JP3694833B2 - Eucentric tilted 3D X-ray CT and 3D image imaging method using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a eucentric tilted three-dimensional X-ray CT (computer tomography) and a method for photographing a three-dimensional image thereby, and more specifically, an industrial X-ray CT apparatus, a semiconductor component, The present invention relates to a eucentric tilted three-dimensional X-ray CT suitable for use in inspection of printed circuit boards, IC chips, solder joints, or inspection of machine parts, composite materials, plastics, and the like, and an imaging method using the same. .
[0002]
[Prior art]
In the conventionally known three-dimensional X-ray CT, as shown in FIG. 3, the X-ray source A, the measurement object D, and the detector B are arranged on the same plane and rotate around the rotation axis C. For X, X-rays are projected from the X-ray source A in a direction perpendicular to the rotation axis C, and projection data is collected by a detector B arranged at a position facing it. In this case, even if it is desired to magnify a part of the measurement object D having a large planar area, the rotation radius of the measurement object is large and the X-ray source A and the measurement object D interfere with each other. The enlargement ratio cannot be increased by bringing A closer. Further, when the projection data is collected from the direction perpendicular to the rotation axis C of the measurement object D, there is a problem that a beam hardening false image is generated in the plane direction in the measurement object having a large plane area.
On the other hand, there is laminography as a method of taking an image with respect to the rotation axis of the measurement object, but the output is two-dimensional image data (see FIG. 4), not three-dimensional data.
[0003]
[Problems to be solved by the invention]
The technical problem to be solved by the present invention is that the centric tilted three-dimensional X not only can image a whole flat measurement object having a large plane area but also can perform a part of high magnification three-dimensional tomography. An object of the present invention is to provide a line CT and a method for photographing a three-dimensional image thereby.
Another technical problem of the present invention is to provide the above-described three-dimensional X-ray CT and an imaging method therefor, which can reduce beam hardening that occurs in tomography of a substance that hardly transmits X-rays.
Another technical problem of the present invention is to image a flat material that is difficult to transmit X-rays, and can improve the contrast of an image by using low-energy X-rays and extend the lifetime of the X-ray source. It is an object of the present invention to provide a three-dimensional X-ray CT and an imaging method using the same.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the eucentric tilted three-dimensional X-ray CT of the present invention includes a eucentric table for placing a measurement object and an X-ray source capable of setting a rotation axis at an arbitrary position of the measurement object. And a two-dimensional detector that is disposed opposite to the object and detects a projection image of the measurement object on the eucentric table, and a normal line of the projection image obtained by the two-dimensional detector is perpendicular to the rotation axis of the measurement object In this way, the image conversion means for image conversion, and the converted projection image are multiplied by the distance between the X-ray focal point and the rotation axis of the object to be measured, the pixel coordinates of the projection image, and a weighting factor composed of a formula based on the angle θ below. Data processing means for processing data, and arranging the X-ray source and the two-dimensional detector so that an axis connecting them intersects at an angle θ smaller than 90 degrees with respect to the rotation axis, from 90 degrees Every small angle It is characterized by enabling 3D tomography.
[0005]
In the eucentric type inclined three-dimensional X-ray CT, using a microfocus X-ray source as X-ray source, and optionally adjustable positional relationship between the measurement object and the X-ray source on Eucentric table, whereby the workpiece It is effective to be able to take a projected image of an arbitrary portion of the image at an arbitrary magnification.
[0006]
Further, in order to solve the above-described problems, the method of photographing a three-dimensional image using the eucentric tilted three-dimensional X-ray CT of the present invention is to place a measurement object on a eucentric table whose rotational axis can be set at an arbitrary position of the measurement object. An X-ray source and a two-dimensional detector that is placed opposite to the X-ray source and detects a projected image are placed on the object to be measured on the eucentric table, and an axis line connecting them is 90 degrees with respect to the rotation axis. Arranged so that they intersect at a smaller angle θ , the projected image of the measurement object is photographed by the detector, and the projection object is photographed by rotating the measurement object around the rotation axis by a eucentric table at minute angular intervals. This is performed at each angle step, and each projection image is image-converted so that its normal is perpendicular to the rotation axis of the measurement object, and the X-ray focal point and the rotation axis of the measurement object are converted into the converted projection image. Distance, And characterized image of the pixel coordinates, and that performs a three-dimensional image reconstruction multiplied by a weighting factor consisting of formulas based on the angle θ data processing performed by the measurement object to obtain a plurality of tomographic images in a set photographing To do.
