Fabrication of gapless triangular micro-lens array

This study presents a new process to fabricate gapless triangular micro-lens array (GTMA) optical film. The process includes ultraviolet (UV) lithography, photoresist reflow process, Ni–Co electroplating and hot embossing technique. After photoresist triangular column array is defined by UV lithography, reflow technique is applied to melt photoresist triangular column array into the shape of triangular micro-lens array. With this reflowed triangular micro-lens array, metal Ni–Co is deposited and covered uniformly on the triangular micro-lens array using electroplating process. The growth rate of Ni–Co is controlled at 0.4–0.6 μm/min at electroplating current density of 1 A/dm2 (ampere square decimetre, ASD). After this electroplating process, a mold of GTMA is obtained, which is served as the primary mold. Next, with passivation technique applied on this primary mold's surface, a secondary mold is obtained by applying the electroplating process again. This secondary mold is served as master for the subsequent hot embossing process to replicate the GTMA pattern onto polymeric material of polymethyl methacrylate (PMMA) sheet. The Ni–Co mold with hardness over hardness of vicker (Hv) 650 is obtained. The stiffness and hardness of the mold play important roles in GTMA hot embossing process. In addition, this PMMA-based GTMA film used as optical film offers a 100% fill factor and high optical coupling efficiency to improve luminance. The optical measurement shows that this optical film with GTMA pattern increases 15.1% of luminance for backlight module (BLM) of liquid crystal display (LCD).