RU2559167C1 - Multiple-energy x-ray imaging method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method includes taking a series of images at different anode voltages, the different anode voltages being achieved by taking images at different moments in time under the effect of alternating or pulsating anode voltage which powers the X-ray tube, wherein the method also includes taking a series of images at different anode current values, the different anode current values being achieved by taking images at different moments in time under the effect of alternating or pulsating anode current flowing through the X-ray tube; by processing the images, an image is obtained on which a given contrast is provided for all functional elements (units) of the microelectronic article with an non-uniform structure.

EFFECT: providing a multiple-energy X-ray imaging method, which broadens the capabilities of digital X-ray imaging of microelectronic articles with a non-uniform structure by improving reliability and speed of radiographic nondestructive inspection.

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Description

The invention relates to digital radiography and can be used for radiographic non-destructive testing, in particular for the detection of latent defects of microelectronic products with an inhomogeneous structure.

, их толщиной d_n и линейным коэффициентом ослабления µ_n (фиг. 1). В дальнейшем под уровнем неоднородности i-го функционального элемента будем пониматьMicroelectronics products with a heterogeneous structure contain heterogeneous functional elements (nodes) with a different number of layers $$n=\overline{\mathrm{one}...N}$$

, their thickness d _n and the linear attenuation coefficient µ _n (Fig. 1). In the future, by the level of heterogeneity of the i-th functional element we mean

where N _i is the number of layers in the i-th functional element.

Then the radiation intensity behind the ith functional element of the microelectronics product

where I ₀ is the radiation intensity on the surface of the control object (microelectronics products).

The radiation intensity should be understood as the energy of x-rays passing per unit time through a unit of surface perpendicular to the direction of the rays [Haraja F.N. General course of X-ray technology. M.-L.: Publishing house "Energy", 1966. - 568 p.]. Often the radiation of an x-ray source (tube) is characterized by energy, which is understood as the energy of x-rays passing through a given surface in a given time.

Known methods of dual energy radiography (see, for example, Jens Ricke, et al., Clinical results of Csl-detector-based dual-exposure dual energy in chest radiography // Eur Radiol (2003) 13. P. 2577-2582; Mazurov A .I. Recent advances in digital X-ray technology // Medical Technology, 2010. No. 5 (263). - P. 10), according to which, from two images taken at different anode voltages on the x-ray tube, images of soft and bone tissues are obtained by subtraction. . The use of methods with switching the anode voltage on the x-ray tube and sequentially obtaining two images enhances the wear of the x-ray tube due to the sharp switching of the anode voltage and the resulting transient processes and increases the study time, which leads to an increase in the dose received by the patient and a larger relative displacement of the images, worsening the result further image processing by subtraction.

In addition, the known methods are unacceptable for X-ray non-destructive testing of microelectronic products, which, as a rule, have more than two levels of heterogeneity, characterized by different thicknesses and linear attenuation coefficients.

The closest in technical essence to the claimed method and selected as a prototype is the multi-energy radiography method (RF patent No. 2366990 of 09/10/2009), which consists in the fact that a number of pictures are taken at different values of the anode voltage, different values of the anode voltage are achieved by recording pictures at different time points of the action of an alternating or pulsating anode voltage supplying the x-ray tube, and processing of the images, separate images of soft and bone tissues are obtained.

The disadvantage of the prototype method is the inability to use it for x-ray non-destructive testing of microelectronic products with a heterogeneous structure, due to the following reasons.

1. To ensure the required contrast of the x-ray image, it is necessary to generate radiation with different intensities I ₀ (different energies) according to the number of levels of inhomogeneities (1) of the control object. The prototype method provides the registration of individual images for two periods of time: one image will be taken at an effective X-ray energy corresponding to the average value of the anode voltage for the range U ₁ -U ₂ , and the second picture - at a different value of the effective X-ray energy corresponding to the average the value of the anode voltage for the range U ₃ -U ₄ . Subtraction of the obtained images will allow obtaining individual images of microelectronics products with only two levels of heterogeneity.

