Solder inspection using an object-oriented approach to machine vision

A generic approach to the development and integration of machine vision, within surface- mount electronics manufacturing, has been proceeding based on the concept of a standard vision framework. A framework is a collection of system components, the connection of which can be configured with appropriate support tools. This is facilitated using object- oriented analysis and design techniques to identify and describe those elements, or modules, that are crucial to all vision systems within the domain. Analysis of surface-mount manufacturing has identified fifteen potential tasks in which machine vision inspection and control is beneficial. The essential functionality which spans these tasks has been identified and incorporated in a set of approximately twenty visual components implemented using the KAPPA programming environment. A practical exploration has been made into using the framework to develop a method of classifying insufficient solder deposits based on the distinct light reflection characteristics of solder fillets when illuminated from different angles. Classification has been reliably achieved by calculating the variation in mean luminance of specific fillet regions between images obtained with high and low angles of lighting using a custom light source. The resulting system architecture has illustrated the potential of object- oriented software and specification techniques, producing an elegant structure based on code reuse and `design by extension'.