3D visual inspection of IC bonding wires

Abstract

During the stage of pre-cap inspection, 3D profiles of bonded wires are inspected to detect defects such as lifted, tight and sagging wires, and to measure the maximum wire height. This paper presents a novel inspection system based on the application of the stereo technique. In our single-camera setup, stereo views are obtained by rotating the IC chip under the camera. Wire bond edges are detected using Canny's method. These are then linked to form curves, and matching is conducted between two curve lists of a stereo pair. Results of local matching are combined to find the global optimum. The depth measurement of our system has an accuracy of 14 μm, which corresponds to one-fortieth of the total range of wire height.