Method and apparatus for imaging obscured areas of a test object

• US 5,594,770 A
• Filed: 11/18/1994
• Issued: 01/14/1997
• Est. Priority Date: 11/18/1994
• Status: Expired due to Term

• Current Assignee: Teradyne Incorporated
• Original Assignee: ThermoSpectra Corp (Thermo Fisher Scientific Incorporated)
• Inventors: Bowles, Philip, Duff, Eric, Thayer, Dale D.
• Primary Examiner(s): Wong, Don
• Application Number:
  US08/342,928
• Time in Patent Office: 788 Days
• Field of Search: 378/57, 378/58, 378/4, 378/62, 378/98.2, 378/24, 378/25, 378/27, 378/21, 378/22, 378/11, 378/98.6
• US Class Current: 378/58
• CPC Class Codes: G01B 15/045 by measuring absorption
• CPC Class Codes: G01N 23/043 using fluoroscopic examination, with visual observation or video transmission of fluoroscopic images
• CPC Class Codes: G01N 23/044 using laminography or tomosynthesis
• CPC Class Codes: G01R 31/304 of printed or hybrid circuits G01R31/305 - G01R31/315 take precedence

Abstract

A method and apparatus are provided for imaging obscured areas of a test object. The apparatus includes an x-ray source having a cathode for producing a steerable electron beam. A controller directs the electron beam to predetermined locations on a target anode. The user may flexibly select appropriate predetermined positions. The predetermined locations may be obtained from the geometry of an obscuration. A detector receives x-rays that are transmitted through the test object from each of the predetermined locations, and produces images corresponding to each of the predetermined locations. The images are digitized and may be combined to produce an unobscured image of a region of interest.

Claims

1. An apparatus for imaging a region of interest that is positioned on or within a test object that is obscured by a first obscuration body positioned on or within said test object but positioned outside said region of interest, comprising:

an x-ray source having a cathode for producing a steerable electron beam;

a controller coupled to the x-ray source, wherein the controller directs the electron beam to predetermined locations on a target anode,

the predetermined locations being determined from an obscuration geometry of the first body relative to the area of interest;

a detector positioned to receive x-rays that are transmitted through the test object from each of the predetermined locations and to produce images corresponding to each of the predetermined locations; and

an imaging system that combines the images to produce an unobscured image of said region of interest.

2. The apparatus of claim 1, wherein said area of interest lies within a plane.

3. The apparatus of claim 1, wherein said object is positioned nearer to said x-ray source than said area of interest.

4. The apparatus of claim 1, wherein said item of interest is a circuit board.

5. The apparatus of claim 4, wherein said object is solder.

6. A method of imaging a region of interest that is positioned on or within a test object that is obscured by a first obscuration body positioned on or within said test object but positioned outside said region of interest, comprising:

generating an electron beam;

directing the electron beam to predetermined locations on a target anode, wherein the predetermined locations are selected from a set of locations on the target anode determined from an obscuration geometry of the first body relative to the area of interest, whereby an x-ray beam is emitted toward the test object from the predetermined locations on the target anode; and

for each of the predetermined locations, forming an image of said region of interest on or within the test object by detecting a portion of the x-ray beam transmitted through the region of interest.

7. A method as claimed in claim 6, wherein the predetermined locations are determined from an obscuration geometry of the first body and a second obscuration body relative to the area of interest.

8. The method of claim 6, wherein said area of interest lies within a plane.

9. The method of claim 6, wherein said object is positioned nearer to said x-ray source than said area of interest.

10. The method of claim 6, wherein said object is separated from said area of interest by a distance t as measured along an axis;

said body having a width w; and

wherein said x-ray beam forms a beam of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

11. The method of claim 10, wherein said area of interest is entirely imaged only by x-ray beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

12. The method of claim 10, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

13. The method of claim 12, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another and the angular separation between consecutive x-ray beams differs by no more than Δ

θ

=2θ

_max /n_integer, where n_integer is equal to the total number of locations.

14. The method of claim 6, comprising a second object, wherein said first and second objects are separated from said area of interest by a distance t as measured along an axis;

said second body having a width w that is greater than or equal to the width of said first object; and

wherein said x-ray beam forms a beam of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

15. The method of claim 14, wherein said area of interest is entirely imaged only by x-ray beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

16. The method of claim 14, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

17. The method of claim 16, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another and the angular separation between consecutive x-ray beams differs by no more than Δ

θ

=2θ

_max /n_integer, where n_integer is equal to the total number of locations.

18. The method of claim 6, comprising a second object and a third object, wherein said first, second and third objects are separated from said area of interest by a distance t as measured along an axis;

said first and second objects are separated from one another by a distance s_min that is smaller than both the distance separating the second and third objects and the distance separating the first and third objects;

wherein the greatest width of said first, second and third bodies is denoted by w; and

wherein said x-ray beam forms an angle of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

19. The method of claim 18, wherein said area of interest is entirely imaged only by x-ray beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

20. The method of claim 18, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

21. The method of claim 20, wherein adjacent locations produce x-ray beams that are angularly separated from one another by no more than arctan(s_min /t).

22. The method of claim 6, comprising a second object and a third object, wherein said first, second and third objects are separated from said area of interest by a distance t as measured along an axis;

said first and second objects are separated from one another by a distance s_min that is smaller than both the distance separating the second and third objects and the distance separating the first and third objects;

wherein the greatest width of said first, second and third bodies is denoted by w; and

wherein said x-ray beam forms a beam of inclination that is less than or equal to arctan(w/2t).

23. The method of claim 22, wherein said area of interest is entirely imaged only by x-ray beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-arctan(w/2t)≦

θ

≦

arctan(w/2t).

