Collimator, application thereof and X-ray tomography system with collimator

Abstract

The invention relates to a collimator for an X-ray testing system, which is formed in the form of a plate with a lower side and an upper side, which is made of a material capable of effectively absorbing an X-ray beam, having a collimator opening, the collimator opening having an inlet surface on the lower side, which has a first surface centroid, and an outlet surface on the upper side, which has a second surface centroid, which has a second surface centroid, which has a second surface centroid, it has a second surface centroid. According to the invention, either the collimator opening is not irradiated by a central beam of a cone beam emitted by an X-ray tube of an X-ray tomography system in a state in which the collimator opening is mounted in the X-ray tomography system, or the first surface centroid and the second surface centroid form a collimation axis, and the collimation axis and the normal of the surface of the collimator form a non-zero collimation angle gamma. The invention further relates to an X-ray tomography system having a collimator according to the invention and to the use of a collimator according to the invention in an X-ray tomography system for reducing the dose load of a test object to be examined.

Description

Field of the Invention

[0001] The present invention relates to a plate-shaped collimator for an X-ray test system, which is made of a material capable of effectively absorbing an X-ray beam and has a collimator opening. The present invention also relates to an X-ray tomography system having such a collimator, and an effective beam is generated from a cone beam generated at the focus of an X-ray tube through the collimator. The present invention also relates to the application of such a collimator in an X-ray tomography system. Background Art

[0002] When testing flat large-area test objects such as circuit boards or wafers, tomographic scanning by means of X-ray radiation is usually used. Since various components with different components usually exist on the circuit board, it is usually necessary to approach each test position on the circuit board and perform multiple scans in sequence. X-ray tomography systems usually have a transmission X-ray tube. Since this type of tube is used, the focus can be as close as possible to the test object, and thus a high magnification can be achieved. In a transmission X-ray tube, the target that generates radiation usually forms the end of the X-ray tube. A cone beam with a large opening angle of, for example, 170° is generated by an X-ray tube of this structural type, and most of the cone beam usually irradiates the circuit board. The combination of many test positions, a very small distance from the focus, and the large opening angle of the cone beam irradiating the circuit board results in a high radiation load on the components to be tested on the circuit board. During the entire detection process, certain areas of the circuit board may be subjected to a high radiation load, and these areas are not visible in the X-ray image. Depending on the components in these areas, radiation damage may be caused to the components, especially in the areas located in the direction of the central beam of the cone beam. Summary of the Invention

[0003] The object of the present invention is to provide a method for significantly reducing the radiation load on components caused by the detection of other components during an X-ray detection process, especially during a tomographic imaging scan.

[0004] In the prior art, some solutions are known, such as using filters to reduce the entire radiation dose. However, such a filter reduces the dose of the entire cone beam, including the part required for examining a partial area of the circuit board of interest. The low-energy components in the spectrum are excessively filtered by the filter. Thereby, the dose load on the test object is reduced because the low-energy radiation component mainly brings a dose load to the test object and hardly adds any value to the image quality. However, filtering always results in the filtering of spectral components beneficial to the image quality. By filtering, the integration time or performance must always be increased to obtain the same image quality as when not filtered.

[0005] According to the present invention, this object is achieved by a collimator, a tomographic X-ray apparatus having such a collimator, and the use of such a collimator in an X-ray tomography system.

[0006] Then, this object is achieved by a collimator which is plate-shaped with a lower side and an upper side and is made of a material capable of effectively absorbing X-ray radiation. The collimator has a collimator opening, wherein the collimator opening has an entrance surface on the lower side, which has a first surface centroid, and an exit surface on the upper side, which has a second surface centroid. There are two possible design solutions to achieve this object. In the first design solution, the collimator opening is not irradiated by the central beam of the cone beam emitted by the X-ray tube of the X-ray tomography system in the state of being installed in the X-ray tomography system. In the second design solution, the first surface centroid and the second surface centroid form a collimation axis, and the collimation axis forms a non-zero collimation angle with the normal of the collimator surface. Thus, in both design solutions, only a small part of the entire X-ray beam emitted by the focus of the X-ray tube can pass through the collimator, and all components of the test object that are not at the alignment of the focus and the collimation opening (i.e., the test area) are not irradiated by X-rays, so that they are not damaged by a high X-ray radiation dose. Through the collimator opening, an X-ray beam with a very limited effective beam divergence angle can be obtained behind the collimator, and this X-ray beam only irradiates the test area of the test object during scanning.

