High-Resolution Pattern Inspection
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Automatic high-precision optical inspection of patterns, such as on printed circuit cards, is performed by comparing the measured grey values of selected picture elements (pels) with reference data that have been stored with subpel resolution. An example of this technique concerns the inspection of cornerlike structures (Fig. 1) with respect to the corner angle a (in this case 90Œ) and the position of the corner apex C (at position 1.1 in the central pel of 4 x 4 subpels). All measured grey values gim of the pels within a circle R around apex C are summed after having been weighted according to the pel surface covered by the circle area; these weighting factors are indicated in the pels of Fig. 1. (The circle thus simulates a diaphragm with an opening R.