JPH05312735A - Method and apparatus for computed x-ray tomography - Google Patents

Abstract

PURPOSE:To take a computed tomography image clearly and with a high resolution while the images of the parts other than a focus plane in an object are shaded off. CONSTITUTION:An X-ray 27 generated by an X-ray tube 35 is applied to an object 2 aslant. The rotary axis 5 of the object 2 is so provided as to be in parallel with the rotary axis 6 of an X-ray detection system. A transmitted X-ray image is detected by an X-ray image intensifier 40. An image rotator 42 is inserted into the midway of an optical system which detects the output image of the X-ray image intensifier 40 with a solid-state image sensing device 45. An object 2 and the image rotator 42 are made to rotate with the ratio of respective revolutions 2:1 and the exposure time of the solid-state image sensing device 45 equal to the time necessary for one turn of the image to obtain the clear tomography image of a focus plane 4. With this constitution, the tomography image of an arbitrary cross section can be obtained easily and a multilayer board having complex internal structure can be tested easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tomographic image capturing method and apparatus using transmission X-rays, and more particularly to an X-ray tomographic capturing method and apparatus suitable for inspecting and measuring the internal structure of a circuit board having a multilayer structure. ..

[0002]

2. Description of the Related Art Conventionally, laminography is known as a technique for detecting a tomographic image on a focal plane of interest inside an object by means of transmitted X-rays. This technique detects two tomographic images by synchronously moving two elements out of three elements of an X-ray source, an object, and a detector.

A technique of this kind is disclosed in, for example, Japanese Patent Laid-Open No. 59-1.
The thing described in the 16040 gazette is known. This technique takes the stage of illuminating an object with a fixed radiation source,
Synchronously in the same direction about the first axis and a second axis respectively the object and a surface which is sensitive to radiation and which is located next to the object with respect to the radiation source and which is contained in one plane. Adapted to rotate so that the first axis and the second axis are parallel to each other and said first axis is transformed into a second axis by a positive ratio similarity transformation and the center of the radiation source. And the radiation source, the object and the sensitive surface are arranged to remain exposed to the radiation during rotation thereof, and the surface including the cross section of the object defines the first axis as the second axis.
When the surface is converted to a surface including the sensitive surface by the similarity conversion to convert the surface to the axis, the surface is aligned with the axis.
To form an image of at least a portion of the cross-section on the sensitive surface, forming an angle of the same value less than 90 degrees or greater than 90 degrees, whereby one surface It is configured to take a tomographic image of an object contained therein along a cross-section of the object. Briefly, this technique relates to a method of synchronously rotating an object and a film to perform cross-section imaging.

Further, in the known example described in Japanese Patent Application Laid-Open No. 2-501411, by rotating and deflecting an electron beam, the X-ray source is moved in a circular pattern and the fluorescent screen is advanced along a circular path. By doing so, tomographic imaging is performed.

[0005]

However, in the above-mentioned first prior art, since the film is used for the detecting portion, the detected image cannot be viewed in real time. Further, since the image moves in parallel on the film surface, the linear structure extending in the moving direction has a drawback that the image is not blurred even if it is on a surface other than the focal plane and is clearly detected.

Further, in the second conventional technique, since the electron beam is rotationally deflected, an aberration occurs in the electron optical system, and a fine electron beam cannot be obtained. Therefore, an X-ray source having a minute focus cannot be obtained, and the detection resolution is low.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and its first object is to make it possible to blur an image of a linear structure on a plane other than the focal plane. An object of the present invention is to provide a linear tomography method and apparatus.

A second object of the present invention is to provide an X-ray tomography apparatus capable of displaying a tomographic image in real time without using a film.

Further, a third object is to provide an X-ray tomography apparatus having high resolution. In addition, a fourth object is to provide an apparatus for automatically inspecting a circuit connecting portion such as a soldering portion on a multilayer circuit board.

[0010]

The first object is to rotate an object to be photographed about a rotation axis inclined with respect to an optical axis of X-rays generated from an X-ray source, and to obtain the object. An X-ray detection system including means for converting an X-ray image transmitted through an object into an optical image, means for rotating the converted optical image, and means for converting the optical image into an electric signal serving as image information is used. In an X-ray tomography method for obtaining an X-ray tomographic image by rotating the optical image by means for rotating the optical image by rotating the optical image in parallel with the rotational axis of the means for converting the optical image. Is achieved by the first means of synchronizing with.

The above first and second objects are an X-ray source,
A rotary stage that rotates an object to be imaged, a unit that converts an X-ray image that has passed through the object into an optical image, a unit that rotates the optical image, and a rotation of the optical image and a rotation of the object. It is achieved by a second means including a means, a means for converting an optical image into an electric signal which becomes image information, and a means for displaying the converted electric signal.

In this case, the means for converting the X-ray image transmitted through the object in the second means into an optical image is an X-ray image intensifier, and the means for rotating the optical image is an image rotator rotated by a rotary stage. The means for converting an optical image into an electric signal that becomes a video signal can be configured by a solid-state image sensor.

