JP3690786B2 - X-ray tomography system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray inspection apparatus that has been established in the field of destructive inspection, and relates to a tomographic imaging method and apparatus using an X-ray imaging apparatus. In particular, the present invention relates to an automatic adjustment function of an X-ray tomographic imaging apparatus that is effective for defect analysis of multilayer printed circuit boards used in electrical and electronic equipment, defect analysis of bump joints, and the like.
[0002]
[Prior art]
Such an X-ray tomographic imaging apparatus is a known technique as described in, for example, JP-A-5-31735. In this technique, that is, X-ray laminography, a plane parallel to the light receiving surface including the intersection of the optical axis of the X-ray and the rotation center axis of the rotary table is obtained as a tomographic image. For this reason, it is necessary to mechanically match the optical axis of the X-ray with the rotation center axis of the rotary table. Conventionally, this adjustment method has required adjustment while visually observing a tomographic image on a TV monitor or the like while manually moving a planar biaxial stage mechanism that electrically moves the rotational axis position of the rotary table. This adjustment needs to be performed for each position where movement of the Z axis (moving axis parallel to the optical axis of the X-ray) for adjusting the magnification of the image is stopped. The Z axis moves stepwise. Dozens of adjustments were made when the equipment was started up.
[0003]
[Problems to be solved by the invention]
The present invention establishes a reference and a method for determining the degree of coincidence between the X-ray optical axis and the rotation center of the rotation axis from the tomographic image, and simplifies the adjustment to match the X-ray optical axis and the rotation center of the rotation axis. The purpose is to eliminate human instability by the coordinator.
[0004]
[Action]
The operation of the present invention will be described. A tomogram of a predetermined chart is taken into an electronic computer, the tomogram is subjected to image processing, and the rotary table rotation axis is adjusted so that the area or the distance between two points approaches a minimum or specified value. When the plane two-axis stage that moves the position of the X-ray is moved by the control from the control computer and the process is repeated so that the X-ray optical axis and the rotation axis of the rotary stage coincide with each other, the X-ray optical axis Instability factors such as simplification of adjustment to match the rotation center of the rotation axis and human variation by the adjuster can be eliminated, and the apparatus can maintain stable performance.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a schematic configuration of an X-ray tomographic imaging apparatus based on a laminography, in which 1 is an X-ray tube for generating X-rays, and 2 is an X-ray generating X-rays. The generation point is shown in FIG. 3 by simulating that X-rays are irradiated conically. Reference numeral 4 denotes an X-ray optical axis connecting the center position of the imaging surface and the X-ray generation point. Reference numeral 5 denotes a sample table, a rotating mechanism, a moving mechanism along the optical axis 4 of the X-ray for enlarging the geometry, a moving mechanism (not shown) perpendicular to the rotating surface for changing the tomographic plane, and A moving mechanism (not shown) in the parallel direction is provided on the rotating surface for changing the imaging position of the sample. Reference numeral 6 denotes a table rotation axis, which indicates the rotation center line of the rotation mechanism. Reference numeral 7 denotes a tomographic plane, which is a plane parallel to the imaging plane including the intersection of the optical axis 4 and the table rotation axis 6. 8 is a rotary table, 9 is an optical axis adjustment stage, 10 is an imaging surface, and is an X-ray fluorescent material, and has a function of converting the intensity of X-ray energy into visible light. Reference numeral 11 denotes a fluorescence multiplier that amplifies the light intensity. Reference numeral 12 denotes the rotation axis of the image rotation prism, and reference numeral 13 denotes the image rotation prism. Reference numeral 14 denotes an accumulation camera, which can obtain an X-ray tomographic image by the action of the rotation mechanism of the sample table, the image rotation prism, and the accumulation camera. Reference numeral 15 denotes a video signal, 16 denotes a control computer, which has an image capturing function, an image processing function, and a stage mechanism control function. A basic description of such an X-ray laminograph has been described in detail in the above-mentioned Japanese Patent Laid-Open Publication No. JP-A-Hei.
[0006]
A chart 20 as shown in FIG. 2 is attached to the sample table 5 for adjustment. This chart 20 is formed with a rectangular back surface pattern 22 formed on the front surface with a copper foil or the like, and on the back surface with a linear back surface pattern 22 that intersects at the center of the front surface pattern 21 with the same copper foil or the like. The overall material of the chart 20 is preferably the same as that of materials such as a printed circuit board to be normally inspected. A tomographic image is obtained by rotating the chart 20 rotating table and the image rotating prism. Next, this operation will be described according to the procedure shown in the flowchart of FIG.
[0007]
The tomographic image of the image of the chart 20 is taken into the control computer 16 in the same manner as in normal examination (image processing step 31). If the image at this time is the image 36 and the optical axis does not coincide with the rotation axis, the screen appears as if the periphery is thinly blurred. Next, binarization processing 32 is performed in accordance with a threshold value specified in advance to calculate the area of the detection region (area calculation processing 33). The binarized image at this time is 37. Reference numeral 361 denotes a boundary line indicating a threshold value. When the positions of the X-ray optical axis 4 and the table rotation axis 6 are misaligned, the area becomes larger than the real image area due to the principle of laminography. For example, when the square pattern surface of the surface pattern 21 shown in FIG. 2 is adjusted as the tomographic plane 7, a shadow spreads in all directions on the real image and a large area appears. This area becomes large when the positions of the X-ray optical axis 4 and the table rotation axis 6 are in the shift direction, and becomes small when they coincide with each other and becomes minimum when they coincide with each other regardless of the moving direction of the optical axis adjustment stage 9. . Reference numeral 38 denotes a screen when the deviation between the optical axis and the rotation axis is large, and reference numeral 40 denotes the binarized image. Reference numeral 39 denotes a screen when the deviation between the optical axis and the rotation axis is small, and reference numeral 41 denotes the binarized image. The control computer 16 stores the obtained area, moves the optical axis adjustment stage 9 by a fixed amount in the X direction plus side (optical axis adjustment stage X / Y axis movement step 34), and captures the second image (step 35). ) After binarization processing 321, the area (area calculation processing step 331) is obtained again. Next, if the area obtained in the determination step 42 is larger than the previous value (determination N), the stage 9 is moved in the X direction minus in the optical axis adjustment stage X / Y axis movement step 34. Move sideways. Such an operation is repeated while moving the optical axis adjustment stage 9. When the change in area due to the movement of the stage 9 in the X-ray direction shows a minimum value, the same processing is repeated in the Y direction. If the area change due to movement in the Y direction shows a minimum value, the amount of movement of one stage 9 is made smaller than the previous time to adjust in the X direction, and then this process is repeated in the Y direction to obtain a real image. This process is repeated until an area close to the value is obtained. Further, this process is performed for each stop position of the Z-axis stage (not shown) for each enlargement ratio. As described above, according to the present invention, all adjustment processing steps can be automatically controlled. It is also possible to record the adjustment result. Furthermore, it goes without saying that there is no human variation in the adjustment results.
[0008]
In the above embodiment, the rectangular front surface pattern 21 and the linear back surface pattern 22 are used as the pattern of the chart 20, but it goes without saying that the shape is not limited to this. In other words, the present invention captures a tomographic image of a predetermined chart in an electronic computer, processes the tomographic image, and sets the position of the rotary table rotation axis so that the area or the distance between two points approaches a minimum or specified value. The moving planar two-axis stage is moved under the control of the control computer, and this process is repeated so that the X-ray optical axis and the rotation axis of the rotary stage coincide with each other.
[0009]
【The invention's effect】
According to the present invention, it is possible to simplify the adjustment for matching the optical axis of the X-ray and the rotation center of the rotary shaft and to eliminate human unstable elements by the adjuster, and to maintain stable performance of the apparatus. .
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of a target X-ray tomographic imaging apparatus according to the present invention.
FIG. 2 is a structural diagram of an optical axis alignment chart used in the present invention.
FIG. 3 is a procedure of automatic adjustment shown in the embodiment of the present invention.

