JP2023053558A - Inspection device - Google Patents

Abstract

To provide an inspection device which can calculate a deviation amount from a prescribed reference surface of an inspection object surface of an inspection object without having a configuration of detecting a position of the inspection object.SOLUTION: An inspection device 1 comprises: a radiation generator 22; a substrate holding part 24 which holds an inspection object 2; a detector 26; drive parts 16, 18, 20 which change relative positions between the inspection object 2 and the detector 26 held by the radiation generator 22 and the substrate holding part 24; and a control part 10. The control part 10, when the inspection object 2 and the detector 26 held by the radiation generator 22 and the substrate holding part 24 are in prescribed relative positions, detects a deviation amount from a prescribed reference surface of an inspection object surface of the inspection object 2 on the basis of at least one transmission image of the inspection object 2 detected and acquired by the detector 26.SELECTED DRAWING: Figure 6

Description

The present invention relates to an inspection device.

Tomosynthesis X-ray inspection apparatuses are known as inspection apparatuses for measuring solder shapes on the front surface and the back surface of a substrate (see Patent Documents 1 and 2).

JP 2006-220424 A Japanese Patent Application Laid-Open No. 2003-240736

In such an inspection apparatus, a plurality of transmission images are taken by changing the relative positions of a radiation source (radiation generator), an object to be inspected (for example, an electronic substrate), and a detector, and these transmission images are reconstructed. and to generate a cross-sectional image of the object to be inspected. In order to shorten the inspection time, such an inspection apparatus is configured to pick up transmission images while changing the relative positions of the radiation source, the object to be inspected, and the detector. However, if a transmission image is taken while changing the relative positions of the radiation source, the object to be inspected, and the detector, depending on the position of the object to be inspected, image blurring called motion blur occurs, reducing inspection accuracy. Resulting in. For example, if the object to be inspected is an electronic substrate, the surface to be inspected of the object to be inspected (hereinafter referred to as the “surface to be inspected”) may be subject to blur due to distortion such as warpage or bending. This may result in blurring of the transmitted image due to deviation from the range (this range is called the "aiming area").

In order to prevent such blurring of the transmission image, a length measuring device or the like is provided for measuring the position on the object to be inspected. Based on this, an inspection apparatus has been put into practical use, which adjusts the inspection target surface of the object to be inspected so that it substantially coincides with a predetermined reference plane provided within the aiming area, for example, within the aiming area. There is a problem that extra cost is required to provide the length measuring device, and since the length measuring device is also irradiated with radiation, there is a problem that confirmation of deterioration due to exposure to radiation and replacement work are required.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and provides a method for calculating the amount of deviation of an inspection target surface of an object to be inspected from a predetermined reference plane without providing a configuration for detecting the position of the object. It is an object of the present invention to provide an inspection device capable of

In order to solve the above problems, an inspection apparatus according to the present invention includes: a radiation source; A driving unit for changing a relative position with respect to the detector, and a control unit, wherein the control unit controls the radiation source and the inspected object and the detector held by the holding unit by the driving unit. based on at least one transmission image of the object to be inspected obtained by detecting radiation emitted from the radiation source and transmitted through the object to be inspected by the detector when and are at predetermined relative positions. A deviation amount of an inspection object surface of an object to be inspected from a predetermined reference surface is detected.

Further, in the inspection apparatus according to the present invention, the control unit detects the displacement amount at a plurality of positions on the object to be inspected, and detects the displacement amount of the position where the displacement amount is not detected. It is preferable to calculate by linear interpolation using quantity.

In addition, in the inspection apparatus according to the present invention, the control unit uses a value of a position with a known displacement amount in addition to the detected displacement amount in calculating the displacement amount of the position where the displacement amount is not detected. It is preferable to perform linear interpolation using

Further, in the inspection apparatus according to the present invention, the control unit controls the transmission image when the radiation source, the object to be inspected held by the holding unit, and the detector are at predetermined relative positions. and a reference image which is a transmission image when the surface to be inspected of the object to be inspected is on the predetermined reference plane at the predetermined relative position.

Further, in the inspection apparatus according to the present invention, the control unit detects the same feature shape in the transmission image and the reference image by a phase-only correlation method, and detects the deviation based on the difference in magnification of the feature shape. It is preferred to detect the amount.

Further, in the inspection apparatus according to the present invention, the control unit detects the same feature shape in the transmission image and the reference image by a feature quantity matching method, and detects the deviation based on the difference in magnification of the feature shape. It is preferred to detect the amount.

Further, in the inspection apparatus according to the present invention, the control unit may generate two or more transmitted images when the radiation source, the object to be inspected held by the holding unit, and the detector are at different positions. Preferably, a cross-sectional image of the object to be inspected is generated by reconstruction, and the deviation amount is detected using the cross-sectional image.

Further, in the inspection apparatus according to the present invention, the control unit determines a cross-sectional image that most matches a reference image of the cross-sectional images from among the cross-sectional images, and detects the displacement amount from the position of the cross-sectional image. is preferred.

Further, in the inspection apparatus according to the present invention, the control unit specifies, from among the cross-sectional images, a cross-sectional image that most matches a reference image of the cross-sectional images by a phase-only correlation method, and from the position of the cross-sectional image, the It is preferable to detect the amount of deviation.

Further, in the inspection apparatus according to the present invention, the control unit calculates a correction value for a position of the predetermined reference plane from the shift amount for each position where the transmission image on the subject is acquired, and correcting the relative positions of the radiation source and the object to be inspected and the detector held by the holding unit based on the values, and moving the radiation source and the detector based on the corrected relative positions by the driving unit. It is preferable to acquire the transmission image at a predetermined relative position while changing the relative positions of the inspected object and the detector held by the holding unit.