24. The method of claim 22, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2arctan(w/2t).

25. The method of claim 24, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another so that angle of inclination θ

_i of an x-ray beam produced at the ith location, P_i, will be θ

_i =tan^-1 (P_i /t), where P_i =-w/2+iw/n and n=w/s_min =the total number of locations or steps.

26. The method of claim 6, wherein said item of interest is a circuit board.

27. The method of claim 26, wherein said object is solder.

28. The method of claim 6, wherein the number of locations is minimized while being of a sufficient number to entirely image said area of interest.

29. An apparatus for imaging a region of interest that is positioned on or within a test object that is obscured by a first obscuration body positioned on or within said test object but positioned outside said region of interest, comprising:

a radiation source that produces a beam of radiation;

a controller coupled to the radiation source, wherein the controller directs the beam of radiation towards predetermined locations of said test object,

the predetermined locations being determined from an obscuration geometry of the first body relative to the area of interest.

30. The apparatus of claim 29, comprising a detector positioned to receive radiation that is transmitted through the test object from each of the predetermined locations and to produce images corresponding to each of the predetermined locations;

and

an imaging system that combines the images to produce an unobscured image of said region of interest.

31. The apparatus of claim 29, wherein said area of interest lies within a plane.

32. The apparatus of claim 29, wherein said object is positioned nearer to said source of radiation than said area of interest.

33. The apparatus of claim 29, wherein said item of interest is a circuit board.

34. The apparatus of claim 33, wherein said object is solder.

35. The apparatus of claim 29, wherein said source of radiation comprises an x-ray source and said radiation beam comprises an x-ray beam.

36. A method of imaging a region of interest that is positioned on or within a test object that is obscured by a first obscuration body positioned on or within said test object but positioned outside said region of interest, comprising:

generating a radiation beam;

directing the radiation beam to predetermined locations on the test object, wherein the predetermined locations are selected from a set of locations on the test object determined from an obscuration geometry of the first body relative to the area of interest.

37. The method of claim 36, comprising the step of for each of the predetermined locations, forming an image of said region of interest on or within the test object by detecting a portion of the radiation beam transmitted through the region of interest.

38. The method of claim 36, wherein the predetermined locations are determined from an obscuration geometry of the first body and a second obscuration body relative to the area of interest.

39. The method of claim 36, wherein said area of interest lies within a plane.

40. The method of claim 36, wherein said object is positioned nearer to said source of radiation than said area of interest.

41. The method of claim 36, wherein said object is separated from said area of interest by a distance t as measured along an axis;

said body having a width w; and

wherein said radiation beam forms an angle of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

42. The method of claim 41, wherein said area of interest is entirely imaged only by radiation beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

43. The method of claim 41, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

44. The method of claim 43, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another and the angular separation between consecutive x-ray beams differs by no more than Δ

θ

=2θ

_max /n_integer, where n_integer is equal to the total number of locations.

45. The method of claim 36, comprising a second object, wherein said first and second objects are separated from said area of interest by a distance t as measured along an axis;

said second body having a width w that is greater than the width of said first object; and

wherein said radiation beam forms a beam of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

46. The method of claim 45, wherein said area of interest is entirely imaged only by radiation beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

47. The method of claim 45, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

48. The method of claim 47, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another and the angular separation between consecutive x-ray beams differs by no more than Δ

θ

=2θ

_max /n_integer, where n_integer is equal to the total number of locations.

49. The method of claim 36, comprising a second object and a third object, wherein said first, second and third objects are separated from said area of interest by a distance t as measured along an axis;

said first and second objects are separated from one another by a distance s_min that is smaller than both the distance separating the second and third objects and the distance separating the first and third objects;

wherein the greatest width of said first, second and third bodies is denoted by w; and

wherein said radiation beam forms an angle of inclination that is greater than or equal to;

space="preserve" listing-type="equation">θ

.sub.max =arctan(w/2t).

50. The method of claim 49, wherein said area of interest is entirely imaged only by radiation beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-θ

.sub.max ≦

θ

≦

θ

.sub.max.

51. The method of claim 49, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2θ

max.

52. The method of claim 51, wherein adjacent locations produce radiation beams that are angularly separated from one another by no more than arctan(s_min /t).

53. The method of claim 36, comprising a second object and a third object, wherein said first, second and third objects are separated from said area of interest by a distance t as measured along an axis;

said first and second objects are separated from one another by a distance s_min that is smaller than both the distance separating the second and third objects and the distance separating the first and third objects;

wherein the greatest width of said first, second and third bodies is denoted by w; and

wherein said radiation beam forms an angle of inclination that is less than or equal to arctan(w/2t).

54. The method of claim 53, wherein said area of interest is entirely imaged only by x-ray beams that have an angle of inclination θ

according to the relationship;

space="preserve" listing-type="equation">-arctan(w/2t)≦

θ

≦

arctan(w/2t).

55. The method of claim 53, wherein the angles of inclination that entirely image said area of interest are subtended by an angular range 2arctan(w/2t).

56. The method of claim 55, wherein adjacent locations produce x-ray beams that consecutive x-ray beams are angularly stepped relative to one another so that angle of inclination θ

_i of an x-ray beam produced at the ith location, P_i, will be θ

_i =tan^-1 (P_i /t) where P_i =-w/2+iw/n and n=w/s_min =the total number of locations or steps.

57. The method of claim 36, wherein said item of interest is a circuit board.

58. The method of claim 57, wherein said object is solder.

59. The method of claim 36, wherein the number of locations is minimized while being of a sufficient number to entirely image said area of interest.

60. The method of claim 36, wherein said radiation beam comprises an x-ray beam.