JPH05164854A - X-ray detector - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an X-ray detection apparatus capable of nondestructively inspecting defects in a printed circuit board, and an X-ray detection apparatus using a fluorescent plate capable of improving both resolution and sensitivity. The purpose is to provide. The X-ray incidence surface 3a of the fluorescent plate 3 is concave so that the X-rays enter the fluorescent plate 3 at a substantially right angle, and the X-rays enter the fluorescent plate 3 at a substantially right angle. The length of the X-ray transmission path inside is constant. Further, since the line sensor 4a is arranged along the X-ray transmission path of the fluorescent plate 3, it is possible to reliably detect the fluorescence generated on the X-ray transmission path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray detection device for detecting the intensity of X-rays transmitted through a living body or a substance, and more particularly to an X-ray detection device capable of nondestructively inspecting defects on a printed circuit board or the like. ..

With the increase in density and integration of electronic computers, it is required to inspect the inside of a printed circuit board that cannot be visually confirmed. Therefore, it is necessary to develop an inspection apparatus using X-rays, which has high penetrability of an object and can inspect the internal structure and defects without destruction.

Further, due to the high density of the inspection object as described above, it is necessary for an inspection apparatus using X-rays to have a high resolution of several microns.

[0004]

2. Description of the Related Art As a method of observing an image of an object to be inspected by X-ray, a method of recording on a photographic plate, a method of recording on an imaging plate, an X-ray image intensifier method, a method of using an X-ray image pickup tube, and There is a method using a fluorescent plate.

FIG. 13 shows a comparative example of the performance of the X-ray detection method in which the merits and demerits of these methods are judged from the viewpoints of real-time property, resolution, sensitivity, image area and price. The method of recording on a photographic dry plate is to visualize an X-ray image transmitted through an object to be inspected as it is on a silver salt film. The method of recording on an imaging plate is to convert the X-ray image into an electric signal through an imaging plate having a luminescence function and a photoelectric conversion device, and then digitally process the image to form a visible image on a film.

As shown in FIG. 13, these methods have advantages such as high resolution and low cost, but have a drawback of real-time property, that is, the inspection result cannot be seen on the spot. Moreover, since the X-ray image cannot be extracted as an electric signal, image processing by a computer cannot be performed.

The X-ray image intensifier method uses X
It is a method of observing as a high-brightness fluorescent image by applying photoelectrons emitted by the external photoelectric effect by line irradiation to a fluorescent plate,
It has good sensitivity and real-time characteristics, but has a problem in resolution. The method using an X-ray image pickup tube enables real-time observation and achieves both sensitivity and resolution, but it is difficult to handle because the target material is extremely unstable in the air, and productivity is poor and X-ray image There is a drawback that the observation area is small.

The method using a fluorescent plate has no particular drawback,
It is difficult to achieve both high sensitivity and high resolution. 14 and 15 are explanatory diagrams showing the relationship between sensitivity and resolution when the fluorescent plate is thin and thick, respectively.

The fluorescent plate 3 has a low conversion efficiency for converting the X-rays emitted from the radiation source 1 into light, and as shown in FIG. 14, the thin fluorescent plate 3 has a short X-ray transmission path and cannot obtain sufficient sensitivity. Therefore, as shown in FIG. 15, if the thickness of the fluorescent plate 3 is increased, the transmission path of X-rays in the fluorescent plate 3 becomes longer, and the sensitivity is improved. However, since the X-rays are radiated from the radiation source 1 through the inspected object 2 to the fluorescent plate 3 in a radial manner, as the thickness of the fluorescent plate 3 increases, the fluorescent light due to the X-rays spreads and overlaps with the projected image. As a result, the resolution is reduced by the amount of A shown in FIG.

Further, when X-rays are obliquely incident on the fluorescent plate 3, the thicker the thickness, the longer the X-ray transmission path becomes. Therefore, when observed from the projection image plane, the fluorescence becomes blurred and the resolution is further improved. descend. That is, it is difficult to achieve both resolution and sensitivity of the fluorescent screen 3.

[0011]

As described above, there is no conventional X-ray detection method that satisfies all of real-time property, resolution, sensitivity, image area and price, and the X-ray using a fluorescent screen is used. The detection method has a problem that both resolution and sensitivity cannot be satisfied.

The present invention has been made in order to solve such a problem, and an X-ray detection apparatus using a fluorescent plate, which is excellent in both resolution and sensitivity, is provided. To aim.

