WO2024210035A1

WO2024210035A1 - Image data correction method, and inspection device

Info

Publication number: WO2024210035A1
Application number: PCT/JP2024/012694
Authority: WO
Inventors: コァンチュガン; 大沢　雅之; 公明近田
Original assignee: 株式会社サキコーポレーション
Priority date: 2023-04-03
Filing date: 2024-03-28
Publication date: 2024-10-10

Abstract

Provided are an image data correction method and an inspection device capable of efficiently removing only images constituting noise, among images having periodicity, from transmission image data or cross-sectional image data.　A control unit 10 of an inspection device 1 executes: a first step for storing information (position and value) of pixels satisfying a first condition, among pixels of image data (transmission image data or cross-sectional image data) of an inspection target object 12; a second step for subjecting the image data to a Fourier transform to generate frequency image data; a third step for correcting the values of pixels satisfying a second condition, among pixels of the frequency image data; a fourth step for subjecting the corrected frequency image data to an inverse Fourier transform to generate corrected image data; and a fifth step for replacing the values of the pixels at the positions stored in the first step with the stored values, in the corrected image data.

Description

Image data correction method and inspection device

The present invention relates to a method for correcting image data and an inspection device.

In electronic boards, the soldered connection state (hereinafter referred to as "solder joint state") between electronic components (e.g., pins) and wiring on the board is difficult to determine by visual inspection, so tomosynthesis-type X-ray inspection equipment is used. In such electronic boards to be inspected, electronic components may be arranged three-dimensionally. For example, an IGBT (insulated gate bipolar transistor), which is one of the power module semiconductors, has a heat sink for heat dissipation mounted on the back side of the semiconductor chip (IGBT) because a large current flows through it. The heat sink for heat dissipation has multiple pin-shaped fins formed thereon, so when an electronic board is irradiated with X-rays to obtain transmission image data, the pins to be inspected and the heat sink for heat dissipation are imaged overlapping each other, and the heat sink becomes a pin shadow (noise) in the transmission image data or the three-dimensional image data (cross-sectional image data) reconstructed from the transmission image data. The fins of this heat sink are arranged side by side at a predetermined interval and have periodicity, so a method is used to remove the periodic shadow (noise) from the transmission image data or cross-sectional image data using Fourier transform and inverse Fourier transform (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 61-114149

However, when using Fourier transform or inverse Fourier transform to remove specific frequency components as noise from transmission image data or cross-sectional image data, there are cases where feature points of the object being inspected are also removed, or shapes (images) that do not actually exist are generated, making it impossible to obtain a clear image of the object being inspected.

The present invention has been made in consideration of these problems, and aims to provide an image data correction method that efficiently removes only noise images from images that have periodicity in image data (transmission image data or cross-sectional image data), and an inspection device in which this correction method is implemented.

In order to solve the above problem, the image data correction method according to the present invention is a method for correcting transmitted image data obtained by irradiating an object to be inspected with radiation emitted from a radiation source and detecting radiation that has passed through the object to be inspected, or three-dimensional image data reconstructed from the transmitted image data, and includes a first step of storing a position and a value in the image data as information on pixels that satisfy a first condition among the pixels of the image data, a second step of Fourier transforming the image data to generate frequency image data, a third step of correcting the values of pixels that satisfy a second condition among the pixels of the frequency image data and outputting corrected frequency image data, a fourth step of inverse Fourier transforming the corrected frequency image data to generate corrected image data, and a fifth step of replacing the pixel values at the positions stored in the first step in the corrected image data with the stored values.

Furthermore, in the image data correction method according to the present invention, it is preferable that the third step divides the frequency image data into a plurality of regions, and corrects the values of pixels in at least one region that satisfy the second condition.

Furthermore, in the image data correction method according to the present invention, it is preferable that the third step performs correction using a correction method based on the second condition set for each of the regions.

In addition, in the image data correction method according to the present invention, it is preferable that the first condition is a pixel having a value greater than a threshold value set as an upper limit value, and a pixel having a value less than a threshold value set as a lower limit value.

In addition, in the image data correction method according to the present invention, it is preferable that the first condition is a pixel in a specified area within the image data.

