A method for inspection of ball bonds in integrated circuits

Wire bonding in IC assembly process involves making a physical connection between the IC pad and the lead by bonding wires between the two. Inspection of wire bond quality is a highly labour intensive process and the continuing increase in packing density of VLSI circuits requires that the inspection process be completely automated. This paper suggests a new method for automated visual inspection of wire bond. A popular type of bonding (connected to bond pad) known as “ball bond” is considered here. Although several approaches for ball bond inspection have been introduced, they do not reveal the efficient results. The suggested method consists of five steps: (1) to enhance the edges using binomial and the modified Laplace filter; (2) to binarize the image; (3) to extract center of the ball bond; (4) to extract the ball bond boundary; (5) to fit the ellipse using direct ellipse-specific fitting. Experimental results illustrate that the proposed method performs the inspection of ball bond more fast and accurately as compared to the conventional ball bond inspection methods and, in addition, our method finds the size and orientation of the ball from the bond image containing the part of the ball