[0013]

FIG. 1 illustrates the principle of the present invention. In order to solve the above-mentioned problems, the invention according to claim 1 includes a fluorescent plate 3 that emits fluorescence when radially irradiated X-rays are incident, and a one-dimensional image sensor 4a that converts the fluorescence into an electric signal. An X-ray detection device provided, wherein the fluorescent plate 3 has an arc shape, and the X-ray incident surface 3a of the fluorescent plate 3 is a concave surface so that the X-rays are incident at a substantially right angle. The one-dimensional image sensor 4a is arranged along the transmission path.

According to a second aspect of the present invention, in the first aspect of the invention, the mask 6 for narrowing the X-rays incident on the X-ray incident surface 3a of the fluorescent plate 3 into a beam and the one-dimensional image sensor 4a. Instead of the delay integration type charge coupled device (T
DI: Time Delay and Integration-CCD) image sensor 9a.

According to a third aspect of the present invention, in the first aspect of the invention, the mask 6 for narrowing the X-rays irradiated onto the X-ray incident surface 3a of the fluorescent plate 3 into a beam, and the fluorescent plate 3 are used. 2 is composed of a plurality of optical fibers 11 that form the fluorescent light guide path, a lens 12 that converges the light from these optical fibers 11, and a point sensor 13 that converts the light from the lens 12 into an electric signal.

[0016]

According to the first aspect of the present invention, as shown in FIG. 1, the fluorescent plate 3 is formed in an arc shape, and the X-ray incident surface 3a of the fluorescent plate 3 is concave so that the X-rays are incident at a substantially right angle. The rays enter the fluorescent plate 3 at a substantially right angle, and the length of the X-ray transmission path in the fluorescent plate 3 becomes constant. In addition, X of the fluorescent plate 3
Since the one-dimensional image sensor (4a) is arranged along the transmission path of the X-ray, it is possible to reliably detect the fluorescence generated on the transmission path of the X-ray.

According to the second aspect of the present invention, the mask 6 forms the X-rays into a beam having a required size to prevent the fluorescence of the phosphor 3 from diffusing and detect the fluorescence efficiently by the TDI-CCD 9a.

According to the second aspect of the present invention, the mask 6 forms the X-rays into a beam having a required size to prevent the fluorescence of the phosphor 3 from diffusing, and the fluorescence from the phosphor plate 3 is supplied to the plurality of optical fibers 11. Take it in and guide it to the lens 12 side,
Then, these lights are condensed by the lens 12, converged on the point sensor 13 and converted into an electric signal.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described with reference to the drawings. [I] First Embodiment FIGS. 2 to 6 show a first embodiment according to the present invention. FIG. 2 is an overall configuration diagram for explaining the X-ray detection apparatus according to the embodiment of the present invention.

In FIG. 2, the X-ray emitted from the radiation source 1 is an object to be inspected (eg, a printed circuit board) 2 on a stage 5.
And is transmitted therethrough, and the image is projected on the X-ray transparent image projection surface (X-ray incident surface) 3a of the fluorescent plate 3. A mask 6 is arranged between the object 2 to be inspected and the fluorescent plate 3 to prevent X-rays scattered from the object 2 to be inspected from entering the side surface of the fluorescent plate 3. The material of the mask 6 is lead, and a slit 6a is provided in the center thereof, and the size of the slit 6a is set so that X-rays are irradiated to the entire X-ray fluoroscopic image projection surface 3a. As will be described later, X-rays that pass through the slits 6a provide image data for one vertical line and one horizontal pixel of the X-ray fluoroscopic image.

A reflection coating is provided on one side surface of the fluorescent plate 3 in order to improve the efficiency of converting X-rays into light, that is, the detection efficiency, and a lens (not shown) and a one-dimensional element are provided at a predetermined position on the other side surface. A fluorescence detector 4 including an image sensor (hereinafter referred to as a line sensor) 4a and the like is arranged. The lens collects and reduces the fluorescence from the fluorescent screen 3, and the line sensor 4 arranged parallel to the transmission path of the X-ray fluorescent screen 3.
It is projected on a. As shown in FIG. 3, the line sensor 4a is rotatable and converts the fluorescence reduced by the lens into an electric signal. The fluorescence detector 4 is connected to a computer (not shown) so that the image data supplied from the fluorescence detector 4 is processed.

As shown in FIG. 4, the fluorescent plate 3 is a fan-shaped or arc-shaped plate. As shown in FIG. 5, this shape allows X-rays to enter the X-ray transparent image projection surface 3a of the fluorescent plate 3 at a substantially right angle, and also makes the length of the X-ray transmission path constant.
Further, the lateral width of the X-ray fluoroscopic image projection surface 3a of the fluorescent plate 3 becomes the width of the image resolution, and the length of the side surface 3b of the fluorescent plate 3 determines the sensitivity (FIG. 6). This length is appropriately set according to the type of the fluorescent plate 3 in consideration of the required sensitivity and the X-ray absorption amount of the fluorescent plate 3.