The inspection device according to the present invention also includes a radiation source, a holder for holding an object to be inspected, a detector for detecting radiation from the radiation source that has passed through the object to be inspected and acquiring transmission image data of the object to be inspected, and a control unit, and the control unit corrects two or more pieces of transmission image data acquired by changing the relative positions of the radiation source, the holder, and the detector, or three-dimensional image data reconstructed from the transmission image data, using the image data correction method described above, and inspects the object to be inspected using the corrected image data.

The image data correction method according to the present invention and the inspection device in which this correction method is implemented can efficiently remove only the noise images from the periodic images in the image data (transmission image data or cross-sectional image data).

FIG. 1 is an explanatory diagram for explaining a configuration of an inspection device according to an embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining each functional block of a control unit of the inspection device. 11 is a flowchart for explaining the inspection process in the above-mentioned inspection device, in which (a) shows the selection process of an imaging region (FOV), and (b) shows the image acquisition and judgment process for the selected imaging region (FOV). 11 is a flowchart for explaining an image correction process in the image acquisition and determination process. 11 is an explanatory diagram for explaining a method of setting a correction region in frequency image data. FIG.

Below, a preferred embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the inspection device 1 according to this embodiment is configured to have a control unit 10, which is made up of a processing device such as a personal computer (PC), a monitor 11, and an imaging unit 32. The imaging unit 32 also has a radiation generator 22, a substrate holding unit 24, a detector 26, a radiation quality changing unit 14, a radiation generator driving unit 16, a substrate holding unit driving unit 18, and a detector driving unit 20.

The radiation generator 22 is a device (ray source) that generates radiation such as X-rays, and generates radiation by colliding accelerated electrons with a target such as tungsten or diamond. Note that, although the radiation in this embodiment is described as being X-rays, this is not limiting. For example, the radiation may be alpha rays, beta rays, gamma rays, ultraviolet rays, visible light, or infrared rays. The radiation may also be microwaves or terahertz waves.

The board holding unit 24 holds the electronic board, which is the object under inspection 12. The object under inspection 12 held by the board holding unit 24 is irradiated with radiation generated by the radiation generator 22, and the radiation that has passed through the object under inspection 12 is detected by the detector 26 to capture an image. Hereinafter, the radiation transmission image of the object under inspection 12 captured by the detector 26 will be referred to as a "transmission image." As will be described later, in this embodiment, the board holding unit 24, which holds the electronic board, which is the object under inspection 12, and the detector 26 are moved relative to the radiation generator 22 to obtain multiple transmission images, and a reconstructed image (cross-sectional image), which is a three-dimensional image, is generated from these transmission images.

The transmission image captured by the detector 26 (transmission image data, which is data of the transmission image output from the detector 26) is sent to the control unit 10, and is reconstructed into image data including the three-dimensional shape of the solder at the joint portion using a known technique such as the Filtered Backprojection method (FBP method). The reconstructed image data and transmission image data are stored in a storage in the control unit 10 (for example, the storage unit 34 described later) or an external storage (not shown). Hereinafter, image data obtained by extracting one cross section of the three-dimensional shape calculated based on the transmission image data is called a cross-sectional image (cross-sectional image data). In addition, a set of one or more cross-sectional image data is called "three-dimensional image data" or "reconstructed image data". In other words, image data obtained by cutting out an arbitrary cross section from the reconstructed image data is cross-sectional image data. Such reconstructed images and cross-sectional images are output to the monitor 11. In addition to the reconstructed images and cross-sectional images, the monitor 11 also displays the inspection results of the solder joint state described later. Hereinafter, the reconstructed image in this embodiment is also called "planar CT" because it is reconstructed from a planar image (transmission image data) captured by the detector 26 as described above.

The radiation quality change unit 14 changes the radiation quality generated by the radiation generator 22. The radiation quality is determined by the voltage (hereafter referred to as "tube voltage") applied to accelerate the electrons to be collided with the target, and the current (hereafter referred to as "tube current") that determines the number of electrons. The radiation quality change unit 14 is a device that controls the tube voltage and tube current. This radiation quality change unit 14 can be realized using known technology such as a transformer or rectifier.

