Browse Prior Art Database

Spatial Filtering System for Inspection and Verification

IP.com Disclosure Number: IPCOM000036829D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 4 page(s) / 64K

Publishing Venue

IBM

Related People

Watts, KW: AUTHOR

Abstract

A technique is described whereby an optical spatial filtering system is used in the inspection and verification of via hole patterns, as used in printed circuitry, to: a) detect the presence or absence of holes, b) accurately gauge the size of each hole, and c) determine if the hole is contaminated or defective.

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Spatial Filtering System for Inspection and Verification

A technique is described whereby an optical spatial filtering system is used in the inspection and verification of via hole patterns, as used in printed circuitry, to: a) detect the presence or absence of holes, b) accurately gauge the size of each hole, and c) determine if the hole is contaminated or defective.

The system consists of a laser scanning section and an optical data processing section so as to provide rapid via hole inspection. It is an improvement over previously used methods, such as: photo- sensing devices which can be affected by crosstalk from nearby holes; laser-scanning verifiers which do not reliably detect contamination or hole defects; or methods which do not detect extra holes that overlap a via.

The concept described herein utilizes spatial filtering techniques * applied to via inspection. The image of a "good" via is blocked by the filter, and only a small amount of light energy will pass to a photo-detector. The concept extends the verification of via hole patterns by using a verifier which cannot only detect the presence, or absence, of vias, but also can detect defects and contamination.

The laser scanning portion of the system consists of laser 10, as shown in the figure, rotating multi-faceted scan mirror 11, telecentric first scan lens 12, off- axis parabolic mirror segment 13 and first photo-detector 14. It is designed to scan, with an eight-millimeter diameter laser spot, across green sheet 15 (shown in the plane of the figure), while green sheet 15 is moved in a plane perpendicular to the figure.

The image of the via is reflected by parabolic mirror segment 13 onto beam splitter 16, which directs half of the light energy onto first photo-detector 14, while the other half enters the optical processing system section. Electrical signals from photo-detector 14 detect the presence of a hole (either good or defective), while a "no" signal indicates the absence of a hole. The eight-millimeter laser spot is large enough to illuminate an entire via, typically 5.5-mil or 6-mil diameter. The entire via must be illuminated, since the optical data processing section is an imaging system as opposed to a sensing system used in prior art.

The optical data processing section is made up of second scan lens 17, first ...