Method and apparatus for object inspection

• US 5,220,617 A
• Filed: 09/04/1991
• Issued: 06/15/1993
• Est. Priority Date: 09/04/1991
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation, Siram SPA (Veolia Environnement SA)
• Original Assignee: International Business Machines Corporation
• Inventors: Bird, Kenneth A., Muller, Kurt R., Kim, Douglas Y., Thorp, Lawrence D., Lambright, Julius J., Kish, Stephen J.
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US07/754,793
• Time in Patent Office: 650 Days
• Field of Search: 382/66, 382/1, 382/8, 358/101, 358/106, 356/237, 364/550, 364/552, 364/488, 364/489, 364/490, 364/491, 250/572
• US Class Current: 382/149
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination

Abstract

A method and apparatus for the inspection and handling of surface level defects is taught. Briefly stated, the object to be inspected is positioned. A Laser light is polarized into at least one orientation and then reflected off of a rotated polygon mirror. This causes the light to "move" over the area of interest. A plurality of fiber optic bundles are used to receive and conduct the reflected light back to photomultipliers. The photomultipliers convert the light into electrical signals while associated electronics digitize the signals, keeping track of pixels which are produced. By keeping track of pixel edge boundaries and determining if certain thresholds are exceeded or not met as appropriate, the area of interest can be checked for a variety of defects. By comparison of the defects to a reference base, the defects and hence the items inspected can be categorized.

Claims

1. A method of inspecting individual circuit board layers adapted to be formed into a multilayer ceramic substrate, each layer having a sheet surface and a plurality of vias passing therethrough, said method comprising:

transporting one of said circuit board layers in a first direction through an inspection area;

shining a light source across a rotating multifaceted mirror so as to can the light across the moving sheet surface of said circuit board layer is a direction substantially perpendicular to said first direction and developing a reflected light signal therefrom;

sampling said reflected light signal at a plurality of discrete angles and developing a plurality of video signals therefrom;

converting said video signals into a plurality of corresponding electrical signals;

comparing said electrical signals to a plurality of reference values; and

classifying said circuit board layer into one of a predetermined number of categories based on said comparison.

2. A method as set forth in claim 1, wherein said step of scanning said light across said moving sheet surface includes scanning said light across a portion of said sheet surface containing no vias and developing a reference light signal and corresponding reference electrical signal therefrom.

3. A method as set forth in claim 2 wherein said step of scanning said light across said moving sheet surface includes scanning said light across the entire region of said layer containing said vias, and comparing the electrical signals generated therefrom to said reference electrical signal.

4. A method as set forth in claim 1 wherein said light source is a laser light source.

5. A method as set forth in claim 1 wherein said video signal is sampled at discrete angles by a multichannel fiber optic sensor assembly.