Further, when the image rotator is used, the object and the image rotator are rotated at a rotation ratio of 2: 1 and the exposure time of the solid-state image pickup device is the same as the time required for one rotation of the optical image, or It is preferable to set the time longer than that.

Further, the means for converting the optical image in the second means into an electric signal which becomes image information may be constituted by an image pickup tube and a circuit for adding the electric signals.

The means for converting the X-ray image transmitted through the object into the optical image in the second means is a means for rotating the optical image from a fluorescent screen and an image intensifier for amplifying the brightness of the optical image. The means for converting an optical image into an electric signal that serves as image information can also be configured by a solid-state image sensor from an image rotator rotated by a rotating stage. In this case, it is possible to rotate the object and the image rotator at a rotation speed ratio of 2: 1 and set the exposure time of the solid-state image pickup device to the same as or longer than the time required for one rotation of the optical image. preferable.

The means for rotating the object in the second means is a rotary stage, and the means for converting the X-ray image transmitted through the object into an optical image is a fluorescent screen and an optical image converted on the fluorescent screen. An image intensifier that amplifies brightness, an image rotator that rotates a means for rotating an optical image by a rotating stage, and a means that converts an optical image into an electric signal that becomes image information, and an image tube and an electricity that becomes image information. It can also be configured with a circuit for adding signals.

Further, the means for rotating the object in the second means is rotated from the rotating stage, and the means for converting the X-ray image transmitted through the object into the optical image is rotated from the fluorescent screen by the rotating stage to rotate the optical image. The means for converting the image rotator rotated by the rotating stage to the means for converting the optical image into the electric signal for the image information may be composed of the image pickup tube and the circuit for adding the electric signal for the image information.

The above first and second objects are an X-ray source,
A rotary stage for rotating an object to be imaged, a means for detecting an X-ray image transmitted through the object while performing rotation processing in synchronization with the rotation of the object, a means for adding detected images, and an adding means. It is also achieved by a third means including a means for displaying the video information added by the above as an image.

In this case, the means for detecting the X-ray image can be composed of the X-ray image pickup tube, and the X-ray image intensifier and the image pickup tube, respectively, and the means for rotating the image is the raster scan of the image pickup tube. It can consist of a rotating circuit.

The above first and second objects are an X-ray source,
A rotary stage that rotates an object to be imaged, a unit that converts an X-ray image that has passed through the object into an electric signal that is video information, a unit that A / D converts the electric signal that is video information, and an image. A digital image processing means for rotating the
It is also achieved by a fourth means including means for adding images and means for displaying the video information added by the adding means as an image. Furthermore, the third object is achieved by constructing the X-ray source in the first, second, third and fourth means by a microfocus X-ray tube having means for eccentricizing and rotating the transmissive target. To be done.

In this case, it is preferable that the transmission type target included in the microfocus X-ray tube is composed of at least two layers of an X-ray generation layer and a support layer.

In addition, the fourth object is achieved by providing the first to fourth means with an image processing circuit for detecting a defect of an object to be inspected from an electric signal serving as image information.

[0023]

The principle of X-ray tomography according to the present invention will be described with reference to FIG. As can be seen from this figure, X-rays 27 are radially generated from the fixed X-ray source 1, and the object 2 to be imaged rotates around a rotation axis 5 inclined with respect to the optical axis 7. The detector 3 rotates about a rotation axis 6 parallel to the rotation axis 5 in synchronization with the object 2. A projected image of a plane (hereinafter referred to as a focal plane) 4 including an intersection of the optical axis 7 and the rotation axis 5 and perpendicular to the rotation axis 5 is detected as a still image by the detector 3, Projected images other than 4 are blurred because they are detected as rotating images. For this reason,
The image of the structure outside the focal plane 4 can be blurred,
Only the X-ray tomographic image of the focal plane 4 can be clearly obtained.

FIG. 2 shows the basic configuration of the X-ray tomography apparatus according to the present invention. As can be seen from this figure, X-rays 27 are radially generated from the fixed X-ray source 1, and the object 2 to be imaged rotates around a rotation axis 5 inclined with respect to the optical axis 7. The X-ray detection system includes a unit 8 for converting an X-ray image into an optical image, a unit 9 for rotating the optical image, and a unit 10 for converting the optical image into an electric signal which serves as a video signal, and an optical assist. Means 12, 13 for transmitting an optical image as means
Is provided. Optical image means 9 for rotating the optical image
Thus, the X-ray tomographic image is obtained in real time by means of rotating the object 2 in synchronization with it and displaying the electric signal as image information.

FIG. 3 shows the principle configuration of the micro focus X-ray source according to the present invention. This means is for improving the resolution, and in order to improve the resolution, it is necessary to reduce the penumbra blur of the projected image, and an X-ray source having a minute focus size is required. The operating principle of this X-ray source is as follows.

