X-ray inspection method and apparatus, prepreg inspecting method, and method for fabricating multi-layer printed circuit board

• US 5,754,621 A
• Filed: 12/18/1996
• Issued: 05/19/1998
• Est. Priority Date: 03/15/1993
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Karasaki, Koichi, Iida, Tadashi, Suzuki, Yoko, Doi, Hideaki, Hara, Yasuhiko
• Primary Examiner(s): Wong, Don
• Application Number:
  US08/769,218
• Time in Patent Office: 517 Days
• Field of Search: 378/51, 378/55, 378/57, 378/58, 378/62
• US Class Current: 378/57
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G01R 31/304 of printed or hybrid circuits G01R31/305 - G01R31/315 take precedence
• CPC Class Codes: H05K 3/0008 for aligning or positioning of tools relative to the circuit board H05K3/4638, H05K3/4679 take precedence; for manufacturing assemblages of components H05K13/0015
• CPC Class Codes: H05K 3/4638 Aligning and fixing the circuit boards before lamination; Detecting or measuring the misalignment after lamination; Aligning external circuit patterns or via connections relative to internal circuits

Abstract

An X-ray inspection apparatus and method in which an object to be inspected is irradiated with characteristic X-rays containing at least one wavelength which affords a high X-ray absorbance in the object to be inspected. A transmitted X-ray image which has passed through the object to be inspected is detected, and the object to be inspected is inspected on the basis of the transmitted X-ray image. The method and apparatus are utilized to fabricate a multi-layer printed circuit board.

Claims

1. An X-ray inspection method comprising the steps of:

generating from a target characteristic X-rays which differ from continuous X-rays generating Bremsstrahlung radiation, the characteristic X-rays containing at least one wavelength having a peak level which affords a high X-ray absorbance in an object to be inspected;

irradiating the object to be inspected with the characteristic X-rays;

detecting a transmitted X-ray image which has passed through the object to be inspected; and

inspecting the object to be inspected on the basis of the transmitted X-ray image.

2. An X-ray inspection method according to claim 1, wherein the step of radiating includes radiating to the object to be inspected characteristic X-rays containing at least two wavelengths which afford a high X-ray absorbance in the object to be inspected.

3. An X-ray inspection method according to claim 1, wherein the object to be inspected is a printed circuit board having wiring patterns, the step of radiating includes radiating to the printed circuit board characteristic X-rays containing at least one wavelength of 0.04 to 0.15 nm which affords a high X-ray absorbance in the wiring patterns on the printed circuit board, the step of detecting includes detecting a transmitted X-ray image which has passed through the printed circuit board, and the step of inspection includes inspecting the printed circuit board on the basis of said transmitted X-ray image.

4. An X-ray inspection method according to claim 3, wherein the printed circuit board has wiring patterns of Cu or Au.

5. An X-ray inspection method according to claim 3, wherein the printed circuit board has wiring patterns of Cr or Au.

6. An X-ray inspection method according to claim 5, wherein the step of radiating includes radiating to the printed circuit board having wiring patterns of Cr or Au characteristic X-rays containing at least one wavelength of 0.04 nm to 0.15 nm and generated by radiating a converged electron beam to a target formed of Mo, Cu or Au, or an alloy thereof.

7. An X-ray inspection method according to claim 6, wherein the step of radiating includes radiating to a printed circuit board having wiring patterns of Cr or Au characteristic X-rays containing at least one wavelength of 0.04 nm to 0.15 nm and generated from a very small area of the target having a dimension or 20 μ

m or less by radiating the converged electron beam to the small area of the target, the target being formed of Mo, Cu or Au, or an alloy thereof.

