Micro-Lens Array (MLA) for diffusing incident light has been widely used for 3D depth measurement. Especially in Time-of-Flight (TOF) 3D sensor, output beam uniformity through the MLA is one of the most important factors to determine the sensor accuracy. This performance is highly related to a MLA lens structure. Randomized MLA, a substitute for regular periodic MLA, does not overcome a low diffusing efficiency due to the leaking light. To tackle this issue, we propose a new MLA design methodology which is comprised of various unit lenses having different curvatures and sizes (hereafter referred to as the “Mini-Lens"). The design method is to randomly overlap a sub lens having different curvatures and sizes into the regular periodic arrange. The Mini-Lens type MLA shows a non-periodic structure and no height difference. The experiments with our design show ~30% improvements in uniformity and efficiency compared to the regular periodic MLA and the randomly distributed MLA, respectively. New Mini-Lens can achieve a fill factor of 100% over various designed base and sub lens. In addition, the suggested methodology will be useful for designing all the structures that are difficult to arrange apart from rectangular and hexagonal type. Our methodology will be a new design method to overcome the limitation of its structure.