That is, the electron beam 2 generated from the cathode 20
When 1 is focused by the lens 22 and irradiated on the target 23, X-rays 27 are generated. The target 23 is a heavy metal X
It is composed of a line generation layer 24 and a light element support layer 25.
In this case, for example, tungsten is selected as the heavy metal and beryllium is selected as the light element. At this time, by focusing the electron beam 21 sufficiently small and thinning the X-ray generation layer 24, a minute focus size can be realized. Further, in order to prevent the target 23 from being damaged by the heat generated when the electron beam 21 collides, the target 23 is rotated around the rotation shaft 26.

The principle structure of an automatic inspection apparatus to which the X-ray tomography apparatus according to the present invention is applied is shown in FIG. As shown in FIG. 4, a sample stage 31 that holds the X-ray source 1 and the circuit board 30 and a detector 32 that detects an X-ray tomographic image of the circuit board 30.
And the defect determination section 33. Sample stage 31
Has a rotation function of driving the circuit board 30 to rotate about the rotation axis 5, and a function of sending the circuit board 30 to change the detection field of view to step and repeat. In the inspection procedure, first, the focal plane is focused on a cross section having a soldering portion or the like to be inspected, and a tomographic image is detected. Then, the detected image is processed by the defect determination unit 33 to extract the defective part. Next, send the sample stage 31 to change the detection field of view,
A tomographic image in the changed detection visual field is detected, and a defective portion is extracted. The same operation is repeated to inspect the entire surface of the circuit board 30. The detector 32 has the configuration shown in FIG.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, constituent elements that can be regarded as the same as the constituent elements described above are designated by the same reference numerals, and redundant description will be omitted.

FIG. 5 is a diagram showing an example of a tomography apparatus according to the present invention. This tomography apparatus basically comprises an X-ray detection system, a sample stage system and a display system. The sample stage system includes an XY stage 37, a rotation stage 38, and a Z stage 39.
An object 2 such as a circuit board is held on a substrate 7 via a chuck 36. Each of the stages 37, 38, 39 is a transmissive type that does not block the optical axis 7. The X-ray detection system includes an X-ray image intensifier 4 from the side of the X-ray tube 35 serving as an X-ray source.
0, lens 41, image rotator 42, lens 44
And a solid-state image sensor (CCD) 45. The display system comprises a display 46.

In the tomography apparatus generally constructed as described above, the X-rays 27 generated from the X-ray tube 35 are emitted to the object 2 side, transmitted through the object 2 and incident on the X-ray image intensifier 40. To do. The brightness of the X-ray image is amplified by the X-ray image intensifier 40 and converted into an optical image. This optical image is CC by the lens 41 and the lens 44.
An image is formed on D45, converted into an electric signal as image information by the CCD 45, and displayed on the display 46.

The procedure for obtaining a tomographic image is shown below. Object 2
The X-ray image intensifier 40 and the X-ray image intensifier 40 are positioned so that the respective rotation axes 5 and 6 are parallel to each other, and the optical axis 7 is inclined with respect to the rotation axis 5. The object 2 is rotated by the rotating stage 38, and at the same time, the image rotator 42 is rotated by the rotating stage 43.

The image rotator 42 includes a Dove prism (image rotating prism) and an image rotating mirror composed of three mirrors, both of which can be used. When using the Dove prism, the light rays incident on the Dove prism must be collimated in order to suppress the occurrence of aberration. The light collimated by the lens 41 is made incident on the Dove prism, and the lens 44 forms an image on the CCD 45. FIG. 5 shows an example using a Dove prism. When using the image rotating mirror, it is not always necessary to make parallel light. When the image rotator 42 rotates once, the optical image rotates twice. Therefore, the driver 47 controls the speed of the rotary stage 43 to be half the speed of the rotary stage 38 to rotate the object 2 and the optical image synchronously. As this control, for example, a stepping motor is used to control the frequency of the drive pulse to 2: 1 or a motor with an encoder is used to monitor the rotation and control the motor rotation so as to be synchronized. It is also possible.

Next, the accumulation time of the CCD 45 is set to the time required for the rotation stage 38 to make one rotation, and the image is read every time the image makes one rotation. Therefore, the image other than the focal plane 4 is rotated and blurred on the surface of the CCD 45.
Only an X-ray tomographic image is obtained. Of course, the read cycle of the CCD 45 can be made longer than one rotation of the image, but thermal noise increases when used in long-time exposure, so cooling the CCD 45 to reduce the thermal noise is effective. Since the focal plane 4 is a plane including the intersection of the optical axis 7 and the rotation axis 5 of the rotary stage 38, if the Z stage 39 that moves in the vertical direction is moved up and down, a tomographic image of the object 2 on an arbitrary plane is obtained. Is obtained. Further, the visual field can be arbitrarily changed by moving the XY stage 37. As a result, it becomes possible to inspect a tomographic plane at an arbitrary position even with a circuit board having a multilayer structure.

The X-ray tube 35 is preferably a microfocus type in order to improve the detection resolution. X-ray tube 3
5 and the sample stage and the X-ray detection system are movable, the detection magnification can be changed and the focusing range of the tomographic image can be adjusted. In this case, when the sample stage is brought close to the X-ray tube 35, the magnification becomes high, and when it is separated, the magnification becomes low. Also, the optical axis 7
When the angle formed by the rotary shaft 5 is increased, the focus range is narrowed, and when it is decreased, the focus range is widened.

