JP3999399B2 - X-ray tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray tube used for X-ray inspection and analysis in the industrial and analytical fields, and more particularly to a target mounting portion of an open structure type transmission X-ray tube.
[0002]
[Prior art]
A technique for observing a fine internal structure by a nondestructive inspection method is required in each field. For example, for the development of semiconductor packages, mounting inspection, and quality assurance, an internal defect or the like is examined using an X-ray tube having a micro focus. This X-ray tube has an open structure and uses a thin tungsten plate as a target. A focused electron beam is injected into the target and X-rays generated there are emitted from the back side. In order to observe the fine structure of the inspection component, a small focal size is used.
FIG. 2 shows a cross-sectional structure of an open transmission X-ray tube. This X-ray tube is composed of a cathode part 50 (lower part), an anode part 51 (middle part), and a target part 52 (upper part). Each part is vacuum-tightly connected to each other by an O-ring. A vacuum chamber 5 is formed in which two stages are drawn by a pump (not shown). In the cathode portion 50, a high voltage cable is inserted into the high voltage cable insertion port 34, and a negative high voltage is applied to the electrode of the Wehnelt 2 and the filament 1. The anode part 51, the target part 52, and the exterior of the vacuum chamber 5 are kept at the ground potential. When a voltage is applied to the filament 1 from a high voltage cable (not shown) and current flows and is heated, thermoelectrons are emitted and accelerated toward the anode 4 to form an electron beam E. The anode portion 51 is obtained by incorporating the anode 4 and the pipe 6 into the lens holder 7. The electron beam E passes through the hollow portion of the pipe 6, is converged to a minute diameter electron beam E by the focusing coil 8 of the target portion 52, and enters the target 12. The target unit 52 incorporates the converging coil 8 in the cylinder of the pole piece 9 and is assembled with the target base 11K sandwiched between the upper part of the pole piece 10 (TOP) and the target holder 11, and the target base 52 A target 12 is mounted on the inside of the table 11K. For example, a tungsten thin film having a thickness of about 0.05 mm is used for the target 12. When the electron beam E enters the target 12, X-rays are emitted there. The radiation direction has directivity, and an X-ray beam in the transmitted direction is used. As the X-ray conditions of the X-ray tube, a tube voltage of 5 to 160 kV, a tube current of about 0.3 mA, and a focal size of about 1 to 200 μm are used.
A part of the kinetic energy of the electrons colliding with the target 12 is converted into X-rays, and the intensity is given by I = k · i · Z · V ² . Here, I is the X-ray intensity, k is a constant, i is the tube current, Z is the atomic number of the target element, and V is the acceleration voltage. The target 12 is fixed, and a foil or thin film having a constant thickness is attached to the target base 11K. The intensity of the generated X-ray has a wavelength distribution, and the distribution includes the acceleration voltage V, the material of the target 12, and the thickness. Determined by. Therefore, a material with good X-ray transmittance is used for the target base 11K.
[0003]
[Problems to be solved by the invention]
The conventional X-ray tube is configured as described above. However, when performing a transmission inspection of a sample of a thick metal material, an X-ray (hard X-ray) having a short wavelength and a high wavelength is increased by increasing the acceleration voltage V. ) To increase the transmission ability of the sample. When the acceleration voltage V is increased to increase the energy of the electron beam E, the surface of the target 12 is roughened or sputtered by the impact of the high-speed electron beam E, the X-ray conversion efficiency is lowered, and the X-ray wavelength distribution characteristics. Changes. Therefore, the target base 11K having the target 12 is exchanged according to the use state.
[0004]
In order to reduce the replacement frequency, an X-ray tube having a target holding mechanism as shown in FIG. 3 has been used recently. This X-ray tube is provided with an O-ring 16 centered on an X-ray beam central axis X at the upper part of a main body 18 and a target base 11K having a target 12 thereon so that the target 12 is on the inside. The target presser 13 having the presser opening 17 is set from above, the ring-shaped leaf spring 20a is sandwiched between the target bases 11K, and the fixing ring 14 is placed from above. The circumferential screw 15 is tightened, the target presser 13 is fixed by the fixing ring 14, and the target base 11K is fixed. The screw 15 is fixed in the mounting screw hole of the main body 18 through the laterally long hole 14 a of the fixing ring 14.
