Chip-on-board (COB) wafer level packaging of LEDs using silicon substrates and chemical foaming process(CFP)-made glass-bubble caps

In this paper, we investigate a novel Chip-On-Board (COB) process for wafer level LED packaging using micro glass-bubble caps and silicon substrates. The COB packaging process is firstly studied experimentally, which consists of the following steps. First, a silicon substrate with lead lines is prepared. Second, LEDs are mounted on the silicon substrate followed by wire-bonding. Third, phosphor is distributed uniformly onto the spherical inner wall surface of glass bubbles. Fourth, the spherical glass bubbles are filled with silica gel. Finally the LEDs on the silicon substrate are encapsulated by the spherical glass-bubble caps. The thermal performance of the LEDs using the COB technology is then simulated by ANSYS and tested. Results show that the COB process is demonstrated successfully and the packaged LED chip has a good thermal and optical performance. Results also indicate that the wafer level COB LED packaging technology using silicon substrates and CFP-made spherical glass-bubble caps would improve the reliability and optical performance of high power white light LEDs greatly.