FIG. 6 shows an embodiment in which the image rotator 42 uses an image rotating mirror composed of three mirrors.
The image rotating mirror 94 is composed of three mirrors 95. Unlike the Dove prism, the image rotation mirror does not need to make the incident light parallel light. Therefore, the optical system for forming the output image of the X-ray image intensifier 40 on the CCD 45 needs to be divided into a collimator lens and an imaging lens. Instead, it can be realized with one lens 41.

As for the X-ray detection system used in the X-ray tomography apparatus, there are several examples other than the above-mentioned examples, so another example of the X-ray detection system will be described subsequently. The following examples of the X-ray detection system are
By replacing the X-ray detection system shown in FIG. 5 (hereinafter also referred to as the first embodiment of the X-ray detection system) and the corresponding components, the X-ray tomography apparatus can be used as it is.

FIG. 7 shows a second embodiment of the X-ray detection system.
In this embodiment, the X-ray image is converted into an optical image by the X-ray image intensifier 40, and the optical image is converted into a lens 41,
At 44, an image is formed on the detection surface of the image pickup tube 50. The image rotator 42 is inserted in the middle of the optical path, and the rotary stage 4
The image rotator 42 can be rotated via the control unit 3. This causes the converted optical image to rotate. The rotary stage 43 that rotates the image rotator 42 is controlled by the driver 47 so as to rotate at half the speed of the rotary stage 38 that rotates the object. Further, the optical image is converted by the image pickup tube 50 into an electric signal (video signal) which becomes video information. Since the image pickup tube 50 outputs the image at the TV rate, that is, every 1/30 seconds, the addition circuit 51 adds the images at the time when the optical image makes one rotation. For example, if the rotation cycle is 0.5 seconds, 15 images are added. The adding circuit 51 can be realized by, for example, converting a video signal into a digital signal by an A / D converter, sampling, adding 15 images to a frame memory, and returning to a video signal by the D / A converter. The displayed image is displayed on the display 46.

FIG. 8 shows a third embodiment of the X-ray detection system.
In this embodiment, the fluorescent screen 52 converts the X-ray image into an optical image. The X-ray image intensifier 40 used in the first and second embodiments has an image distortion of about 5%.
Also, the resolution is about 5 lp (line pair) / m
m is low. However, the fluorescent screen 52 has no image distortion and a resolution of up to about 20 lp / mm. As the fluorescent screen 52, in order to improve the resolution, a single crystal scintillator, for example, CsI (Tl) (thallium activated cesium iodide), or CaF ₂ (Eu) is polished to a thickness of about 0.4 mm. Those obtained are preferred.
Further, since the light excited by the X-ray irradiation is weak, an optical image with a sufficient light quantity cannot be obtained. Therefore, the image of the fluorescent screen 52 is formed on the image intensifier 54 by the lens 53, and the brightness is amplified by the image intensifier 54. Image intensifier 54
For this purpose, a proximity image intensifier having no image distortion is suitable. Further, it goes without saying that an image fiber may be used instead of the lens 53.
The optical image amplified by the image intensifier 54 is formed on the CCD 45 by the lens 41 and the lens 44, and the image is rotated by the image rotator 42 located in the middle of the optical path. Then, it is converted into an electric signal (video signal) by the CCD 45 and displayed on the display 46. The configuration after the image intensifier 54 is the same as that of the first embodiment (FIG. 5) of the X-ray detection system. In this case CC
Instead of D45, it is also possible to use an image pickup tube as shown in the second embodiment (FIG. 7) of the X-ray detection system. FIG. 9 shows a fourth embodiment of the X-ray detection system. In this embodiment, the fluorescent screen 5 is used similarly to the third embodiment (FIG. 8) of the X-ray detection system.
2 converts the X-ray image into an optical image. Fluorescent screen 5
2 is configured to be rotatable by a rotary stage 55, and is controlled by a driver 47 so as to rotate at the same speed as the object 2. By rotating the fluorescent screen 52 and the object 2 synchronously, the image of the focal plane 4 of the object 2 stands still on the fluorescent screen 52. Therefore, by using a material having a long afterglow time for the fluorescent screen 52, the focal plane 4
Image is detected brightly. And the fluorescent screen 52
The upper optical image is the CCD 45 by the lens 41 and the lens 44.
The image is rotated by the image rotator 42, which is formed in the middle of the optical path. CCD45
Displays the detected electric signal (video signal) on the display 46 with the exposure time being the time required for the image to make one rotation.
The configuration after the lens 41 is similar to that of the first embodiment (FIG. 5) of the X-ray detection system. It is also possible to insert an image intensifier in the middle of the optical path to amplify the brightness. Further, instead of the CCD 45, it is possible to use an image pickup tube as shown in the third embodiment (FIG. 7) of the X-ray detection system. It is preferable that the image pickup tube has high sensitivity. For example, SIT (Silicon Intensi)
fied Target) tube, avalanche multiplication type imaging tube, or ICCD (Image Intensif)
ied CCD) camera and the like.

