Development of LED Wafer-level Packaging Process and Micro-structure Hybrid Lens Mold

LED has been widely used in illumination and display. However, most LEDs are packaged by dispensing method, which is low in productivity and complicated in process. Developing an efficient packaging technology has become an important issue. Wafer level packaging integrated with lens has drawn great research effort. In this study, transfer molding technique and gas-assisted imprinting UV curing process are employed to perform the wafer level packaging.
First, a transfer molding machine was designed and implemented for wafer-level LED packaging integrated with lens. The effects of resin volume, mold temperature, clamping force and injection pressure on lens formability were investigated. 8 × 8 packaging with lens has been successfully realized on a 4-inch wafer. The replication rate of lens’ height is more than 96%. With temperature of 100 ℃ and injection pressure of 20 psi, the 97.7% replication rate of lens height can be reached.
The gas-assisted UV curing process for wafer-level LED lens packaging was also developed. The UV transparent mold was fabricated with gas-assisted hot embossing and PDMS casting. The reversal imprinting process was used for bubble free. The effects of forming parameters including imprinting pressure, size of PDMS mold, UV resin coating time on lens formability were investigated. An 8×8 packaging with integrated lens structure on 4-inch wafer had been successfully realized. Homogeneous lens shape with a 98% replication rate of lens’ height can be reached.
Since lens’ shape affects optical performance, this study further investigated the effects of microstructures on lens surface with simulation. The optical performances of micro-lens hybrid lens and V-cut structure hybrid lens were analyzed and confirmed. The molds for the micro-structured hybrid lens were manufactured by 2-step gas-assisted hot embossing and PDMS casting. Using the micro-structured hybrid mold and the gas-assisted imprinting UV curing process, wafer level packaging integrated with micro-structured hybrid lens has been successfully realized. This study demonstrates the potential of the gas-assisted imprinting UV curing process and micro-structured hybrid lens in LED wafer level packaging.