High Definition Image Acquisition for Automatic Optical Inspection Using Light Sources Characteristics

Major parts of an automatic optical inspection (AOI) system, which is widely used in chip-on-glass modules, are differential interference contrast (DIC) microscope, light source, and a camera. This paper describes the relationship between DIC microscope and three major light sources—halogen, xenon, LED—with line scan and area camera. It is verified that there is a periodic change in the mean gray-scale value of the acquired image in accordance with the displacement of the DIC prism slider for both the line scan and area cameras. Each light source has a characteristic periodic pattern. Among the three light sources, LED shows excellent detecting ability and accuracy ratio on indentation marks for both line scan and area camera. Considering low power consumption, longer lifetime, and cheaper price of LED, it is highly recommended in conjunction with a line scan camera for an AOI system in a factory setting.