Fabrication of integrated microlens array mold/mold insert for mass production

This article describes a mass fabrication method for integrated microlens arrays mold by using UV lithography, thermal reflow, and electroforming process. The designed microlens array can be used for back light modules to enhance panel illumination. Refractive microlens with diameter 30 and 70 mum in array are designed in certain layout. Lithographic fabrication of photoresist cylinder is applied by using the designed microlens array patterns. Thermal reflow resulted in photoresist melting and diameter shrinkage. Due to surface tension the shape of the photoresist cylinders changes to spherical shape. The sags of microlens with diameter 30 and 70 mum are 7.5 and 25 mum, respectively. The cross-section profile of microlens is measured by the Taylor Hobson's profiler. It proved that thermal reflow can produce microlens array in photoresist materials. Replication process is applied by using electroforming process. Ni-Co composite electroforming can make metallic mold with hardness Hv 500 which is close to ordinary mold materials. Sputtering silver as a seed layer is applied onto microlens array in photoresist. Electroforming can start a "build-up" process to make required microlens array mold or mold insert. Refractive microlens arrays with high dense 700 lenses per mm(2) were fabricated. The surface roughness of microlens arrays is less than Ra 0.02 mum that adapt to the conventional lens surface roughness. Since the higher accuracy and lower cost of microlens fabrication methods are needed to meet the rapid growth of micro-optical devices, the contributed fabrication techniques are essential for the industry.