RU2112209C1 - Device for determination of coating thickness by x-ray-fluorescent method - Google Patents

Abstract

FIELD: electronic, clock, and jewelry industries; mechanical engineering. SUBSTANCE: device has blow-out X-ray tube 1 with magnetic focusing facility 2, mirror 3 with round hole in center for passage of radiation, collimator 4, detector, drum with filters, protective screen, and telecamera with optical system 8. Collimator 4 is positioned at minimum permissible distance from surface of specimen 9 to be measured, placed on stage 10 illuminated through light guides 11 secured in hinge support 12. Aluminium rod 13 rotated by electric motor with drive is positioned under collimator 4, close to the latter. When measuring, specimen picture observed on telecamera monitor is combined with picture of luminous graphical computer information. EFFECT: higher results of coating thickness determination. 2 cl, 1 dwg

Description

 The invention relates to non-contact methods for determining the thickness of coatings using x-ray or gamma radiation and can be used in the electronic, watch, jewelry industry and in mechanical engineering.

 Known devices [1 - 4] for determining the thickness of coatings using the X-ray fluorescence method, consisting of an X-ray source, a group of collimators, a detector, a microscope or a television camera for observing the measurement site of a sample using a mirror, which makes it possible to align the optical axis of the microscope with the longitudinal geometric axis of the X-ray beam in the field of measurement. The sample, the thickness of the coatings of which is measured, is installed on the object table, moving in three coordinates. In the device [1 and 2], where a microscope or a television camera with a monitor is used, the sample is illuminated by a source of visible light.

 The disadvantage of this device is that the detector during registration of fluorescent radiation also detects multiple scattered (background) radiation coming from structural elements, which affects the accuracy of the measurement. The X-ray detector has a finite resolution and poorly separates the fluorescent radiation of closely emitting elements.

 To solve this problem, special filters are used that are installed in front of the detector. The filter material is selected so that the filter absorbs radiation above the absorption jump of the filter material and weakly absorbs radiation below the absorption jump. Thus, first one of the closely standing elements is registered, and then (after changing the filter) another.

 The known device [1 and 2] provides for the use of filters, but their change does not occur automatically. In addition, in the known device, a conventional X-ray tube is used as an X-ray source, which requires sufficiently sophisticated diaphragm devices to form a narrow beam of X-rays.

 The proposed device allows to eliminate these disadvantages.

 This is achieved by the fact that in order to reduce the amount of multiply scattered radiation falling onto the detector, a protective screen is installed in the area of fluorescence emission registration, and a drum with filters is installed between the irradiated sample and installed with the possibility of rotation and automatic change of filters when the drum rotates. In addition, in the proposed device for producing an x-ray beam, a straight-through x-ray tube with magnetic focusing of the electron beam was used, which allows one to obtain a sufficiently narrow x-ray beam already at the first stage and also allows to achieve a high specific intensity of the x-ray radiation (x-ray beam). In the future, as in the known device [1 and 2], secondary collimation is provided, but in a simpler way.

 The drawing shows a block diagram of the proposed device.

 The device consists of a shooting X-ray tube 1 with a magnetic focusing device 2, a mirror with a round through hole in the center 3, mounted on a metal prism, the hole in which coincides with the hole in the mirror. Prism with a mirror is the primary radiation collimator. Mirror coating is applied to the outer surface of the mirror. This is followed by a collimator 4, a detector 5 with a measuring device, a drum with filters 6, protective screens 7, a television camera with an optical system 8 and a monitor. The measuring device, monitor, power supply unit of the x-ray tube are not shown in the drawing. The collimator 4 is located at the minimum allowable distance (4 - 5 mm) from the surface of the measured sample 9 mounted on the object table 10. X-rays from the tube 1 pass through the hole in the mirror 3 and fall on the collimator 4, made of material absorbing x-rays and transparent to visible light. A lead optical glass of a sufficiently large thickness was selected as the material for the collimator 4. The holes in the collimator are pierced by a laser beam. Then the holes are shaped and processed in such a way that their inner surface reflects x-rays of a certain wavelength. This ensures additional focusing of the x-ray beam at the measurement site. The ratio of the diameters of the holes in the collimator at the input and output of the x-rays is 2: 1, and due to additional focusing, a gain in the intensity of the x-ray beam by 20% is achieved.

 Between the irradiated sample and the X-ray detector there is a drum with filters installed, which can be rotated and automatically change filters when the drum rotates. The number of filters varies in the range 4 - 12. The excited fluorescent radiation of the coating materials passes through the filter 6 to the detector and is recorded by the measuring device.

