Lens Forming by Stack Dispensing for LED Wafer Level Packaging

In this paper, a moldless stack dispensing method to form an light-emitting diode (LED) lens at the wafer level is presented. This method uses a dispensing process to form a lens with high H/L ratio, where H and L stand for the height and the base length of the lens. Silicon wafer is used as the substrate. V-groove trenches are made on the surface of the wafer to define the size of the substrates. In the dispensing process, a droplet of encapsulant is dispensed on the substrate to form a base heap. After the base heap is cured, a second droplet of encapsulant is dispensed on top of the base heap and cured. The stacked encapsulant forms a lens with high H/L ratio. Dispensing on substrates sized from 3 mm × 3 mm to 5 mm × 5 mm is investigated. For each size of substrate, experiments are performed to obtain the maximum volume of the encapsulant without overflowing (the critical volume) for both the base heap and the stacked layer. The results show that despite size differences, substrates of different sizes have a similar critical volume for both the base heap and the stacked layer. The ratio of critical volume of base heap to stacked layer remains at around 1:1. Consequently, the highest H/L values of substrates with different sizes stay at around 0.33. Both critical k and H/L show no obvious correlation to the size of substrate. The method is implemented on a functional LED package. Investigations on the geometry of the lens and optical characteristics of the encapsulated LED packages are shown. The results show that the stacked encapsulation modifies the light distribution and improves the radiant power of an LED package.