According to the inspection apparatus of the present invention, it is possible to provide an inspection apparatus capable of calculating the amount of deviation of an inspection target surface of an object to be inspected from a predetermined reference plane without providing a configuration for detecting the position of the object to be inspected. can do.

It is an explanatory view for explaining composition of an inspection device concerning this embodiment. It is an explanatory view for explaining each functional block which a control part of the above-mentioned inspection device processes. 4 is a flowchart for explaining inspection processing. 4 is a flowchart for explaining the flow of processing for capturing a transmission image and generating a reconstructed image; FIG. 4 is an explanatory diagram for explaining the movement of the substrate holder and the detector, and the timing of X-ray radiation from the radiation generator and imaging by the detector, where (a) is a timing chart and (b) is It shows the timing of exposure. It is explanatory drawing which represented typically the structure which looked at the said inspection apparatus from the side. 9 is a flowchart for explaining processing of a first correction method; 9 is a flowchart for explaining processing of a second correction method;

Preferred embodiments of the present invention are described below with reference to the drawings. As shown in FIG. 1, an inspection apparatus 1 according to the present embodiment includes a control unit 10, a monitor 12, and an imaging unit 32, which are configured by a processing device such as a personal computer (PC). . 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. have.

The radiation generator 22 is a device (radiation source) that generates radiation such as X-rays, and generates radiation by, for example, colliding accelerated electrons with a target such as tungsten or diamond. In addition, although the case of X-rays will be described as the radiation in this embodiment, the radiation is not limited to this. For example, the radiation can be alpha, beta, gamma, ultraviolet, visible, infrared. Alternatively, the radiation may be microwaves or terahertz waves.

The board holding part 24 holds a board, which is an object to be inspected. The object to be inspected held by the substrate holding unit 24 is irradiated with the radiation generated by the radiation generator 22, and the radiation transmitted through the object to be inspected is detected by the detector 26 and captured as an image. Hereinafter, the radiographic image of the object to be inspected captured by the detector 26 will be referred to as a "transmission image". As will be described later, in the present embodiment, the substrate holder 24 holding the substrate to be inspected and the detector 26 are moved relative to the radiation generator 22 to acquire a plurality of transmission images. to generate a reconstructed image (cross-sectional image).

A transmission image captured by the detector 26 is sent to the control unit 10, and a stereoscopic image of the solder at the joint is obtained using a known technique such as the Filtered-Backprojection method (FBP method). It is reconstructed into an image containing shapes. Then, the reconstructed image and the transparent image are stored in the storage within the control unit 10 or an external storage (not shown). Hereinafter, an image reconstructed into a three-dimensional image including the three-dimensional shape of the solder of the joint based on the transmission image will be referred to as a "reconstructed image". An image obtained by cutting out an arbitrary cross section from a reconstructed image is called a "cross section image". Such reconstructed images and cross-sectional images are output to the monitor 12 . Note that the monitor 12 displays not only the reconstructed image and the cross-sectional image, but also an inspection result of the joint state of solder, which will be described later, and the like. Further, the reconstructed image in the present embodiment is also called "planar CT" because it is reconstructed from the plane image (transmission image) captured by the detector 26 as described above.

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

Here, the quality of radiation is determined by the brightness and hardness of radiation (spectral distribution of radiation). If the tube current is increased, the number of electrons that collide with the target increases, and the number of photons of generated radiation also increases. As a result, the brightness of the radiation is increased. For example, some parts, such as capacitors, are thicker than other parts, and it is necessary to irradiate them with high-brightness radiation in order to capture a transmission image of these parts. In such a case, the luminance of radiation is adjusted by adjusting the tube current. Further, when the tube voltage is increased, the energy of electrons colliding with the target increases, and the energy (spectrum) of the generated radiation increases. In general, the higher the energy of radiation, the greater the penetration power of a substance and the less it is absorbed by a substance. Transmission images taken with such radiation have low contrast. Therefore, the tube voltage can be used to adjust the contrast of the transmitted image.

The radiation generator driving unit 16 has a driving mechanism such as a motor (not shown), and rotates the radiation generator 22 along an axis A passing through its focal point (an axis passing through the center of the radiation direction of the radiation emitted from the radiation generator 22). (optical axis), and the direction of this axis is referred to as the "Z-axis direction"). As a result, the distance between the radiation generator 22 and the object (substrate) held by the substrate holding unit 24 can be changed to change the irradiation field and to change the magnification of the transmission image picked up by the detector 26. It becomes possible. The position of the radiation generator 22 in the Z-axis direction is detected by the generator position detector 23 and output to the controller 10 .

The detector drive unit 20 also has a drive mechanism such as a motor (not shown), and rotates the detector 26 along the detector rotation track 30 . Further, the substrate holding portion driving portion 18 also has a driving mechanism such as a motor (not shown), and translates the substrate holding portion 24 on the plane on which the substrate rotation track 28 is provided. Further, the substrate holding part 24 is configured to rotate on the substrate rotation track 28 in conjunction with the rotational movement of the detector 26 . This makes it possible to pick up a plurality of transmission images with different projection directions and projection angles while changing the relative positional relationship between the substrate held by the substrate holding section 24 and the radiation generator 22 .

Here, the rotation radii of the substrate rotation orbit 28 and the detector rotation orbit 30 are not fixed but can be freely changed. As a result, it is possible to arbitrarily change the irradiation angle of the radiation applied to the components arranged on the board, which is the object to be inspected. The orbital planes of the substrate rotation orbit 28 and the detector rotation orbit 30 are orthogonal to the above-described Z-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. It is detected and output to the control unit 10 .

