Micro vision-based measurement of concentricity for both the TO base and active area of an APD chip in optical component packaging

Abstract

The avalanche photodiode (APD) chip is the core component of the transistor outline (TO). The concentricity between the inner circle (IC) of the APD active area and the outer circle (OC) of the TO base will directly affect a component’s key performance indicators, such as external quantum efficiency, receiving sensitivity and responsivity, thereby impacting quality assurance, performance improvement, and stable operation. Nevertheless, as the surge in demand for components increases, the traditional visual inspection relying on manual and microscope has been unable to meet the requirements of mass manufacturing for real-time quality and efficiency. Thus, a Concentricity Microscopic Vision Measurement System (CMVMS) mainly composed of a microscopic vision acquisition unit and an intelligent concentricity measurement unit has been proposed, designed, and implemented. On the basis of analyzing the 3D complex environment of TO components, a coaxial illumination image acquisition scheme that can take into account the characteristics of the OC and IC has been proposed. Additionally, a concentricity image measurement method based on dynamic threshold segmentation has been designed to reduce the interference of complex industrial environment changes on measurement accuracy. The experiment results show that the measurement accuracy of the CMVMS system is over 97%, and with a single measurement time of less than 0.2s, it can better meet the real-time and accuracy requirements. To the best of our knowledge, this is the first report on the realization of real-time concentricity measurement in optical component packaging, and this technology can be extended to other fields of concentricity measurement.