JP6425458B2 - X-ray inspection apparatus, X-ray inspection method and X-ray inspection program - Google Patents

Description

  The present invention relates to an X-ray inspection apparatus, an X-ray inspection method, and an X-ray inspection program.

  Conventionally, there is known a technique for determining the quality of a product based on the filling rate of the filling formation portion formed by filling the through holes. For example, in Patent Document 1, a two-dimensional transmission X-ray image is acquired based on X-rays transmitted through the filling and forming part, void portions are specified based on the two-dimensional transmission X-ray image, and filling of the filling and forming part is performed. An arrangement for obtaining rates is disclosed.

JP, 2014-106113, A

In the conventional X-ray inspection apparatus described above, the void portion is specified based on the two-dimensional transmission X-ray image, but in the two-dimensional transmission X-ray image, capturing of the three-dimensional feature of the void It was not possible to judge the quality correctly. In particular, in the case where the through-hole is filled by plating to form a filling-formed portion, the three-dimensional shape and position of the void causing the defect are significantly different from the usual spherical void and three-dimensional. It was difficult to make a good / bad decision accurately if you did not capture a specific feature.
This invention is made in view of the said subject, and an object of this invention is to provide the technique which determines the presence or absence of the void in the filling formation part formed by being filled with the through hole by plating.

  In order to achieve the above object, the X-ray inspection apparatus irradiates X-rays to a filling formation portion formed by filling the through holes by plating, and photographs and reconstructs a plurality of X-ray images from different directions. Perform an operation. And the said X-ray inspection apparatus extracts the feature-value peculiar to the void in the filling formation part formed by the through hole being filled by plating from the reconstruction information obtained by the reconstruction calculation, The said feature-value And determine the presence or absence of a void in the filling formation part.

  That is, in the filling formation portion formed by filling the through holes by plating, a void different from a normal void (for example, a spherical void in a solder bump) in another inspection object is easily formed. Therefore, if an index different from a normal void detection index is not used, the presence or absence of voids (or the quality of the void formation in the portion formed by the void) can be accurately determined by filling the through holes with plating. It can not be determined.

  Therefore, in the X-ray inspection apparatus according to an embodiment of the present invention, a characteristic amount specific to the void in the filling and forming portion formed by filling the through hole by plating is extracted from the reconstruction information, It was set as the structure which determines the presence or absence of the void in a filling formation part based on quantity. According to this configuration, it is possible to determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating.

  Here, in the X-ray image acquiring means, acquiring a plurality of X-ray images so that an image of the filling formation portion formed by filling the through holes by plating can be generated by a reconstruction operation. I hope you can. That is, X-ray images may be taken at a plurality of imaging positions by imaging the filling and forming unit from different directions. The imaging of the X-ray image may be performed by disposing the filling and forming unit within the output range of the X-ray and imaging the transmitted X-ray by the detector. When taking an X-ray image, it may be disposed so as to include a desired filling forming portion within the X-ray irradiation range. For this purpose, it is preferable to adopt a configuration in which the filling and forming unit can be easily moved. For example, a configuration in which the filling and forming unit is mounted on an XY stage or a rotation stage can be adopted.

  In addition, it is comprised so that X-rays can be irradiated to a filling formation part from a different direction. For example, the X-ray source and the detector are arranged such that the predetermined rotational axis intersects with the X-ray irradiation direction at an inclined angle, and it can be considered that the X-ray irradiation direction is rotated about the rotational axis. Are arranged at a plurality of imaging positions so that reconstruction information can be acquired. According to this configuration, it is possible to analyze X-ray images of different cutting positions by changing the position at which the reconstruction information is cut in a predetermined direction.

  The reconstruction computing means only needs to be able to obtain information (reconstruction information) on the three-dimensional structure of the filling and forming unit by executing the reconstruction computation based on the plurality of X-ray images. That is, the reconstruction calculation means generates the reconstruction information so that the feature amount reflecting the feature of the void in the filling formation portion formed by the filling of the through hole by plating can be obtained from the reconstruction information. I wish I could. Note that it is possible to execute a reconstruction operation by the reconstruction operation means by using X-ray images taken from different directions, but in the case of performing this reconstruction operation, it is possible to perform predetermined operations on the filling and forming unit. It is preferable to take an X-ray image from a position having symmetry.

  For this purpose, it is assumed that the detection surface of the X-ray detector has been rotated about an axis having a predetermined relationship with the plane on which the filling formation portion is disposed (hereinafter referred to as a rotational position) Place a detector on the More specifically, the rotational position may be assumed on the circumference of a predetermined radius centered on an axis perpendicular to the movement plane (the movement plane or the like by the XY stage) of the inspection object. As described above, when the detection surface is disposed at a plurality of rotational positions, the inspection target portion can be imaged from a position having rotational symmetry, and the three-dimensional structure in consideration of the rotational symmetry of the captured X-ray image It becomes possible to analyze

  The determination means extracts a feature amount specific to the void in the filling formation portion formed by the through hole being filled by plating from the reconstruction information obtained by the reconstruction operation, and forms the filling based on the feature amount. It is sufficient if it can determine the presence or absence of a void in the part. That is, in the filling formation portion formed by filling the through hole by plating, the three-dimensional structure of the void in which the filling formation portion should be regarded as a defect is different from the void of a normal sphere.

  For example, in the process of forming a through hole by plating, plating is gradually formed from the back side of the through hole toward the opening. If normal, the plating is formed to be gradually laminated on the wall surface in the through hole from the back side toward the opening, so the growth of the plating is from the wall surface of the through hole along the central axis direction and Advance gradually towards the opening. Therefore, the thickness of the wall surface gradually increases over the entire circumference of the inner periphery of the through hole, and eventually the plating reaches the open end of the through hole. For this reason, if the plating grows normally, no void will occur. However, if a site with a large curvature occurs in the process of plating, plating will grow faster than other curved surfaces starting from that site, and the opening will be blocked before the growth of plating on the wall reaches the opening. There is a case. Such abnormal growth of plating is likely to occur at a portion where the curvature is larger than other portions, such as the edge of the through hole opening.