[0007]
In the method of the present invention, the projection image obtained by arranging the detector so that the normal line standing at the center of the detection surface of the detector faces the focal point of the X-ray source (that is, the X-ray focal point) The step of converting the image so that the normal line is perpendicular to the rotation axis of the object to be measured, and measuring the X-ray focal point obtained from the coordinate system having the origin in the plane including the focal point of the X-ray source. A step of creating weighted projection data by multiplying a weighting coefficient comprising a mathematical formula based on the distance from the rotation axis of the object, the pixel coordinates of the projection image , and the angle θ, and performing a Fourier transform on the weighted projection data and the filter function. Preferably, the projection image is processed by an algorithm having a step of performing a convolution operation and a step of obtaining a three-dimensional absorption coefficient distribution by performing back projection on a three-dimensional reconstruction grid based on the result of the convolution operation.
[0008]
In the eucentric tilted three-dimensional X-ray CT having the above-described configuration and the imaging method using the same, the rotation axis of the eucentric table can be set at an arbitrary position, so that the measurement object is not moved on the table. A part of a flat measurement object having a large area can be enlarged and three-dimensional tomographic imaging can be performed, and in particular, X-rays are collected by irradiating X-rays obliquely with respect to the rotation axis of the measurement object. The source and the measurement object do not interfere with each other, and the X-ray source can be arranged near the measurement object to perform high-magnification three-dimensional tomography. Moreover, by irradiating X-rays obliquely with respect to the rotation axis of the measurement object, the transmission distance of the X-rays in the measurement object is shortened, so that the influence of beam hardening can be greatly reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a eucentric tilted three-dimensional X-ray CT according to the present invention. The inclined three-dimensional X-ray CT includes a eucentric table T that can set the rotation axis at an arbitrary position. In this eucentric table T, the rotation axis is shown as a virtual rotation axis E in FIG. 1, but the position of the virtual rotation axis E can be set to an arbitrary position of the measuring object D on the table T, and the measurement can be performed. There is no need to move the object D on the table T, and the eucentric table T can be adjusted by moving it three-dimensionally while maintaining its posture, so that a part of a flat measured object with a large area can be enlarged. Three-dimensional tomography can also be performed.
[0010]
The two-dimensional detector B that detects the projected image of the measurement object D on the eucentric table T that is disposed opposite to the X-ray source A has an angle that makes the axis connecting them smaller than 90 degrees with respect to the virtual rotation axis E. The X-ray cone beam G from the X-ray source A is transmitted through the object D placed so as to intersect at θ and placed on the table T, and the projection image is detected by the detector B. I am doing so. As the X-ray source, a microfocus X-ray source having a small focal diameter is used in order to obtain a clear image with high magnification. In addition to the above-described method using a part of the X-ray cone beam G having a large divergence angle, an X-ray source A ′ can be configured in which the X-ray source A is arranged facing the detector B.
For the enlarged region F that is a part of the measurement object D, by changing the angle θ of the axis connecting the X-ray source A and the detector B, an X-ray irradiation direction that does not excessively increase X-ray attenuation can be selected. The magnification of a part of the measurement object D can be arbitrarily adjusted by changing the distance between the X-ray source A and the measurement object D by adjusting the height of the eucentric table T.
[0011]
Using the eucentric tilted three-dimensional X-ray CT having the above-described configuration, for example, a three-dimensional image of a part of the measurement object D having a large planar area and a small thickness, such as a printed board placed on the table T First, as shown in FIG. 1, the X-ray from the X-ray source A is transmitted through a part of the measurement object D placed on the eucentric table T, and the projection image is two-dimensionally detected. Detector B detects. At this time, of course, the axis connecting the X-ray source and the detector intersects the virtual rotation axis at an angle θ.