Here, the quality of radiation is determined by the brightness and hardness of the radiation (spectral distribution of radiation). Increasing the tube current increases the number of electrons that collide with the target, and the number of radiation photons generated. As a result, the brightness of the radiation increases. For example, some components such as capacitors are thicker than other components, and in order to capture a transmission image of these components, it is necessary to irradiate them with radiation of high brightness. In such cases, the brightness of the radiation is adjusted by adjusting the tube current. Also, increasing the tube voltage increases the energy of the electrons that collide with the target, and the energy (spectrum) of the generated radiation increases. In general, the greater the energy of radiation, the greater its penetrating power into materials, and the less likely it is to be absorbed by materials. A transmission image captured using such radiation has low contrast. For this reason, the tube voltage can be used to adjust the contrast of a transmission image.

The radiation generator driving unit 16 has a driving mechanism such as a motor (not shown) and can move the radiation generator 22 up and down along axis A passing through its focal point (axis (optical axis) passing through the center of the radiation direction of the radiation emitted from the radiation generator 22, the direction of this axis being referred to as the "Z-axis direction"). This makes it possible to change the distance between the radiation generator 22 and the inspected object (electronic board) 12 held by the board holding unit 24 to change the irradiation field and change the magnification ratio of the transmitted image captured by the detector 26. The position of the radiation generator 22 in the Z-axis direction is detected by the generator position detection unit 23 and output to the control unit 10.

The detector driving unit 20 also has a driving mechanism such as a motor (not shown) and rotates the detector 26 along the detector rotation track 30. The substrate holding unit driving unit 18 also has a driving mechanism such as a motor (not shown) and moves the substrate holding unit 24 in parallel on the plane on which the substrate rotation track 28 is provided. The substrate holding unit 24 is configured to rotate on the substrate rotation track 28 in conjunction with the rotation of the detector 26. This makes it possible to capture multiple transmission images with different projection directions and projection angles while changing the relative positional relationship between the test object 12 held by the substrate holding unit 24 and the radiation generator 22. In the inspection device 1 according to this embodiment, the area on the test object 12 where a transmission image can be acquired is determined by the size of the area where the detector 26 detects radiation and the relative positions of the radiation generator 22, the test object 12 (substrate holding unit 24), and the detector 26. The area where this transmission image can be acquired (imaging area) is called the "FOV (field of view)".

The rotation radius of the board rotation orbit 28 and the detector rotation orbit 30 is not fixed, but can be freely changed. This makes it possible to arbitrarily change the irradiation angle of the radiation irradiated to the electronic board substrate, which is the inspected object 12, and the components attached to this substrate. The orbital plane of the board rotation orbit 28 and the detector rotation orbit 30 is perpendicular to the Z-axis direction described above, and if the directions perpendicular to this orbital plane are the X-axis direction and the Y-axis direction, the positions of the board holding part 24 in the X-axis direction and the Y-axis direction are detected by the board position detection part 29 and output to the control part 10, and the positions of the detector 26 in the X-axis direction and the Y-axis direction are detected by the detector position detection part 31 and output to the control part 10.

The control unit 10 controls all operations of the inspection device 1 described above. Below, the main functions of the control unit 10 are explained using FIG. 2. Although not shown, input devices such as a keyboard and a mouse are connected to the control unit 10.

The control unit 10 includes a memory unit 34, an imaging processing unit 35, a cross-sectional image generating unit 36, a board inspection surface detecting unit 38, a pseudo cross-sectional image generating unit 40, and an inspection unit 42. Although not shown, the imaging processing unit 35 of the control unit 10 also has the function of an imaging control unit that controls the operation of the radiation quality changing unit 14, the radiation generator driving unit 16, the board holding unit driving unit 18, and the detector driving unit 20. Furthermore, each of these functional blocks is realized by the cooperation of hardware, such as a CPU that executes various arithmetic processes, and a RAM that is used as a work area for storing data and executing programs, and software. Therefore, these functional blocks can be realized in various ways by combining hardware and software.

The memory unit 34 stores information such as the imaging conditions for capturing a transmission image of the electronic board and the design of the electronic board to be inspected. The memory unit 34 also stores image data such as transmission images and reconstructed images (cross-sectional images, pseudo-cross-sectional images) of the electronic board, as well as the inspection results of the inspection unit 42 described below. The memory unit 34 also stores information for driving the radiation generator driving unit 16, the board holder driving unit 18, and the detector driving unit 20 (e.g., the speed at which the radiation generator driving unit 16 drives the radiation generator 22, the speed at which the board holder driving unit 18 drives the board holder 24, and the speed at which the detector driving unit 20 drives the detector 26).