The control unit 10 controls all operations of the inspection apparatus 1 described above. Various functions of the control unit 10 will be described below with reference to FIG. 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 , an imaging processing unit 35 , a cross-sectional image generation unit 36 , a board inspection surface detection unit 38 , a pseudo cross-sectional image generation unit 40 and an inspection unit 42 . Although not shown, the imaging processing unit 35 of the control unit 10 functions as an imaging control unit for controlling the 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. also have Further, each of these functional blocks is implemented by cooperation of hardware such as a CPU that executes various arithmetic processes, 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 combining hardware and software.

The storage unit 34 stores information such as imaging conditions for capturing a transmission image of the substrate and the design of the substrate that is the object to be inspected. The storage unit 34 also stores transmission images and reconstructed images (cross-sectional images and pseudo-cross-sectional images) of the substrate, inspection results of the inspection unit 42, which will be described later, and the like. The storage unit 34 further stores information for driving the radiation generator driving unit 16, the substrate holding unit driving unit 18, and the detector driving unit 20 (for example, the speed at which the radiation generator driving unit 16 drives the radiation generator 22, The speed at which the substrate holder drive 18 drives the substrate holder 24 and the speed at which the detector drive 20 drives the detector 26, etc.) are also stored.

The imaging processing unit 35 drives the radiation generator 22, the substrate holding unit 24, and the detector 26 by the radiation generator driving unit 16, the substrate holding unit driving unit 18, and the detector driving unit 20, and the substrate holding unit 24 A transmitted image of the object to be inspected is captured, and a reconstructed image (cross-sectional image) is generated from the transmitted image. A method of capturing a transmission image and generating a reconstructed image (cross-sectional image) by the image capturing processing unit 35 will be described later.

The cross-sectional image generation unit 36 generates cross-sectional images based on the plurality of transmission images acquired from the storage unit 34 . This can be realized using known techniques such as the FBP method and the maximum likelihood estimation method. Different reconstruction algorithms result in different properties of reconstructed images and different times required for reconstruction. 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. As a result, it is possible to provide the user with a degree of freedom of selection, such as giving priority to shortening the time required for reconstruction, or giving priority to good image quality even if it takes time. Each of the generated cross-sectional images is stored in the storage unit 34 together with attribute information such as information for determining the position of each cross-sectional image in the Z-axis direction and the position (coordinates) of pixels in the cross-sectional image in the X-axis direction and the Y-axis direction. output and stored in the storage unit 34 .

The board inspection surface detection unit 38 selects a position (cross-sectional image) where a surface to be inspected on the board (for example, the surface of the board) is projected from among the plurality of cross-sectional images generated by the cross-sectional image generating unit 36. Identify. Hereinafter, a cross-sectional image showing the inspection surface of the substrate will be referred to as an "inspection surface image".

For the cross-sectional images generated by the cross-sectional image generating unit 36, the pseudo cross-sectional image generation unit 40 accumulates a predetermined number of continuous cross-sectional images, thereby forming an image of a region of the substrate that is thicker than the cross-sectional images. The number of cross-sectional images to be stacked is determined by the thickness of the region of the substrate projected by the cross-sectional images (hereinafter referred to as "slice thickness") and the slice thickness of the pseudo cross-sectional images. For example, if the slice thickness of the cross-sectional image is 50 μm and the height (for example, 500 μm) of the BGA solder balls (hereinafter simply referred to as “solder”) as the pseudo cross-sectional image is to be the slice thickness, 500/50=10 It suffices to pile up the cross-sectional images. At this time, the inspection surface image specified by the board inspection surface detection unit 38 is used to specify the position of the solder.

The inspection unit 42 determines the solder joint state 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. to inspect. Since the solder that joins the board and the component is in the vicinity of the board inspection surface, by inspecting the inspection surface image and the cross-sectional image showing the area on the side of the radiation generator 22 with respect to the inspection surface image, the solder and the board can be detected. It can be determined whether or not the parts are properly joined.

Here, the "solder bonding state" refers to whether or not the substrate and the component are bonded together by soldering to form an appropriate conductive path. The solder joint state inspection includes a bridge inspection, a molten state inspection, and a void inspection. A "bridge" is an undesirable conductive path between conductors caused by solder joints. Further, the "melting state" refers to a state of insufficient bonding between the board and the component due to insufficient melting of the solder, that is, a state of "floating" or not. A "void" refers to a solder joint failure due to air bubbles in the solder joint. Accordingly, inspection section 42 includes bridge inspection section 44 , molten state inspection section 46 , and void inspection section 48 .

Details of the operations of the bridge inspection unit 44, the molten state inspection unit 46, and the void inspection unit 48 will be described later. The molten state inspection unit 46 inspects the molten state of the solder based on the inspection surface image specified by the board inspection surface detection unit 38 . The inspection results of the bridge inspection unit 44 , the molten state inspection unit 46 and the void inspection unit 48 are stored in the storage unit 34 .

FIG. 3 is a flow chart showing the flow from capturing of a transmission image, generation of a reconstructed image (cross-sectional image), specification of an inspection surface image, to inspection of the solder bonding state. Also, FIG. 4 is a flow chart showing the flow of processing for picking up a transmission image and generating a reconstructed image (cross-sectional image). The processing in this flowchart starts, for example, when the control unit 10 receives an inspection start instruction from an input device (not shown).