  Such abnormal plating growth and plating growth from the wall surface of the through hole are simultaneously performed, and the plating growth gradually progresses from the wall surface of the through hole toward the central axis direction and the opening direction. Therefore, in most cases the void in the filling formation is formed near the central axis of the through hole, and in the inspection for determining the quality of the filling formation, the void is formed at a position far from the central axis of the through hole. It can be considered that

  Therefore, the determination means identifies the candidate of the void in the filling and forming unit based on the reconstruction information, acquires the distance between the central axis of the through hole and the center of gravity of the candidate of the void as the feature amount, and the distance is predetermined. A configuration may be adopted in which a candidate of void is considered not to be void if it is longer than the distance criterion. According to this configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating. In addition, the candidate of the void may be specified in the image of the filling and forming part, and the determination means determines the portion where the X-ray is absorbed by the plating material (electrical conductor such as copper) based on the reconstruction information. By specifying, the image of the filling and forming part can be specified, and further, the void candidate can be specified by specifying the part where the X-ray is not absorbed by the plating material in the image of the filling and forming part. If the candidate of the void is identified, the determination means can easily identify the center of gravity of the candidate of the void.

  Further, the central axis of the through hole may be an axis passing through the center in the depth direction of the through hole, and the determination means may be perpendicular to the extending direction of the filler forming portion based on the reconstruction information. The central axis can be easily identified by identifying the axis passing through the center of gravity of the face in any direction. Therefore, the distance between the central axis of the through hole and the center of gravity of the candidate of the void can be easily specified.

  The predetermined distance criterion for analyzing the distance between the center axis of the through hole and the center of gravity of the candidate for the void is that the candidate for the void is far from the center axis and there is a void causing the defect at the position of the candidate for the void. It is a determination criterion that can be regarded as impossible, and it may be determined in advance. Judgment based on such distance judgment criteria can adopt various methods. For example, when the distance between the central axis of the through hole and the center of gravity of the candidate of the void is longer than a predetermined reference distance, the void is used. It is possible to adopt a configuration in which the candidates for are not considered void.

  In addition, since a two-dimensional transmission X-ray image shows the state which projected the three-dimensional image on the detection surface, it is difficult to pinpoint the presence or absence of a void correctly by analysis of the said two-dimensional transmission X-ray image. For example, when the central axis of the through hole is inclined with respect to the detection surface of the detector, it is impossible to specify the central axis of the through hole in the first place. Therefore, the analysis itself based on the shape of the void can not be performed, and the presence or absence of the void can not be accurately determined. However, in the X-ray inspection apparatus according to one embodiment of the present invention, since reconstruction information indicating a three-dimensional structure is analyzed, the distance between the central axis of the through hole and the center of gravity of the void candidate or the void It is possible to identify the diameter of the candidate, and it is possible to accurately determine the presence or absence of the void in the filling formation portion formed by filling the through hole by plating.

  Furthermore, the distance between the center axis of the through hole and the center of gravity of the candidate void is normalized, and when the normalized distance is equal to or greater than a predetermined distance threshold, the center axis of the through hole and the center of gravity of the candidate void A configuration may be adopted in which the distance is considered to be equal to or greater than a predetermined distance determination reference. As a configuration for this, for example, a value obtained by dividing the distance between the central axis of the through hole and the center of gravity of the candidate of the void by the size of the candidate of the void (the value after normalization) is a predetermined distance threshold In the above case, a configuration may be adopted in which candidates for voids are regarded as not being voids. The value after normalization in this configuration increases as the size of the void candidate decreases in the plurality of void candidates having the same distance between the center axis of the through hole and the center of gravity of the void candidate. Therefore, based on the judgment using the normalized value, the judging means considers that candidates for relatively small voids are not void even if the distance between the central axis of the through hole and the center of gravity of the candidate for void is the same. Candidates of a large void can be considered to be a void.

  Furthermore, even if the size of the void candidate is the same, the value after normalization increases as the distance between the central axis of the through hole and the center of gravity of the void candidate increases. Therefore, the judging means should regard the candidate of the void relatively distant from the central axis of the through hole as non-void and the candidate of the relatively near void as void, even if the size of the candidate of the void is the same. It is possible. According to the above configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating. In addition, the size of the candidate of a void can be specified by various indexes, for example, the diameter and radius of a void can be assumed. Since the candidate for the void is a spheroid long on one side, it can be configured by the diameter or radius or the diameter of a certain reference position, for example, the diameter in the major axis direction or the diameter in the minor axis direction.

  Furthermore, since the through hole is usually a long hole in the central axis direction of the through hole, in the process of growing the plating along the wall surface, the shape of the space left without being plated inside the wall surface is It becomes a long shape in the central axis direction. Therefore, the void formed in the filling formation portion is shaped like a long spheroid in the central axis direction of the through hole and is not spherical. Therefore, in the inspection for determining the quality of the filling formation portion, it can be regarded as not a void unless the shape of the void is a spheroid long in the central axis direction of the through hole.

  Therefore, the determination means identifies the candidate of the void in the filling and forming unit based on the reconstruction information, acquires the length of the candidate of the void in the depth direction of the through hole as the feature quantity, and the length is predetermined. If it is less than the depth criterion, a configuration may be adopted in which void candidates are regarded as not being void. According to this configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating. As described above, the candidate for the void is identified by the determination unit, based on the reconstruction information, by identifying a portion in the image of the filling and forming portion where X-rays are not absorbed by the plating material. . In addition, the image of the through hole is identified by the determination means, based on the reconstruction information, by identifying a portion in the image of the filling and forming portion where the X-ray is absorbed by the plating material. Therefore, if the candidate of the void and the image of the through hole are specified, the determination means can easily specify the length of the candidate of the void in the depth direction of the through hole.

  The predetermined depth criterion for analyzing the candidate length of the void in the depth direction of the through hole is that the void having a short length in the depth direction is a cause of the defect in the filling formation portion formed by the plating filling. It is a determination criterion that can be regarded as not existing as a void, and it may be determined in advance. As the determination based on such depth criteria, various methods can be adopted. For example, when the length in the depth direction of the candidate for the void is less than a predetermined reference length, A configuration may be employed in which it is determined that the candidate length of the void in the depth direction is less than a predetermined depth criterion.