The imaging processing unit 35 drives the radiation generator 22, the substrate holding unit 24, and the detector 26 using the radiation generator driving unit 16, the substrate holding unit driving unit 18, and the detector driving unit 20 to image the specimen 12 held by the substrate holding unit 24, obtain transmission image data, and generate reconstructed image data (cross-sectional image data) from the transmission image data. The method of obtaining the transmission image data (capturing the transmission image) and generating the reconstructed image data (cross-sectional image data) by this imaging processing unit 35 will be described later.

The cross-sectional image generating unit 36 generates reconstructed image data (cross-sectional image data) based on the multiple transmission image data acquired from the storage unit 34. This can be achieved using known techniques, such as the FBP method or the maximum likelihood estimation method. Different reconstruction algorithms result in different properties of the reconstructed image data and different times required for reconstruction. Therefore, multiple reconstruction algorithms and parameters used in the algorithms may be prepared in advance and the user may select one. This provides the user with the freedom to choose, such as prioritizing a shorter reconstruction time or prioritizing better image quality even if it takes more time. Each of the generated cross-sectional image data is stored in the storage unit 34 together with attribute information, such as information that determines the position of each cross-sectional image data in the Z-axis direction and the positions (coordinates) of pixels in the cross-sectional image data in the X-axis direction and the Y-axis direction.

The board inspection surface detection unit 38 identifies image data (cross-sectional image data) that shows the surface to be inspected on the electronic board, which is the object to be inspected 12, (e.g., the surface of the electronic board), from among the multiple cross-sectional image data generated by the cross-sectional image generation unit 36. Hereinafter, the cross-sectional image (cross-sectional image data) that shows the inspection surface of the electronic board will be referred to as the "inspection surface image (inspection surface image data)."

The pseudo cross-sectional image generating unit 40 images the area of the board thicker than the cross-sectional image by stacking a predetermined number of consecutive cross-sectional images (cross-sectional image data) for the cross-sectional image data generated by the cross-sectional image generating unit 36. The number of cross-sectional images to be stacked is determined by the thickness of the area of the board shown by the cross-sectional image (hereinafter referred to as the "slice thickness") and the slice thickness of the pseudo cross-sectional image. For example, if the slice thickness of the cross-sectional image is 50 μm and the height (e.g., 500 μm) of a BGA solder ball (hereinafter simply referred to as "solder") is to be used as the slice thickness of the pseudo cross-sectional image, then 500/50 = 10 cross-sectional images should be stacked. At this time, the inspection surface image data identified by the board inspection surface detecting unit 38 is used to identify the position of the solder.

The inspection unit 42 inspects the solder joint condition based on the cross-sectional image data generated by the cross-sectional image generation unit 36, the inspection surface image data identified by the board inspection surface detection unit 38, and the pseudo cross-sectional image data generated by the pseudo cross-sectional image generation unit 40. Since the solder that joins the electronic board and the component is located near the board inspection surface, by inspecting the inspection surface image data and the cross-sectional image data that shows the area on the radiation generator 22 side relative to the inspection surface image data, it is possible to determine whether the solder is properly joining the board and the component.

Here, "solder joint condition" refers to whether or not an appropriate conductive path is formed when the electronic board and the component are joined by solder. Inspection of the solder joint condition includes bridge inspection, molten state inspection, and void inspection. "Bridge" refers to an undesirable conductive path between conductors caused by solder joining. "Melted state" refers to a state in which the joint between the electronic board and the component is insufficient due to insufficient melting of the solder, that is, whether or not there is a so-called "floating" state. "Void" refers to a defect in the solder joint caused by air bubbles in the solder joint. Therefore, the inspection unit 42 includes a bridge inspection unit 44, a molten state inspection unit 46, and a void inspection unit 48.

The operation of the bridge inspection unit 44, molten state inspection unit 46, and void inspection unit 48 will be described in detail later, but the bridge inspection unit 44 and void inspection unit 48 inspect bridges and voids, respectively, based on the pseudo cross-sectional image data generated by the pseudo cross-sectional image generation unit 40, and the molten state inspection unit 46 inspects the molten state of the solder based on the inspection surface image data identified by the board inspection surface detection unit 38. The inspection results in the bridge inspection unit 44, molten state inspection unit 46, and void inspection unit 48 are stored in the memory unit 34.