With this structure, the peripheral screw 15 is loosened and the fixing ring 14 is slid in the lateral direction of the laterally long hole 14a, so that the target base center T is separated from the X-ray beam central axis X as shown in FIG. By shifting by Δd, the new target 12 can be set at the position of the X-ray beam central axis X of the electron beam E. Further, by rotating the target base 11K slightly around the target base center T, the new target 12 can be set at the position of the X-ray beam central axis X of the electron beam E.
However, since the target holder 11K has the target presser 13 and the fixing ring 14 fixed by a plurality of screws 15 in the peripheral portion, in order to change the position where the electron beam E of the target 12 hits, It was necessary to work by loosening a plurality of screws 15. Moreover, the same operation | work was required also when replacing | exchanging the target base 11K which has the target 12. FIG. This operation has a problem that it takes time and labor to loosen or remove the screws 15 using a screwdriver.
[0005]
The present invention has been made in view of such circumstances, and the new target 12 can be easily set at the position of the X-ray beam central axis X of the electron beam E without much effort. The purpose is to provide a tube.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the X-ray tube of the present invention accelerates electrons emitted from the cathode filament to form an electron beam, converges it to collide with the anode target, and generates X-rays in the transmission direction. An X-ray tube of an open structure type, and an X-ray tube main body having a screw portion, a target presser capable of mounting the target eccentrically with respect to the central axis of the electron beam, and a screw of the X-ray tube main body And a fixing ring for fixing the target presser to the X-ray tube main body, and the target has a radius that is equal to or greater than the eccentric distance. A new target surface of the same target can be set on the central axis of the electron beam by loosening and rotating the target.
[0007]
The X-ray tube of the present invention is configured as described above, and can be attached to the target eccentrically with respect to the central axis of the electron beam. Since the shaft is fixed with the screw on the outer peripheral part of the X-ray tube main body through the fixing ring, the target becomes free just by rotating the fixing ring on the outer peripheral part, and the target can be rotated. And a new target can be set on the central axis of the electron beam.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the X-ray tube of the present invention will be described with reference to FIG. The X-ray tube of the present invention has the same structure for the cathode portion 50 and the anode portion 51 of the conventional X-ray tube shown in FIG. 1 includes an O-ring 16 at the top, and the center of the O-ring 16 is provided at a position eccentric from the X-ray beam central axis X and Δd, and meshes with the female screw of the fixing ring 14 at the periphery. A screw fitting portion 19 is provided. The target 12 is made of, for example, a tungsten thin film and is mounted on the back surface of a high melting point metal material having good X-ray transmission, for example, a beryllium target base 11K. The size of the thin film may be larger than the above-mentioned eccentricity Δd in radius and smaller than the inner diameter of the O-ring. A ring-shaped thin film having a predetermined width may be used at a position where the target electron beam E hits. In addition, since an X-ray tube for analysis requires a predetermined characteristic X-ray, a metal that generates the characteristic X-ray is selected and used as a thin film. The target presser 13 is provided at a position where the presser opening 17 faces the O-ring, that is, at a position where the center of the presser opening 17 is decentered by the X-ray beam central axis X and Δd. The structure is made slightly smaller than the diameter of the ring 16 and can uniformly press the target base 11K against the main body 18 through the O-ring 16. The ring-shaped leaf spring 20 is configured so that when the fixing ring 14 is rotated and the target presser 13 is tightened, the force is uniformly distributed over the entire circumference, and the target presser 13 is rotated when the fixing ring is rotated. Plays a role in making it difficult to rotate. The fixing ring 14 includes a screw fitting portion 19 that meshes with the male screw on the outer peripheral portion of the main body portion 18 inside the outer periphery.