FIG. 10 shows a fifth embodiment of the X-ray detection system. This example does not use an image rotator,
This is an example of rotating an image by image processing. The X-ray detection system in this embodiment is the X-ray image sensor 56, A / D.
Converter 57, image processing unit 58, frame memory 59
And a D / A converter 60.

In such an X-ray detection system, the X-ray image is first converted into an electric signal (video signal) by the X-ray image sensor 56. The X-ray image sensor 56 outputs an electric signal (video signal) every TV rate, that is, every 1/30 second. This video signal is converted into a digital signal by the A / D converter 57, whereby a digital image is obtained. next,
The obtained digital image is rotated by an angle synchronized with the rotation of the object in the image processing unit 58, and the image for one rotation is added to the frame memory 59. For example, when the object is rotated in a cycle of 2 seconds, the image rotates by 6 ° in 1/30 seconds. Therefore, the first detected image is rotated by 0 °, the second detected image is rotated by 6 °, and the nth detected image is rotated by 6 °.
Rotate x (n-1) °. Then, the image detected up to the 60th time is added to the frame memory 59. The digital image thus integrated is converted into an analog video signal by the D / A converter 60, and the display 4
6 is displayed. The X-ray image sensor 56 in this embodiment can be replaced with, for example, an X-ray vidicon, a system combining an X-ray image intensifier and an image pickup tube, a system combining a fluorescent screen and an image pickup tube, and the like.

FIG. 11 shows a sixth embodiment of the X-ray detection system. This embodiment is an embodiment using a rotary raster scanning image pickup tube. The X-ray detection system in this embodiment includes an X-ray image intensifier 40 and a lens 9.
0, the image pickup tube 50, the rotating raster waveform generating circuit 91, the clock generating circuit 92, the adding circuit 51, and the driver 47.

In this embodiment, the X-ray image is converted into an optical image by the X-ray image intensifier 40, and the optical image is formed on the detection surface of the image pickup tube 50 by the lens 90. The image pickup tube 50 is subjected to rotary raster scanning by the drive waveform generated by the rotary raster waveform generation circuit 91. Therefore, the rotated image is detected as a still image. In order to synchronize the rotational speed of the rotary stage 38 for rotating the object 2 shown in the first embodiment (FIG. 5) of the X-ray detection system with the rotary raster scanning speed of the image pickup tube 50, the clock generation circuit 9 is provided.
The rotary raster waveform generating circuit 91 and the driver 47 are driven in accordance with the clock signal from 2. The images detected by the image pickup tube 50 are added by the adding circuit 51 for one rotation or more of the image, and displayed on the display 46. In this embodiment, instead of the X-ray image intensifier 40, a fluorescent screen or a combination of a fluorescent screen and an image intensifier can be used.

FIG. 12 shows a seventh embodiment of the X-ray detection system. The X-ray detection system in this embodiment is an X-ray vidicon 9
3, an adding circuit 51, a clock generating circuit 92, a rotating raster waveform generating circuit 91 and a driver 47.

In this embodiment, first, the X-ray image is detected by the X-ray vidicon 93. At this time, the rotation image is detected as a still image by performing a rotary raster scan with the drive waveform generated by the rotation raster waveform generation circuit 91.
In order to synchronize the rotation speed of the rotary stage 38 (FIG. 5) and the speed of the rotary raster scanning of the image pickup tube 50, the rotary raster waveform generating circuit 91 and the driver 47 are driven according to the clock signal from the clock generating circuit 92. The images detected by the image pickup tube 50 are added by the adder circuit 51 for one rotation or more of the image, and displayed on the display 46.

In order to improve the detection resolution of the X-ray tomography apparatus according to the present invention, it is necessary to miniaturize the X-ray source. For this purpose, it is necessary to miniaturize the irradiation electron beam and to make the target a thin film transmission type.

FIG. 13 shows X for obtaining a fine focus size.
An example of a wire tube is shown. The X-ray tube mainly includes a filament 61, a Wehnelt 62, an electric field lens 63, an X-ray generation layer 24, a support layer 25, and a target 23, and is housed in a glass bulb 64. Then, the X-rays 27 can be emitted from the X-ray transmission window 69 provided in the glass bulb 64 portion facing the target 23.

That is, in the X-ray tube, the filament 61
The electron beam 21 generated from the electron beam is focused on the target 23 by the Wehnelt 62 and the electric field lens 63. Target 23
Is fixed to the bearing shaft 68 around its circumference and has a structure rotatable by the bearing 67. A stator 65 is provided outside the glass bulb 64, and by exciting the stator 65, the rotor 66 inside the glass bulb 64 rotates, which causes the target 23.
Rotates. The X-rays 27 generated by the target 23 by the irradiation of the electron beam 21 are emitted to the outside from the X-ray transmission window 69 and taken out as described above.

