Study of micro-lens array by reflow process

In this study, different diameters of photoresist AZ4620 are defined using lithography. According to the specification of the back light module (BLM) for a liquid crystal display (LCD), the diameters of micro-lenses are divided into two groups. The first group includes lenses with diameters of 90, 95, 100, 105, 110 and 150 µm at a 100 µm pitch; the reflow temperatures for this first group range from 175–300°C with heating times of 6–24 h. The second group includes lenses with diameters of 10, 20, 30, 40, and 50 µm at pitches of 40, 30, 20, 10, and 25 µm, respectively; the reflow temperatures are the same as for the first group with heating times of 1–12 h. In this study, the parametric effects of reflow time and temperature on micro-opticals are characterized and discussed, and optical properties such as the focal length of micro-lenses are measured and analyzed. Then, each micro-lens is sputtered with a conductive seed layer of silver (Ag) for the subsequent eletroforming process, which is the mold for hot embossing. The mold is further incorporated with hot embossing materials and hot embossing techniques to produce the micro-lens required.