Patent Publication Number: US-2023160841-A1

Title: Inspection device

Description:
RELATED APPLICATIONS 
     The present application is a National Phase of International Application No. PCT/JP2021/014135, filed Apr. 1, 2021, and claims priority based on Japanese Patent Application No. 2020-066589, filed Apr. 2, 2020. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an inspection device. 
     BACKGROUND ART 
     As an inspection device for measuring a solder shape on a front surface or a back surface of a substrate, there is a tomosynthesis X-ray inspection device (see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Laid-Open No. 2008-026334 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In such an inspection device, an inspection object is irradiated with X-rays, but there is a problem in that the dose of X-rays irradiated to the inspection object cannot be known at the time of inspection unless the exposure dose is measured using a dosimeter. 
     The present invention has been made in view of such a problem, and an object thereof is to provide an inspection device capable of estimating a dose applied to an inspection object at the time of inspection without measuring an exposure dose using a dosimeter by applying radiation such as X-rays. 
     Solution to Problem 
     In order to solve the problem, an inspection device is an inspection device for changing the relative position of a radiation source and an inspection object, irradiating the inspection object with radiation from the radiation source, acquiring an image of the inspection object, and inspecting the inspection object, wherein the inspection device has a storage unit for storing, as a reference dose, the dose from the radiation source irradiated at a predetermined position with respect to the radiation source, and a calculation unit for calculating the dose irradiated to the inspection object in the inspection, wherein the calculation unit executes: a first step for calculating the dose irradiated to the inspection object from the relative position between the radiation source and the inspection object while acquiring the image while fixing or changing the relative position between the radiation source and the inspection object based on the reference dose stored in the storage unit; a second step for calculating the dose irradiated to the inspection object from the relative position between the radiation source and the inspection object while changing the relative position between the radiation source and the inspection object based on the reference dose stored in the storage unit; a third step for calculating the total value of the dose irradiated to the inspection object from the total of the dose calculated in the first step and the dose calculated in the second step; and a fourth step for outputting the total value calculated in the third step. 
     Advantageous Effects of Invention 
     According to the inspection device of the present invention, it is possible to estimate a dose applied to an inspection object at the time of inspection without irradiating radiation such as X-rays. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an explanatory diagram for explaining a configuration of an inspection device according to an embodiment. 
         FIG.  2    is an explanatory diagram for explaining functional blocks processed by a control unit of the inspection device. 
         FIG.  3    is a flowchart for explaining the flow of inspection. 
         FIG.  4    is a flowchart for explaining the flow of exposure dose calculation processing. 
         FIGS.  5 A and  5 B  are explanatory views for explaining types of radiation generators (radiation sources):  FIG.  5 A  shows a transmission type X-ray source, and  FIG.  5 B  shows a reflection type X-ray source. 
         FIGS.  6 A to  6 C  are explanatory diagrams for explaining the distribution of the exposure dose:  FIG.  6 A  shows the distribution of the exposure dose at the imaging position  1 ,  FIG.  6 B  shows the exposure dose at the time of stopping, and  FIG.  6 C  shows the exposure dose at the time of moving. 
         FIGS.  7 A to  7 C  are explanatory diagrams for explaining the distribution of the exposure dose:  FIGS.  7 A to  7 C  show the exposure dose at each position within the movement range. 
         FIG.  8    is an explanatory diagram for explaining a distribution of an exposure dose at an imaging position  2 . 
         FIGS.  9 A and  9 B  are explanatory diagrams for explaining a distribution of an exposure dose when moving from an imaging position  1  to an imaging position  2 :  FIG.  9 A  shows a case where radiation is always generated from the radiation generator, and  FIG.  9 B  shows a case where radiation is generated from the radiation generator only at the imaging position. 
         FIG.  10    is an explanatory diagram for explaining the distribution of the total exposure dose when the entire inspection target region is imaged. 
         FIGS.  11 A and  11 B  are explanatory diagrams for explaining an exposure dose distribution when imaging is performed while moving a substrate holding unit and a detector:  FIG.  11 A  shows a case where radiation is always generated from a radiation generator, and  FIG.  11 B  shows a case where radiation is generated from a radiation generator only at an imaging position. 
