Research On Integrated Packaging Technology For High-power White-light LED With Vertical Electrode Structure

Recently, along with higher demands on high light and high power white LED,the high power white LED integrated packaging technology is confronted with greatchallenge. Firstly, as for LED with ipsilateral electrode, when packaged integrally, it iseasy to achieve series-parallel connection between chips. Accordingly, theseries-parallel connection ensures the high brightness of integrated packaging devices.However, as for the bottom of LED chips with vertical electrode structure isconductive electrode, therefore we meet great challenge when encapsulating LEDchips. Secondly, when getting the high brightness white LED through integratedpackaging, we may find that the overall luminous efficiency of integrated devices islower because of different distances among multi-chips.Based on the technical problems mentioned above, we made the integratedpackage of LED chips with vertical electrode structure come true by improving theintegrated packaging structure for the first time. By altering the distances amongmulti-chips in the integrated packaging structure, we also found the prior chip distanceto get higher luminous efficiency. Detailed research contents are as follows:By adding aluminium oxide insulating layer onto the coppery support with theLED chips with vertical electrode structure, we achieved series connection. Moreover,in order to improve the luminous efficiency of the devices, we added silver reflectivelayer onto the aluminium oxide insulating layer, then by connecting several groupsLED chips serially connected in parallel, thus the integrated structure of LED chipswith vertical electrode structure is finally achieved. The integrated device designed inthis paper consists of3series branches and each series branch consists of three1WLED chips.As for the prepared LED integrated device with vertical electrode structure, bychanging the ratio between fluorescent powder and packaging adhesive, we achievedthe white light LED with different color temperature. Moreover, we analyzed therelationship between the color temperature of integrated device, luminous efficiencyand current and the relationship between the forward voltage drop and device operating hours. We found that with the increase of the current, the luminous efficiencydecreases, the color temperature increases. With the increase of the operating hours,the forward voltage drop decreases until equilibrium state.By preparing samples of different chip distance, we analyzed the relationshipbetween the distance of each chip of integrated device and device luminous efficiencyand found out the most moderate distance for the luminous efficiency of the integrateddevice is2.0mm. Finally, we analyzed the two main reasons which lead to the changeof luminous efficiency of integrated packaging devices. The first reason is the differentdistance between chips resulted in bright speck and dark speck, which leads to the lowluminous efficiency. The second reason is that the integrated devices with shorterdistance between chips can be easier to bring about amount of heat. The temperaturerise will cause the LED chip PN junction carrier recombination probability to drop,resulting in lower luminous efficiency of the integrated device.