Identifying solder surface orientation from color highlight images

As an attempt to obtain effective machine vision of solder joints, the authors describe a surface slant estimation technique which presents a color highlight map of a solder joint surface partitioned with colored regions. The imaging geometry consists of a single camera placed along the z axis and three circular sources of different elevations with respective colors of red, green, and blue. The concept of this approach is derived from a consideration of the surface tension which acts primarily in solder shape formation and also from a consideration of the relation between the surface normal and the wettability and volume of solder applied. Implementation of the technique has demonstrated its practical applicability to automatic inspection of wave- or reflow-soldered printed circuit boards (PCBs) inserted or mounted with a variety of component parts