         FIGS.  12 A and  12 B  are explanatory views for explaining the exposure dose depending on the presence or absence of a filter:  FIG.  12 A  shows a case where there is no filter, and  FIG.  12 B  shows a case where there is a filter. 
         FIG.  13    is an explanatory diagram showing an output example of the calculated exposure dose. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the invention will now be described with reference to the drawings. As shown in  FIG.  1   , the inspection device  1  according to the present embodiment includes a control unit  10  configured by a processing device such as a personal computer (PC), a monitor  12 , and an imaging unit  32 . The imaging unit  32  further includes a radiation quality changing unit  14 , a radiation generator driving unit  16 , a substrate holding unit driving unit  18 , a detector driving unit  20 , a radiation generator  22 , a substrate holding unit  24 , and a detector  26 . 
     The radiation generator  22  is a device (radiation source) that generates radiation such as X-rays, and generates radiation by causing accelerated electrons to collide with a target such as tungsten or diamond, for example. The radiation in this embodiment will be described in the case of X-rays, but is not limited thereto. For example, the radiation may be alpha radiation, beta radiation, gamma radiation, ultraviolet radiation, visible radiation, or infrared radiation. The radiation may be a microwave or a terahertz wave. 
     The substrate holding unit  24  holds a substrate which is an inspection object. A substrate held by a substrate holding unit  24  is irradiated with radiation generated by a radiation generator  22 , and the radiation transmitted through the substrate is imaged as an image by a detector  26 . Hereinafter, the radiation transmission image of the substrate imaged by the detector  26  is referred to as a “transmission image”. As will be described later, in the present embodiment, the substrate holding unit  24  holding the substrate and the detector  26  are moved relative to the radiation generator  22  to acquire a plurality of transmission images, thereby generating a reconstructed image. 
     The transmission image captured by the detector  26  is sent to the control unit  10  and reconstructed into an image including the three-dimensional shape of the solder of the joint portion using a known technique such as a filtered-back projection method (FBP method). The reconstructed image and the transmission image are stored in a storage in the control unit  10  or an external storage (not illustrated). Hereinafter, an image reconstructed into a three-dimensional image including the three-dimensional shape of the solder of the joint portion based on the transmission image is referred to as a “reconstructed image”. An image obtained by cutting out an arbitrary cross section from the reconstructed image is referred to as a “cross-sectional image”. Such reconstructed images and cross-sectional images are output to the monitor  12 . The monitor  12  displays not only the reconstructed image and the cross-sectional image, but also an inspection result of a bonding state of solder, which will be described later, and the like. The reconstructed image in the present embodiment is also referred to as “planar CT” because it is reconstructed from a planar image captured by the detector  26  as described above. 
     The radiation quality changing unit  14  changes the radiation quality of the radiation generated by the radiation generator  22 . The radiation quality of radiation is determined by a voltage (hereinafter referred to as a “tube voltage”) applied to accelerate electrons to collide with a target, and a current (hereinafter referred to as a “tube current”) that determines the number of electrons. The radiation quality changing unit  14  is a device that controls the tube voltage and the tube current. The radiation quality changing unit  14  can be realized by using a known technique such as a transformer or a rectifier. 
     Here, the radiation quality of the radiation is determined by the brightness and hardness of the radiation (spectral distribution of the radiation). When the tube current is increased, the number of electrons colliding with the target increases, and the number of photons of radiation generated also increases. As a result, the brightness of the radiation increases. For example, some components such as capacitors are thicker than other components, and it is necessary to irradiate high-intensity radiation in order to capture a transmission image of these components. In such a case, the luminance of the radiation is adjusted by adjusting the tube current. Further, when the tube voltage is increased, the energy of the electrons colliding with the target increases, and the energy (spectrum) of the generated radiation increases. In general, as the energy of radiation increases, the penetration force of a substance increases and the radiation is less likely to be absorbed by the substance. A transmission image captured using such radiation has a low contrast. Therefore, the tube voltage can be used to adjust the contrast of the transmission image. 
