Fabrication of microlens array by the tilted milling method to improve the surface morphology

In this paper, we propose the tilted milling method for the fabrication of the precise microlens array (MLA) by eliminating the influence of tool error. In the conventional milling process, the surface morphology problem especially hump formation is often provoked by tool error on the center area of the machined surface. The hump formation initiated by tool error is very difficult to remove, unless the cutting tool is replaced by a new one. It was found that the hump formation was completely suppressed by the tilted milling method which the tool-axis angle is tilted by 35° to the on-axis of lens curvature. The form accuracy of the MLA was also drastically improved the peak-to-valley ratio from (0.991 to 0.141) µm. The tilted milling method was confirmed to be a highly robust fabrication process, because the surface morphology was rarely affected by tool error, especially the run-out deviation.