  In addition, since a two-dimensional transmission X-ray image shows the state which projected the three-dimensional image on the detection surface, it is difficult to pinpoint the presence or absence of a void correctly by analysis of the said two-dimensional transmission X-ray image. For example, when the central axis of the through hole is inclined with respect to the detection surface, it is not possible to specify the candidate length of the void in the depth direction of the through hole. Therefore, the analysis itself based on the shape of the void can not be performed, and the presence or absence of the void can not be accurately determined. However, in the X-ray inspection apparatus according to the embodiment of the present invention, since reconstruction information indicating a three-dimensional structure is analyzed, it is possible to specify the candidate length of the void in the depth direction of the through hole. It is possible to accurately determine the presence or absence of a void in the filling formation formed by filling the through hole by plating.

  Further, the candidate candidate lengths in the through hole depth direction are normalized, and the candidate candidate lengths in the through hole depth direction when the normalized distance is less than a predetermined depth threshold. A configuration may be adopted in which it is regarded that the value is less than a predetermined depth judgment standard. As a configuration for this, for example, a value obtained by dividing the candidate length of the void in the depth direction of the through hole by the length of the candidate of the void in the radial direction of the through hole (value after normalization) In the case where is less than a predetermined depth threshold, a configuration may be adopted in which candidates for voids are regarded as not being voids. The value after normalization in this configuration becomes smaller as the radial length of the through hole becomes longer in the plurality of void candidates having the same length in the depth direction of the through hole. Therefore, even if the candidate for the void in the depth direction of the through hole has the same length, the determination means does not have to use the spheroid that is long in the central axis direction of the through hole (for example, if it is close to a sphere) The void candidate can be regarded as not being a void, and the void candidate can be regarded as a void if the spheroid is long in the central axis direction of the through hole.

  Furthermore, the value after standardization becomes smaller as the length in the depth direction of the through hole becomes shorter in the plurality of void candidates having the same radial length in the through hole. Therefore, even if the radial length of the through hole is the same, if the void candidate is not a long spheroid in the central axis direction of the through hole (for example, if it is close to a sphere), the determination means The candidate is considered not to be a void, and if the spheroid is long in the direction of the central axis of the through hole, the candidate for the void can be considered to be a void. According to the above configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating. The candidate length of the void in the radial direction of the through hole can be specified by various indexes, and the area (maximum value) of the image of the void in the cross section of the candidate of the void in the direction perpendicular to the axis of the through hole It may be converted, or it may be the diameter of an approximate circle approximating the circumference of the image of the void, or a specific coordinate axis direction (for example, the X axis when the depth direction of the through hole is the Z axis direction It can be configured by the length of the image of the void in the direction or Y axis direction).

  In any case, the voids in the filling formation portion formed by the through holes being filled by plating have a three-dimensional shape different from normal voids (spherical voids) in other inspection objects (eg, bumps). There is a feature. Therefore, the determination means acquires, from the reconstruction information, a feature amount reflecting the three-dimensional feature specific to the void in the filling and forming unit. As a result, the determination means determines the presence or absence of the void in the filling formation portion by the presence of the void in the filling formation portion based on the feature amount, thereby accurately determining the presence or absence of the void in the filling formation portion formed by the through hole being filled by plating. can do.

  Although the above has described the case where the present invention is realized as an apparatus, the present invention is also applicable to a method or program for realizing such an apparatus. The X-ray inspection apparatus as described above may be realized alone, may be applied to a method, or may be used in a state in which the method is incorporated into another device. The invention is not limited to this, and includes various aspects. Of course, the embodiment of the invention may be changed as appropriate, such as software or hardware. The software recording medium may be a magnetic recording medium or a magneto-optical recording medium, and any recording medium developed in the future can be considered in the same way. The same applies to the replication stages of primary and secondary copies. In addition, even when using a communication line as a supply device, the present invention is still used. Furthermore, even when a part is software and a part is realized by hardware, the concept of the invention is not completely different, and a part is stored on a recording medium and appropriately used as needed. It may be in a form to be read.

1 is a schematic block diagram of an X-ray inspection apparatus. (2A) is a schematic view showing a formation process of plating, and (2B) is a flowchart of X-ray inspection processing. (3A) shows an example of an image of the filling formation part, (3B) to (3D) shows an example of a cross sectional view of the image of the filling formation part, (3E) to (3G) schematically show voids. FIG.

Here, embodiments of the present invention will be described in the following order.
(1) Configuration of X-ray inspection apparatus:
(2) X-ray inspection process:
(3) Other embodiments:

(1) Configuration of X-ray inspection apparatus:
FIG. 1 is a schematic block diagram of an X-ray inspection apparatus according to an embodiment of the present invention. The X-ray inspection apparatus includes an X-ray imaging mechanism unit 10 and a control unit 20. The X-ray imaging mechanism unit 10 includes an X-ray generator 11 and an X-ray detector 12. In the X-ray imaging mechanism unit 10, the part W including the filling formation portion formed by filling the through holes by plating, the X-ray generator 11, and the X-ray detector 12 have a predetermined relative positional relationship. In the state, the part W is irradiated with X-rays by the X-ray generator 11.

  The X-ray generator 11 includes an X-ray output unit 11 a that outputs X-rays, and can irradiate the component W with X-rays at a predetermined intensity. The X-ray detector 12 includes a detection surface 12 a that detects the intensity of X-rays, and can capture an X-ray image reflecting the amount of transmission of X-rays transmitted through the component W. That is, the X-ray detector 12 generates X-ray image data 26 b indicating an image of the X-ray transmission amount at each position of the detection surface 12 a.