2. The dynamic range of variation of the intensity I ₀ (effective energy) of the x-ray radiation should provide the required contrast (or other selected quality indicator) of the x-ray image for all N levels of heterogeneity. As shown in the book [Haraja F.N. General course of X-ray technology. M.-L.: Publishing house "Energy", 1966. - 568 p.] On p. 43, with increasing current i _A flowing through the x-ray tube, the number of electrons decelerating at the anode increases, therefore, the radiation intensity I ₀ increases. In the prototype method, the change in the effective energy of x-ray radiation is achieved only by adjusting the anode voltage U _A , which does not allow to achieve the desired dynamic range and to provide with a given accuracy the radiation intensity with the required wavelength λ.

3. An important requirement for non-destructive testing is to increase its efficiency (reduce the implementation time) [Shmakov M. Choosing an x-ray control system. The view of the technologist // Technologies in the electronic industry, No. 4, 2006. - S. 60-68]. Obtaining individual images in the prototype method increases the time of their analysis.

The objective of the invention is to provide a method of multi-energy radiography, which allows to expand the capabilities of digital radiography on microelectronics products with a heterogeneous structure, to increase the reliability and efficiency of radiographic non-destructive testing.

In the claimed method, this problem is solved by the fact that in the multi-energy radiography method, which consists in the fact that a number of pictures are taken at different values of the anode voltage, different values of the anode voltage are achieved by recording pictures at different times of the action of an alternating or pulsating anode voltage supplying the x-ray tube additionally produce a series of images at different values of the anode current, different values of the anode current are achieved by recording images at different times During the action of the alternating anode current flowing through the x-ray tube, by processing the images, an image is obtained on which a predetermined contrast or other selected quality indicator is provided for all functional elements (nodes) of a microelectronics product with an inhomogeneous structure.

The listed new set of essential features allows you to achieve the specified technical result due to:

- accurate setting of the intensity (effective energy) of X-ray radiation with a given wavelength, ensuring the achievement of a given contrast (or other selected quality indicator) of all functional elements (nodes) of a microelectronics product with an inhomogeneous structure (increasing the reliability of control);

- the formation of a single image of such a product that meets the requirements for reliability and minimizes the time of its analysis (increased efficiency).

The analysis of the prior art has established that analogues that are characterized by a combination of features that are identical to all the features of the claimed method of multi-energy radiography are absent. Therefore, the claimed invention meets the condition of patentability "novelty."

Search results for known solutions in this and related fields of technology in order to identify features that match the distinctive features of the claimed object from the prototype showed that they do not follow explicitly from the prior art. The prior art also did not reveal the popularity of the impact provided by the essential features of the claimed invention, the transformations on the achievement of the specified technical result. Therefore, the claimed invention meets the condition of patentability "inventive step".

The claimed invention is illustrated by the following figures:

FIG. 1 - microelectronics product with a heterogeneous structure;

FIG. 2 - dependence of the intensity of bremsstrahlung x-rays from the anode voltage;

FIG. 3 - dependence of the intensity of bremsstrahlung x-rays from the anode current;

FIG. 4 - dependence of the intensity of bremsstrahlung x-rays from the anode voltage and the anode current.

To increase the reliability and efficiency of radiographic non-destructive testing of microelectronics products with a heterogeneous structure (Fig. 1), according to the proposed method, the following operations are performed.

, где λ_m - длина волны, отвечающая максимуму интенсивности.A number of images are produced at different values of the anode voltage U _A , for which M monochromatic radiation with corresponding intensities I ₀ (λ _m ) is used, $$(m=\overline{\mathrm{one}...M})$$

where λ _m is the wavelength corresponding to the maximum intensity.

In this case, different values of the anode voltage are achieved by recording images at different times of the action of an alternating or pulsating anode voltage supplying the x-ray tube. If the x-ray tube operates with a constant current strength i _A and a constant voltage U _A that does not change with time, then the distribution curve of the intensity density in the emission spectrum at each instant corresponds to the curve U _A1 (Fig. 2).

The intensity density in the spectrum should be understood as the ratio of the intensity of the rays enclosed in a narrow range of wavelengths of the spectrum to this interval [F. Haraja General course of X-ray technology. M.-L.: Publishing house "Energy", 1966. - 568 p.].

If the x-ray tube will operate at a constant current strength i _{A of} the same magnitude as in the first case, but with a pulsating anode voltage, then the intensity distribution in the radiation spectrum corresponding to the curve U _A1 will be only at one moment in time, when the changing voltage reaches its maximum (U _max = U _A1 ). At all other moments, the voltage will be lower and, therefore, the distribution curves of the radiation intensity will be different (curves U _A2 and U _A3 ) having a larger minimum wavelength and lower total radiation intensity. Therefore, in the case of a pulsating voltage, the intensity distribution curve in the emission spectrum will change in time. The minimum wavelength will be the same as in the case of a constant voltage U _A = U _max , but the maximum intensity will be shifted towards longer wavelengths, and the intensity of the entire radiation spectrum will become less.