When the examination is started, as shown in FIG. 3, the control unit 10 first performs processing for calculating a correction value for the aiming height for determining the position of the radiation generator 22 in the Z-axis direction (step S100). ). The aiming height and the processing for calculating the correction of the aiming height will be described later. When the correction value for the aiming height is calculated, the control unit 10 sets the irradiation field of the radiation emitted by the radiation generator 22 by the radiation generator driving unit 16, and the substrate holding unit driving unit 18 sets the substrate holding unit. 24 is moved, and the detector driving unit 20 moves the detector 26 to change the imaging position, while the radiation quality changing unit 14 sets the radiation quality of the radiation generator 22 and irradiates the substrate with radiation. A transmission image is captured, and a reconstructed image is generated from the plurality of transmission images thus captured by the cross-sectional image generator 36 and the pseudo cross-sectional image generator 40 (step S101). The movement path of the substrate holding part 24 by the substrate holding part drive part 18 and the movement path of the detector 26 by the detector drive part 20 when capturing a transmission image are based on the information stored in the storage part 34. It is assumed that the information is set in advance in the substrate holding section driving section 18 and the detector driving section 20 according to the reading method or the input method from the input device. It is also assumed that the position of the radiation generator 22 in the Z-axis direction is set in advance in the radiation generator driving section 16 by the same method.

Details of the processing in step S101 will be described with reference to FIGS. 4 and 5. FIG. In the inspection apparatus 10 according to the present embodiment, a plurality of inspection areas including a portion to be inspected on the inspection object is provided for inspection of the inspection object. is configured to generate a reconstructed image (cross-sectional image, etc.) using In the following description, each inspection area is called an imaging area (FOV), and the processing shown in FIGS. 4 and 5 is performed for each imaging area.

As shown in FIG. 4, when step S100 is started, the imaging processing unit 35 of the control unit 10 moves the radiation generator 22, the substrate holding unit 24, and the detector 26 to initial positions corresponding to the current imaging region. In order to move, a signal corresponding to the initial position is sent to the radiation generator driving section 16, the substrate holding section driving section 18 and the detector driving section 20 (step S1000). Note that the control unit 10 controls the radiation generator drive unit 16 to set a preset aiming height based on a correction value calculated in the aiming height correction value calculation process (step S100), which will be described later. Then, a signal indicating the position of the radiation generator 22 in the Z direction is transmitted so that the reference plane (details of which will be described later) is positioned at the corrected aiming height. Further, since the movement paths of the substrate holding portion 24 and the detector 26 are set in advance as described above, the control portion 10 sends signals indicating their initial positions to the substrate holding portion driving portion 18 and the detector driving portion 20. Send. Upon receiving this signal, the radiation generator driving section 16, the substrate holding section driving section 18 and the detector driving section 20 move the radiation generator 22, the substrate holding section 24 and the detector 26 to their respective initial positions based on the signal. Move (steps S1002, S1004, S1006).

Next, the control section 10 turns on the actuation signal output to the substrate holding section driving section 18 and the detector driving section 20 (step S1008). This corresponds to time t0 in FIG. 5(a). When this actuation signal is turned on, the substrate holder driver 18 starts moving the substrate holder 24 (step S1010), and the detector driver 20 starts moving the detector 26 (step S1012). The substrate holder 24 and the detector 26 are moved along the preset movement path as described above.

The imaging processing unit 35 determines whether or not it is the imaging timing (step S1014). If it is determined that it is not the imaging timing (“N” in step S1014), the imaging processing unit 35 repeats this step again after a predetermined time. If it is determined that there is ("Y" in step S1014), an imaging start signal (trigger) is transmitted to the detector 26 (step S1016). For example, in the example of FIG. 5(a), the trigger for the detector 26 is turned on at time t1.

The detector 26 that has detected that the trigger has been turned on by the imaging processing unit 35 starts imaging a transmission image, and also transmits a response signal indicating the start of imaging to the imaging processing unit 35 (step S1018). Also, the detector 26 transmits an exposure signal to the radiation generator driving section 16 (step S1020). For example, in the example of FIG. 5A, the exposure signal to be output to the radiation generator driving section 16 is turned on during a period of time T from time t2. By configuring the detector 26 to transmit the exposure signal to the radiation generator driving unit 16 in this manner, the delay from the start of imaging to the start of exposure can be minimized.

Upon receiving the exposure signal from the detector 26, the radiation generator driving section 16 causes the radiation generator 22 to generate radiation while the exposure signal is on, and the radiation is applied to the object to be inspected (step S1022). Here, when the detector 26 employs a rolling shutter method, the information (intensity, etc.) of the X-rays detected by the light-receiving element of this detector 26 is distributed along a plurality of scanning lines arranged in a predetermined direction. However, the start time is shifted for each scanning line. For example, as shown in FIG. 5B, when the detector 26 is composed of n scanning lines extending in the horizontal direction, D1, D2, D3, . The information detected with the start time shifted in the order of . Therefore, by generating X-rays from the radiation generator 22 while all scanning lines are acquiring data (during time T in the case of FIG. 5B), the information obtained from each scanning line is , the information is based on the X-rays irradiated at the same time, so that distortion of the acquired transmission image can be prevented.

Further, the imaging processing unit 35 that has received the response signal transmitted from the detector 26 acquires the position information of the substrate holding unit 24 from the substrate position detection unit 29, and detects the position of the detector 26 from the detector position detection unit 31. Acquire and store (step S1024). Since the movement of the substrate holding part 24 by the substrate holding part drive part 18 and the movement of the detector 26 by the detector drive part 20 are controlled along the predetermined movement path as described above, the substrate holding part If either the position of the part 24 or the position of the detector 26 is known, the position of the other can also be known. You can remember. Further, the positions of the substrate holder 24 and the detector 26 may be stored in the above-described XY orthogonal coordinate system (in the form of positions (x, y) in the X-axis direction and the Y-axis direction), or the substrate rotation track 28 may be stored. and may be stored in a polar coordinate system (in the form of a position (r, θ) specified by a distance r from the origin and an angle θ) with the center of the orbital plane of the detector rotation orbit 30 as the origin.

