A dedicated multichip module automatic optical inspection system

The design of an automatic optical inspection (AOI) system for multichip modules (MCMs) is discussed. The system differs from AOI tools designed for other applications due to the special characteristics of MCMs. The system consists of two subsystems: image acquisition and image processing. The critical issues concerning the components of each subsystem are discussed together with the different possible solutions. The image acquisition unit acquires the module´s image and transforms it into the electronic data that are transferred to the image processor. Acquiring the image involves an XY stage, an illumination module, an optical column, and a sensor. The image processing function is divided into preprocessing and defect detection, both containing sophisticated algorithms that are applied to the image, resulting in a reliable and accurate report of the flaws