Line inspection system

• US 4,661,984 A
• Filed: 08/29/1979
• Issued: 04/28/1987
• Est. Priority Date: 06/03/1977
• Status: Expired due to Term

• Current Assignee: BMC Industries Incorporated National Bank Building St Paul Minnesota 55101
• Original Assignee: BMC Industries Incorporated National Bank Building St Paul Minnesota 55101
• Inventors: Bentley, William A.
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US06/070,899
• Time in Patent Office: 2,799 Days
• Field of Search: 340/146.3 E, 340/146.3 H, 340/146.3 AE, 340/146.3 AC, 340/146.3 F, 340/146.3 R, 364/515, 250/560, 250/562, 250/563, 250/572, 356/372, 356/376, 356/381-387, 356/394, 356/237, 235/92 PC, 358/106, 382/65, 382/8
• US Class Current: 382/147
• CPC Class Codes: G01N 2021/95638 for PCB's
• 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 2201/103 Scanning by mechanical motion of stage
• CPC Class Codes: G06T 2207/30141 Printed circuit board [PCB]
• CPC Class Codes: G06T 7/0008 checking presence/absence

Abstract

A line inspection system suitable for inspecting printed circuit boards for defects. In a first embodiment disclosed, a plurality of sensors which detect the presence or absence of conductor material on the board are grouped in a preestablished pattern. The area of the circuit board to be inspected is scanned by the sensing pattern and logical sequences of sensor condition which indicate defects are searched for. In a second embodiment disclosed, the area to be inspected is scanned serially, and the resultant data stored. Logical analysis is then performed on the stored data to determine whether the pattern of data is or is not consistent with an acceptable part.

Claims

1. A line defect detection system which comprises:

means for sensing the presence or absence of a line at a plurality of points in an area to be inspected, said points being in a circular pattern, said plurality of points including;

(i) first and second points spaced apart a distance related to the minimum acceptable line width; and

(ii) a third point between said first and second points;

means responsive to the relative states of said sensing means for recognizing the presence of a line segment having a width less than said acceptable line width; and

means for determining whether the center of said circular pattern is on a line.

2. The line defect detection system as recited in claim 1 wherein said means for determining whether the center of said circular pattern is on a line comprises means for sensing the presence or absence of a line at one or more points inside said circular pattern.

3. The line defect detection system as recited in claim 1 where all of said points are sensed simultaneously, and further including means for causing the center of said circular pattern to scan a region being inspected.

4. The line defect detection system as recited in claim 3 where the means for causing the center of said circular pattern to scan moves said center in raster fashion.

5. The line defect detection system as recited in claim 1 where said sensing means comprises means for scanning a region to be inspected in raster fashion and further including:

means for storing data from said sensing means; and

means for retrieving data from said storing means, said retrieved data being data representing the presence or absence of a line at said pluralities of points.

6. The line defect detection system as recited in claim 5 where said means for retrieving data retrieves all of the data representing circular pattern which have one center simultaneously.

7. The line defect detection system as recited in claim 5 where said storing means is a group of shift registers and where said means for retrieving data is responsive to the states of a plurality of stages of said shift registers.

8. The line defect detection system as recited in claim 1 and further including means for inhibiting the signalling of a defect smaller than a predetermined size.

9. A line defect detection system which comprises:

a plurality of sensors, each for sensing the presence or absence of said line in an area, said sensors sensing areas in a preestablished pattern, said plurality of sensors including;

(i) first and second sensors spaced apart a distance related to the minimum acceptable line width; and

(ii) a third sensor between said first and second sensors;

means responsive to the relative states of said sensors for recognizing the presence of a line segment having a width less than said minimum line width; and

scanning means for causing the region containing said line to be traversed by said pattern, said plurality of sensors including a plurality of sensors arranged to sense a pattern of areas comprised of two concentric circles, said first and second sensors sensing areas on the smaller of said two concentric circles and said third sensor sensing an area on the larger of said two concentric circles.

10. A line defect detection system which comprises:

a plurality of sensors arranged in a circular pattern, each for sensing the presence or absence of said line in an area, said sensors sensing areas in a preestablished pattern, said plurality of sensors including;

(i) first and second sensors spaced apart a distance related to the minimum acceptable line width; and

(ii) a third sensor between said first and second sensors;

means responsive to the relative states of said sensors for recognizing the presence of a line segment having a width less than said minimum line width;

scanning means for causing the region containing said line to be traversed by said pattern; and

means for detecting whether said circular pattern is substantially centered on a line.