When the transmissive image is captured as described above, the detector 26 transmits the captured transmissive image to the imaging processing unit 35 (step S1026). Then, the imaging processing unit 35 that has acquired this transmission image associates the position information of the substrate holding unit 24 and the position information of the detector 26 acquired in step S1024 with the acquired transmission image and stores them in the storage unit 34 ( step S1028).

The imaging processing unit 35 also determines whether or not there is a next imaging position (step S1030), and if it determines that there is a next imaging position (“Y” in step S1030), returns to step S1014 and The processing (steps S1014 to S1028) is repeated. On the other hand, when the imaging processing unit 35 determines that there is no next imaging position (“N” in step S1030), the imaging processing unit 35 turns off the operation signals output to the substrate holding unit driving unit 18 and the detector driving unit 20 (step S1032), the substrate holder driver 18 that has detected that the activation signal has turned off stops the movement of the substrate holder 24 (step S1034), and the detector driver 20 stops the movement of the detector 26 (step S1034). step S1036). For example, it corresponds to time t3 in FIG.

Finally, the imaging processing unit 35 uses the cross-sectional image generating unit 36 and the pseudo cross-sectional image generating unit 40 to generate a reconstructed image (cross-sectional image) from the transmission image stored in the storage unit 34 (step S1038). The generated reconstructed image (cross-sectional image) may be stored in the storage unit 34 . Then, the control unit 10 determines whether or not there is a next imaging area, and if there is a next imaging area, returns to step S1000 and repeats the above-described processing for that imaging area. Note that the reconstructed image generation processing in step S1038 may be executed in parallel with the processing for the next imaging region.

Next, returning to FIG. 3, the board 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 the inspection surface image from among them (step S102). The bridge inspection unit 44 acquires a pseudo cross-sectional image having a slice thickness similar to that of the solder ball showing the solder ball from the pseudo cross-sectional image generation unit 40, and inspects the presence or absence of a bridge (step S104). If no bridge is detected ("N" in step S106), the molten state inspection unit 46 acquires an inspection surface image from the board inspection surface detection unit 38, and inspects whether or not the solder is melted (step S108). ). If the solder is melted ("Y" in step S110), the void inspection unit 48 acquires a pseudo cross-sectional image partially showing the solder ball from the pseudo cross-sectional image generating unit 40, and detects that voids are present. It is checked whether or not (step S112). If no void is found (“N” in step S114), the void inspection unit 48 determines that the solder joint state is normal (step S116), and outputs that fact to the storage unit 34. FIG. If a bridge is detected ("Y" in step S106), if the solder is not melted ("N" in step S110), or if a void exists ("Y" in step S114), The bridge inspection unit 44, the molten state inspection unit 46, and the void inspection unit 48 determine that the joint state of the solder is abnormal (step S118) and output that effect to the storage unit . When the state of soldering is output to the storage unit 34, the processing in this flow chart ends.

Note that the processing of steps S102 to S118 shown in FIG. 3 is also performed for each imaging region described above. Alternatively, steps S102 to S118 may be executed in parallel with the imaging of other imaging regions in order from the imaging region for which generation of the reconstructed image has been completed.

According to the above method, the position at which the transmission image was captured is not information about the time when the imaging processing unit 35 sent the trigger to the detector 26, but the time when the detector 26 started acquiring the image (from the detector 26). time at which the response signal was received). When the relative positions of the radiation generator 22 and the substrate holder 24 and the detector 26 are changing (the substrate holder 24 and the detector 26 continue to move), the imaging processing unit 35 activates the trigger. Since there is a delay from the transmission until the detector 26 starts acquiring an image, the positions of the substrate holding unit 24 and the detector 26 at the time the trigger is transmitted are the positions where the transmitted image is actually captured. may have deviated from Therefore, as described above, when the detector 26 starts acquiring an image and the imaging processing unit 35 receives the response signal transmitted from the detector 26 at that time, the substrate holding unit 24 and the detector 26 By acquiring the position, it is possible to acquire accurate position information, thereby improving the accuracy of the reconstructed image. Further, the path of movement of the substrate holder 24 by the substrate holder drive section 18 and the path of movement of the detector 26 by the detector drive section 20 may deviate from the predetermined positions due to the characteristics of the drive section. , as described above, since these positions are the positions detected by the substrate position detector 29 and the detector position detector 31, accurate position information can be obtained, further improving the accuracy of the reconstructed image. can be made

The positional information of the substrate holding unit 24 and the detector 26 and the transmission image are stored by cyclically using a predetermined area in the storage area (memory, hard disk, etc.) of the control unit 10 (predetermined area). The storage area can be used efficiently by adopting a method in which information is stored sequentially from the beginning of the storage area, and when information is stored at the end of a predetermined area, the information is stored back to the beginning of the predetermined area. .

In addition, when the detector 26 captures a transmitted image by the rolling shutter method, if the transmitted image is obtained while the relative positions of the radiation generator 22, the substrate holder 24, and the detector 26 are being changed, the image will be Although it may be distorted, as described above, the on/off of the X-rays emitted from the radiation generator 22 (on/off of the exposure signal) is synchronized with the signal of the rolling shutter of the detector 26 (response signal). Thereby, a distortion-free transmission image can be acquired.

