Surface Orientation Recovery of Specular Micro-surface via Binary Pattern Projection

With the continuous effort of the electronic industry in miniaturizing device size, the task of inspecting the various electrical parts becomes increasingly difficult. For instance, solder bumps grown on wafers for direct die-to-die bonding need to have their 3D shape inspected for assuring electrical contact and preventing damage to the processing equipments or to the dies themselves in the bonding process. Yet, the inspection task is made difficult by the tiny size and the highly specular and textureless nature of the bump surfaces. In an earlier work we proposed a mechanism for reconstructing such highly specular micro-surfaces as wafer bumps. However, the mechanism is capable of recovering 3D positions only. In this paper we describe a new mechanism that recovers surface orientations as well which are as important in describing a surface. The mechanism is based upon projecting light from a point or parallel light source to the inspected surface through a specially designed binary grid. The grid consists of a number of black and transparent blocks, resembling a checker board. By shifting the grid in space a number of times in a direction not parallel to either boundary of the grid elements, and each time taking a separate image of the illuminated surface, we could determine the surface orientations of the inspected surface at points which appear in the image data as grid corners. Experimental results on real objects are shown to illustrate the effectiveness of the proposed mechanism. Keyword: Surface Orientation, Specular Surface, Structured Light, Checker Board Pattern, Grid Corners.