In order to miniaturize the X-ray source diameter, the beam diameter of the electron beam 21 with which the target 23 is irradiated must be miniaturized. Therefore, the filament 61 is preferably a high-luminance material, and a LaB ₆ (lanthanum hexabolite) filament is more suitable than a conventionally used tungsten filament, which also has the advantage of a long life. Alternatively, a field emission type filament may be used. Further, if the number of the electric field lens 63 that focuses the electron beam 21 is plural, it is easy to obtain a fine electron beam diameter.

The electrons incident on the target 23 collide and scatter with atoms and spread inside the target. Tube voltage 100
The size of the spread at kV is said to be about 5 μm. Therefore, even if the electron beam is focused (spread 0) at one point, the X-ray source diameter becomes 5 μm or more. In order to reduce the X-ray source diameter, it is necessary to use a thin film target to limit the electron scattering region. In the present invention, the target 23 has a multilayer structure of the X-ray generation layer 24 and the support layer 25. The X-ray generation layer 24 is optimally made of tungsten or an alloy of tungsten and rherium, and its film thickness depends on the target X-ray source diameter, but is 0.5 to 5 μm.
m. The support layer 25 is optimally made of beryllium, which is a light element, and may be about 10 μm. The support layer 25 has an action of increasing the mechanical strength of the target 23 and at the same time having a function of releasing heat generated by irradiation of the electron beam 21. Further, the target 23 is rotated by the stator 65 and the rotor 66 so as not to irradiate the electron beam 21 on one place of the target 23, the strength against heat is increased, and damage is prevented.

The embodiment shown in FIG. 13 (hereinafter, also referred to as the first embodiment of the X-ray tube) is an embodiment using an electric field lens as an electron lens, but an embodiment using an electromagnetic lens is shown. 14 shows. In this embodiment, the electron beam 21 generated from the filament 61 is focused on the target 23 by the Wehnelt 62 and the magnetic lens 70. The target 23 has a structure in which the periphery is fixed to a bearing shaft 68 and can be rotated by a bearing 67.
In the same manner as the above embodiment, the stator 65 and the rotor 66 rotate the same. The inside of the glass bulb 64 is in high vacuum. The electric field lens 63 of the first embodiment of the X-ray tube was inside the glass bulb 64, but in this embodiment, the glass bulb 64 passes through the center of the electromagnetic lens 70. Therefore, when the life of the filament 61 or the target 23 is exhausted, the glass bulb 64 only needs to be replaced, and the electromagnetic lens 70 can be used as it is.

Further, as in the first embodiment of the X-ray tube, a plurality of electromagnetic lenses 70 makes it easier to obtain a fine focus size.

The above two embodiments are the glass bulb 64.
FIG. 15 shows an example of a sealed tube type X-ray tube in which various elements are contained, and an example of an open type X-ray tube. This embodiment of the X-ray tube is of the open type, and instead of the glass bulb 64 in the first embodiment of the X-ray tube, a vacuum container 71 is used.
By using the vacuum pump 74 to suck the air in the container to maintain the vacuum state, and replace the combination of the stator 65 and the rotor 66 with the combination of the motor 72 and the gear 75.
Further, the magnetic field lens 70 is used instead of the electric field lens 63.

In this embodiment, the electron beam 21 generated from the filament 61 is supplied to the Wehnelt 62 and the magnetic field lens 70.
To focus on the target 23. The target 23 has its periphery fixed to a bearing shaft 68,
It has a rotatable structure. Target 23
Is rotated by a motor 72 outside the vacuum container 71, and is rotated via a rotation introducing shaft 73 and a gear 75. Needless to say, the target 23 may be rotated by the stator and the rotor as in the first embodiment of the X-ray tube. The X-rays 27 generated on the target 23 by the irradiation of the electron beam 21 are taken out through the X-ray transmission window 69. The vacuum container 71 is kept vacuum by a vacuum pump 74. The structure of the target 23 is the same as that of the first embodiment of the X-ray tube shown in FIG.

It is also possible to use synchrotron radiation light (SR light) as the X-ray source to improve the detection resolution. In this case, since the SR light is parallel light, penumbra blur does not occur, and therefore the resolution does not decrease.

Next, FIG. 16 shows an embodiment of an automatic inspection device for soldering parts and circuit connecting parts of a circuit board using the X-ray tomography apparatus according to the present invention. The part of the X-ray tomography apparatus from the X-ray tube 35 to the CCD 45 of this automatic inspection apparatus is the same as that of the first X-ray detection system of the embodiment described with reference to FIG. A converter 57, an image processing unit 80, a result output unit 81, and a control computer 82 are added.

In this automatic inspection apparatus, the video signal output from the CCD 45 is converted into a digital image by the A / D converter 57, the image processing unit 80 extracts the defective portion, and the result output unit 81 outputs the position and type of the defect. To do. The control computer 82 controls the operation of the entire inspection apparatus and manages the inspection procedure.

The inspection procedure will be described below.

(1) The circuit board 30 is set on the stage.

(2) XY stage 37 and Z stage 39
To move the inspection area into view.