[0009]
The surface of the target 12 is roughened or sputtered by the impact of the high-speed electron beam E, the X-ray conversion efficiency is lowered, and the X-ray wavelength distribution characteristic is changed. A procedure for setting or replacing the target 12 at a new position will be described.
First, the vacuum state in the main body 18 is opened by opening a leak valve (not shown) of an evacuation system, and the X-ray tube is brought to atmospheric pressure. Next, the outer peripheral portion of the fixing ring 14 is grasped, and the screw fitting portion 19 is rotated counterclockwise and loosened. When setting the target 12 at a new position, the target base 11K is slightly rotated (about 1 to 2 degrees). In this state, the fixing ring 14 is rotated clockwise to fix it. Then, the X-ray tube is evacuated by an evacuation system. When the target 12 is replaced, the screw fitting portion 19 is rotated and loosened counterclockwise, further rotated and removed, and the ring-shaped plate spring 20 is removed, and the target presser 13 is removed. Then, the target base 11K with the target 12 is replaced with a target base 11K with a new target 12. Then, the target presser 13 is placed, the ring-shaped leaf spring 20 is fitted, the fixing ring 14 is tightened, and the target base 11K is fixed. Then, the X-ray tube is evacuated by an evacuation system.
[0010]
In the above embodiment, the step where the target base 11K is set is provided on the main body 18 side as shown in FIG. 1, but this step is provided not on the main body 18 but on the target presser 13 side. It is also possible. The position of the target base 11K is more stable when it is provided on the main body 18 side. However, if it is provided on the target presser 13 side, the manufacturing process becomes easy.
[0011]
Furthermore, the relationship between the male screw and the female screw attached to the fixing ring 14 and the screw fitting portion 19 of the main body portion 18 may be provided in either one.
[0012]
【The invention's effect】
The X-ray tube of the present invention is configured as described above, and can be attached to the target eccentrically with respect to the central axis of the electron beam. Since the shaft is fixed with the screw on the outer peripheral part of the X-ray tube main body through the fixing ring, the target becomes free just by rotating the fixing ring on the outer peripheral part, and the target can be rotated. It is possible to set a new target on the central axis of the electron beam, and the work related to the target, the time is greatly reduced, and the work tool is not required.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an X-ray tube according to the present invention.
FIG. 2 is a view showing a cross section of a conventional open transmission X-ray tube.
FIG. 3 is a view showing a target holding portion of a conventional open transmission X-ray tube.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Filament 2 ... Wehnelt 3 ... High voltage receptacle 4 ... Anode 5 ... Vacuum chamber 6 ... Pipe 7 ... Lens holder 8 ... Converging coil 9 ... Pole piece 10 ... Pole piece 11 ... Target holder 11K ... Target base 12 ... Target 13 ... target presser 14 ... fixing ring 14a ... horizontal hole 15 ... screw 16 ... O-ring 17 ... presser opening 18 ... main body 19 ... screw fitting part 20 ... ring-shaped leaf spring 20a ... leaf spring 34 ... high-voltage cable insertion Slot 50 ... Cathode part 51 ... Anode part 52 ... Target part X ... X-ray beam central axis E ... Electron beam T ... Target base center

Claims (1)

  An open-structure X-ray tube that accelerates electrons emitted from a cathode filament to form an electron beam, converges it, collides with an anode target, and generates X-rays in the transmission direction. An X-ray tube main body, a target presser capable of mounting the target eccentrically with respect to the central axis of the electron beam, and a screw portion that fits into a screw portion of the X-ray tube main body, thereby A fixing ring for fixing the tool to the X-ray tube main body, the target having a radius equal to or larger than the eccentric distance, and the central axis of the electron beam by rotating the target by loosening the screw portion An X-ray tube characterized in that a new target surface of the same target can be set on the X-ray tube.

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