Next, the operation of the X-ray detection apparatus of this embodiment will be described with reference to FIGS. FIG. 7 is an explanatory diagram showing a signal example of the line sensor. In each figure, the horizontal axis represents time and the vertical axis represents amplitude. FIG. 8 is a flowchart showing the signal processing procedure of the line sensor, and FIG. 9 is a flowchart showing the procedure of creating a two-dimensional X-ray transmission image.

The X-ray emitted from the radiation source 1 is the object to be inspected 2
It is irradiated radially. The X-rays that have passed through the object 2 to be inspected are narrowed down by the slits 6 a of the mask 6, and the X-rays of the fluorescent screen 3 are reduced.
The projection image plane 3a of the fluoroscopic image is irradiated at a right angle. Then, the X-rays are gradually attenuated and transmitted while generating fluorescence. At this time, the length of the X-ray transmission path in the fluorescent plate 3 is constant regardless of the irradiation direction, and the X-rays are sufficiently converted into light. The fluorescence of the X-rays is condensed and reduced by the lens of the fluorescence detector 4 arranged on the side surface of the fluorescent plate 3, projected on the line sensor 4a, and converted into an electric signal.

The fluorescence detector 4 detects the video signal of the line sensor 4a shown in FIG. 7 (a) from when the horizontal synchronizing signal shown in FIG. 7 (c) rises to when it falls.
Image data of one pixel is created by taking in only the number of clocks of the pixel clock signal shown in (b). This processing will be described with reference to the flowchart in FIG.

First, it is judged whether or not the horizontal synchronizing signal has risen (step S1). If the answer is negative, that is, No, the process returns to the start. If the answer is affirmative, that is, Yes, the clock of the pixel clock signal is counted. Then, the number obtained by multiplying the number of pixel clocks in the horizontal synchronizing signal by the number of pixels of the line sensor 4a is detected (step S2), and these are integrated (step S3). Next, the electric signal of the integration result is converted from an analog signal to a digital signal (step S4), and this is supplied to a computer (not shown) as image data of one pixel (step S4).
5), this program ends.

As described above, one line of the line sensor 4a (the number of elements of the line sensor) corresponds to one pixel of the X-ray transmission image. Then, as shown in FIG. 3, while rotating the line sensor 4a from the upper side to the lower side, the fluorescence collected by the lens is detected, and the above-described one pixel creation is repeated,
Image data of one vertical line is created. When this image data is supplied to the computer, the line sensor 4a reversely rotates from bottom to top and returns to the original position.

Next, by moving the stage 5,
The object 2 to be inspected is moved in the horizontal direction and the next one vertical line
Create the data. This operation is sequentially repeated to create a two-dimensional X-ray transmission image. The creation of this two-dimensional X-ray transmission image will be described in more detail with reference to the flowchart of FIG.

As initial values, the number of vertical input pixels and the number of horizontal input pixels are set to zero (step S1), and then the stage is set to the initial position (step S2). One is added to the initial value of zero to set the number of horizontal input pixels to 1 (step S3), and image data of 1 pixel is created by the above method (step S4). Then, 1 is added to the initial value of 0 to set the vertical input pixel number to 1 (step S5), and it is further determined whether the vertical input pixel number is equal to the vertical effective pixel number (step S).
6). If the answer is negative, that is, No, the process returns to step 4 and image data of one pixel is created again, and the number of vertical input pixels is set to 2 (step S5). Hereinafter, this procedure is sequentially repeated until the answer in step S6 is affirmative, that is, Yes, and when the answer is Yes, that is, when the vertical input pixel number becomes equal to the vertical effective pixel number, one vertical line Since the image data has been captured, the number of vertically input pixels is cleared to zero (step S7).

Next, it is judged whether or not the number of horizontally input pixels is equal to the number of horizontally effective pixels (step S8). If the answer is No, the process returns to step S2 and the stage is moved to the next position (step S8). Step S2). Then, the number of horizontal input pixels is set to 2 (step S3), and steps S4 to S6 are performed.
The loop processing up to is repeated, and after the capture of the image data of one vertical line is completed, the number of vertical input pixels is cleared to zero (step S7).