A series of shots are taken at different values of the anode current i _A , while different values of the anode current are achieved by recording pictures at different times of the action of the alternating anode current flowing through the x-ray tube.

With an increase in the current flowing through the x-ray tube, the number of electrons braking at the anode increases, therefore, the radiation of the source increases. From the curves of the distribution of the intensity density in the radiation spectrum at various currents i _A (Fig. 3), it can be seen that with increasing current, the intensity of each wavelength of the spectrum increases so many times how many times the current increases. The shape of the intensity distribution curve remains unchanged, and the wavelength corresponding to the maximum intensity retains its value.

Further, by processing the images, an image is obtained on which a predetermined contrast is provided for all functional elements (nodes) of a microelectronics product with an inhomogeneous structure.

For this, the images of a microelectronics product with a heterogeneous structure, obtained at different values of the anode voltage U _A and anode current i _A , are divided into images of individual ix functional elements (nodes) by solving a system of equations

with respect to ρ _i (λ _m ). In expression (3), I (λ _m ) is the intensity of x-rays with a given wavelength λ _m , achieved by recording images at different times of the action of an alternating or pulsating anode voltage and anode current.

Despite the decrease in the signal-to-noise ratio in the divided images, the detection of defects in microelectronic products increases due to a decrease in “structural noise”, i.e. exceptions from images of interfering structures.

Images of individual functional elements (nodes), for which the desired contrast is achieved, are combined into an image on which a specified contrast is provided for all functional elements (nodes) of a microelectronics product with an inhomogeneous structure.

The possibility of solving the formulated problem of the invention was verified by the full-scale experiment of the described actions with the following initial data.

1. The radiation source was a portable X-ray machine for industrial use RAP-220.

2. As a control object, a single-layer printed pulse PC power supply unit was used.

3. When changing the anode voltage in the range from 80 to 180 kV and the anode current in the range from 3 to 5 mA, five images were recorded at the following values of the anode voltage and current:

1) U _A1 = 80 kV, i _A1 = 3 mA;

2) U _A2 = 100 kV, i _A2 = 3.5 mA;

3) U _A3 = 140 kV, i _A3 = 3.5 mA;

4) U _A4 = 40 kV, i _A3 = 4 mA;

5) U _A5 = 180 kV, i _A3 = 4 mA.

4. The energy of the x-ray radiation was measured by the photographic method described in the book [Haraja F.N. General course of X-ray technology. M.-L.: Publishing house "Energy", 1966. - 568 p. ] on p. 422-424.

The results of the assessment of the radiation intensity (Fig. 4) indicate the possibility of accurately setting the intensity I ₀ (U _A , i _A ) of X-ray radiation with a given wavelength and, as a result, the possibility of digital radiography of microelectronic products with an inhomogeneous structure.

The analysis of the obtained images showed that they with the required (for the task of detecting hidden defects) contrast are clearly distinguishable:

1) in the first picture - the circuit board tracks;

2) on the second - resistors, small capacitors and semiconductor elements (diodes and transistors);

3) on the third - microcircuits, connectors and electrolytic capacitors of large capacity;

4) on the fourth - output transformers;

5) on the fifth - input transformer.

Images of these functional elements using a specialized software tool were combined into an image on which a predetermined contrast was provided for all functional elements of a switching power supply. The generated image was presented to a specialist for visual analysis of hidden defects.

Thus, the experimental results confirm the possibility of solving the problem of the invention.

Claims (1)

The method of multi-energy radiography, which consists in the fact that a series of pictures are taken at different values of the anode voltage, different values of the anode voltage are achieved by recording pictures at different times of the action of an alternating or pulsating anode voltage supplying the x-ray tube, characterized in that a series of pictures are taken at different values of the anode current, different values of the anode current are achieved by recording images at different time points of the action of an alternating or pulsating of the anode current flowing through the X-ray tube, images processing, an image in which all the functional elements (nodes) of the product microelectronic structure is provided with an inhomogeneous predetermined contrast.

Images