FIGS. 3 and 4 are flowcharts showing the flow (inspection process) of capturing a transmission image (acquiring transmission image data), generating reconstructed image data (cross-sectional image data), identifying inspection surface image data, and inspecting the solder joint state. The process in this flowchart starts, for example, when the control unit 10 receives an instruction to start the inspection from an input device (not shown).

When the inspected object 12 is carried into the inspection device 1 and the inspection is started, the imaging processing unit 35 of the control unit 10 sets the irradiation field of radiation emitted from the radiation generator 22 by the radiation generator driving unit 16 (the imaging area where the radiation is irradiated to obtain the transmission image data of the field of view FOV described above) (step S100) as shown in Fig. 3(a), and starts the image acquisition and judgment process (step S102). Note that when there are multiple imaging areas (FOV) on the inspected object 12, the imaging areas (FOV) are selected and set in a predetermined order.

When the image acquisition and determination process of step S102 is started, the image capture processing unit 35 of the control unit 10 executes a transmission image capture and reconstructed image generation process as shown in FIG. 3B, captures the test object 12 to acquire transmission image data, and generates reconstructed image data using the transmission image data (step S1020). Specifically, in the transmission image capture and reconstructed image generation process S1020, the image capture processing unit 35 of the control unit 10 moves the substrate holder 24 by the substrate holder drive unit 18, and moves the detector 26 by the detector drive unit 20 to change the imaging position, while setting the radiation quality of the radiation generator 22 by the radiation quality change unit 14, irradiates the current imaging field (FOV) of the test object 12 with radiation, acquires transmission image data, and stores it in the storage unit 34. In addition, the cross-sectional image generation unit 36 of the control unit 10 reads out a plurality of transmission image data from the storage unit 34, generates reconstructed image data (cross-sectional image data) using the transmission image data, and stores it in the storage unit 34.

The movement path of the substrate holder 24 by the substrate holder driver 18 and the movement path of the detector 26 by the detector driver 20 when acquiring the transmission image data are set in advance in the substrate holder driver 18 and the detector driver 20 by reading information stored in the memory 34 or inputting information from an input device. The position of the radiation generator 22 in the Z-axis direction is also set in advance in the radiation generator driver 16 by a similar method. In this case, the substrate holder driver 18 and the detector driver 20 may move the substrate holder 24 and the detector 26 to a desired position, and the substrate holder 24 and the detector 26 may be stopped at a position where the transmission image data is acquired before acquiring the transmission image data, or the substrate holder driver 18 and the detector driver 20 may move the substrate holder 24 and the detector 26 to a desired position and acquire the transmission image data. The acquired transmission image data is stored in the memory 34 for each imaging area (FOV).

The board inspection surface detection unit 38 of the control unit 10 receives the transmission image data or the reconstructed image data (cross-sectional image data) from the cross-sectional image generation unit 36, and executes a board inspection surface detection/pseudo cross-sectional image generation process to identify the inspection surface image from the received data (step S1040). Here, the storage unit 34 stores in advance cross-sectional image data (called "reference image data") of the board inspection surface of a normal inspected object 12 that has no abnormalities in the solder joint state, etc. In the board inspection surface detection/pseudo cross-sectional image generation process S1040, the board inspection surface detection unit 38 of the control unit 10 compares the reference image data with each of the cross-sectional image data generated in step S1020, identifies the cross-sectional image data that most closely matches the reference image data as the inspection surface image data, stores the identified cross-sectional image data (inspection surface image data) in the storage unit 34, and stores the position in the Z-axis direction in the storage unit 34 as the position of the board inspection surface in the current field of view FOV. As a method for identifying the cross-sectional image data that most closely matches the reference image data from among the cross-sectional image data, for example, a phase-only correlation method can be used to quickly determine the coincidence rate regardless of positional deviation. In addition, the pseudo cross-sectional image generating unit 40 of the control unit 10 generates pseudo cross-sectional image data based on the identified inspection surface image data and the Z-direction position of the substrate inspection surface, and stores the data in the storage unit 34.