[0007] An advantageous improvement of the present invention provides that both the entrance surface and the exit surface are circular, are elliptical, are trapezoidal, are quadrilateral, are pentagonal or are hexagonal. In a preferred variant with two symmetric trapezoids as the entrance and exit surfaces, if these surfaces are geometrically selected correctly, a truncated pyramid-shaped volume of the collimator opening can be created, which results in a rectangular beam as the effective beam behind the collimator, and it can illuminate the rectangular detector in the best way. In a variant with two ellipses as the entrance and exit surfaces, if these surfaces are geometrically selected correctly, a truncated conical volume of the collimator opening can be created, which results in a conical beam as the effective beam behind the collimator; this is preferred when there is a circular detector. Other variants represent collimator openings that are easy to manufacture, and these can also produce a good effective beam, although the efficiency is slightly lower.

[0008] Another advantageous improvement setting of the present invention is that the collimator opening does not include the centroid of the surface on the lower side of the collimator, and the second centroid of the exit surface is located at a more outward position on the collimator than the first centroid of the entrance surface. In this way, a collimator with mass in its central region can be created, so that the central beam of the X-ray tube is absorbed, avoiding direct irradiation of the test object by the rays, and the collimation axis extends outward in the collimator in the direction component in the beam direction. Thus, the central beam can irradiate the middle of the collimator in the installed state of the collimator, and the collimation axis of the collimator opening extends along the effective beam, and the effective beam forms a non-zero angle with the central beam, so that the effective beam is directed towards the test area arranged at the alignment of the focus and the collimator opening, avoiding unnecessary absorption of the effective beam at the edge part of the collimation opening, thereby avoiding the generation of interference effects.

[0009] Another advantageous improvement setting of the present invention is that the entrance surface of the collimator opening and the exit surface of the collimator opening each extend to the edge of the collimator. This shape is easy to manufacture because the collimator opening coincides with the edge of the collimator on one side.

[0010] Preferably, the collimator has a thickness of 0.1 mm to 5.0 mm.

[0011] Another advantageous improvement setting of the present invention is that the opening angle of the collimator opening is between 1° and 40°. In this way, a part can be selected from the entire X-ray beam emitted from the focus, and this part is sufficient to illuminate the test area of the test object to be inspected. The other uninspected areas of the test object will not be subjected to unnecessary radiation dose load.

[0012] Another advantageous improvement setting of the present invention is that the collimation angle is between 10° and 70°, preferably between 40° and 60°. Thereby, the test area can be inspected at a certain angle during the X-ray tomography process, so that the possible defects in the component can be well detected, and the different planes in the test area can be better separated.

[0013] Another advantageous improvement setting of the present invention is that the collimator is made of a material with a high average atomic number and high density, especially tungsten or tungsten alloy, and the material preferably has as large a dimensional stability as possible. This ensures effective shielding of all areas in the test object that do not need to be inspected, and the collimator can also be made very thin.

[0014] Another advantageous improvement setting of the present invention is that the collimator has more than one collimator opening. This means that multiple test areas of the test object outside the central beam of the X-ray tube can be inspected simultaneously.

[0015] Furthermore, this object can also be achieved by an X-ray tomographic imaging system according to the present invention. It has an X-ray tube, in particular a transmission X-ray tube, which has a focal point at which X-ray radiation in the form of a cone beam is generated. It also has a detector which is irradiated by the effective beam of the cone beam. A collimator according to the present invention is arranged between the focal point and the detector. The collimator opening of the collimator is oriented such that only a part of the X-ray radiation of the cone beam generated at the focal point passes through it, forming an effective beam, such that a test object to be tested, which can be introduced into the X-ray beam between the collimator and the detector, is exposed to X-ray radiation only in a test area. Thereby, the above advantages of the collimator and its application are achieved.

[0016] In an advantageous refinement of the X-ray tomographic imaging system according to the present invention, the detector is fully illuminated. As described above for the application, this can avoid a limited field of view. In the case of precise illumination, i.e., when the entire effective beam precisely illuminates the active surface of the detector, an optimal ratio can be obtained between the best possible radiation dose introduced into the test area and the minimum information loss. Preferably, all X-ray radiation from the effective beam irradiates the detector. Since this is practically almost impossible to achieve, the design should ensure that as small a proportion as possible of the effective beam does not irradiate the detector.

[0017] In another advantageous refinement of the X-ray tomographic imaging system according to the present invention, the normal to the collimator surface is parallel to the central beam of the cone beam. This makes the arrangement of the collimator in the X-ray tomographic imaging system very simple.