Then, again, it is judged whether or not the horizontal input pixel number is equal to the horizontal effective pixel number (step S8), and the answer is N.
When it is o, the process returns to step S2 again to move the stage to the next position (step S2). Hereinafter, this procedure is sequentially performed until the answer to step S8 is Yes, that is, the horizontal input pixel number becomes equal to the horizontal effective pixel number.

Then, when the acquisition of the horizontal image data is completed, a two-dimensional X-ray transmission image is created based on these image data (step S9). The two-dimensional X-ray transmission image created here is an image in which the center of a plate-shaped object such as a printed circuit board extends. Therefore, in such a case, correction such as thinning is performed (step S1).
0) to obtain the final X-ray transmission image (step S1)
1) End this program.

As described above, according to this embodiment, both the resolution and sensitivity of the fluorescent plate 3 can be improved, and the object 2 to be inspected
Since a two-dimensional X-ray transmission image is created by moving, the required image area can be easily obtained. [II] Second Embodiment FIG. 10 shows an overall configuration diagram of a second embodiment of the X-ray detection apparatus according to the present invention.

In this embodiment, instead of the mask 6 interposed between the object 2 to be inspected and the fluorescent plate 3, a scattering prevention filter 7 is used.
Is different from the first embodiment in that a fluorescent plate 8 having a small thickness and high sensitivity and a fluorescent detector 9 having a TDI-CCD 9a as a line sensor are arranged.

The anti-scatter filter 7 is made of lead,
An annular member having a predetermined thickness and width is provided at the center with a plurality of holes 7a each having a vertical and horizontal dimension of one pixel, and is rotatably arranged. The hole 7a forms the X-ray in the form of a diaphragm beam to suppress the diffusion of fluorescence from the fluorescent plate 8 having high sensitivity.

As shown in FIG. 11, the TDI-CCD 9a is a two-dimensional image sensor in which line sensors are arranged in a plane, and light from an object is collected by a lens and irradiated onto the two-dimensional image sensor for detection. The accumulated light is integrated in one direction to 1
Output as a three-dimensional image sensor. By making the speed at which the detection light is integrated and the moving speed of the object the same, the images are integrated and detected with high sensitivity.

In the STL mode of the TDI-CCD 9a, the data is accumulated without accumulating for a fixed time, and then accumulated and output at a high speed for a fixed time. In this case, if the accumulation time is long enough to ignore the detection of light within the integration time,
It is possible to output a two-dimensional image. In this embodiment, the STL mode is used, and it is used to detect all the two-dimensionally diffused fluorescence.

Next, the operation of this embodiment will be described. When the hole 7a of the anti-scattering filter 7 is fixed to the lower end of the phosphor 8 and X-rays are emitted from the radiation source 1, the X-rays pass through the object 2 to be inspected, and then are narrowed down by the hole 7a of the anti-scattering filter 7 to form a beam shape. Then, the fluorescent plate 8 is irradiated. Then, X-rays generate fluorescence on the fluorescent plate 8, but this fluorescence is condensed and reduced by the lens of the fluorescence detector 9, and the STL mode TDI-CCD 9 is used.
The amount of light diffused by the fluorescence is integrated by a, and this is detected as the light amount (X dose) of one pixel.

After that, the anti-scattering filter 7 moves upward by one pixel and detects the fluorescence as described above. Thereafter, by repeating this operation in sequence, an X-ray fluoroscopic image of one vertical line can be obtained.

Next, as in the first embodiment, the object 5 to be inspected is moved in the horizontal direction by the stage 5, and the next one vertical line X
Obtain a fluoroscopic image. By repeating this, a two-dimensional X-ray transmission image is obtained.

As described above, in this embodiment, the fluorescent plate 8 having high sensitivity and the TDI-CCD 9a are used to detect even the amount of the diffused light, so that even a fluorescent plate thinner than the fluorescent plate shown in the first embodiment can be detected. Good, high sensitivity and high resolution X-ray detection can be performed. [III] Third Embodiment FIG. 12 is an overall configuration diagram of a third embodiment of the X-ray detection apparatus according to the present invention.

In this embodiment, the fluorescence from the fluorescent plate 10 received by the TDI-CCD 9a is taken in by an optical fiber plate 11 composed of a bundle of optical fibers, and the light propagated through the optical fiber plate 11 is condensed by a lens 12,
It differs from the second embodiment in that it converges on a photodetector 13 composed of a point sensor (for example, a photo sensor) and converts it into an electric signal.

