Automatic 2 1/2 D shape inspection system for via-hole fillings of green sheets by shadow image analysis

The authors describe an automatic 2 1/2 D shape-inspection system for via-hole fillings of green sheets, which are unsintered layers of multilayer ceramic substrates. Two shadow images re taken with two oblique illuminations from different directions. To determine whether the shadow results from a convex structure or a concave structure, the shadow regions are labelled by analyzing the relation between their edge positions. After labelling, concave and convex defects as small as 30 μm can be detected independently by measuring the length of the shadow and comparing it to the predetermined criteria. In addition to concave and convex defects, lack-of-filling defects can also be detected with very high accuracy by counting the area of the filling pattern detected from an oblique direction