Interferometric Measurements Of Mold-Plate Assemblies Designed For High-Volume Manufacturing Of Aspheric Microlenses

Injection molding is the leading high-volume production method for aspheric lenses used in consumer electronics. The design tolerances of these lenses require careful metrology of pins, resultant lenses and the injection molding plates themselves. Pins determine the form of the lenses, while the alignment of the pins to the mold plate determines apex distance, decenter and tilt. One key parameter of the mold plate is the overall flatness, as it is a critical datum for the pins. We demonstrate flatness metrology on a platform capable of sub-micron lateral resolution that can be used for roughness measurements as well as high resolution measurements of sub-millimeter features such as apex centration. The platform is capable of measuring the full 200 mm by 200 mm mold plate in under 30 minutes. The flatness results are correlated with measurements from a laser Fizeau interferometer and demonstrate better than +/- 1 mu m correlation on samples with 20 microns of departure and better than +/- 0.2 mu m correlation on plates with sub-micron departure.