  In the present embodiment, the component W is a substrate (or a core material of the substrate) having plated through holes, and the component W is transported along a predetermined plane by a transport mechanism (not shown). That is, an uninspected part W is carried in along a predetermined plane, disposed in the X-ray irradiation range, inspected, and then taken out by the transport mechanism again. In the present embodiment, a positioning mechanism (not shown) for changing the relative positional relationship between the X-ray generator 11, the X-ray detector 12 and the component W is provided. That is, the positioning mechanism can move the part W two-dimensionally along a predetermined plane (referred to as an X-Y plane) within the X-ray irradiation range, and the filling formation portion and the X-ray output A moving mechanism for moving at least one position of the unit 11a and the detection surface 12a is provided, and the filling and forming unit, the X-ray output unit 11a, and the detection are performed so as to obtain an X-ray image for performing a reconstruction operation. The relative positional relationship with the surface 12a can be adjusted.

  Although the relative positional relationship for carrying out the reconstruction calculation can be realized in various aspects, for example, the relative positional relationship between the filling and forming unit, the X-ray output unit 11a and the detection surface 12a is relative to a predetermined rotational axis. It is possible to adopt a configuration in which the rotation is made to change. That is, the positioning mechanism moves the X-ray output unit 11a and the detection surface 12a substantially with respect to the rotation axis by moving at least one of the filling forming unit, the X-ray output unit 11a, and the detection surface 12a. You can change the position to In such a configuration, for example, both the X-ray output unit 11a and the detection surface 12a may be rotationally moved, or the X-ray output unit 11a is fixed, and the detection surface 12a and the component W rotate in the output range The X-ray output unit 11a and the detection surface 12a may be fixed, and the component W may be rotated in the output range of the X-ray output unit 11a.

  Next, the control unit 20 will be described. The control unit 20 includes a generator control unit 21, a detector control unit 22, a positioning mechanism control unit 23, an input unit 24, an output unit 25, a memory 26 and a CPU 27. The memory 26 is a storage medium capable of storing data, and stores program data 26 a and X-ray image data 26 b. The CPU 27 reads and executes the program data 26 a to execute calculations for various processes described later. The memory 26 only needs to store data, and various storage media such as a RAM, an EEPROM, and an HDD can be employed.

  The positioning mechanism control unit 23 adjusts at least one position of the filling and forming unit, the X-ray output unit 11a, and the detection surface 12a so as to be an imaging position for capturing an X-ray image of the filling and forming unit. The generator control unit 21 controls the X-ray generator 11 so that the X-ray generator 11 emits X-rays to the component W. The detector control unit 22 acquires X-ray image data 26 b indicating the intensity of the X-rays detected by the X-ray detector 12, that is, the transmission amount. The X-ray image data 26 b is image data composed of gradation values of a plurality of pixels, and the gradation value of each pixel indicates the intensity of X-rays detected by the X-ray detector 12. The detector control unit 22 acquires the X-ray image data 26 b from the X-ray detector 12 and stores the data in the memory 26. The output unit 25 is a display that displays the inspection result of the part W and the like, and the input unit 24 is an operation input device that receives an input from the user.

  The CPU 27 performs each function of the X-ray image acquisition unit 27a, the reconstruction calculation unit 27b, the determination unit 27c, and the quality determination unit 27d based on the program data 26a in order to determine the quality of the filling formation unit included in the part W. Run. The X-ray image acquiring unit 27a causes the CPU 27 to execute a function of irradiating the X-rays to the filling and forming unit formed by filling the through holes by plating and acquiring a plurality of X-ray images captured from different directions. It is a program module. That is, the CPU 27 outputs predetermined instructions to the generator control unit 21, the detector control unit 22, and the positioning mechanism control unit 23 by the processing of the X-ray image acquisition unit 27a, and executes the reconstruction operation. The CPU 27 is caused to execute processing for acquiring the X-ray image data 26 b.

  The reconstruction calculation unit 27 b is a program module that causes the CPU 27 to execute processing to execute reconstruction calculation based on a plurality of X-ray images. That is, the CPU 27 executes the reconstruction calculation based on the X-ray image data 26b by the processing of the reconstruction calculation unit 27b. As a result, the state in which the reconstruction information is defined in the three-dimensional space constituted by the X, Y, and Z axes, that is, the value corresponding to the X-ray absorption amount is defined for each coordinate in the three-dimensional space It becomes a state. Hereinafter, reconstruction information in a particular plane is referred to as an X-ray image of a cross section obtained by cutting the reconstruction information at the plane.

  The determination unit 27 c extracts a feature amount specific to the void in the filling and forming unit formed by the through hole being filled by plating from the reconstruction information obtained by the reconstruction operation, and filling based on the feature amount. It is a program module that causes the CPU 27 to execute the function of determining the presence or absence of a void in the forming unit. That is, the CPU 27 extracts the image of the filling and forming unit based on the reconstruction information by the processing of the determination unit 27c, and extracts the feature amount specific to the void in the filling and forming unit from the image. The feature amount is identified focusing on the fact that the filling formation part is a spheroid close to the central axis of the through hole and long in the depth direction of the through hole.

  FIG. 2A shows a state in which the plating M is formed in the through holes T formed in the substrate (or the core material of the substrate) in a state in which the substrate P is cut in a cross section passing through the central axis of the through holes T. There is. (1) (2) (3a) shown in FIG. 2A shows a state in which the through hole T is filled with the plating M through a normal process. In the normal process, as shown in (1) of FIG. 2A, the plating is formed to be gradually stacked from the back side with respect to the wall surface in the through hole T. When the plating reaches the open end of the through hole, the through hole T is filled as shown in (3a) of FIG. 2A, and the filling formation portion F is formed in the portion which was the through hole T.

  However, if a site with a large curvature occurs in the process of plating, plating will grow faster than other curved surfaces starting from that site, and the opening will be blocked before the growth of plating on the wall reaches the opening. There is a case. When such abnormal plating growth occurs, for example, when a void V is formed in the filling formation portion F as in (3b) after a process such as (1) and (2) shown in FIG. 2A There is.

  The three-dimensional structure of the void V formed in the filling and forming portion F in this manner is different from the void of a sphere usually found in a solder bump or the like (void which becomes substantially sphere due to surface tension). That is, since growth of plating from the wall surface of through hole T gradually progresses from the back of the through hole toward the opening, plating growth gradually from the wall surface of through hole T toward the central axial direction and the opening direction It will progress. Moreover, in this process, as shown in (2) of FIG. 2A, a long space is formed in the depth direction D of the through hole T near the central axis Ax of the through hole T, and plating is performed to fill the space. Will grow. Therefore, the void in the filling formation portion F is almost formed in the vicinity of the central axis of the through hole T, and in the inspection for determining the quality of the filling formation portion F, the void is located at a position far from the central axis of the through hole T. It can be considered that no void to be considered is formed.

