REDUCTION OF FALSE ALARMS IN PCB INSPECTION

• US 20070165939A1
• Filed: 12/29/2006
• Published: 07/19/2007
• Est. Priority Date: 09/10/2000
• Status: Abandoned Application

• Current Assignee: Orbotech Limited (KLA Corporation)
• Original Assignee: Orbotech Limited (KLA Corporation)
• Inventors: Savareigo, Nissim, Shalom, Dan, Arad, Nur
• Application Number:
  US11/618,471
• Publication Number:
  US 20070165939A1
• Time in Patent Office: Days
• US Class Current: 382/145
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G01R 31/309 of printed or hybrid circuits or circuit substrates
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/30141 Printed circuit board [PCB]
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06V 10/22 by selection of a specific region containing or referencing a pattern; Locating or processing of specific regions to guide the detection or recognition
• CPC Class Codes: G06V 10/44 Local feature extraction by analysis of parts of the pattern, e.g. by detecting edges, contours, loops, corners, strokes or intersections; Connectivity analysis, e.g. of connected components
• CPC Class Codes: G06V 10/56 relating to colour

Abstract

A method for automatically optically inspecting an electrical circuit, comprising: acquiring at least one optical image of an electrical circuit; generating at least one first inspection image from the at least one image and determining regions of candidate defects therefrom; generating at least one additional inspection image for regions surrounding candidate defects, said at least one additional inspection image at least partially including optical information not included in the at least one first inspection image; and determining whether the candidate defect is a specious defect by inspecting the at least one additional inspection image.

Claims

1. A method of determining defects in electrical circuits, comprising:

acquiring an optical image of an electrical circuit;

generating a representation of the electrical circuit from the image;

analyzing at least part of the representation at a region near a candidate to detect an attribute of the electrical circuit;

revising the representation in response to a detected attribute of the electrical circuit;

processing the revised image to determine the presence of a real defect the electrical circuit.

2. A method according to claim 1 wherein the representation is a representation of contours in the electrical circuit.

3. A method according to claim 2 wherein the contours are representative of putative edges between metalized portions and substrate portions in the electrical circuit.

4. A method according to claim 1 wherein revising includes:

evaluating a region in the representation to determine whether it is a metal; and

revising the contours if metal is detected.

5. A method according to claim 4 wherein the metal is oxidized or non-oxidized metal.

6. A method according to claim 5 wherein the metal is copper.

7. A method according to claim 4 wherein the evaluating includes analyzing a monochromatic image of the region.

8. A method according to claim 4 wherein the evaluating includes analyzing a polychromatic image of the region.

9. A method according to claim 1 wherein revising includes calculating a directed convex hull for a section of the contours, and replacing the section with the directed convex hull.

10. A method according to claim 5 wherein revising includes locating points representing corners in a contour located near the candidate defect.

11. A method according to claim 10 wherein the directed convex hull extends between corner contour points.

12. A method according to any of claim 1 wherein revising includes detecting contour points that are situated on oxidized conductors.

13. A method according to claim 12 wherein revising includes identifying at least three contiguous oxidized contour points.

14. A method according to claim 13 wherein revising includes identifying from among the at least three contiguous oxidized contour points, at least two oxidized contour points each of which is bounded by a contour point that is not oxidized.

15. A method according to claim 13 wherein revising includes identifying from among the at least three contiguous oxidized contour points, at least one oxidized contour point that is also a corner.

16. A method according to claim 15 wherein revising includes identifying from among the at least three contiguous oxidized contour points an additional contour point that is bounded by a contour point that is not oxidized.

17. A method according to claim 14 wherein revising includes calculating a directed convex hull between any pair of:

oxidized contour points which are bounded by a combination of contour points that are not oxidized and oxidized contour points that are a corner

18. A method according to claim 1 wherein the attribute comprises an optical attribute characteristic of an oxide.

19. A method according to claim 1 and wherein the attribute is an optical attribute comprising a level of reflective intensity in at least two spectral ranges.

20. A method according to claim 19 and wherein the attribute is an optical attribute comprising a level of reflective intensity in at least three spectral ranges.

21. A method according to claim 19 wherein the spectral ranges comprise at least two of red, green and blue.

22. A method according to claim 20 wherein the spectral ranges comprise at least two of red, green and blue.

23. A method according to claim 1 wherein processing is performed in response to the detection of metal in the vicinity of the candidate defect.

24. A method according to claim 1 wherein processing is performed in response to the detection of an oxide in the vicinity of the candidate defect.

25. A method according to claim 24 wherein the detection of an oxide is performed on contour points located along a putative border between metal conductor and substrate.

26. A method according to claim 24 wherein the detection of an oxide is performed on the values obtained by pixels for regions in the electrical circuit that are located near the candidate defect.

27. A method according claim 1 wherein revising includes revising a putative contour to include a directed convex hull.

28. A method according to claim 27 wherein revising includes measuring the distance between putative contours, wherein at least part of the putative contours includes the directed convex hull.

29. A method for inspecting printed circuit boards for defects, comprising:

acquiring an image of a printed circuit board;

performing automated optical inspection on the image to identify candidate defects on the printed circuit board;

providing an image of a region surrounding a candidate defect to a processor, said image including a map of putative contours corresponding to the candidate defect;

analyzing the image of the region surrounding the candidate defect;

revising the putative contour map to provide a revised contour map in response to a predetermined condition occurring in the image, the revised contour map including revised contours corresponding to the candidate defect; and

inspecting the revised contour map to determine the presence of an actual defect in the electrical circuit.

30. A method according to claim 29 wherein the image comprises contours that are determined using a first method for determining contours.

31. A method according to claim 30 wherein the first method employs a difference of Gaussians calculation.

32. A method according to claim 29 wherein the contours are representative of putative edges between metalized portions and substrate portions in the printed circuit board.

33. A method according to claim 29 wherein revising includes:

evaluating the image to detect whether the region includes a metal; and

revising the contours if metal is detected.

34. A method according to claim 33 wherein the metal is oxidized or non-oxidized metal.

35. A method according to claim 34 wherein the metal is copper.

36. A method according to claim 33 wherein the evaluating includes analyzing a monochromatic image of the region.

37. A method according to claim 33 wherein the evaluating includes analyzing a polychromatic image of the region.

38. A method according to claim 29 wherein revising contours includes calculating a directed convex hull for a section of the putative contours, and replacing the section with the directed convex hull.

39. A method according to claim 29 wherein the predetermined condition comprises an optical attribute characteristic of a metal in the image.

40. A method according claim 29 wherein revising includes revising a putative contour to include a directed convex hull.

41. A method according to claim 40 wherein revising includes measuring the distance between putative contours, wherein at least part of the putative contours includes the directed convex hull.