Fabrication of gapless dual-curvature microlens as a diffuser for a LED package

Abstract The light-emitting diode (LED) has been the subject of much interest in the role of a backlight module for liquid crystal displays (LCDs). However, a traditional LED lamp is a point-light source, and so is not suitable for use in large LCD panels. This study presents a new packaging method for LEDs, which uses a gapless dual-curvature microlens array (GDMLA) to improve its ability to illuminate a panel. GDMLAs of different dimensions were simulated and fabricated in order to examine their light luminance and uniformity. Commercial optical simulation software, “Tracepro”, was used to obtain a GDMLA of optimized geometry and dimensions. Based on the simulated data, a GDMLA mold was first fabricated using a LIGA-like process (Lithographie Galvanoformung Abformung, LIGA); this was known as the first mold. In this study, the first mold was obtained using a nickel cobalt (Ni–Co) electroplating process. In order to obtain a highly accurate and strong mold, a bulk metallic glass (BMG) alloy, Mg 58 Cu 31 Y 11 , was chosen as the material for the second mold, which exhibits excellent forming ability and high hardness. The pattern of the first mold was replicated onto BMG by hot-embossing, and the shrinkage between the first and the second mold was less than 0.2%. Next, the pattern of the GDMLA on the second mold was replicated onto ultraviolet (UV)-curable resin, producing the final optical film for a LED package. The shrinkage between the second mold and the UV-cured optical film was less than 0.4%; this means that the process exhibits a high replication ability. The fabricated GDMLA had the characteristics of dual curvatures and a high fill-factor of 100%. The light uniformity of the LED package with the GDMLA optical film was measured, and the results demonstrated that the GDMLA is a good optical device for use in LED packages. In addition, the relationship between the simulation and experimental results is assessed and discussed.