 In the field of registration of fluorescence radiation (between the detector and the irradiated sample), a protective screen is installed to absorb the scattered radiation. The screen is made of chemically pure cadmium or other material, depending on the energy of the recorded fluorescence radiation. The screen allows you to minimize the impact on the detector of multiple scattered x-ray (background) radiation. Thereby, an increase in measurement accuracy is achieved.

The television camera 8 is located so that its optical axis coincides with the longitudinal geometric axis of the x-ray beam. A television camera using a mirror 3 with an opening for the passage of the x-ray beam looks at the sample through the hole of the collimator, through which the x-ray beam is focused on the surface of the measured sample. Thus, the optical axis of the camera and the longitudinal geometric axis of the x-ray beam are practically coaxial and directed perpendicular to the surface of the sample. In order that the image of the hole in the mirror is not superimposed on the exact place where the coating thickness is focused on the coating thickness, the mirror surface is located at an angle of 41 ^° 50 'to the longitudinal geometric axis of the x-ray beam and at an angle of 42 ^° 10' to the optical axis of the television camera. The use of an optical path with a shallow depth of field in the camera allows to increase the accuracy of installation of the measured object along the Z axis (vertical), i.e., to precisely set the distance from the tube to the measured object. The source of illumination in the area of installation and measurement of the sample are two optical fibers 11, mounted in hinged supports 12, which allow you to adjust the level of illumination of the measured surface area, to eliminate glare and shadows.

 Under the collimator 4, as close as possible to it, is an aluminum rod 13, rotating by means of an electric motor with a drive. The rod rotates perpendicular to the beam of X-rays incident on the measured sample and serves as a safety measure against the sample colliding with the glass collimator while moving the object table along the Z axis. A conventional knitting needle can be used as the rod. The position of the rotating rod, the plane of rotation of which intersects the optical axis of the optocoupler pair, is controlled in such a way that it stops in a position that does not interfere with the measurements.

 The object table 10 is mounted with the possibility of movement (in the X, Y, and Z directions) using small-pitch spindles on which disks with slots are mounted, perpendicular to which optocoupler pairs are installed LEDs and a photodiode fixing the coordinates of the object table (with an accuracy of 25 μm) .

 For the convenience of the operator on the same monitor screen, a combination of sample images with the image of text and graphic information with a computer is provided. At the same time, it is planned to construct, using a computer, a map of the relief of the surface of the coating from a sample of coordinates of fixed points at which the thickness of the coatings on the sample was measured.

The proposed device is implemented in the device "Thickness gauge RTF-3". Made several reverse samples. The analyzed coatings are gold, silver, nickel, copper, tin, platinum, palladium and other metal coatings, non-metals (paint coatings, polymer coatings, etc.). The minimum surface area of the sample with which information about the thickness of the coating is obtained is 0.1 mm ² . The range of measured thicknesses in microns is 0.01-100 depending on the coating material. Measurement error 0.05 - 5%. The coordinate table travel in mm horizontally - 100, vertically - 50. The accuracy of determining the position of the sample is 25 microns. The average time of one measurement is 10 s.

 The proposed device allows you to measure the thickness of the coatings on flat and convex surfaces of products, for example, on housings for integrated circuits, needles, micro-tools for medical and other purposes, a variety of products, the dimensions of which allow their installation on a measuring table.

 Sources of information.

 1. Fisher H., patent N 4597093 (USA), 06.24.1986, class. 378-50.

 2. Fisher H., patent N 4799246 (USA), 01/17/1989.

 3. Latter T., patent N 4648107 (USA), 03/06/1987.

 4. Spongz I.I. Sawyer B.E., patent N 4962518 (USA), 10/09/1990.

Claims (2)

 1. Device for determining the thickness of coatings by the X-ray fluorescence method, containing an X-ray source in the form of an X-ray tube, a mirror with an opening for the passage of an X-ray beam, a collimator transparent to visible light and located at the minimum allowable distance from the surface of the measured sample, an X-ray detector, subject a table for mounting the measured sample and a television camera with an optical system, characterized in that a sample placed between the irradiated m and an X-ray detector, a drum with filters installed with the ability to rotate and automatically change filters when the drum rotates, a protective screen installed in the field of registration of fluorescence radiation to absorb scattered radiation, disks with slots, spindles and optocoupler LED-photodiode pairs, with a collimator has a hole with a ratio of diameters at the input and output of x-ray radiation two to one, the object table is mounted with the possibility of movement using spindles, on which disks with slots are installed, perpendicular to which optocoupler pairs of LED - photodiode are installed, fixing the coordinates of the object table.  2. The device according to claim 1, characterized in that the protective screen is made of cadmium.