[0012]
In order to perform three-dimensional CT, the X-ray source A and the two-dimensional detector B are fixed, the measurement object D is rotated together with the table T around the virtual rotation axis E of the eucentric table T at a minute angle interval, At each angle step, the projection image projected on the detector B is recorded in a data recording device (personal computer) for data recording.
Then, using each of the recorded projection images, only a part of the measurement object D is reconstructed by using the calculation code of the inclined three-dimensional X-ray CT in the analyzer (personal computer) to obtain a three-dimensional image.
[0013]
In photographing the three-dimensional image, it is desirable to process the projected image with an algorithm having the following steps. What are the above steps?
(1). A projection image obtained by arranging the detector so that the normal line standing at the center of the detection surface of the detector faces the focal point of the X-ray source is displayed so that the normal line is perpendicular to the rotation axis of the object to be measured. Converting step,
(2). In this converted projection image, the distance between the X-ray focal point obtained from the coordinate system having the origin in the plane including the focal point of the X-ray source and the rotation axis of the measurement object, the pixel coordinates of the projection image , and the X-ray source A step of creating weighted projection data by multiplying a weighting factor consisting of a mathematical formula based on an angle θ at which the axis connecting the two-dimensional detector and the rotation axis of the measurement object intersect ;
(3). Performing a Fourier transform on the weighted projection data and the filter function to perform a convolution operation;
(4). Based on the result of the convolution operation, backprojecting onto a three-dimensional reconstruction grid to obtain a three-dimensional absorption coefficient distribution;
It is.
[0014]
In obtaining the image, the magnification of a part of the measurement object D can be arbitrarily adjusted by changing the distance between the X-ray source A and the measurement object D according to the height of the eucentric table T.
Further, the position of the virtual rotation axis E can be set to any position of the measuring object D by moving the eucentric table T. At this time, it is not necessary to stop the X-ray or move the measuring object D by a person.
[0015]
As described above with reference to FIG. 2, in the conventional three-dimensional X-ray CT, since the X-ray source A, the measurement object D, and the detector B are on the same plane, a part of the measurement object D is enlarged. When tomography is performed, when the measuring object D having a large plane area rotates, the X-ray source A and the measuring object D interfere with each other, and the measuring object D cannot be brought close to the X-ray source A to increase the magnification. However, according to the eucentric tilted three-dimensional X-ray CT described above, as shown in FIG. 1, there is no X-ray source on the same plane as the measurement object D having a large plane area. Since the object to be measured D can be rotated after being brought close to the very vicinity of the region to be imaged and the enlargement ratio increased, local three-dimensional X-ray CT can be performed.
[0016]
Further, in the positional relationship between the measurement object D and the X-ray source as shown in FIG. 1, since the X-ray is not transmitted in the plane direction of the measurement object D, the transmission distance of the X-ray is shortened, and the influence of beam hardening is greatly increased. And a clear image with higher contrast can be obtained. Further, since X-rays with low energy can be used, the life of the X-ray source is also extended.
[0017]
FIG. 2 shows an example in which a part of the printed circuit board after mounting is subjected to magnified tomography at a 45-degree tilt angle and visualized three-dimensionally. The shape of the void generated in the solder joint is visualized three-dimensionally.
On the other hand, FIG. 4 shows an example in which a part of the printed circuit board is visualized by laminography. Since this is a two-dimensional plane display at a certain height, the two-dimensional surface looks good, but the resolution in the height direction is poor, and the void in the thickness direction is not known. As a result, it is difficult to grasp the entire measurement object.
From these comparisons, it can be seen that according to the three-dimensional X-ray CT of the present invention, the structure such as voids can be clearly grasped by three-dimensional visualization, compared to laminography in which the whole image of the measurement object is difficult to grasp.