     The radiation generator driving unit  16  has a drive mechanism such as a motor (not shown), and can move the radiation generator  22  up and down along an axis passing through the focal point of the radiation generator  22  (the direction of this axis is referred to as the “Z-axis direction”). This makes it possible to change the irradiation field by changing the distance between the radiation generator  22  and the inspection object (substrate) held by the substrate holding unit  24 , and to change the magnification ratio of the transmission image captured by the detector  26 . The position of the radiation generator  22  in the Z-axis direction is detected by a generator position detection unit  23  and output to the control unit  10 . 
     The detector driving unit  20  also has a drive mechanism such as a motor (not shown), and rotationally moves the detector  26  along a detector rotation trajectory  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 trajectory  28  is provided. Further, the substrate holding unit  24  is configured to rotationally move on the substrate rotation trajectory  28  in conjunction with the rotational movement of the detector  26 . This makes it possible to capture a plurality of transmission images having different projection directions and projection angles while changing the relative positional relationship between the radiation generator  22  and the substrate held by the substrate holding unit  24 . 
     Here, the rotation radius of the substrate rotation trajectory  28  and the detector rotation trajectory  30  is not fixed, but can be freely changed. This makes it possible to arbitrarily change the irradiation angle of the radiation with which the component disposed on the substrate is irradiated. It should be noted that the trajectory surfaces of the substrate rotation trajectory  28  and the detector rotation trajectory  30  are perpendicular to the above-described Z-axis direction, and that the directions perpendicular to these trajectory surfaces are defined as the X-axis direction and the Y-axis direction, the positions of the substrate holding unit  24  in the X-axis direction and the Y-axis direction are detected by the substrate position detection unit  29  and output to the control unit  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 unit  31  and output to the control unit  10 . 
     The control unit  10  controls all operations of the inspection device  1  described above. Hereinafter, various functions of the control unit  10  will be described with reference to  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 storage unit  34 , a cross-sectional image generation unit  36 , a substrate inspection surface detection unit  38 , a pseudo cross-sectional image generation unit  40 , and an inspection unit  42 . Although not illustrated, the control unit  10  also includes an imaging control unit that controls operations of the radiation quality changing unit  14 , the radiation generator driving unit  16 , the substrate holding unit driving unit  18 , and the detector driving unit  20 . In addition, each of these functional blocks is realized by cooperation of hardware such as a CPU that executes various arithmetic processing 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 forms by a combination of hardware and software. 
     The storage unit  34  stores information such as an imaging condition for imaging a transmission image of the substrate and a design of the substrate which is an inspection object. The storage unit  34  also stores a transmission image or a reconstructed image (a cross-sectional image or a pseudo cross-sectional image) of the substrate, an inspection result of an inspection unit  42  to be described later, and the like. The storage unit  34  further stores a speed at which the radiation generator driving unit  16  drives the radiation generator  22 , a speed at which the substrate holding unit driving unit  18  drives the substrate holding unit  24 , and a speed at which the detector driving unit  20  drives the detector  26 . 
     The cross-sectional image generation unit  36  generates a cross-sectional image based on the plurality of transmission images acquired from the storage unit  34 . This can be realized by using a known technique such as an FBP method or a maximum likelihood estimation method. When the reconstruction algorithm is different, the property of the obtained reconstructed image and the time required for reconstruction are also different. Therefore, a configuration may be adopted in which a plurality of reconstruction algorithms and parameters used in the algorithms are prepared in advance and the user is allowed to select one of them. As a result, it is possible to provide the user with a degree of freedom in selection such as giving priority to shortening of the time required for reconstruction or giving priority to good image quality even if it takes time. The generated cross-sectional image is output to the storage unit  34  and recorded in the storage unit  34 . 
     The substrate inspection surface detection unit  38  specifies a position (cross-sectional image) where a surface to be inspected on the substrate (for example, the surface of the substrate) is projected from the plurality of cross-sectional images generated by the cross-sectional image generation unit  36 . Hereinafter, the cross-sectional image showing the inspection surface of the substrate is referred to as an “inspection surface image”. A method of detecting the inspection surface image will be described in detail later. 