(3) Rotating stage 38 and rotating stage 4
3 is rotated and the CCD 45 is exposed to obtain a tomographic image of the inspection portion.

(4) The Z stage 39 is moved to obtain a second tomographic image of the inspection portion. Further, the Z stage 39 is moved little by little to obtain the required number of tomographic images. If only one tomographic image is sufficient, this operation is not necessary.

(5) From the n tomographic images, the determination image processing unit 80 determines whether the product is a good product or a defect. Since the solder has a high X-ray absorption rate, it is detected as a dark shadow. Defect determination is performed by comparing the detected shadow with a non-defective shadow, comparing the detected shadow with a shadow calculated based on design data, and calculating the feature amount of the detected shadow.

(6) The XY stage 37 is moved to change the inspection part. Then, the operations (3) to (5) are repeated. Further, the XY stage 37 is moved to move the circuit board 30.
The entire surface of the.

(7) The position and type of the defect are output.

(8) The circuit board 30 is removed.

By taking such an inspection procedure, a tomographic image of the circuit board 30 to be inspected by X-ray is obtained,
Even with a multi-layer structure, the position and type of the defect can be surely grasped.

[0067]

As is apparent from the above description, the present invention has the following effects. That is, the rotation axis of the means for converting into an optical image and the rotation axis of the object are made parallel,
According to the invention of claim 1, wherein the rotation of the optical image is synchronized with the rotation of the object by the means for rotating the optical image, the rotation axis of the object is perpendicular to the rotation axis. Since only the projected image of the focal plane can be detected as a static image, the image of the linear structure on the surface other than the focal plane is detected as a blur and only the detection target surface can be detected clearly. Become.

X-ray source, means for rotating an object to be imaged, means for converting an X-ray image transmitted through the object into an optical image, means for rotating the optical image, and rotation of the optical image. 3. The invention according to claim 2, further comprising: means for synchronizing the rotation of the target portion, means for converting an optical image into an electric signal serving as image information, and means for displaying the converted electric signal. For the above-mentioned reason, the image of the linear structure on the plane other than the focal plane is blurred and detected, and only the detection target surface can be clearly detected. In addition, this detection can be performed by displaying in real time by means of displaying the video information.

Also, the inventions according to claims 3 to 13 configured as described above have the same effect as the invention according to claim 2 for the above reason.

Further, according to the invention of claim 14, wherein the X-ray source is a microfocus X-ray tube having means for eccentrically rotating the transmissive target, the diameter of the X-ray source is reduced, and Since the electron beam is not radiated onto one part of the target, the thermal strength is increased and stable detection with high resolution can be performed.

Further, according to the invention of claim 15, wherein the transmission type target included in the microfocus X-ray tube is composed of at least two layers of an X-ray generation layer and a support layer.
The X-ray generation layer is made thin to limit the electron scattering region to miniaturize the X-ray source diameter, the mechanical strength of the target is secured by the support layer, and the heat generated by electron beam irradiation is radiated from the support layer. Therefore, it is possible to stably perform high-resolution detection.

According to the invention of claim 16, further comprising an image processing circuit for detecting a defect of the object to be inspected from an electric signal as image information, a tomographic image of an arbitrary cross section of the object to be inspected can be obtained. An image processing circuit can automatically detect a defect in a complicated internal structure of the object from the tomographic image, and an inspection of a circuit connecting portion such as a soldering portion of the multilayer substrate can be automatically performed.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of an X-ray tomography method according to the present invention.

FIG. 2 is a diagram showing a principle configuration of an X-ray tomography apparatus according to the present invention.

FIG. 3 is a diagram showing a principle configuration of a micro X-ray source according to the present invention.

FIG. 4 is a diagram showing a principle configuration of an automatic inspection device for an inside of a multilayer circuit board according to the present invention.

FIG. 5 is a diagram showing a configuration of an embodiment of an X-ray tomography apparatus according to the present invention.

FIG. 6 is a diagram showing another example of an image rotator.

FIG. 7 is a diagram showing a configuration of a second embodiment of an X-ray detection system.

FIG. 8 is a diagram showing a configuration of a third embodiment of an X-ray detection system.

FIG. 9 is a diagram showing the configuration of a fourth example of the X-ray detection system.

FIG. 10 is a diagram showing the configuration of a fifth example of the X-ray detection system.

FIG. 11 is a diagram showing a configuration of a sixth example of the X-ray detection system.

FIG. 12 is a diagram showing the configuration of a seventh embodiment of the X-ray detection system.

FIG. 13 is a diagram showing the configuration of a first embodiment of a microfocus X-ray tube according to the present invention.

FIG. 14 is a diagram showing a configuration of a second embodiment of a micro focus X-ray source according to the present invention.

FIG. 15 is a diagram showing the configuration of a third embodiment of the micro focus X-ray source according to the present invention.

FIG. 16 is a diagram showing the configuration of an example of an internal automatic inspection apparatus for a circuit board according to the present invention.