8. An X-ray inspection method according to claim 1, wherein the object to be inspected is an insulating member, the step of radiating includes radiating to the insulating member characteristic X-rays containing at least one wavelength of 0.04 nm to 0.15 nm and generated by radiating a converged electron beam to a target formed of Mo, Cu or Au, or an alloy thereof, the step of detecting includes detecting a transmitted X-ray image which has passed through insulating member, and the step of inspecting includes inspecting a fine, electroconductive, metallic foreign matter present on the surface or in the interior of the insulating member on the basis of the transmitted X-ray image.

9. An X-ray inspection method according to claim 8, wherein the step of radiating includes radiating to the insulating member characteristic X-rays containing at least one wavelength of 0.04 nm to 0.15 nm and generated from a very small area of the target having a dimension of 20 μ

m or less by radiating the converged electron beam to the small area of the target.

10. An X-ray inspection method according to claim 1, wherein the object to be inspected is a prepreg.

11. A method according to claim 1, wherein:

the step of radiating includes radiating X-rays to a prepreg as the object to be inspected; and

the steps of detecting and inspecting include checking whether a specified electroconductive foreign matter is mixed in the interior of the prepreg or adhered to the surface of the prepreg on the basis of a transmitted X-ray light/shade image which has passed through the at least one prepreg.

12. A method according to claim 11, wherein the at least one prepreg is disposed in a bag and the X-rays are radiated through the bag.

13. A method according to claim 11, further comprising the steps of:

providing a prepreg free of the specified electroconductive foreign matter mixed in or adhered to the interior or the surface of the prepreg; and

laminating and heating the provided prepreg and a printed circuit board having wiring patterns on an insulating material to fabricate a multi-layer printed circuit board.

14. A method according to claim 13, further comprising the steps of extracting only the portion where the wiring patterns are present on the printed circuit board on the basis of a design information of the printed circuit board which is in contact with a prepreg, and inspecting only the extracted portion of the prepreg or the printed circuit board to eliminate defects.

15. An X-ray inspection method according to claim 1, wherein the characteristic X-rays generated from the target pass through a filter before the characteristic X-rays radiated the object to be inspected.

16. An X-ray inspection method according to claim 15, wherein the filter cuts off an X-ray of a wavelength affording a low X-ray absorbance in the object to be inspected.

17. An X-ray inspection apparatus comprising:

an X-ray target for generating characteristic X-rays which differ from continuous X-rays generating Bremsstrahlung radiation, the characteristic X-rays containing at least one wavelength having a peak level which affords a high X-ray absorbance in an object to be inspected;

means for radiating the characteristic X-rays to the object to be inspected;

means for detecting a transmitted X-ray image which has passed through the object; and

means for inspecting the object to be inspected on the basis of the transmitted X-ray image.

18. An X-ray inspection apparatus according to claim 17, further comprising a stage for resting the object to be inspected thereon and for positioning the object, and a stage controller for controlling the movement of the stage, the X-ray source radiating X-rays to the object to be inspected which has been positioned by the stage, the means for detecting including an optical image converter for detecting and converting a transmitted X-ray image which is passed through the object into an optical image and a photoelectric converter for converting the optical image obtained by the optical image converter into a transmitted X-ray image signal, the means for inspecting including an image processor for inspecting the object to be inspected on the basis of the transmitted X-ray image signal obtained by the photoelectric converter.

19. An X-ray inspection apparatus according to claim 18, wherein the X-ray source radiates X-rays containing a plurality of wavelengths which afford a high X-ray absorbance in the object to be inspected.

20. An X-ray inspection apparatus according to claim 19, wherein the X-ray source is constituted by an X-ray tube having a controllable tube voltage and a controllable tube current.

21. An X-ray inspection apparatus according to claim 20, wherein the X-ray tube has a target formed of the same material as that of the object to be inspected.

22. An X-ray inspection apparatus according to claim 20, wherein the X-ray tube has a target formed of an alloy of two or more kinds of metals.