[0018] Finally, this object is also achieved by the application of a collimator according to the present invention in an X-ray tomographic imaging system, since this results in a significant reduction of the above-mentioned dose for all areas of the test object that are not the test area. In tomographic applications, the detector is usually positioned at as large an angle as possible with respect to the central beam emitted by the focal point. By the present invention, the collimator limits the angular range of the effective ray beam to the angular area where the detector is located. This reduces the dose load on all components that are not in the effective beam. This makes it possible to particularly significantly reduce the dose load on components located directly above the focal point during tomographic scans. Due to their position, these components would be irradiated more strongly when used without a collimator according to the present invention than the components located in the image during the scan. In particular, when testing sensitive test components, the present invention reduces damage to components such as semiconductor components, in particular wafers or semiconductor memories.

[0019] According to an advantageous improvement setting of the application according to the invention, the collimator is arranged between the focus of the X-ray tube and the test object to be tested, while the detector is located behind the test object in the beam direction, such that the part of the cone beam emitted by the X-ray tube passing through the collimator opening penetrates the test object in the test area to be examined and in particular completely illuminates the detector. By completely illuminating the detector, the field of view is not restricted and no information loss occurs.

[0020] Description of the Drawings

[0021] The further details and advantages of the present invention will now be explained in more detail using the embodiments shown in the drawings. The drawings show:

[0022] Figure 1 A schematic view of a known X-ray tomography system is shown,

[0023] Figure 2 A schematic view of an X-ray tomography system according to the invention is shown,

[0024] Figure 3 A first embodiment of a collimator according to the invention is shown in plan view and cross-section,

[0025] Figure 4 A second embodiment of a collimator according to the invention is shown in plan view and cross-section,

[0026] Figure 5 A third embodiment of a collimator according to the invention is shown in plan view and cross-section,

[0027] Figure 6 A fourth embodiment of a collimator according to the invention is shown in plan view and cross-section. Detailed Description of the Invention

[0028] Figure 1Shows a schematic example of the structure of an X-ray tomography system known from the prior art. It has an X-ray tube 4, here a transmission X-ray tube, which generates a cone beam 6 with a half-angle α of approximately 85° at its focal point 5. In the cone beam 6 there is a test object 2 in the form of a circuit board. The central beam 7 of the cone beam 6 is substantially perpendicular to the surface of the test object 2. Instead of examining the entire test object 2, only a partial area, called the test area 12, should be examined. The test area 12 is not in the direction of the central beam 7, but is inclined relative to the central beam at an observation angle γ. In the example shown, the observation angle is approximately 60°. In X-ray tomography, the larger the observation angle γ, the better the separation of the layers within the test object 2. The test area 12 is located between the focal point 5 and the detector 3. The rays of the cone beam 6 that emanate from the focal point 5 and illuminate the outermost part of the detector 3 form a field of view 8 that is formed around an observation axis 13, the observation axis being at an observation angle γ to the central beam 7 and illuminating the middle of the detector 3. The field of view 8 has a field-of-view opening angle δ of approximately 20°. During the examination of the test area, i.e., during the tomographic scan, the test area 12 must be located within the field of view 8. In the example shown, most of the test object 2 is located within the cone beam 6 and is subjected to a dose load, but is not within the field of view 8. Thus, the dose load is of no benefit to most parts of the test object 2. For X-ray sensitive components on the test object 2, such a high dose load can cause damage. The implementation of the tomographic scan is known from the prior art and is not the subject of the present invention and will therefore not be discussed further.

[0029] The present invention prevents such damage due to the high dose load. Figure 2 Shows a schematic example of the structure of an X-ray tomography system according to the present invention. According to Figure 2 The structure of the X-ray tomography system according to the present invention is the same, except for the collimator 1 according to the present invention arranged between the focal point 5 and the test object 2. Therefore, the same features have the same reference numerals and no further explanation will be given below. Instead, only the differences will be discussed in more detail.

[0030] The collimator 1 is plate-shaped and thus has a very small thickness compared to its extent in a plane. It has a lower side 14 facing the X-ray tube 4 and an upper side 17 facing away from the X-ray tube 4. In order to shield the X-ray radiation from the cone beam 6 as much as possible in all areas except the test area 12, the collimator is made of a material with a high atomic number, and if the collimator 1 is made of an alloy or various different materials, it should have a high average atomic number. A value above 26 is considered a high (average) atomic number. Additionally, the collimator 1 is made of a high-density material, preferably with a density exceeding 7,500 kg / m 3。To achieve simple production and low sensitivity to mechanical deformation, materials with as stable dimensions as possible are used. In the present case, the material used is a tungsten alloy, namely

[0032] The collimator 1 has a collimator opening 11, in addition to Figure 2 and can also be clearly seen from Figure 3 and Figure 4 of the two embodiments.