  Also, since the through hole T is usually a long hole in the central axis direction of the through hole T, the shape of the space left without being plated on the inner side of the wall in the process of growing the plating along the wall Is elongated in the central axis direction. Therefore, the void formed in the filling formation portion is shaped like a long spheroid in the central axis direction of the through hole T, and is not spherical. For this reason, in the inspection for determining the quality of the filling formation portion, it can be considered that the void should not be regarded as a defect unless the shape of the void is a spheroid long in the central axis direction of the through hole T. Therefore, in the present embodiment, the CPU 27 specifies the candidate of the void based on the reconstruction information by the processing of the determination unit 27c, and the feature amount indicating the relationship between the candidate of the void and the central axis of the through hole T, and the through hole The feature amount indicating the candidate length of the void in the depth direction of T is analyzed.

  Specifically, the CPU 27 specifies an image of the filling and forming unit F to be inspected from among the reconstruction information and specifies a candidate of a void in the filling and forming unit F (details will be described later). Further, the CPU 27 identifies the central axis in the case where it is considered that the filler forming part F is a cylinder based on the image of the filler forming part F, and regards it as the central axis Ax of the through hole T. Furthermore, the CPU 27 specifies the center of gravity of the candidate void. Then, the CPU 27 acquires the distance between the central axis Ax and the center of gravity of the candidate of the void as the feature amount, and regards the candidate of the void as not a void when the distance is longer than a predetermined distance determination reference. The predetermined distance criterion for analyzing the distance between the central axis Ax of the through hole T and the center of gravity of the candidate of the void is that the candidate of the void is far from the central axis Ax and the cause of the defect at the position of the candidate of the void It is determined in advance that it is a determination criterion that can be regarded as a void that can not be present, and is a determination criterion that compares a value after the distance is normalized with a threshold (details will be described later) .

  Furthermore, the CPU 27 regards the direction parallel to the central axis Ax of the through hole T as the through hole depth direction D, and acquires the candidate candidate length in the through hole depth direction as the feature amount. Then, when the length is less than the predetermined depth determination standard, the CPU 27 considers that the candidate of the void is not a void. The predetermined depth criterion for analyzing the candidate length of the void in the depth direction D of the through hole is the cause of the failure when the candidate of the void is not a long spheroid in the depth direction of the through hole. It is determined in advance that it is a judgment standard that can be regarded as not a void that is to be a standard, and is a judgment standard that compares a threshold value with a value after normalization of the length in the depth direction Later). According to the above configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion formed by filling the through hole by plating.

  The quality determination unit 27d is a program module that causes the CPU 27 to execute the function of determining the quality of the filling and forming unit F. That is, when the candidate of the void remains in the filling and forming part F by the process of the quality determination part 27d, the CPU 27 regards the candidate as the void causing the defect, and the filling and forming part F is defective. It is determined that Then, when no candidate for void remains in the filling and forming unit F, the CPU 27 determines that the filling and forming unit F is not defective.

(2) X-ray inspection process:
FIG. 2B is a flowchart showing the X-ray inspection process. The X-ray inspection process is performed after the part W to be inspected is transported to the X-ray irradiation range. In the X-ray inspection process, the CPU 27 performs a CT imaging process by the process of the X-ray image acquisition unit 27a (step S100). That is, the CPU 27 outputs a predetermined instruction to the generator control unit 21, the detector control unit 22, and the positioning mechanism control unit 23 by the processing of the X-ray image acquisition unit 27a, and makes an angle inclined in the Z axis direction. The arrangement of each part is adjusted so that X-rays are irradiated to the filling and forming part F. Furthermore, the CPU 27 causes the generator control unit 21 to output a predetermined instruction to output an X-ray with a predetermined output, and causes the detector control unit 22 to output a predetermined instruction by the processing of the X-ray image acquisition unit 27a. The instruction is output to acquire the X-ray image data 26b. Furthermore, the CPU 27 executes the process of capturing the X-ray image data 26b as described above at a plurality of imaging positions where it can be considered that rotation about the axis A is performed, and X taken at a plurality of imaging positions. The line image data 26 b is recorded in the memory 26.

  Next, the CPU 27 executes the reconstruction calculation processing by the processing of the reconstruction calculation unit 27b (step S110). As long as the reconstruction operation can reconstruct the three-dimensional structure of the filling and forming unit F, various processes can be adopted. For example, a filtered back projection method can be employed. In this process, the CPU 27 first performs Fourier transform on any of the plurality of X-ray images, and multiplies the result obtained by the Fourier transform by the filter correction function in the frequency space. Furthermore, an inverse Fourier transform is performed on this result to obtain an image subjected to filter correction. Note that this filter correction function can adopt a function or the like for emphasizing the edge of the image.

  Subsequently, the image after the filter correction is backprojected onto the three-dimensional space along the trajectory on which it is projected. That is, since the locus corresponding to the image at a certain position on the detection surface 12a of the X-ray detector 12 is a straight line connecting the focal point of the X-ray generator 11 and this position, the image is backprojected onto this straight line. When the above-described back projection is performed on all of the plurality of X-ray images, the X-ray absorption coefficient distribution of the portion where the filling formation portion F exists in three-dimensional space is emphasized, and the three-dimensional shape of the filling formation portion F is shown again Configuration information is obtained.

  Next, the CPU 27 acquires an image of the filling and forming unit F by the process of the determination unit 27c (step S120). That is, the CPU 27 specifies the scanning range of the image of the filling and forming unit F based on the approximate position of the filling and forming unit F in the substrate P which is known in advance, and the X-ray is based on the reconstruction information within the scanning range. Identifies the portion absorbed by the plating material, and acquires it as an image of the filling formation portion F. FIG. 3A is a view schematically showing an image of the filling and forming unit F acquired by the CPU 27. In FIG. 3A, X, Y and Z axes which are coordinate systems of the reconstruction information are shown together.

