Browse Prior Art Database

Optical Test System

IP.com Disclosure Number: IPCOM000034187D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Fellows, TC: AUTHOR [+4]

Abstract

A two-stage electro-optical system used for inspection of printed circuit patterns is disclosed. The two-stage test process consists of a full reference test for suspected defective locations followed by a rules test that inspects localized areas around the suspected defects. The second level rules test eliminates up to 90% of the false calls made by the first level data test while confirming all of the real defect locations. An image is scanned into an NxN memory with a number of bits per pixel representing shades of gray. The image is turned into an NxNX1 (binary image) through use of a special thresholding algorithm. The binary image is correlated to a reference data pattern within +/- 1 pixel for the NxN image.

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Optical Test System

A two-stage electro-optical system used for inspection of printed circuit patterns is disclosed. The two-stage test process consists of a full reference test for suspected defective locations followed by a rules test that inspects localized areas around the suspected defects. The second level rules test eliminates up to 90% of the false calls made by the first level data test while confirming all of the real defect locations. An image is scanned into an NxN memory with a number of bits per pixel representing shades of gray. The image is turned into an NxNX1 (binary image) through use of a special thresholding algorithm. The binary image is correlated to a reference data pattern within +/- 1 pixel for the NxN image. This is accomplished through unique scanning patterns to find center points of known features followed by a least squares best-fit algorithm that describes a correction to X,Y points. Once X,Y data points of known features are corrected, these features can be tested for presence of copper (opens test) toward the interior of features and absence of copper (shorts/spacing) around the outside of these features using vector scans. A third algorithm that checks for a certain number of copper pixels on lands and vias is used as a fast check for area. If a copper pixel is missing during an opens scan or a copper pixel is found during a shorts scan, the X,Y location is flagged and a small mxm window around the suspected area is passed to th...