[Explanation of symbols]

 1 X-ray source 2 Object 4 Focal plane 5 Rotation axis 6 Rotation axis 7 Optical axis 27 X-ray 35 X-ray tube 37 XY table 38 Rotation stage 39 Z stage 40 X-ray image intensifier 42 Image rotator (Dub prism) 43 Rotating stage 45 Solid-state image sensor (CCD) 46 Display 47 Driver

Claims (16)

[Claims] 1. A means for rotating an object to be imaged around a rotation axis tilted with respect to an optical axis of X-rays generated from an X-ray source, and an X-ray image transmitted through the object as an optical image. X-ray tomography for obtaining an X-ray tomographic image by using an X-ray detection system including a converting unit, a unit that rotates the converted optical image, and a unit that converts the optical image into an electric signal serving as image information. In the method, the rotation axis of the means for converting into the optical image and the rotation axis of the object are parallel to each other, and the rotation of the optical image is synchronized with the rotation of the object by the means for rotating the optical image. How to shoot. 2. An X-ray source, a means for rotating an object to be imaged, a means for converting an X-ray image transmitted through the object into an optical image, a means for rotating the optical image, and an optical image An X-ray tomography apparatus comprising: a unit that synchronizes rotation with a rotation of an object; a unit that converts an optical image into an electric signal that serves as image information; and a unit that displays the converted electric signal. 3. A means for converting an X-ray image transmitted through the object into an optical image is an X-ray image intensifier,
The X-ray tomography apparatus according to claim 2, wherein the means for rotating the optical image is an image rotator rotated by a rotary stage, and the means for converting the optical image into an electric signal which is a video signal is a solid-state imaging device. 4. The exposure time of the solid-state image pickup device is controlled by means for synchronizing the rotation of the optical image and the rotation of the object so that the image rotator rotates with respect to the object at a rotation speed of 1: 2. The X-ray tomography apparatus according to claim 3, wherein the time required for one rotation of the optical image is set to be the same. 5. The X-ray tomography apparatus according to claim 2, wherein the means for converting the optical image into an electric signal which becomes image information comprises an image pickup tube and a circuit for adding the electric signals. 6. The means for converting an X-ray image transmitted through an object into an optical image is a fluorescent screen and an image intensifier for amplifying the brightness of the optical image, and the means for rotating the optical image is rotated by a rotary stage. 3. The X according to claim 2, wherein the means for converting the optical image from the image rotator to an electric signal serving as image information comprises a solid-state image sensor.
X-ray tomography equipment. 7. The exposure time of the solid-state image pickup device is controlled by means for synchronizing the rotation of the optical image with the rotation of the object so that the image rotator rotates with respect to the object at a rotation ratio of 1: 2. The X-ray tomography apparatus according to claim 6, wherein the optical image is set to have the same time as one rotation. 8. The means for rotating the object is a rotary stage, and the means for converting an X-ray image transmitted through the object into an optical image amplifies the brightness of the fluorescent screen and the optical image converted on the fluorescent screen. A circuit for adding an image intensifier and an electric signal to be image information by a means for converting the optical image to an electric signal to be image information from an image rotator in which a means to rotate an optical image from an image intensifier is rotated by a rotating stage. The X-ray tomography apparatus according to claim 2, each of which comprises 9. A means for rotating an object is from a rotary stage, and a means for converting an X-ray image transmitted through the object into an optical image is a fluorescent screen rotated by the rotary stage.
The means for rotating the optical image comprises an image rotator rotated by a rotating stage, and the means for converting the optical image into an electric signal which becomes image information respectively comprises an image pickup tube and a circuit for adding the electric signal which becomes image information. X described
X-ray tomography equipment. 10. An X-ray source, a means for rotating an object to be imaged, a means for detecting an X-ray image transmitted through the object, and an image detected by the detecting means for rotating the object. An X-ray tomography apparatus comprising: a unit that performs rotation processing in a synchronized manner; a unit that adds images rotated by the rotation processing unit; and a unit that displays the video information added by the adding unit as an image. 11. The X-ray tomography apparatus according to claim 10, wherein the means for rotating the object is a rotary stage and the means for detecting the X-ray image is an X-ray image sensor. 12. An X-ray image intensifier for converting an X-ray image into an optical image by a means for detecting an X-ray image and an image pickup tube for detecting an optical image, and a means for rotating an image is a raster of the image pickup tube. 11. The X-ray tomography apparatus according to claim 10, each comprising a circuit for rotating the scan. 13. The X-ray tomography apparatus according to claim 10, wherein the means for detecting the X-ray image is an image pickup tube. 14. A microfocus X having means for eccentrically rotating a transmission target as an X-ray source.
A line tube is used, and claim 2 and claim 1 characterized by the above-mentioned.
The X-ray tomography apparatus described in 0. 15. The X-ray tomography apparatus according to claim 14, wherein the transmissive target included in the microfocus X-ray tube comprises at least two layers of an X-ray generation layer and a support layer. 16. The image processing circuit according to claim 2, further comprising an image processing circuit for detecting a defect of an object to be inspected from an electric signal serving as video information.
16. The X-ray tomography apparatus according to any one of 1 to 15.