11. A line defect detection system which comprises:

a plurality of sensors, each for sensing the presence or absence of said line in an area, said sensors sensing areas in a preestablished pattern, said plurality of sensors including;

(i) first and second sensors spaced apart a distance related to the minimum acceptable line width; and

(ii) a third sensor between said first and second sensors;

means responsive to the relative states of said sensors for recognizing the presence of a line segment having a width less than said minimum line width, the relative states of said sensors corresponding to a line segment having a width less than said minimum acceptable line width comprising said first and second sensors sensing an absence of said line and said third sensor sensing presence of said line; and

scanning means for causing the region containing said line to be traversed by said pattern.

12. The line defect detection system as recited in claim 11 and further including means for inhibiting the signalling of a defect smaller than a predetermined size.

13. The line detection system as recited in claim 11 where said third sensor is equally spaced from said first and second sensors.

14. The line defect detection system as recited in claim 11 where said plurality of sensors includes a plurality of sensors arranged to sense a pattern of areas comprised of two concentric circles, said first and second sensors sensing areas on the smaller of said two concentric circles and said third sensor sensing an area on the larger of said two concentric circles.

15. The line defect detection system as recited in claim 14 wherein each of said two concentric circles includes sensors 1 through n, n being an even number, and further including means responsive to the relative states of said sensors for detecting the absence of line sensing by at least two odd numbered sensors on the outer of said concentric circles.

16. The line defect detection system as recited in claim 15 and further including at least one additional sensor disposed to sense the presence or absence of said line inside said concentric circular pattern, said additional sensors inhibiting the operation of detecting a defect unless said additional sensors detect the presence of a line.

17. The line defect detection system as recited in claim 11 where said plurality of sensors includes a plurality of sensors arranged in a circular pattern.

18. The line defect detection system as recited in claim 17 and further including means for detecting whether said circular pattern is substantially centered on a line.

19. The line defect detection system as recited in claim 18 wherein said means for detecting whether said circular pattern is substantially centered on a line comprises at least one sensor disposed to sense areas in the central region of said circular pattern.

20. The line defect detection system as recited in claim 17 and further including means responsive to the relative states of said sensors for detecting the absence of line sensing by a predetermined number of contiguous sensors on said circular pattern.

21. The line defect detection system as recited in claim 11 where said sensors are responsive to light.

22. The line defect detection system as recited in claim 21 where said scanning means comprises:

a source of light;

means for impinging a spot of light from said source on the medium containing the line being inspected;

a moving mirror interposed between said source of light and said medium whereby said spot of light is made to move across said medium; and

means for focusing an image of said spot of light on said sensors.

23. The line defect detection system as recited in claim 22 wherein said moving mirror causes said spot of light to move across said medium repeatedly, and further including means for causing said spot of light to move across changing areas of said medium.

24. The line defect detection system as recited in claim 23 where said means for causing said spot of light to move across changing areas of said medium comprises means for moving said medium in a direction other than the direction of motion of said spot of light whereby a scanning raster is formed.

25. The line defect detection system as recited in claim 24 and further including adjusting means for adjusting the size of said image.

26. The line defect detection system as recited in claim 25 where light from said spot is reflected off said moving mirror.

27. The line defect detection system as recited in claim 26 where said moving mirror is a rotating polyhedron.

28. The line defect detection system as recited in claim 27 and further including adjusting means for adjusting the size of said spot.

29. The line defect detection system as recited in claim 28 where said adjusting means for adjusting the size of said spot and the adjusting means for adjusting the size of said image are coupled.

30. The line defect detection system as recited in claim 29 wherein said image is formed at a plane, and further including a fiber optics link conducting light from said image to said sensors said sensors being located away from said plane.

31. The line defect detection system as recited in claim 22 where said plurality of sensors includes a plurality of sensors arranged to sense a pattern of areas comprised of two concentric circles, first and second sensors sensing areas on the smaller of said two concentric circles and said third sensor sensing an area on the larger of said two concentric circles.

32. The line defect detection system as recited in claim 31 wherein each of said two concentric circles includes sensors 1 through n, n being an even number, and wherein a logical condition comprising the absence of line sensing by at least two odd numbered sensors on the outer of said concentric circles corresponds to a defect.

33. The line defect detection system as recited in claim 32 and further including at least one additional sensor disposed to sense the presence or absence of said line inside said concentric circular pattern, said sensor inhibiting the operation of detecting a defect unless said additional sensors detect the presence of a line.

34. A line defect detection system for detecting breaks in lines which comprises:

means for sensing the presence or absence of a line at a plurality of points in an area to be inspected, said plurality of points being arranged in a circle; and

means responsive to said sensing means for determining whether the number of contiguous points at which an absence of a line is sensed is greater than a predetermined number.

35. The line defect detection system as recited in claim 34 and further including means for determining whether the center of said circle is on a line.

36. The line defect detection system as recited in claim 34 where said means for determining whether the center of said circle is on a line comprises means for sensing the presence or absence of a line at one or more points within said circular pattern.