  As described above, when the portion where X-rays are absorbed is scanned, an image of a shape reflecting the shape of the through hole T is acquired. Since the through holes T in the present example are cylindrical holes, the image of the filling formation portion F is also cylindrical. When the image of the filling and forming unit F is specified, as shown in FIG. 3A, the image of the filling and forming unit F may be inclined with respect to the coordinate axis of the reconstruction information. It is possible to specify the cylinder axis of the filling formation portion F corresponding to the central axis Ax of the through hole T by specifying a straight line connecting the center of gravity of a circle appearing in a cross section perpendicular to the longitudinal direction of the image. Therefore, in the present embodiment, the CPU 27 specifies the central axis Ax based on the image of the filling and forming unit F, and coordinates of the reconstruction information are set in advance so that the central axis Ax is parallel to the Z axis direction. Convert. Therefore, after the conversion, the central axis direction of the through hole and the depth direction of the through hole are parallel to the Z axis direction, and the radial direction of the through hole is parallel to the XY plane.

  Next, the CPU 27 acquires void candidates by the process of the determination unit 27c (step S130). That is, the CPU 27 specifies a portion in the image of the filling and forming portion F in which the X-ray is not absorbed by the plating material. In the present embodiment, the CPU 27 extracts a portion having a shape that can be a void from the portion (a portion where X-rays are not absorbed) and sets it as a candidate of a void. The extraction can be performed by various methods, and in the present embodiment, the CPU 27 is based on the cross-sectional area, the roundness, the flatness, and the roughness in the cross section in the direction parallel to the XY plane of the part. Extraction.

  Specifically, the CPU 27 regards a range in which a region where X-rays are not absorbed is continuous as a region corresponding to one void, and determines it as a region to be determined. Furthermore, if the CPU 27 cuts the portion to be determined in the direction parallel to the XY plane, whether or not the portion to be determined should be extracted as a candidate for a void, when the cross section having the largest cut surface is extracted. It is the cross section of the object to be determined. Further, the CPU 27 binarizes the cross section of the target to specify a portion where X-rays are not absorbed and a portion where the X-ray is absorbed, and acquires the number of pixels of the portion not absorbed as a cross-sectional area. Then, when the cross-sectional area is less than the predetermined cross-sectional area threshold, the portion to be determined is small or noise, and thus the CPU 27 determines that the portion to be determined is not a candidate for a void.

Furthermore, the CPU 27 specifies the perimeter of the cross section from the position of the edge of the portion where X-rays are not absorbed in the target cross section and also determines the length P of the perimeter, and acquires 4πS / P ² as the roundness. . Here, S is a cross-sectional area of a portion where X-rays are not absorbed. The value of 4πS / P ² is greater than 0 and less than or equal to 1 and becomes closer to 1 as the shape of the circumference is closer to a circle, and becomes smaller as the shape of the circumference becomes more complex. Since a void is a hollow in plating and the surface does not have a complicated shape, when the roundness is less than a predetermined roundness threshold, the portion to be determined is noise, and the CPU 27 determines the portion to be determined It is assumed that the site of is not a candidate for void.

  Furthermore, the CPU 27 specifies the maximum value a and the minimum value b of the diameter of the portion where X-rays are not absorbed in the cross section of the target, and acquires a / b as the flattening. The a / b is a value of 1 or more, and is larger as the cross section of the portion to be determined is flat. Since a void is a hollow in plating and the cross section does not become flat, if the flatness is equal to or more than a predetermined flatness threshold, the portion to be determined is noise, and the CPU 27 determines the portion to be determined as a void Not a candidate for

  Furthermore, the CPU 27 identifies the circumference of the region where X-rays are not absorbed in the cross section of the subject, identifies the burial line, identifies the length of the burial line (burlap perimeter) E, and Get E as the coarseness. Here, P is the circumferential length described above. The value of P / E is a value larger than 1, and the larger the number of irregularities on the circumference, the larger the value. Since a void is a hollow in plating and the surface does not have a complicated shape, when the roughness is equal to or greater than a predetermined roughness threshold, the portion to be determined is noise, and the CPU 27 determines the portion to be determined Is not a candidate for a void.

  The CPU 27 executes the above processing for all the determination target portions present in the image of the filling and forming unit F, and when the determination target portion is not considered not to be a candidate for a void, the relevant portion is void Get as a candidate. In FIG. 3A, candidates Vc of voids which may exist in the image of the filling and forming portion F are schematically shown.

  When the candidate of the void is acquired, the CPU 27 selects the candidate of the void by the process of the determination unit 27c (step S140). That is, the candidate of the void which should be regarded as a defect and the candidate of the void which should not be regarded as a defect are selected. Specifically, the CPU 27 divides the distance between the central axis Ax of the through hole T and the center of gravity of the candidate of the void by the size of the candidate of the void (the value of the distance after normalization) is equal to or greater than a predetermined distance threshold If, the distance is considered to be longer than a predetermined distance criterion.

  For this purpose, the CPU 27 regards the central axis of the image of the filling and forming portion F as the central axis Ax of the through hole T. Further, the CPU 27 specifies the center of gravity of the void based on the image of the candidate of the void, and acquires the largest diameter among the diameters passing through the center of gravity as the diameter. Of course, the diameter can be identified in various other manners. Then, the CPU 27 acquires the distance between the central axis Ax and the center of gravity, and acquires a value obtained by dividing the distance by the diameter as the size of the void candidate as the value of the normalized distance.

FIG. 3B, FIG. 3C, and FIG. 3D are figures which show typically the image at the time of cut | disconnecting the image of the filling formation part F by the cross section parallel to XY plane while passing through the gravity center of a void. In FIG. 3B, the diameter of the candidate V _{1 for} the void is R ₁ , the distance between the central axis Ax and the center of gravity of the candidate V _{1 for} the void is L _{1. In} FIG. 3C, the diameter of the candidate V ₂ for void is R ₂ , the distance between the central axis Ax and the center of gravity of the candidate V ₂ of the void is L ₁ , and in FIG. 3D, the diameter of the candidate V ₃ for void is R ₂ , the center axis A x and the center of gravity of the candidate V ₃ of the void Distance is L ₂ .