FIG. 6 schematically shows the configuration of the inspection apparatus 1 viewed from the side. Description will be made below with reference to FIG. As described above, in the inspection apparatus 1 according to this embodiment, the position of the radiation generator 22 is fixed, and a plane perpendicular to the axis A (for example, the optical axis of the radiation generator 22) is centered. A transmission image of the inspection object 2 is acquired at a predetermined position while the inspection object 2 held by the substrate holding part 24 and the detector 26 are moved inside. When a transmission image is acquired while moving the object 2 in this manner, the transmission image of the inspection target surface of the inspection object 2 moving within a predetermined range in the Z-axis direction does not blur, and the transmission image of the inspection target surface does not blur. As they move away, so-called "motion blur" occurs resulting in blurred images. At this time, a surface on which motion blur does not occur is called a "reference plane S", and a region on which motion blur occurs only at a level that does not affect inspection is called a "aiming region". This reference plane S includes the distance L between the position Pf of the radiation generator 22 in the Z-axis direction and the position Pd of the detector 26 in the Z-axis direction, the radius of rotation of the detector 26, and the object to be inspected 2 (substrate holding portion 24). In the following description, for the sake of simplification, the plane located substantially in the center of the aiming area (the plane perpendicular to the axis A) will be referred to as a "reference plane S". However, this reference plane S may be anywhere within the sighting area, and is not particularly limited to the center. As described above, in order to perform an accurate inspection, the surface to be inspected (surface perpendicular to the axis A) of the object to be inspected 2 must be moved to be within the aiming area, that is, to be on or near the reference plane S. It is necessary to obtain a transmission image by

In the inspection apparatus 1 according to the present embodiment, as described above, the aiming height H is set in order to specify the position Ps of the reference plane S in the Z-axis direction with respect to the inspection object surface of the object 2. There is a need. Although FIG. 6 shows the case where the origin 0 in the Z-axis direction is the surface of the substrate holder 24 on which the object to be inspected 2 is placed, the position of the reference surface S can be specified. The origin can be set anywhere within the range. As described above, in the inspection of the inspected object 2, the position of the radiation generator 22 in the Z-axis direction is determined based on the information on the aiming height H, so that the reference plane S is positioned at the aiming height H position. In FIG. 6, the substrate rotation orbit 28 is positioned on a plane passing through the origin 0 and perpendicular to the axis A, and the detector rotation orbit 30 is positioned on a plane passing through the position Pd and perpendicular to the axis A. It will happen.

Here, if the object 2 to be inspected is, for example, a substrate, warping or bending may occur, and the surface to be inspected may not always be positioned on the reference surface S specified by the aiming height H. Therefore, it is necessary to measure the position of the inspected object 2 in the Z-axis direction for each imaging area (FOV), detect the amount of deviation from the reference plane S, and correct the aiming height H based on the amount of deviation. . Two methods for detecting the amount of deviation from the reference plane S and correcting the aiming height H will be described below.

(First correction method)
In the first correction method, one transmission image (this image is This is called a “reference image”) and compared with the reference transmitted image captured in advance (this image is called a “reference image”). to detect. Here, the reference image is a transmission image captured under the same conditions as the detection image, and is an image of the object 2 to be inspected that has no distortion on the substrate surface (the reference surface S and the surface to be inspected are substantially coincident). It is a transparent image.

For example, when the object 2 to be inspected is not distorted, the reference plane S and the surface to be inspected of the object 2 to be inspected match, so that the inspection image and the reference image have the same magnification. On the other hand, when the substrate surface of the object to be inspected 2 is bent so as to be convex toward the radiation generator 22, the surface to be inspected of the object to be inspected 2 approaches the radiation generator 22. becomes smaller. That is, the magnification of the inspection image is smaller than that of the reference image. On the contrary, when the surface of the object to be inspected 2 is bent so as to be concave toward the radiation generator 22, the substrate surface of the object to be inspected 2 is separated from the radiation generator 22. The image will be larger. That is, the magnification of the inspection image is greater than that of the reference image. As described above, since the amount of deviation of the aiming height H (the amount of deviation of the surface to be inspected from the reference plane S) is proportional to the magnification ratio, the deviation amount of the aiming height H can be obtained from the difference between the magnification ratios. . Note that the enlargement ratio is the reference for the portion to be compared (the specific pattern or mark that serves as a reference, or the external shape of the component mounted on the board, which is called a “characteristic shape”). (Ratio to the reference size of the feature shape in each of the reference image and the inspection image), or the size of the comparison object (feature shape) in the reference image is set to 1, and the inspection image for it It may be the ratio of the size of the comparison object (feature shape) in .

Calculation processing of the correction value of the aiming height in such a first correction method will be described with reference to FIG. Here, a plurality of imaging regions (FOV) are set in the object to be inspected 2, and an imaging region for calculating a correction value is selected from among these imaging regions in advance and stored in the storage unit 34. shall be kept. Similarly, a transmission image (reference image) that serves as a reference for the selected imaging region is also acquired in advance and stored in the storage unit 34 . Even if the amount of deviation from the reference plane S is not detected in all the imaging areas, the values of the imaging areas around the imaging area for which the amount of deviation has been detected are calculated. can be calculated by linear interpolation using

When execution of the target height correction value calculation processing in step S100 is started, the control unit 10 selects one of the imaging regions of the object to be inspected 2 for detecting the deviation amount, as shown in FIG. one is selected (step S2000). In addition, the control unit 10 controls the substrate holding unit 24 and the detection unit so that the center of the imaging region of the subject 2 and the center of the detector 26 are positioned on the axis A (on the optical axis of the radiation generator 22). The device 26 is moved (step S2002). At this time, there is no particular need to specify the position of the radiation generator 22 in the Z-axis direction, and the radiation generator 22 is set in step S2002 to a position where the entire imaging region can be clearly imaged. However, the positions of the radiation generator 22, the substrate holder 24, and the detector 26 must be the same positions as when the reference image was obtained. Then, the control unit 10 emits radiation from the radiation generator 22 to the currently selected imaging region of the subject 2, detects the radiation transmitted through this imaging region by the detector 26, and obtains a transmitted image (detected image). ) is acquired (step S2004).