[0033] In the first embodiment according to Figure 3 the collimator opening 11 is configured in the shape of a truncated cone around the central axis. For this purpose, an entrance surface 15 exists on the lower side 14 of the collimator 1, which is elliptical and has a first surface centroid 16. An exit surface 18 exists on the upper side 17 of the collimator 1, which is also elliptical and has a second surface centroid 19. The geometric features of the entrance surface 15 and the exit surface 18 cooperate with each other such that the volume of the collimator opening 11 forms a truncated cone (the specific design solution is easily obtainable for those skilled in the art). The collimation axis 20 defined by the first surface centroid 16 and the second surface centroid 19 corresponds to the intermediate beam 10. Thereby, a conical effective beam 9 symmetric about the intermediate beam 10 is obtained behind the collimator 1, which illuminates the detector 3. If the detector 3 is circular, optimal illumination can be achieved.

[0034] The intermediate beam 10 corresponds to the observation axis 13 described above in Figure 1 and the opening angle, namely Figure 3 the semi-effective beam opening angle β shown in Figure 1The field of view angle δ therein. The quasi-right angle γ depends on the position of the detector 3. Thus, the farther the observation axis 13 is from the central beam 7, the larger the quasi-right angle. If an ideal layout is pursued, the size of the field of view angle δ depends on the size of the detector 3, the distance between the collimator 1 and the focus 5, and the distance between the collimator 1 and the detector 3. This means that different tomographic angles of scanning require different collimators 1, which must be replaced before performing tomographic scanning. To obtain the best results, different collimators 1 must also be used at different distances between the collimator 1 and the focus 5 and between the collimator 1 and the detector 3. The collimator opening 11 is formed outside the center of the collimator 1. Thus, the collimator 1 can be arranged at the center above the central beam 7 and shield X-ray radiation emitted not in the region of the effective beam 9 in all directions of the conical beam 6, thereby protecting the unexamined area of the test object 2. This minimizes the dose load on the part of the test object 2 that is not in the field of view 8 and thus not in the effective beam 9. By using the collimator 1 according to the present invention, when the radiation-sensitive components of the test object 2 are not in the field of view 8, they are subjected to significantly less load. Thus, multiple test positions on the test object 2 can be accessed without irradiating the entire test object 2 and subjecting all components to load. This is particularly advantageous in circuit boards having X-ray sensitive components.

[0035] Figure 4 The second embodiment of Figure 3 The first embodiment of Figure 3 This will not pose any difficulties to those skilled in the art. Thus, the volume of the collimator opening 11 now has a truncated pyramid shape instead of the Figure 3 truncated cone shape according to

[0036] Figure 5 Figure 14 shows a third embodiment having a rectangular inlet surface 15. However, different from the previous two embodiments, this inlet surface extends to the edge of the collimator 1, and thus one side thereof coincides with the edge of the collimator 1. Although this increases the dose load on the components in the outer region, the collimator opening 11 is easier to manufacture. Due to the geometric conditions, the mating of the outlet surface 18 with the inlet surface 15 is easy to determine for those skilled in the art.

[0037] Figure 6 Figure 15 shows a fourth embodiment, which is Figure 5The difference in the third embodiment is only that, in addition to the collimator opening on the right (represented by the entrance surface 15), there is another collimator opening on the left (represented by the entrance surface 15'). Thus, two different test regions 12 in the test object 2 can be examined simultaneously. The left entrance surface 15' has different dimensions from the right entrance surface 15, as can be clearly seen from the cross-sectional view from the right side, and thus there are also different collimation angles (right γ and left γ'), where in this embodiment, the right collimation angle γ is smaller than the left collimation angle γ'. This is only an example, and the actual design to be selected depends on the requirements of the corresponding application, especially where the test region 12 is located in the test object 2.

[0038] Instead of setting two collimator openings 11 as shown in Figure 6 , there can be more collimator openings 11, or the collimator openings 11 can be formed at other positions in the collimator 1. However, it should be noted that for each additional one of these collimator openings 11 according to Figure 5 and Figure 6 , the dose load in the external region increases.

