful to the yield and quality of the flip-chip LED package light source.The key to the conversion of blue LED into white light is the phosphor layer covering on the LED chip,and the different phosphor covering technology will directly determine the lighting quality of white LED light source.In this paper,the optimization mechanism of the phosphor layer is studied,we mainly research the effects of different phosphor ratio and phosphor layer structure on luminous efficacy,color rendering index and color temperature of the LED light source by analyzing the spectral power distribution of LED light source.The experiments show that the white LED light source with the stack phosphor layer technology can achieve color rendering index over 95 and luminous efficacy over 100lm/W.In addition,under the condition of keeping the concentration of the two phosphor layers unchanged,thestack phosphor layer technology can realize the range of color temperature variation for3000K-6500 K by changing the covering quantity of the two phosphor layer.And the color rendering index is also maintaining at high level.Finally,we optimize the structure of the general remote coating phosphor layer by combining the stack phosphor layer technology with the remote phosphor technology.The experiments show that under the condition of the same color temperature and the luminous efficacy is increased by 5.4%,the color rendering index can be up to 95.