Next, the control unit 10 reads the reference image of the currently selected imaging region from the storage unit 34 (step S2006), and calculates the feature amounts of each of the reference image and the detection image captured in step S2004. Then, the same location (characteristic shape to be compared) is detected by the feature quantity matching method (step S2008). Alternatively, a feature shape may be detected by a phase-only correlation method. For example, the characteristic shape can be a specific pattern or mark set on the substrate of the device under test 2, or the outline of a component arranged on the substrate. From these patterns, marks, and the contours of parts, locations with a high matching rate of feature quantities are detected. Then, in each of the reference image and the detection image, the enlargement ratio of the characteristic shape (for example, the pattern, the mark, the outer shape of the part) is calculated (step S2010), and the deviation amount is calculated from the difference in the enlargement ratio between the reference image and the detection image. Then, this deviation amount is stored in the storage unit 34 as a correction value for the aiming height H (step S2012). Note that the characteristic shape (pattern, mark, external shape of the part) for which the magnification ratio is calculated may be the characteristic shape arranged at the center of the currently selected imaging region or in the vicinity thereof, or It may be a matching feature shape. Alternatively, the difference in magnification may be calculated for each of a plurality of feature shapes, and the average value thereof may be used as the difference in magnification of the currently selected imaging region. Also, if the rotation-invariant phase-only correlation method is used instead of the phase-only correlation method, the same location can be detected and the magnification can be calculated.

When the calculation of the shift amount (correction value for aiming height H) of the currently selected imaging area is completed, the control unit 10 determines whether or not the shift amount has been detected in all of the imaging areas for which the shift amount is to be detected. (step S2014), and if it is determined that there is still an imaging region for which the displacement amount has not been detected (“N” in step S2014), the control unit 10 selects the next imaging region (step S2016), and Returning to S2002, the above-described processing is repeated. On the other hand, if it is determined that the amount of displacement has been detected in all of the imaging regions for which the amount of displacement is to be detected (“Y” in step S2014), the control unit 10 detects the amount of displacement of the imaging regions for which the amount of displacement is not detected. is calculated from the value of the detected image pickup area, and stored in the storage unit 34 as a correction value for the aiming height H (step S2018). Terminate the calculation process. The displacement amount can be obtained by linear interpolation from the displacement amounts of at least three imaging areas among the surrounding imaging areas.

The device under test 2 held by the substrate holding portion 24 is fixed at its peripheral portion by a holding member or the like. Therefore, the height of the vicinity of the portion held by the substrate holding portion 24 is known. Therefore, the imaging region near the portion held by the substrate holding unit 24 is not subject to deviation amount detection, and the deviation amount from the reference plane S is specified from the information of the object 2 to be imaged. It may be the amount of deviation of the area (correction value of the aiming height H). The shift amount of this imaging area may be used as data for linear interpolation when determining the shift amount of surrounding imaging areas.

According to such a first correction method, one transmission image (detection image) is captured in each imaging region for detecting the deviation amount, and the detection image and the reference image are enlarged. Since the correction value of the aiming height H (the deviation amount of the inspection object surface of the object to be inspected from the reference surface S) can be calculated from the ratio difference, the time required for imaging for calculating the correction value can be shortened, Since the time for the correction value calculation process can be shortened, the overall time for the inspection can be shortened. In addition, since one transmission image is acquired for one imaging region, the exposure dose in the process of calculating the correction value can be reduced. In addition, for an imaging region with a known height, a known value is used without detection, and for other imaging regions, the detected deviation amount or the known deviation amount is linearly complemented to determine the height of the imaging region. (correction value of aiming height H) can be calculated, the imaging process for calculating the correction value can be shortened, and the overall time for inspection can be shortened. In addition, since transmission images are not acquired in imaging regions in which correction values are not detected, the exposure dose can be reduced. Further, since the aiming height H can be corrected only by the configuration for acquiring the transmission image of the object 2 to be inspected, a length measuring device or the like for measuring the height of the object 2 to be inspected is unnecessary, and this inspection can be performed. The cost of the device 1 can be reduced, and maintenance such as confirmation of deterioration due to exposure to radiation and replacement of parts is not required.

(Second correction method)
A second correction method detects the amount of deviation between the surface to be inspected of the object to be inspected 2 and the reference surface S, that is, the correction value of the aiming height H from the cross-sectional image generated by reconstructing the transmission image. It is. Specifically, similarly to the inspection of the object 2 to be inspected, the object 2 to be inspected held by the substrate holding part 24 and the detector 26 are moved to a plurality of predetermined positions while being moved with respect to the radiation generator 22 . A cross-sectional image obtained by reconstructing this transmitted image (this image is called a "detection image") and a reference cross-sectional image captured in advance (a cross-sectional image corresponding to the surface to be inspected, This image is called a “reference image”), and the image that most matches this reference image is specified from among the detected images, and the actual position in the Z direction is determined from the specified detected image (cross-sectional image). to detect. The difference between this Z-direction position and the current aiming height H is the correction value for the aiming height H. FIG.