In the first and second embodiments, the fluorescence of one radiation of the fluorescent plate is integrated by the line sensor or TDI-CCD 9a to obtain the data of one pixel. In this embodiment, the fluorescence of one radiation is measured by the lens. It converges to one point and obtains data for one pixel. The two-dimensional X-ray transmission image can be obtained in the same manner as in the first and second embodiments.

Thus, the T used in the second embodiment was
As in the second embodiment, it is possible to perform X-ray detection with high detection efficiency, high sensitivity, and high resolution without using the DI-CCD 9a, even with a fluorescent plate thinner than that shown in the first embodiment.

[0045]

As described above, according to the first aspect of the present invention, the fluorescent plate has an arc shape, and the X-ray incidence surface of the fluorescent plate has a concave surface so that X-rays are incident at a substantially right angle. Since the line sensor is arranged along the X-ray transmission path of the fluorescent plate, the X-ray enters the fluorescent plate at a substantially right angle, and
The length of the X-ray transmission path in the fluorescent screen becomes constant. Also,
Fluorescence generated on the X-ray transmission path can be reliably detected. Therefore, the performance of both resolution and sensitivity can be improved.

According to a second aspect of the present invention, in the first aspect of the invention, a mask for narrowing the X-rays incident on the X-ray incidence surface of the fluorescent plate into a beam and a TDI- Since a CCD is used, even the amount of light that has diffused the fluorescence can be detected, and even a thin fluorescent plate has a high detection efficiency,
X-ray detection with high sensitivity and high resolution can be performed.

Further, according to the invention of claim 3, in the invention of claim 1, a mask for narrowing the X-rays irradiating the X-ray incident surface of the fluorescent plate into a beam shape, and a fluorescent light from the fluorescent plate are used. Since a plurality of optical fibers that form the guide path, a lens that converges the light from these optical fibers, and a point sensor that converts the light from the lenses into an electrical signal are used, even a thin fluorescent plate has good detection efficiency and high sensitivity. High resolution X-ray detection can be performed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an overall configuration diagram of an X-ray detection apparatus according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a rotating operation of the line sensor of the first embodiment.

FIG. 4 is a perspective view of the fluorescent plate of the first embodiment.

FIG. 5 is a side view of the fluorescent plate of the first embodiment.

FIG. 6 is a cross-sectional view of the fluorescent plate of the first embodiment.

FIG. 7 is an explanatory diagram showing a signal example of the line sensor of the first embodiment.

FIG. 8 is a flowchart showing a signal processing procedure of the line sensor of the first embodiment.

FIG. 9 is a flowchart showing a procedure for creating a two-dimensional X-ray transmission image according to the first embodiment.

FIG. 10 is an overall configuration diagram of an X-ray detection device according to a second embodiment of the present invention.

FIG. 11 is an operation explanatory diagram of the TDI-CCD of the second embodiment.

FIG. 12 is an overall configuration diagram of an X-ray detection device according to a third embodiment of the present invention.

FIG. 13 is an explanatory diagram showing a comparative example of the performance of the conventional X-ray detection method.

FIG. 14 is an explanatory diagram showing the relationship between sensitivity and resolution when the thickness of the fluorescent plate is thin.

FIG. 15 is an explanatory diagram showing a relationship between sensitivity and resolution when a fluorescent plate has a large thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Radiation source 3 ... Fluorescent plate 3a ... X-ray incident surface 4a ... Line sensor

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoji Nishiyama 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (3)

[Claims] 1. An X-ray detection device comprising a fluorescent plate (3) which emits fluorescence when radially irradiated X-rays are incident, and a one-dimensional image sensor (4a) which converts the fluorescence into an electric signal. Then, the fluorescent plate (3) is formed into an arc shape, and the X-ray incidence surface (3a) of the fluorescent plate (3) is arranged so that the X-rays are incident substantially at right angles.
Is a concave surface, and the one-dimensional image sensor (4a) is arranged along the X-ray transmission path of the fluorescent plate (3).
Line detection device. 2. An X-ray incident surface (3a) of the fluorescent plate (3)
(6) A mask for narrowing the X-rays to be irradiated onto the beam
2. An X-ray detection device according to claim 1, wherein a delay integration type charge coupled device image sensor (9a) is used as the one-dimensional image sensor (4a). 3. An X-ray incident surface (3a) of the fluorescent plate (3)
(6) A mask for narrowing the X-rays that are irradiated onto the beam into a beam shape
A plurality of optical fibers (11) forming a guide path for fluorescent light from the fluorescent plate (3), a lens (12) for converging light from these optical fibers (11), and light from the lens (12) 2. A point sensor (13) for converting electric energy into an electric signal is used.
The X-ray detection device described.