[0018]
【The invention's effect】
According to the eucentric tilted three-dimensional X-ray CT and imaging method using the same according to the present invention described in detail above, the inside of a multilayer printed circuit board or a chip joint in which a large number of solder balls are distributed in a planar shape. In addition to being able to image the entire flat measurement object with a large planar area, it is also possible to perform some high-magnification three-dimensional tomography, and beam hardware generated by tomography of materials that are difficult to transmit X-rays In addition, it is possible to improve the contrast of an image by using low energy X-rays and to extend the lifetime of the X-ray source when photographing a flat material that hardly transmits X-rays. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram for explaining a eucentric three-dimensional tilted X-ray CT according to the present invention.
FIG. 2 is a drawing-substituting photograph showing an example of enlarged tomography of a part of a printed circuit board by X-ray CT of the present invention.
FIG. 3 is a configuration diagram showing an outline of a conventional three-dimensional X-ray CT.
FIG. 4 is a drawing-substituting photograph showing an example of two-dimensional tomography by laminography.
[Explanation of symbols]
A X-ray source B Two-dimensional detector D Measured object E Virtual rotation axis F Enlarged area T Eucentric table

Claims (5)

A eucentric table that can set the rotation axis to any position of the object to be measured;
A two-dimensional detector for detecting a projected image of an object to be measured on an eucentric table disposed opposite to the X-ray source;
Image conversion means for converting the projection image obtained by the two-dimensional detector so that the normal line is perpendicular to the rotation axis of the measurement object;
A data processing means for processing the converted projection image by multiplying the distance between the X-ray focal point and the rotation axis of the object to be measured, the pixel coordinates of the projection image, and a weighting factor based on the following angle θ ;
The X-ray source and the two-dimensional detector are arranged so that the axis connecting them intersects the rotation axis at an angle θ smaller than 90 degrees, and three-dimensional tomography can be performed at any angle smaller than 90 degrees. ,
A eucentric tilted three-dimensional X-ray CT. Using a microfocus X-ray source as the X-ray source,
The eucentric tilted three-dimensional X-ray CT according to claim 1. The positional relationship between the object to be measured on the eucentric table and the X-ray source can be arbitrarily adjusted, so that a projected image of an arbitrary part of the object to be measured can be taken at an arbitrary magnification.
The eucentric inclined three-dimensional X-ray CT according to claim 1 or 2. A measurement object is placed on a eucentric table whose rotation axis can be set at an arbitrary position of the measurement object, and an X-ray source and the projection image are detected with respect to the measurement object on the eucentric table. A two-dimensional detector is arranged so that an axis connecting them intersects at an angle θ smaller than 90 degrees with respect to the rotation axis, and a projected image of the measurement object is photographed by the detector,
The projection image is taken at each angle step by rotating the measurement object around the rotation axis by a eucentric table at a minute angle interval.
Each projected image is transformed so that its normal is perpendicular to the axis of rotation of the measurement object,
The converted projection image is subjected to data processing by multiplying the distance between the X-ray focal point and the rotation axis of the object to be measured, the pixel coordinates of the image to be measured, and a weighting coefficient based on the above-described angle θ, and performing data processing to obtain a three-dimensional object. Perform image reconstruction and obtain multiple tomographic images with one set of imaging.
A method of photographing a three-dimensional image by a eucentric tilted three-dimensional X-ray CT. A projection image obtained by arranging the detector so that the normal line standing at the center of the detection surface of the detector faces the focal point of the X-ray source is displayed so that the normal line is perpendicular to the rotation axis of the object to be measured. Converting step,
In this converted projection image, the distance between the X-ray focal point obtained from the coordinate system having the origin in the plane including the focal point of the X-ray source and the rotation axis of the measurement object, the pixel coordinates of the projection image , and the angle θ Creating weighted projection data by multiplying by a weighting factor consisting of a mathematical formula based thereon,
Performing a Fourier transform on the weighted projection data and the filter function to perform a convolution operation;
Based on the result of the convolution operation, backprojecting onto a three-dimensional reconstruction grid to obtain a three-dimensional absorption coefficient distribution;
Processing the projected image with an algorithm comprising:
5. The method for photographing a three-dimensional image by using an eucentric tilted three-dimensional X-ray CT according to claim 4.

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