In-line computational shear interferometry of insert molded micro parts for optical application

Abstract

Micro injection moulding is a mass production of micro optics that offers the possibility of a high functional integration within a single micro part by insert moulding. Since the functionality of the micro parts depends on the homogeneity of the overmoulded polymer layer, a robust, accurate and fast metrology system is needed for a quantitative quality assessment. Here, we demonstrate an in-line metrology approach for the optical inspection of insert molded micro parts. In contrast to standard interferometers, the proposed system has low demands regarding the coherence of illumination. Thus, an LED light source can be used instead of a laser, reducing the cost and increasing the safety of the production platform. In addition, the system is robust against mechanical distortions, since it is based on a common path approach. These advantages make the system a good candidate that fulfills the needs in regard to the in-line inspection of insert molded micro parts. As an example of application, the proposed system is used to inspect a cannula with overmolded thermoplastic as a light sleeve providing illumination over a specific area of surgery.