Note that here, multiple cross-sectional image data are generated as reconstructed image data from the transmission image data, and reference plane image data is determined and pseudo cross-sectional image data is generated for the cross-sectional image data. However, each time a piece of cross-sectional image data is generated as reconstructed image data, the reference plane image data may be determined and pseudo cross-sectional image data may be generated, and the next cross-sectional image data may be generated.

Next, the imaging processing unit 35 of the control unit 10 performs image correction processing on the cross-sectional image data generated by the cross-sectional image generating unit 36, the inspection surface image data identified by the board inspection surface detecting unit 38, and the pseudo cross-sectional image data generated by the pseudo cross-sectional image generating unit 40 (collectively referred to as "cross-sectional image data") (step S1060).

As shown in FIG. 4, the image processing unit 35 of the control unit 10 judges whether correction is required for the cross-sectional image data of the current imaging field (FOV) (step S1061). If there is a heat sink under the pin to be inspected, as in the above-mentioned IGBT, the heat sink is also reflected in the cross-sectional image data and becomes noise (shadow) on the solder state of the pin to be inspected. Therefore, in order to improve the inspection accuracy, it is necessary to remove the noise of the heat sink by correction processing. Whether or not correction processing is required may be judged from information such as the design of the electronic board, which is the inspected object 12, or information on whether or not correction is required for each imaging field (FOV) may be set in advance. If it is judged that correction of the cross-sectional image data is required (step S1061: Y), the image processing unit 35 of the control unit 10 selects one of the multiple cross-sectional image data (cross-sectional image data, inspection surface image data, pseudo cross-sectional image data) selected in step S1040 and reads it from the storage unit 34 (step S1062).

The image processing unit 35 of the control unit 10 saves the information of the selected pixels of the cross-sectional image data by storing the position in the cross-sectional image data and the value (brightness value) of the pixel that satisfies the first condition in the memory unit 34 (step S1063). Here, the first condition is a pixel with a value greater than a threshold value set as an upper limit value and a pixel with a value smaller than a threshold value set as a lower limit value. In the inspection device 1 of this embodiment, Fourier transform and inverse Fourier transform are used to remove images of shapes arranged at a predetermined interval, such as heat sinks (periodic noise), from the cross-sectional image data. At this time, if the frequency component corresponding to the shadow of the heat sink is erased from the frequency image data obtained by Fourier transforming the cross-sectional image data, when the corrected frequency image data is inverse Fourier transformed, a shape (image) that does not actually exist may be generated in a part having a frequency component higher than that frequency component. Therefore, before performing the Fourier transform, the pixel values of the high frequency parts of the cross-sectional image data are evacuated, and after correction by the Fourier transform and inverse Fourier transform, the evacuated values are returned to their original positions (pixels), thereby preventing the formation of an image (the generation of noise) by the Fourier transform. Here, to select pixels in the high frequency parts, the first condition is to select information on pixels with values greater than a threshold value set as an upper limit value and pixels with values smaller than a threshold value set as a lower limit value.

Alternatively, pixels in a specified region in the cross-sectional image data may be set as the first condition. In the cross-sectional image data, portions that do not include periodic noise such as a heat sink do not require correction (noise removal) using Fourier transform and inverse Fourier transform, so such regions, i.e., pixels specified at coordinates where it is known in advance that noise removal is not required, can be set as the first condition, and can be set aside in advance so as not to be affected by correction. Note that, as the first condition, both pixels with values greater than the threshold value set as the above-mentioned upper limit value and pixels with values less than the threshold value set as the lower limit value, and pixels in a specified region in the cross-sectional image data (pixels specified at coordinates where it is known in advance that noise removal is not required), or other conditions may be set.

Next, the imaging processing unit 35 of the control unit 10 performs a Fourier transform on the selected cross-sectional image data to generate frequency image data (step S1064). This Fourier transform detects how much the pixel value (brightness value) changes within a unit pixel, and converts the transmission image data in the spatial domain into frequency image data in the spatial frequency domain; specifically, a two-dimensional Fourier transform is performed on the cross-sectional image data to generate frequency image data.

Then, the imaging processing unit 35 of the control unit 10 corrects the frequency image data. If the frequency components corresponding to the image of the heat sink are removed from the entire frequency image data, then when the corrected frequency image data is inverse Fourier transformed, images that do not need to be deleted may be deleted from the corrected cross-sectional image data, or images that do not actually exist may be generated. Therefore, the inspection device 1 according to this embodiment is configured to divide the frequency image data into multiple regions (called "correction regions") and perform correction on at least one of these correction regions.