     Regarding the cross-sectional images generated by the cross-sectional image generation unit  36 , the pseudo cross-sectional image generation unit  40  generates an image of a region of the substrate that is thicker than the cross-sectional images by stacking a predetermined number of continuous cross-sectional images. The number of cross-sectional images to be stacked is determined by the thickness of the region of the substrate on which the cross-sectional image is projected (hereinafter referred to as “slice thickness”) and the slice thickness of the pseudo cross-sectional image. For example, when the slice thickness of the cross-sectional image is 50 μm and the height (for example, 500 μm) of a solder ball (hereinafter, simply referred to as “solder”) of BGA is used as the slice thickness as the pseudo cross-sectional image, 500/50=10 cross-sectional images may be stacked. At this time, in order to specify the position of the solder, the inspection surface image specified by the substrate inspection surface detection unit  38  is used. 
     The inspection unit  42  inspects the joint state of the solder based on the cross-sectional image generated by the cross-sectional image generation unit  36 , the inspection surface image specified by the substrate inspection surface detection unit  38 , and the pseudo cross-sectional image generated by the pseudo cross-sectional image generation unit  40 . Since the solder that joins the substrate and the component is present in the vicinity of the substrate inspection surface, it is possible to determine whether or not the solder joins the substrate and the component appropriately by inspecting the inspection surface image and the cross-sectional image showing the region on the radiation generator  22  side with respect to the inspection surface image. 
     As used herein, “solder joint state” refers to whether or not a substrate and a component are joined by solder to create an appropriate conductive path. The inspection of the bonding state of the solder includes a bridge inspection, a melting state inspection, and a void inspection. “Bridge” refers to an undesirable conductive path between conductors caused by solder joining. In addition, the “melting state” refers to a state of whether or not bonding between the substrate and the component is insufficient due to insufficient melting of the solder, that is, a state of whether or not so-called “floating” occurs. “Void” refers to a failure of a solder joint due to air bubbles in the solder joint. Accordingly, the inspection unit  42  includes a bridge inspection unit  44 , a melting state inspection unit  46 , and a void inspection unit  48 . 
     Although the details of the operations of the bridge inspection unit  44 , the melting state inspection unit  46 , and the void inspection unit  48  will be described later, the bridge inspection unit  44  and the void inspection unit  48  inspect bridges and voids, respectively, based on the pseudo cross-sectional image generated by the pseudo cross-sectional image generation unit  40 , and the melting state inspection unit  46  inspects the melting state of the solder based on the inspection surface image identified by the substrate inspection surface detection unit  38 . The inspection results of the bridge inspection unit  44 , the melting state inspection unit  46 , and the void inspection unit  48  are recorded in the storage unit  34 . 
       FIG.  3    is a flow chart illustrating a flow from capturing a transmission image, generating a reconstructed image, and identifying an inspection surface image to inspecting a solder joint state. The processing in this flowchart is started, for example, when the control unit  10  receives an instruction to start inspection from an input device (not illustrated). 
     As described above, the control unit  10  sets the irradiation field of the X-ray emitted from the radiation generator  22  by the radiation generator driving unit  16 , moves the substrate holding unit  24  by the substrate holding unit driving unit  18 , moves the detector  26  by the detector driving unit  20  to change the imaging position, sets the radiation quality of the radiation generator  22  by the radiation quality changing unit  14 , irradiates the substrate with the radiation, and captures a transmission image, and further generates a reconstructed image by the cross-sectional image generation unit  36  and the pseudo-cross-sectional image generation unit  40  from the plurality of transmission images thus captured (step S 100 ). 
     Next, the substrate inspection surface detection unit  38  of the control unit  10  receives the transmission image or the reconstructed image (cross-sectional image) from the cross-sectional image generation unit  36 , and specifies an inspection surface image therefrom (step S 102 ) The bridge inspection unit  44  acquires a pseudo cross-sectional image having a slice thickness similar to that of the solder ball, which reflects the solder ball, from the pseudo cross-sectional image generation unit  40 , and inspects the presence or absence of a bridge (step S 104 ). If a bridge is not detected (“N” in step S 106 ), the melting state inspection unit  46  acquires an inspection surface image from the substrate inspection surface detection unit  38  to inspect whether or not the solder is melted (step S 108 ). If the solder is melted (“Y” in step S 110 ), the void inspection unit  48  acquires a pseudo cross-sectional image partially projecting the solder ball from the pseudo cross-sectional image generation unit  40  to inspect whether or not a void exists (step S 112 ). If no void is found (“N” in step S 114 ), the void inspection unit  48  determines that the bonding state of the solder is normal (step S 116 ), and outputs the result to the storage unit  34 . If a bridge is detected (“Y” in step S 106 ), if the solder is not melted (“N” in step S 110 ), or if a void exists (“Y” in step S 114 ), the bridge inspection unit  44 , the melting state inspection unit  46 , and the void inspection unit  48  determine that the bonding state of the solder is abnormal (step S 118 ), and outputs the result to the storage unit  34 . When the state of the solder is output to the storage unit  34 , the process in this flowchart ends. 