  Furthermore, when the value of the normalized distance is equal to or greater than a predetermined distance threshold, the CPU 27 considers that the candidate for void is not a void. The normalized distance value obtained by dividing the distance between the central axis Ax and the center of gravity by the diameter of the void candidate is a plurality of plural equal distances between the central axis Ax of the through hole T and the center of gravity of the candidate for void. In the candidate for void, the smaller the candidate for void becomes, the larger it becomes. Therefore, by comparing the value of the normalized distance with a predetermined distance threshold, the CPU 27 determines a relatively small void candidate even if the distance between the central axis Ax of the through hole T and the center of gravity of the void candidate is the same. Can be considered not to be void, and candidates for relatively large voids can be considered to be voids.

For example, comparing FIG. 3B and FIG. 3C, the distance between the center axis Ax of gravity of the voids of the candidate of the through hole T is the same distance L _1. On the other hand, the diameter R ₁ > the diameter R ₂ , and the diameter of the candidate V ₁ of the void shown in FIG. 3B is larger than the diameter of the candidate V ₂ of the void. Therefore, if the predetermined distance threshold is set in advance so that L ₁ / R ₁ <predetermined distance threshold <L ₁ / R ₂ , the CPU 27 determines that the candidate V ₁ of the void is a void, Candidate V ₂ can be considered not to be void.

Furthermore, the CPU 27 considers void candidates relatively far from the central axis Ax of the through hole T as non-voids and relatively close void candidates as void even if the sizes of the candidate candidates are the same. Is possible. For example, comparing FIG. 3C and FIG. 3D, the diameter of the candidates V ₃ of the diameter and the void of the candidate of the void V ₂ are the same a R ₂ both. On the other hand, the distance between the center of gravity of the central axis Ax and voids candidate through hole T is the direction of the distance L ₁ in FIG. 3C is greater than the distance L ₂ in FIG. 3D. Therefore, if the predetermined distance threshold is set in advance such that L ₂ / R ₂ <predetermined distance threshold <L ₁ / R ₂ , the CPU 27 determines that the candidate V ₃ of the void is a void and the candidate of the void V ₂ can be considered not to be void.

  According to the above configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion F formed by filling the through hole T by plating. The predetermined distance threshold can be regarded as a void candidate far away from the central axis Ax of the through hole T or a void candidate (or a void candidate which is a noise) having a small size not being a void. It may be specified in advance by statistics or the like.

  Further, the CPU 27 sets a value (a value of the depth after normalization) obtained by dividing the candidate length of the void in the depth direction of the through hole T by the length of the candidate of the void in the radial direction of the through hole T. When it is less than the depth threshold, the candidate length of the void in the depth direction is considered to be less than a predetermined depth criterion (that is, the candidate of the void is not considered to be a void). For this purpose, the CPU 27 regards the length in the central axis direction of the image of the filling and forming portion F as the length in the depth direction of the through hole T. In addition, the CPU 27 acquires the diameter of the above-described void candidate. Then, the CPU 27 obtains a value obtained by dividing the candidate length of the void in the depth direction of the through hole T by the length of the candidate of the void in the radial direction of the through hole T as a normalized depth value.

FIGS. 3E, 3F, and 3G are views schematically showing an image of a void, in which the vertical direction is the depth direction D of the through hole T, and the horizontal direction is the radial direction Ra of the through hole. It is shown schematically. In FIG. 3E, the length in the depth direction of through hole T of candidate void V ₄ is D ₁ and the length in the radial direction is Ra ₁ , and in FIG. 3F, the through hole T of candidate void V ₅ is Has a length in the depth direction D ₁ and a length in the radial direction Ra ₂ , and in FIG. 3G, the length in the depth direction of the through hole T of the candidate V ₆ of the void is D _{2 in} the radial direction The length is Ra ₁ .

  Furthermore, when the value of the normalized depth is less than a predetermined depth threshold, the CPU 27 considers that the candidate void is not a void. The normalized depth value obtained by dividing the candidate length of the void in the depth direction of the through hole T by the length of the candidate of the void in the radial direction of the through hole T is the length in the depth direction of the through hole T In the plurality of void candidates having the same length, the smaller the radial length of the through hole T, the smaller it becomes. Therefore, by comparing the value of the normalized depth with the predetermined depth threshold, the CPU 27 determines that the candidate void is a through hole even if the candidate void in the depth direction of the through hole T has the same length. If the spheroid is not long in the central axis Ax direction of T (for example, if it is close to a sphere), the candidate of the void is considered not void, and if the spheroid is long in the central axis Ax direction of the through hole T Candidates for voids can be considered to be voids.

For example, comparing FIG. 3E and FIG. 3F, the length of the void of the candidate in the depth direction of the through hole T is the same length D _1. On the other hand, the candidate lengths Ra ₁ and Ra ₂ of the voids in the radial direction of the through hole T are such that the length Ra ₂ > the length Ra ₁ , and the candidate void shown in FIG. Close to the body, the candidate void shown in FIG. 3F is close to spherical. Then, if the predetermined distance threshold is set in advance so that D ₁ / Ra ₂ <predetermined depth threshold <D ₁ / Ra ₁ , the CPU 27 determines that the value of the normalized depth is a predetermined depth. candidate V ₅ of voids is less than the threshold value is not void, candidate V ₄ of voids can be regarded as void.

  Furthermore, even if the radial length of the through hole T is the same, the CPU 27 does not have a candidate void that is a long spheroid in the direction of the central axis Ax of the through hole T (for example, if it is close to a sphere), The candidate of void can be regarded as not being void, and if the spheroid is long in the direction of the central axis Ax of the through hole T, the candidate of void can be regarded as being void.