FIG. 5 shows the case where frequency image data Ip is divided into four regions: correction region A1 divided by boundary Lb1, correction regions A2a and A2b divided by boundary Lb2, and the remaining correction region A3. The image capture processing unit 35 of the control unit 10 selects one correction region from these multiple correction regions (step S1065), and corrects pixels within the correction region that satisfy a condition set for the correction region (this condition is called the "second condition") (step S1066). Here, the second condition is pixels with frequency components within a specified range, and the correction involves removing the value (setting it to 0). In other words, the shadow of the heat sink can be removed by removing the pixel value of the frequency component that takes into account the placement interval of the heat sink, etc.

When the image capture processing unit 35 of the control unit 10 completes the correction of the correction area selected in step S1065, it determines whether or not there is a next correction area (step S1067), and if it determines that there is a next correction area (step S1067: Y), it returns to step S1065 to select the next correction area and repeats the above-mentioned steps S1066 and S1067.

Note that while FIG. 5 shows a case where boundaries Lb1 and Lb2 are arranged to overlap, these boundaries do not have to overlap. The second condition may be changed for each correction area. For example, the range of frequency components to be removed may be changed between correction area A1 and correction areas A2a and A2b, that is, the parameters of the second condition may be changed. The content of the second condition (the method of determining whether or not to perform correction) may be changed such that pixels within a predetermined frequency component range are removed in correction area A1, and pixels with frequency components greater than a predetermined threshold value are removed in correction areas A2a and A2b. Alternatively, the second condition may be configured such that correction area A3 is not corrected.

Furthermore, if there is a correction target in the current imaging field (FOV) (for example, there is a heat sink), information regarding the position and shape of the heat sink (what shape the heat dissipation fins are and at what intervals) is clear from the design information of the electronic board, so the size and position of the correction area and the correction conditions for each correction area (second conditions and their parameters) may be determined in advance or may be configured to be selected during inspection. Furthermore, the position of the correction area in the frequency image data and the correction method may be determined by learning using AI.

If the image capture processing unit 35 of the control unit 10 determines that there is no next correction region (step S1067: N), it performs an inverse Fourier transform on the frequency image data corrected in step S1066 to generate corrected transmission image data (step S1068). Furthermore, the image capture processing unit 35 of the control unit 10 reads out the information on the pixels saved in step S1063 from the storage unit 34, and replaces the values of the saved pixels with the values of the saved positions in the corrected cross-sectional image data (step S1069). As a result, the values of the pixels at the positions saved in step S1063 return to the state before correction using the Fourier transform and inverse Fourier transform, and are not affected by this correction.

Furthermore, the image capturing processing unit 35 of the control unit 10 stores the transmission image data corrected by the above processing in the storage unit 34 (step S1070), and determines whether or not there is next cross-sectional image data (step S1071). If the image capturing processing unit 35 of the control unit 10 determines that there is next transmission image data (step S1071: Y), it returns to step S1062 to select the next cross-sectional image data, and repeats the above-mentioned steps S1063 to S1071.

If the image capture processing unit 35 of the control unit 10 determines that there is no next cross-sectional image data (step S1071: N), it ends the image correction process S1060.

Returning to FIG. 3B, the bridge inspection unit 44 of the control unit 10 obtains a pseudo cross-sectional image of a slice thickness equivalent to that of the solder ball that shows the solder ball from the pseudo cross-sectional image generation unit 40 (read from the storage unit 34) and inspects whether or not a bridge exists (step S1100). If no bridge is detected (step S1100: N), the molten state inspection unit 46 of the control unit 10 obtains an inspection surface image from the board inspection surface detection unit 38 (read from the storage unit 34) and inspects whether or not the solder is molten (step S1120). If the solder is molten (step S1140: Y), the void inspection unit 48 of the control unit 10 obtains a pseudo cross-sectional image that partially shows the solder ball from the pseudo cross-sectional image generation unit 40 (read from the storage unit 34) and inspects whether or not a void exists (step S1160). If no voids are found (step S1180: N), the inspection unit 42 of the control unit 10 determines that the solder joint condition is normal (step S1200) and outputs this information to the memory unit 34. If a bridge is detected (step S1100: Y), the solder is not melted (step S1140: N), or a void is present (step S1180: Y), the inspection unit 42 determines that the solder joint condition is abnormal (step S1220) and outputs this information to the memory unit 34. When the solder condition is output to the memory unit 34, the image acquisition and judgment process S102 in this flowchart ends.