     The addition, the control unit  10  of the inspection device  1  includes an exposure dose calculation unit  50  that calculates the amount (dose or exposure dose) of radiation (X-rays) with which an inspection object (substrate) is irradiated at the time of inspection by calculation. The exposure dose calculation unit  50  calculates the exposure dose by simulating the action of the inspection device  1  (relative movement of the substrate holding unit  24  with respect to the radiation generator  22 ) using a personal computer (PC) or the control unit  10  which is a device incorporating some arithmetic mechanism without actually performing exposure dose measurement using a dosimeter in the X-ray inspection of an inspection object such as an electronic substrate or an electronic component. 
     The exposure dose calculation unit  50  calculates an exposure dose of the inspection object placed on the substrate holding unit  24  based on information about the radiation generator  22  stored in advance in the storage unit  34 . Specifically, a value (reference dose) measured by arranging a dosimeter at a predetermined position directly below the radiation generator  22  (a predetermined position on the axis (Z-axis) passing through the focal point of the radiation generator  22 ) while setting the tube voltage, tube current, and the like to predetermined values by the radiation quality changing unit  14  is stored in the storage unit  34  in association with the position (coordinates) in the Z-axis direction and the values of the tube voltage, tube current, and the like. For example, the dosimeter is disposed at a predetermined position, the tube voltage is measured at intervals of 10 kV, and the tube current is measured at intervals of 50 μA, and the measured values are stored in the storage unit  34 . The dose to be measured in advance may be measured not only directly below the radiation generator  22  but also, for example, at a plurality of points moved in the X-axis and Y-axis directions from a measurement point directly below the radiation generator  22 . Information to be measured in advance can be reduced by using plane approximation, linear interpolation, or the like for the relationship between the tube voltage and the tube current and the dose. In addition, since the exposure dose of the inspection object is attenuated in inverse proportion to the square of the distance between the inspection object (substrate holding unit  24 ) and the radiation generator  22 , by obtaining the attenuation amount of the X-ray dose immediately below and around the radiation generator  22  by a calculation formula, the preliminary measurement can be performed only at a predetermined position immediately below the radiation generator  22 . 
     Processing performed by the exposure dose calculation unit  50  will be described with reference to  FIGS.  4  to  13   . As shown in  FIG.  4   , when the exposure dose calculation processing is started, the exposure dose calculation unit  50  of the control unit  10  first reads inspection information from the storage unit  34  (step S 200 ). Here, the inspection information includes the size of an inspection object (the size of a substrate), the positions and names of components mounted on the substrate, the sizes of the components, and the like. Next, the exposure dose calculation unit  50  reads the imaging conditions (X-ray imaging conditions at the time of examination) from the storage unit  34  (step S 202 ). Here, the imaging conditions include the tube voltage of the radiation generator  22 , the tube current, the exposure time, the magnification (the distance between the radiation generator  22  and the substrate holding unit  24  and the inspector  26 ), the tilt angle in planar CT (the angle with respect to the axis passing through the focal point of the radiation generator  22 ), the number of transmission images used for CT calculation, and the like. 
