Browse Prior Art Database

High-Resolution Pattern Inspection

IP.com Disclosure Number: IPCOM000060149D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Kallmeyer, M: AUTHOR [+4]

Abstract

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.

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High-Resolution Pattern Inspection

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 90OE) 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.) Angle a is then calculated according to the relation a = (360OE x S gim) : S gi, where gi are the weighted grey values of the pels if no corner is present. Calculation is performed at high speed in the circuit of Fig. 2. The weighting factors are stored in a programmable read-only memory (PROM); the calculated sums of weighted grey values are then checked for tolerance limits to reject defective patterns. The circuits for implementing the example of grey value evaluation are standard and relatively simple; the high processing speed obtainable by this method permits high- accuracy evaluation of complicated patterns in a short time.

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