37. A line defect detection system which comprises:

means for sensing the presence or absence of a line at a plurality of points in an area to be inspected, said points being in a circular pattern, said plurality of points including;

(i) first and second points spaced apart a distance related to the minimum acceptable line width; and

(ii) a third point between said first and second points; and

means responsive to the relative states of said sensing means for recognizing the presence of a line segment having a width less than said minimum acceptable line width, the relative states of said sensing means corresponding to a line segment having a width less than said minimum acceptable line width comprising sensing an absence of said line at said first and second points and a presence of said line at said third point.

38. The line defect detection system as recited in claim 37 and further including means for determining whether the center of said circular pattern is on a line.

39. The line defect detection system as recited in claim 37 where said plurality of points includes a plurality of points arranged in two concentric circles, said first and second points being on one of said two concentric circles and said third point being on the other of said two concentric circles.

40. The line defect detection system as recited in claim 39 where said first and second points are on the smaller of said two concentric circles.

41. A printed circuit board trace defect detection system which comprises:

a first plurality of sensors each for sensing the presence or absence of a trace in an area of a printed circuit board, the sensed areas being symmetrically disposed on a first circle;

a second plurality of sensors, each sensing the presence or absence of a trace on an area on a printed circuit board, said second plurality of sensors being equal in number to said first plurality of sensors and each being disposed to sense an area of said circuit board equally distant from two of said first plurality of sensors and being on a second circle concentric with an inside said first circle, the areas sensed by first and second pluralities of sensors comprising a sensing pattern;

scanning means for causing said sensing pattern to traverse said printed circuit board; and

logic means responsive to the relative states of said sensors to produce a signal whenever said states are inconsistent with at least one preestablished criterion, one of said states inconsistent with a preestablished criterion being the sensing of the presence of a trace by a first sensor disposed on said first circle accompanied by the sensing of absence of a trace by both of two sensors disposed on said second circle, said two sensors and said first sensor being a predetermined group.

42. The printed circuit board trace defect detection system as recited in claim 41 wherein there are sensors numbered 1 to n on said first circle, n being an even number, and one of said states inconsistent with a preestablished criterion is the sensing of the presence of a trace by less than two odd numbered sensors on said first circle.

43. The printed circuit defect detection system as recited in claim 41 wherein a logical condition comprising a predetermined number of contiguous sensors on one of said concentric circles sensing the absence of a trace corresponds to a condition inconsistent with preestablished criteria.

44. The printed circuit board defect detection system as recited in claims 41, 42 or 43 and further including means for detecting whether said sensing pattern is substantially centered on a line.

45. The printed circuit board defect detection system as recited in claim 44 wherein said means for detecting whether said sensing pattern is substantially centered on a line comprises at least one sensor disposed to sense areas in the central region of said circular pattern.

46. The line defect detection system as recited in claims 41, 42 or 43 and further including means for inhibiting the signalling of a defect smaller than a predetermined size.

47. The printed circuit board trace defect detection system as recited in claims 41, 42, or 43 where said sensors are responsive to light.

48. The printed circuit board trace defect detection system as recited in claim 47 where said scanning means comprises:

a source of light;

means for impinging a spot of light from said source on the printed circuit board being inspected;

a moving mirror interposed between said source of light and said printed circuit board whereby said spot of light is made to move across said printed circuit board;

means for focusing an image of said spot of light on said sensors.

49. The printed circuit board trace defect detection system as recited in claim 48 wherein said moving mirror causes said spot of light to move across said printed circuit board repeatedly, and further including means for causing said spot of light to move across changing areas of said circuit board.

50. The printed circuit board trace defect detection system as recited in claim 49 where said means for causing said spot of light to move across changing areas of said circuit board comprises means for moving said circuit board in a direction other than the direction of motion of said spot of light whereby a scanning raster is formed.

51. The printed circuit board trace defect detection system as recited in claim 50 and further including means for adjusting the size of said image.

52. The printed circuit board trace defect detection system as recited in claim 51 where the light forming said image is reflected off said mirror both on the way to said printed circuit board and after being reflected off said printed circuit board.

53. The printed circuit board trace defect detection system as recited in claim 52 where said moving mirror is a rotating polyhedron.

54. The printed circuit board trace defect detection system as recited in claim 53 where said second mirror is interposed between said source of light and said moving mirror, the light from said source of light being focused into a small spot on said second mirror, the size of said second mirror being larger than the size of the returning beam reflected off said moving mirror whereby said second mirror does not completely obstruct said returning beam.