23. An X-ray inspection apparatus according to claim 17,

wherein the object to be inspected is a test sample, the X-ray source being an X-ray source for radiating X-rays to the test sample in X and Y axis directions;

the means for detecting including an X-ray photoconverter for detecting and converting a transmitted X-ray image which has passed through the test sample positioned by an XY positioning stage into an optical image;

a photoelectric converter for receiving and converting the optical image detected by the X-ray photoconverter as a transmitted light/shade X-ray image signal;

a noise eliminating unit for eliminating a noise component from the transmitted light/shade image signal obtained by the photoelectric converter;

at least one level conversion unit for converting the level of the transmitted light/shade X-ray image signal after noise elimination by the noise eliminating unit into a signal level proportional to the thickness of the test sample; and

a level correction unit for correcting a change in a detected signal level of the transmitted light/shade image signal after conversion by the level conversion unit; and

the means for inspecting inspects foreign matter mixed into the test sample and foreign matter adhered to the surface of the test sample on the basis of the transmitted light/shade X-ray image signal after correction by the level correction unit.

24. An X-ray inspection apparatus according to claim 23, wherein the X-ray source is constructed so as to radiate an electron beam convergedly in a very small area of a target and to cause X-rays to be generated from the very small area of the target so as to be radiated therefrom.

25. An X-ray inspection apparatus according to claim 23, further including an imaging magnification controller for controlling an imaging magnification of the transmitted X-ray image detected by the X-ray photoconverter.

26. An X-ray inspection apparatus according to claim 23, further including a conveyor for carrying the test sample as a test sample tray in and out between an auxiliary stage disposed outside a protective cabinet and the XY positioning stage through a window having an opened and closed position and formed in the protective cabinet.

27. An X-ray inspection apparatus according to claim 23, further including an X-ray measuring unit for measuring the intensity of X-rays emitted from the X-ray source, and wherein the detected signal level is corrected by the level correction unit in accordance with the intensity of X-rays measured by the X-ray measuring unit.

28. An X-ray inspection apparatus according to claim 23, further including an X-ray measuring unit for measuring the intensity of X-rays emitted from the X-ray source, and a controller for controlling the X-rays emitted from the X-ray source in accordance with the intensity of X-rays measured by the X-ray measuring unit.

29. An X-ray inspection apparatus according to claim 23, further including a display unit for displaying the transmitted light/shade X-ray image signal after correction by the level correction unit.

30. An X-ray inspection apparatus according to claim 23, further including at least one non-X-ray detection unit wherein positions of the detected foreign matter are distinguished in accordance with the result of detection by the at least one non-X-ray detection unit on the basis of coordinates detected using X-rays.

31. An X-ray inspection apparatus according to claim 30, further including a signal processing circuit for detecting a degree of a change in a detection signal contained in the transmitted X-ray image, and wherein the kind of each foreign matter is classified on the basis of the degree of the change, and further in combination with the result of detection corresponding to a coordinate position and obtained by the at least one non-X-ray detection unit, and the result obtained is outputted.

32. An X-ray inspection apparatus according to claim 23, wherein the photoelectric converter comprises a detecting optical system and a photoelectric converter device, the detecting optical system being constructed so as to correct a distortion generated in the X-ray photoconverter.

33. An X-ray inspection apparatus according to claim 32, wherein a read scan signal is provided for the photoelectric converter device so as to correct distortion generated in the X-ray photoconverter.

34. An X-ray inspection apparatus according to claim 23, wherein the photoelectric converter has a plurality of picture elements and that picture elements are larger in size at a marginal portion of a detection field than at a central portion of the detection field.

35. An X-ray inspection apparatus according to claim 23, further including a mechanism for switching one of a plurality of level conversion units from one to another among the plurality of level conversion units, and a mechanism for making the corrected value from the at least one level correction unit rewritable, whereby a change in detection sensitivity caused by one of a change in sensitivity characteristic of the X-ray photoconverter or by a change in the type of the test sample is corrected into a predetermined reference characteristic.