[0039] List of reference numerals

[0040] 1 Collimator

[0041] 2 Test object

[0042] 3 Detector

[0043] 4 X-ray tube

[0044] 5 Focus

[0045] 6 Cone beam

[0046] 7 Central beam

[0047] 8 Field of view

[0048] 9 Effective beam

[0049] 10 Intermediate beam

[0050] 11 Collimator opening

[0051] 12 Test region

[0052] 13 Observation axis

[0053] 14 Lower side

[0054] 15, 15' Entrance surface

[0055] 16 Centroid of the first surface

[0056] 17 Upper side

[0057] 18 Exit surface

[0058] 19 Centroid of the second surface

[0059] 20 Collimation axis

[0060] α Half-angle

[0061] β Half effective beam divergence angle

[0062] γ, γ' Collimation angle

[0063] δ Field of view angle

Claims

1. A collimator (1) for an X-ray test system, The collimator is designed in a plate-like manner with a bottom side (14) and a top side (17). The collimator is made of a material that can effectively absorb X-ray beams. having a collimator opening (11), wherein the collimator opening (11) has an entrance surface (15) on the lower side (14) having a first surface centroid (16) and an exit surface (18) on the upper side (17) having a second surface centroid (19), The collimator opening (11) is not irradiated by the central beam (7) of the cone beam (6) emitted by the X-ray tube (4) of the X-ray tomography system when the collimator opening (11) is installed in the X-ray tomography system.

2. A collimator (1) for an X-ray test system, The collimator is designed in a plate-like manner with a bottom side (14) and a top side (17). The collimator is made of a material that can effectively absorb X-ray beams. having a collimator opening (11), wherein the collimator opening (11) has an entrance surface (15) on the lower side (14) having a first surface centroid (16) and an exit surface (18) on the upper side (17) having a second surface centroid (19), The first surface centroid (16) and the second surface centroid (19) form a collimation axis (20), and the collimation axis forms a non-zero collimation angle (γ) with a normal to the surface of the collimator (1).

3. The collimator (1) according to claim 1 or 2, wherein: Its inlet surface (15) and its outlet surface (18) are each circular, each elliptical, each quadrilateral, each pentagonal or each hexagonal.

4. The collimator (1) according to claim 1 or 2, wherein the volume of the collimator opening (11) is a truncated cone or a truncated pyramid, the respective central axis of which is the collimation axis (20).

5. A collimator (1) according to claim 1 or 2, wherein the collimator opening (11) does not include the surface centroid of the lower side (14) of the collimator (1) and the second surface centroid (19) of the exit surface (18) is located further outward on the collimator (1) than the first surface centroid (16) of the entrance surface (15).

6. The collimator (1) according to claim 1 or 2, wherein the entrance surface (15) of the collimator opening (11) and the exit surface (18) of the collimator opening (11) each extend to an edge of the collimator (1).

7. The collimator (1) according to claim 1 or 2, wherein: It has a thickness of 0.1 mm to 5.0 mm and / or the opening angle of the collimator opening (11) is between 1° and 40° and / or the collimation angle (γ) is between 10° and 70°, preferably between 40° and 60°.

8. The collimator (1) according to claim 1 or 2, wherein: It consists of a material having a high average atomic number and a high density, in particular tungsten or a tungsten alloy, wherein the material preferably has the greatest possible dimensional stability.

9. The collimator (1) according to claim 1 or 2, wherein: It has more than one collimator opening (11) according to claim 1 or 2.

10. An X-ray tomography system, comprising an X-ray tube (4), in particular a transmission X-ray tube, having a focal spot (5), at which X-ray radiation is generated in the form of a cone beam (6), a detector (3), which is irradiated by an effective beam (9) of the cone beam (6), and a collimator (1) according to any one of claims 1 to 9, arranged between the focal spot (5) and the detector (3), wherein the collimator opening (11) of the collimator (1) is oriented such that only part of the X-ray radiation of the cone beam (6) generated at the focal spot (5) passes through the collimator opening (11) to form the effective beam (9), so that a test object (2) to be tested, which can be introduced into the X-ray beam between the collimator (1) and the detector (3), is exposed to the X-ray radiation only in a test area (12).

11. The X-ray tomography system according to claim 10, wherein the detector (3) is fully illuminated, but as little as possible of the X-ray radiation of the active beam (9) does not irradiate the detector (3).

12. The X-ray tomography system according to claim 10 or 11, wherein the normal to the surface of the collimator (1) is parallel to the central beam (7) of the cone beam (6).

13. Use of a collimator (1) according to any one of claims 1 to 9 in an X-ray tomography system for reducing the dose exposure of a test object (2) to be examined, in particular a semiconductor component such as a wafer or a semiconductor memory.

14. The method according to claim 13 , wherein the collimator ( 1 ) is arranged between the focal point ( 5 ) of the X-ray tube ( 4 ) and the test object ( 2 ) to be tested, and the detector ( 3 ) is located behind the test object in the beam direction, so that the part of the cone beam ( 6 ) emitted by the X-ray tube ( 4 ) which passes through the collimator opening ( 11 ) penetrates the test object ( 2 ) in the test area ( 12 ) to be examined and in particular completely illuminates the detector ( 3 ).

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