55. A printed circuit board trace defect detection system which comprises:

sensors 1 through 15 symmetrically disposed to sense a first circular pattern of areas of a printed circuit board;

sensors 16 through 30 symmetrically disposed to sense a second circular pattern of areas on said printed circuit board, said second circular pattern being concentric with and smaller than said first circular pattern and angularly displaced therefrom approximately 12 degrees, all of said sensors 1 through 30 forming a sensing pattern;

means for causing said sensing pattern to scan the area of said printed circuit board to be inspected; and

logic means responsive to the relative states of said sensors for indicating a trace defect, where one of said relative states indicating a trace defect may be stated in boolean notation as follows;

##EQU5##

57. The line defect detection system as recited in claims 55 or 56 and further including means for inhibiting the signalling of a defect smaller than a predetermined size.

58. The line defect detection system as recited in claims 55 or 56 and further including means for detecting whether said sensing pattern is substantially centered on a line.

59. The line defect detection system as recited in claim 58 wherein said means for detecting whether said sensing pattern is substantially centered on a line comprises at least one sensor disposed to sense areas in the central region of said circular pattern.

60. A printed circuit board trace defect detection system as recited in claims 55 or 56 and further including adjusting means for adjusting the size of said sensing pattern relative to the area being inspected.

61. A printed circuit board trace defect detection system as recited in claims 55 or 56 wherein said sensors are responsive to light level.

56. A printed circuit board trace defect detection system which comprises:

sensors 1 through 15 symmetrically disposed to sense a first circular pattern of areas of a printed circuit board;

sensors 16 through 30 symmetrically disposed to sense a second circular pattern of areas on said printed circuit board, said second circular pattern being concentric with a smaller than said first circular pattern and angularly displaced therefrom approximately 12 degrees, all of said sensors 1 through 30 forming a sensing pattern;

means for causing said sensing pattern to scan the area of said printed circuit board to be inspected; and

logic means responsive to the relative states of said sensors for indicating a trace defect, where one of said relative states indicating a trace defect may be stated in boolean notation as follows;

##EQU6##

62. A line defect detection system which comprises:

means for sensing the presence or absence of a line at each of a plurality of points in an area to be inspected; and

means responsive to the relative presence or absence of said line at one or more groups of said points for recognizing the presence of a line segment having a width less than the minimum acceptable line width, the points comprising said groups having preestablished geometrical relationships with one another, at least one of said geometrical relationships between points comprising first and second points separated by a distance equal to said minimum acceptable line width, and a third point between said first and second points, the criterion for said recognition comprising an absence of a line at said first and second points and a presence of a line at said third point.

63. A line defect detection system as recited in claims 62 wherein said groups of points form a pattern of points, said pattern including points symmetrically arranged around a central region.

64. A line defect detection system as recited in claim 62 wherein said third point is equidistant from said first and second points.

65. A line defect detection system as recited in claims 62 and further including scanning means whereby said area to be inspected is scanned by said sensing means, points within said area to be inspected being sequentially sensed.

66. A line defect detection system which comprises:

a plurality of sensors, each for sensing the presence or absence of said line in an area, said sensors sensing areas in a preestablished pattern, said plurality of sensors including;

(i) first and second sensors spaced apart a distance related to the minumum acceptable line width; and

(ii) a third sensor between said first and second sensors;

means responsive to the relative states of said sensors for recognizing the presence of a line segment having a width less than said minimum line width;

scanning means for causing the region containing said line to be traversed by said pattern; and

means for inhibiting the signalling of a defect smaller than a predetermined size.

67. Apparatus for inspection of square or circular figures which comprises:

means for sensing the presence or absence of said figure at a plurality of points in the region of said figure, said plurality of points being arranged in two concentric circles, the inner of said circles having a diameter equal to the minimum acceptable smallest dimension of said figure; and

logic means responsive to the relative state of said sensing means for determining if said figure is acceptable, a logic state wherein all of the points on the inner of said concentric circles contain said figure, and no more than a predetermined number of adjacent points on the outer of said circles contain said figure corresponding to an acceptable figure.

68. An apparatus for inspection of square or circular figures as recited in claim 67 and further including means for determining that the center of said concentric circles is on a figure to be inspected.

69. An apparatus for inspection of square or circular figures as recited in claim 68 where said means for determining that the center of said concentric circles is on a figure to be inspected comprises means for sensing the presence or absence of a figure at at least one point within the inner of said concentric circles.

70. A line defect detection system which comprises:

means for sensing the presence or absence of a line at a plurality of points in an area to be inspected, said points being in a circular pattern, said plurality of points including;

(i) first and second points spaced apart a distance related to the minimum acceptable line width; and

(ii) a third point between said first and second points; and

means responsive to the relative states of said sensing means for recognizing the presence of a line segment having a width less than said acceptable line width, said plurality of points including a plurality of points arranged in two concentric circles, said first and second points being on one of said two concentric circles and said third point being on the other of said two concentric circles.