Returning to FIG. 3(a), when the image acquisition and determination process S102 is completed, the image capture processing unit 35 of the control unit 10 determines whether or not there is a next imaging area (FOV) (step S104), and if it is determined that there is a next imaging area (step S104: Y), the control unit 10 returns to step S100, selects the next imaging area (FOV), and repeats the image acquisition and determination process S102. On the other hand, if the image capture processing unit 35 of the control unit 10 determines that there is no next imaging area (FOV) (step S104: N), it ends the inspection process and removes the inspected object 12 from the inspection device 1.

As described above, the image acquisition and determination process S102 may be performed for each imaging field (FOV), or the examination may be performed in parallel with the acquisition of transmission image data and the generation of reconstructed image data for other imaging fields (FOVs), starting from the imaging field (FOV) for which generation of reconstructed image data (cross-sectional image data and pseudo cross-sectional image data) has been completed.

In the above configuration, a case has been described in which correction processing is performed on cross-sectional image data to remove periodic noise, but the image correction processing described with reference to FIG. 4 may also be performed on the transmission image data before generating the reconstructed image data (cross-sectional image data). By removing periodic noise such as heat sink noise from the transmission image data, it is possible to remove this noise from the reconstructed image data (cross-sectional image data) generated from the corrected transmission image data.

The effects of the image data correction method of the inspection device 1 according to this embodiment are summarized below.

First, a correction method using Fourier transform and inverse Fourier transform is used to remove periodic noise in the transmission image data or cross-sectional image data. However, before this correction, information on pixels that do not require correction is saved, and after correction, it is returned to the transmission image data or cross-sectional image data. This means that there is no effect of the correction, and only the periodic noise can be removed efficiently.

Secondly, when correcting frequency image data obtained by performing a Fourier transform on transmission image data or cross-sectional image data, this frequency image data can be divided into multiple correction regions, and the correction method and its parameters (second condition) can be changed for each correction region, so that only the noise that is intended to be removed can be efficiently removed from the frequency components of a periodic image.

1 Inspection device 10 Control unit 12 Object to be inspected 22 Radiation generator (radiation source)
24 Board holding part (holding part)
26 Detector

Claims

A method for correcting transmission image data acquired by irradiating an object to be inspected with radiation emitted from a radiation source and detecting the radiation transmitted through the object to be inspected, or three-dimensional image data reconstructed from the transmission image data, comprising the steps of:
a first step of storing a position and a value in the image data as information of each pixel of the image data that satisfies a first condition;
a second step of Fourier transforming the image data to generate frequency image data;
a third step of correcting values of pixels that satisfy the second condition among the pixels of the frequency image data, and outputting the corrected frequency image data;
a fourth step of inverse Fourier transforming the corrected frequency image data to generate corrected image data;
a fifth step of replacing the pixel values at the positions stored in the first step in the corrected image data with the stored values;
The image data correction method includes the steps of:
2. The method of claim 1, wherein the third step divides the frequency image data into a plurality of regions, and corrects values of pixels that satisfy the second condition among pixels in at least one of the regions.
3. The method of correcting image data according to claim 2, wherein the third step corrects the image data using a correction method based on the second condition set for each of the regions.
The method of correcting image data according to claim 1 , wherein the first condition is a pixel having a value greater than a threshold value set as an upper limit value and a pixel having a value smaller than a threshold value set as a lower limit value.
The method of claim 1 , wherein the first condition is a pixel in a predetermined area within the image data.
A radiation source;
A holder for holding an object to be inspected;
a detector that detects radiation from the radiation source that has passed through the object to be inspected and acquires transmission image data of the object to be inspected;
A control unit,
The control unit corrects two or more pieces of transmission image data obtained by changing the relative position of the radiation source, the holding unit, and the detector, or three-dimensional image data reconstructed from the transmission image data, by the image data correction method described in any one of claims 1 to 5, and inspects the object to be inspected using the corrected image data.