For example, comparing FIG. 3E with FIG. 3G, the candidate lengths of the voids in the radial direction of the through hole T are both the same in length Ra ₁ . On the other hand, the candidate lengths of the void in the depth direction of the through hole T are D ₁ and D ₂ , and the length D ₁ of the candidate V ₄ of the void is longer than the length D ₂ of the candidate V ₆ of the void long. And, the candidate of the void shown in FIG. 3E is close to a spheroid elongated in the D direction, and the candidate of the void shown in FIG. 3G is close to a spherical shape. Therefore, if the predetermined distance threshold is set in advance so that D ₂ / Ra ₁ <predetermined depth threshold <D ₁ / Ra ₁ , the CPU 27 determines that the value of the normalized depth is predetermined. candidate V ₆ of the voids is less than the depth threshold is not void, candidate V ₄ of voids can be regarded as void.

  According to the above configuration, it is possible to accurately determine the presence or absence of a void in the filling formation portion F formed by filling the through hole T by plating. It should be noted that the predetermined depth threshold is a void candidate whose shape is not a long spheroid long in the depth direction of the through hole T but a void candidate short in the depth direction (or a candidate for a void that is noise) As long as it can be considered that it does not exist, it should just be specified by statistics etc. beforehand.

  When the voids are sorted as described above, the CPU 27 performs the quality determination process by the process of the quality determination unit 27d (step S150). That is, when the candidate of the void remains in the filling and forming part F by the process of the quality determination part 27d, the CPU 27 regards the candidate as the void causing the defect, and the filling and forming part F is defective. It is determined that If it is determined that not all of the void candidates are void, the CPU 27 determines that the filler-formed portion F is not defective.

(3) Other embodiments:
The above embodiment is an example for carrying out the present invention, and a characteristic amount specific to the void in the filling formation portion formed by filling the through hole by plating is extracted, and the filling is performed based on the characteristic amount. Various other embodiments can be adopted as long as the presence or absence of a void in the formation portion is determined. For example, the process for determining the quality is not limited to the above-described example, and the quality may be determined based on the distance between the void and the end of the filling formation portion in the Z-axis direction.

  Furthermore, when the candidates for the void are selected, the selection may be performed without standardizing the distance or the length in the depth direction. That is, when the CPU 27 determines whether the distance between the center axis of the through hole and the center of gravity of the candidate for the void is equal to or greater than a predetermined distance determination reference, the distance between the center axis of the through hole and the center of gravity of the candidate for the void And the threshold may be compared. In addition, when the CPU 27 determines whether the candidate length of the void in the depth direction of the through hole is less than a predetermined depth determination criterion, the length and the threshold of the candidate of the void in the depth direction of the through hole And may be compared with each other. Furthermore, in the above-mentioned embodiment, although X-rays are used, other radiation which penetrates an examination object, for example, gamma rays etc. may be used.

  DESCRIPTION OF SYMBOLS 10 ... X-ray imaging mechanism part, 11 ... X-ray generator, 11a ... X-ray output part, 12 ... X-ray detector, 12a ... detection surface, 20 ... control part, 21 ... generator control part, 22 ... detector Control unit 23 Positioning mechanism control unit 24 Input unit 25 Output unit 26 Memory 26a Program data 26b X-ray image data 27a X-ray image acquisition unit 27b Reconstruction operation unit , 27c ... determination unit, 27d ... quality determination unit

Claims (8)

X-ray image acquisition means for irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
Reconstruction operation means for executing a reconstruction operation based on the plurality of X-ray images;
From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by the said through hole being filled by plating, the central axis of the said through hole and the void A determination unit that acquires a distance from the barycenter of the candidate and determines that the candidate of the void is not a void if the distance is equal to or greater than a predetermined distance determination criterion ;
X-ray examination apparatus provided with   X-ray image acquisition means for irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
  Reconstruction operation means for executing a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by the said through hole being filled by plating, the central axis of the said through hole and the void A determination unit that determines that the candidate void is not a void if a value obtained by dividing the distance from the center of gravity of the candidate by the size of the candidate void is equal to or greater than a predetermined distance threshold;
X-ray examination apparatus provided with   X-ray image acquisition means for irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
  Reconstruction operation means for executing a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by being filled with the said through hole by plating, the said void in the depth direction of the said through hole Determining means for determining that the candidate for void is not a void if the length of the candidate for candidate is less than a predetermined reference length;
X-ray examination apparatus provided with   X-ray image acquisition means for irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
  Reconstruction operation means for executing a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by being filled with the said through hole by plating, the said void in the depth direction of the said through hole Determination that the void candidate is not a void if the value obtained by dividing the candidate length by the candidate length in the radial direction of the through hole is less than a predetermined reference length Means,
X-ray examination apparatus provided with   An X-ray image acquiring step of irradiating the X-rays to the filling formation portion formed by filling the through holes by plating and acquiring a plurality of X-ray images photographed from different directions;
  A reconstruction operation step of executing a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by the said through hole being filled by plating, the central axis of the said through hole and the void Determining whether a candidate of the void is not a void if a distance to the center of gravity of the candidate is acquired and the distance is equal to or greater than a predetermined distance determination criterion;
X-ray examination method including.   An X-ray image acquiring step of irradiating the X-rays to the filling formation portion formed by filling the through holes by plating and acquiring a plurality of X-ray images photographed from different directions;
  A reconstruction operation step of executing a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by being filled with the said through hole by plating, the said void in the depth direction of the said through hole Determining whether the candidate for void is not a void if the length of the candidate for candidate is less than a predetermined reference length;
X-ray examination method comprising.   An X-ray image acquiring function of irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
  A reconstruction operation function that executes a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by the said through hole being filled by plating, the central axis of the said through hole and the void A determination function of acquiring a distance from the barycenter of the candidate and determining that the candidate of the void is not a void if the distance is equal to or greater than a predetermined distance determination criterion;
An X-ray examination program that realizes a computer.   An X-ray image acquiring function of irradiating the X-rays to the filling formation part formed by filling the through holes by plating and acquiring a plurality of X-ray images taken from different directions;
  A reconstruction operation function that executes a reconstruction operation based on the plurality of X-ray images;
  From the reconstruction information obtained by the reconstruction operation, while specifying the candidate of the void in the said filling formation part formed by being filled with the said through hole by plating, the said void in the depth direction of the said through hole A determining function of determining that the candidate for void is not a void if the length of the candidate for candidate is less than a predetermined reference length;
An X-ray examination program that realizes a computer.

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