     Further, the exposure dose calculation unit  50  acquires the type (radiation source type) of the specified type of the radiation generator  22  (step S 204 ). Here, the radiation source type is information on the type of the X-ray source, which is the radiation generator  22 , physical filter attached to the X-ray source, and the radiation source type may be stored in advance in the storage unit  34  and acquired from the storage unit  34 , or may be input using an input device such as a keyboard or a mouse (not illustrated) and acquired. For example, the type of the X-ray source is a transmission-type X-ray source in which X-rays are generated by a tungsten target as shown in  FIG.  5 A  and the generated X-rays are transmitted through tungsten as they are, or a reflection-type X-ray source in which X-rays are generated by being reflected by a tungsten target as shown in  FIG.  5 B , and the type of the filter is information on the material of the filter (for example, zinc) and the thickness in the case of a plate shape (for example, 100 μm or 200 μm). Further, the filter is not limited to a plate type, and may be a bowtie filter, a collimator, or the like having a non-uniform thickness or having holes. 
     Returning to  FIG.  4   , as described above, the exposure dose calculator  50  simulates an operation in which imaging is performed by moving the substrate holding unit  24  along the substrate rotation trajectory  28 , and calculates the exposure dose at this time. To be specific, the exposure dose calculation unit  50  calculates the exposure dose at the time of capturing one transmission image in the simulation region and adds the exposure dose to the total exposure dose (total value of exposure doses) (step S 206 ), determines whether there is a next imaging location (step S 208 ), and when it is determined that there is a next imaging location (Y in step S 208 ), calculates the exposure dose during movement to the next imaging location and adds the exposure dose to the total exposure dose (step S 210 ), and returns to step S 206  to repeat the processing. The exposure dose during movement can be obtained by integrating the exposure dose at a specific position in a short time while advancing the time by a short time. The exposure dose is calculated from the relative position between the radiation generator  22  and the subject, based on the imaging conditions and the reference dose stored in the storage unit  34 . 
       FIG.  6 A  is a graphical representation of the exposure dose calculated at an imaging position (e.g., imaging position  1 ) in step S 206 . The inside of the black rectangle is the outer shape of the inspection object (printed circuit board or the like), and is a target region for calculation of the exposure dose in the exposure dose calculation processing. In addition, a broken-line rectangle indicates an electronic component to be inspected which is mounted on an inspection object, and a concentric circular white region indicates an exposure dose. Here, the larger the exposure dose, the whiter the image. 
     Here, when the exposure time during imaging is set to 100 ms and the distance on the order of several tens of mm is moved in the order of 100 ms during the movement, the distribution of the exposure dose when imaging is performed while the substrate holding unit  24  and the detector  26  are stopped becomes as shown in  FIG.  6 B , and the distribution of the exposure dose during the minute time during which the substrate holding unit  24  and the detector  26  are moving becomes as shown in  FIG.  6 C . In this way, the exposure dose when the substrate holding unit  24  and the detector  26  are moving is less than the exposure dose when the substrate holding unit  24  and the detector  26  are stopped. 
     Further,  FIGS.  7 A to  7 C  show, as drawings, exposure doses calculated during movement when it is determined in step S 208  that there is a next imaging location. As described above, the exposure doses calculated at the moved positions (three positions) at predetermined time intervals (minute time intervals) are shown. 
     Further,  FIG.  8    shows the exposure dose calculated in step S 206  at the next imaging position (imaging position  2 ). 
       FIG.  9 A  shows an exposure dose obtained by integrating an exposure dose ( FIG.  6 A  and  FIG.  8   ) at the time of imaging at the above-mentioned two positions (imaging positions  1  and  2 ) and an exposure dose ( FIGS.  7 A to  7 C ) at the time of moving in the case where imaging and movement are repeated in a state where radiation is generated from the radiation generator  22 , and the exposure dose ( FIGS.  7 A to  7 C ) at the time of moving. The exposure dose at the time of moving when generation of radiation from the radiation generator  22  is stopped (when radiation is generated from the radiation generator  22  only at the imaging position) is as shown in  FIG.  9 B . 
       FIG.  10    shows the distribution of the total exposure dose when imaging and moving are repeated in a state where radiation is generated from the radiation generator  22 , and all of the inspection target regions are imaged. In this way, by obtaining the total exposure dose during imaging and during movement in one examination, it is possible to obtain the exposure dose not only during imaging but also during movement. 