Claims (3)

A first rotation axis inclined with respect to the optical axis of the X-ray generated from the X-ray source;
First rotating means for rotating an object to be imaged fixed to the first rotating shaft;
A second rotating shaft disposed parallel to the first rotating shaft;
An X-ray image transmitted through the object rotated by the first rotating means is parallel to a tomographic plane including an intersection of the first rotation axis and the optical axis of the X-ray, and the X-ray light Means for converting an optical image having a plane including an intersection of an axis and the second rotation axis as an imaging surface;
Second rotating means for rotating the converted optical image about the second rotating shaft;
Using an X-ray detection system comprising a means for converting the optical image rotated by the second rotating means into an electrical signal as video information, and taking in the electronic signal as the video information into an electronic computer In the device with the function to
The first rotating means includes means for stopping the first rotating shaft in a stepwise manner in the optical axis direction of the X-ray, and for making the first rotating shaft coincide with the optical axis of the X-ray. Have the means to move,
The moving means fixes an object for adjustment to the first rotation axis, and the first rotation is performed by the movement stopping means based on information obtained from a tomographic image obtained by imaging the object for adjustment. An X-ray tomographic imaging apparatus, wherein the first rotation axis is adjusted to coincide with the optical axis of the X-ray at each position where the axis is moved stepwise in the X-ray optical axis direction. .   The X-ray tomographic imaging apparatus according to claim 1, wherein the information obtained from the captured tomographic image binarizes the tomographic image and detects a pattern on the object for adjustment based on the binary image. Then, the X-ray tomographic imaging apparatus is characterized in that the first rotation axis is adjusted so that the detected area is an area of the detected pattern and the area approaches a minimum value or a specified value. The object to be imaged fixed to the first rotation axis inclined with respect to the optical axis of the X-ray generated from the X-ray source is rotated by the first rotation means,
  An X-ray image transmitted through the object is converted into an optical image having a plane including an intersection of a second rotation axis arranged in parallel to the first rotation axis and the optical axis of the X-ray as an imaging surface. And
  Rotating the optical image around the second rotation axis;
  Converting the rotated optical image into an electrical signal;
  The electrical signal is captured by a computer as a tomographic image, image processed,
  An object for adjustment is fixed to the first rotating shaft,
  The first rotation axis and the optical axis of the X-ray for each stop position of the Z-axis stage that adjusts the enlargement ratio of the tomographic image based on information obtained from the tomographic image obtained by imaging the object for adjustment. And an X-ray tomography method for an X-ray tomography apparatus, wherein the X-ray tomography apparatus is adjusted so as to match.

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