36. An X-ray inspection apparatus according to claim 23, further including a signal processing circuit for detecting a degrees of a change in a detection signal contained in the transmitted X-ray image, and wherein the position of each foreign matter is distinguished on the basis of the degree of the change.

37. An X-ray inspection apparatus according to claim 23, wherein the test sample includes a test sample tray for X-rays having a test sample holding portion formed of a material low in X-ray transmittance, and a frame portion which supports only the peripheral part of the holding portion so as not to be an obstacle to detection.

38. An X-ray inspection apparatus according to claim 37, wherein the test sample tray has a shape which causes the test sample to be distorted convexly to correct a pincushion distortion generated in an X-ray photoconverter.

39. An X-ray inspection apparatus according to claim 23, further comprising a standard sample which has been made clear with respect to the amount of X-rays passing therethrough, the amount of X-rays passing through the standard sample being detected before the start of inspection of a test sample to obtain a reference value of a detected signal level, and on the basis of the reference value, the detected signal level is corrected by the at least one level correction unit, or X-rays emitted from an X-ray source are controlled by an X-ray controller.

40. An X-ray inspection apparatus according to claim 23, wherein an X-ray passage is formed in a frame portion, a standard sample which has been made clear with respect to the amount of X-rays passing therethrough is placed on the passage, the amount of X-rays passing through said standard sample being detected before the start of inspection of a test sample to obtain a reference value of a detected signal level, and on the basis of the reference value, the detected signal level is corrected by the at least one level correction unit, or X-rays emitted from an X-ray source are controlled by an X-ray controller.

41. A system including an inspection apparatus according to claim 17, for controlling the state of generation of dust, comprising one of dust collecting filters and adhesive sheets disposed in positions within the inspection apparatus, and transmitting X-rays for inspection of the state of generation of dust.

42. An X-ray inspection apparatus according to claim 17, further including:

an auxiliary stage disposed outside of a protective cabinet;

an XY positioning stage for moving and positioning a test sample in X and Y axis directions;

a conveyor for carrying the test sample in and out between the auxiliary stage and the XY positioning stage through a window having an opened and closed position and formed in the protective cabinet;

the X-ray source being constructed so as to radiate an electron beam convergedly to a very small area of a target and to cause X-rays to be generated from the very small area of the target;

the detecting means including a sensitizing unit for picking up and sensitizing a transmitted X-ray image which has passed through the test sample irradiated with X-rays from said X-ray source and positioned by the XY positioning stage onto a film so as to obtain an X-ray transmitted image; and

the inspecting means inspecting foreign matter mixed into the test sample and a foreign matter adhered to the surface of the test sample after detection by the sensitizing unit.

43. An X-ray inspection apparatus according to claim 17, wherein the means for radiating includes a filter located between the target and the objected to be inspected.

44. An X-ray inspection apparatus according to claim 43, wherein the filter cuts off an X-ray of a wavelength affording a low X-ray absorbance in the object to be inspected.

45. An X-ray inspection method comprising the steps of:

irradiating an electron beam to a target which contains at least one element of Mo, Cu and Au;

generating characteristic X-rays from the target which contain at least one wavelength having a peak level between 0.04 and 0.15 nm in relation to an object to be inspected;

radiating the characteristic X-rays to a printed circuit board having-wiring patterns of Cu or Au as the object to be inspected;

detecting a transmitted X-ray image which has passed through the object to be inspected; and

inspecting the object to be inspected on the basis of the transmitted X-ray image.

46. An X-ray inspection apparatus comprising:

an X-ray tube which generates characteristic X-rays from a target containing at least one element of Mo, Cu and Au, the characteristic X-rays containing at least one wavelength having a peak level between 0.04 and 0.15 nm in relation to an object to be inspected, and which irradiates the characteristic X-rays generated from the target to the object to be inspected;

a detector which detects a transmitted X-ray image which has passed through the object to be inspected; and

means for inspecting the object to be inspected on the basis of the transmitted X-ray image.