     In addition, although the above-described processing has been described based on a configuration in which the substrate holding unit  24  is stopped to perform imaging and is moved to the next imaging position, it is possible to obtain the total exposure dose in a similar method in a case of a configuration in which the substrate holding unit  24  is moved and imaged without being stopped. In this case, as described above, the total exposure dose can be obtained by integrating the exposure dose at a specific position in a short time while advancing the time by a short time. The exposure dose in this case is shown in  FIG.  11 A . Further, in the case of a configuration in which X-rays are not irradiated from the radiation generator  22  when the substrate holding unit  24  is moving, as shown in  FIG.  11 B , the exposure dose during movement is 0. 
     In the calculation of the exposure dose at the time of imaging in step S 206  and the calculation of the exposure dose at the time of moving in step S 210 , non-uniformity or unevenness corresponding to an angle with respect to the radiation generator  22  may be corrected with respect to the exposure dose calculated based on the positions (distances) of the substrate holding unit  24  from the radiation generator  22 . For example, as shown in  FIG.  5 A , when X-rays are transmitted through a plate-shaped filter  22   a  with a thickness of 100 μm, the passage length is 100 μm with respect to the inspection object immediately below, but the passage length is 141 μm, which is √{square root over (2)} times, in the 45° direction, and thus the difference in passage length is corrected.  FIG.  12 A  shows the exposure dose in the case where the filter  22   a  is not provided. On the other hand,  FIG.  12 B  shows the exposure dose in the case where the filter  22   a  is arranged. In this way, since the passing distance of the filter becomes longer and the attenuation amount of the X-ray becomes larger toward the outer side, the exposure dose becomes smaller. On the other hand, in the case of a beryllium window having a small amount of X-ray absorption, there is almost no absorption in an oblique direction, so that it is not necessary to perform correction. 
     In the calculation of the exposure dose in step S 206  and step S 210 , the entire region of the substrate to be simulated (the region of the substrate holding unit  24  on which the substrate is placed) is divided into partial regions of a specific size (for example, 1 mm), and the exposure dose of each partial region is calculated and added to the total exposure dose of each partial region, thereby obtaining the distribution of the total exposure dose on the inspection object. 
     Returning to  FIG.  4   , when the exposure dose calculation unit  50  determines that there is no next imaging point (N in step S 208 ), the exposure dose calculation unit  50  performs the above-described analysis processing of the total exposure dose (step S 212 ). For example, when the entire substrate is divided into partial regions as described above and the total exposure dose of each partial region is calculated, the distribution of the exposure dose is obtained. Further, for each component arranged on the substrate, the total exposure dose of the partial regions within the region of the component is obtained, so that the exposure dose (total value) of each component can be obtained. For example, in  FIG.  10   , the total exposure dose of each component is obtained according to the area of the component and the exposure dose distribution indicated by a broken line. 
     Finally, the exposure dose calculation unit  50  outputs the analytical result (calculation result) (step S 214 ). The output destination may be the storage unit  34  or the monitor  12 .  FIG.  13    shows an example in which the analytical results are output to the  12   a  of the screen of the monitor  12 . For example, the entire region of the substrate can be displayed as a region  12   b  on the screen, and the distribution of the exposure dose can be displayed by contour lines for each predetermined exposure dose. At this time, the most exposed region may be displayed in red, the least exposed region may be displayed in blue, and the other regions may be displayed in other colors. Further, the exposure dose may be displayed as a numerical value. 
     When the exposure dose for each component is calculated, the components can be arranged in descending order of exposure dose and displayed together with the exposure dose in the  12   c  of the region on the screen. In addition, when the distribution of the exposure dose on the substrate is displayed in the region  12   b , by displaying the image of the substrate in an overlapping manner, it is possible to visually confirm the relationship between the components mounted on the substrate and the distribution of the exposure dose. 
     As described above, the exposure dose calculation unit  50  of the control unit  10  calculates the exposure dose of the inspection object in the inspection, so that the exposure dose of the inspection object can be estimated in advance before the inspection object is actually irradiated with X-rays (before the inspection). The user can set the imaging conditions that provide the optimum exposure dose by repeating the process of setting predetermined imaging conditions (as described above, the number of transmission images taken for CT calculation, tube voltage, tube current, exposure time, magnification ratio, etc.), calculating the exposure dose, displaying it on the monitor  12 , changing the imaging conditions in consideration of image quality and tact time, calculating the exposure dose again, and displaying it on the monitor  12 .