Calculation processing of the correction value of the aiming height in such a second correction method will be described with reference to FIG. In this second correction method as well, a plurality of imaging regions (FOV) are set on the object to be inspected 2, and the correction value of the sighting height H is calculated from among these imaging regions in advance. is selected and stored in the storage unit 34. Similarly, a cross-sectional image that serves as a reference for the selected imaging region (a reference image that is a cross-sectional image representing the surface to be inspected) is also acquired in advance and stored in the storage unit 34 . Even if the correction value of the aiming height H (the amount of deviation between the surface to be inspected and the reference surface S) is not detected in all the imaging regions, for the imaging regions in which the correction value is not detected, can be calculated by linear interpolation using the correction value of the imaging area in .

When execution of the aiming height correction value calculation process in step S100 is started, the control unit 10 calculates the correction value of the aiming height H in the imaging region of the object 2 as shown in FIG. One of the imaging regions to be scanned is selected (step S2100). Then, as described with reference to FIG. 4, the control unit 10 sets the position of the radiation generator 22 in the Z-axis direction based on the aiming height H set for the currently selected imaging area. Furthermore, while moving the substrate holder 24 and the detector 26 according to a preset trajectory, a transmission image of the inspection object 2 is acquired at a predetermined position (step S2102). Furthermore, the control unit 10 reconstructs the obtained transmission image to generate a cross-sectional image (detection image described above) in a predetermined range in the Z-axis direction (step S2104).

Next, the control unit 10 reads the reference image (cross-sectional image of the surface to be inspected) of the currently selected imaging region from the storage unit 34 (step S2106), and extracts the reference image and the detection image generated in step S2104. (cross-sectional image) to identify the detected image (cross-sectional image) that most closely matches the reference image, and the position of the identified detected image (cross-sectional image) in the Z-axis direction It is stored as the position of the surface (step S2108). That is, in step S2108, the amount of deviation between the reference surface S and the surface to be inspected in the aiming area is detected. Here, as a method of specifying the detected image (cross-sectional image) that best matches the reference image from among the detected images (cross-sectional images), for example, a phase-only correlation method can be used to achieve high-speed matching regardless of positional deviation. rate can be calculated. Then, when the control unit 10 specifies the position in the Z-axis direction of the image that most matches the reference image from the inspection images, the control unit 10 obtains the difference between that position and the currently set aiming height H, and calculates this difference. , is stored in the storage unit 34 as a correction value for the aim height H of the currently selected imaging area (step S2110).

When the calculation of the correction value for the aiming height H of the currently selected imaging area is completed, the control unit 10 determines whether or not the correction value has been calculated for all the imaging areas for which the correction value is to be calculated (step S2112). ), and if it is determined that there is still an imaging region for which correction values have not been calculated (“N” in step S2112), the control unit 10 selects the next imaging region (step S2114), and returns to step S2102. Repeat the subsequent steps. On the other hand, if it is determined that correction values have been calculated for all imaging regions for which correction values are to be calculated (“Y” in step S2112), the control unit 10 calculates correction values for imaging regions for which correction values have not been calculated. is calculated by linear interpolation from the correction value of the imaging region for which the correction value is being calculated among the imaging regions, and is stored in the storage unit 34 (step S2116), and the processing for calculating the correction value of the aiming height ends. As in the first correction method, correction values can be obtained by linear interpolation from correction values of at least three imaging regions among the surrounding imaging regions. Further, as in the first correction method, for an imaging region whose height (position in the Z-axis direction) is known, such as the vicinity of the portion held by the substrate holding unit 24, the information is used. A correction value for the aiming height H may be used.

According to such a second correction method, since a reconstructed image (cross-sectional image) is generated by reconstructing a transmission image, the radiation generator 22 is exposed to the inspected object 2 (substrate holder 24) and Time is required to move the detector 26 to acquire the transmitted image, and time is required to reconstruct a reconstructed image (cross-sectional image) from the transmitted image. Therefore, the time required to calculate the correction value for the aiming height H is longer than in the first correction method, resulting in a longer overall inspection time. However, since the plane to be inspected is specified from the cross-sectional image obtained by reconstructing the transmission image, and the correction value for the aiming height H is calculated from the position of the specified cross-sectional image in the Z-axis direction, Therefore, it becomes easy to match the surface to be inspected with the reference surface S, and a reconstructed image (cross-sectional image) without motion blur can be obtained, thereby improving the accuracy of inspection.

In the second correction method, the number of transmission images acquired in each imaging region in the process of calculating the correction value of the aiming height is acquired for inspecting the object 2 to be inspected. may be less than the number of transmitted images for generating a reconstructed image (cross-sectional image). If the number of transmission images is reduced, the accuracy of the cross-sectional image generated by reconstruction also decreases. There is no problem because it is wider than the step width of the cross-sectional image). Further, as in the first correction method, since the aiming height H can be corrected only by the equipment for acquiring the transmission image of the object 2 to be inspected, the height of the object 2 to be inspected can be measured. This eliminates the need for a long instrument and the like, making it possible to reduce the cost of the inspection apparatus 1, and eliminates the need for maintenance such as confirmation of deterioration due to exposure to radiation and replacement of parts. Moreover, it is no longer necessary to arrange the pattern or mark for length measurement near the part to be inspected.

In order to correct the aiming height H, both the first correction method and the second correction method described above are implemented in the inspection apparatus 1, and the user of the inspection apparatus 1 uses which method for aiming. It may be configured to allow the user to select whether to correct the height H. In this case, the first correction method may be the prescribed correction method, and the second correction method may be selected only when the user wants to use the second correction method.

1 inspection apparatus 2 inspected object 10 control unit 16 radiation generator driving unit (driving unit)
18 Substrate holding portion driving portion (driving portion)
20 detector driving unit (driving unit)
22 radiation generator (source)
24 substrate holding portion (holding portion)
26 detector

Claims (10)

a source;
a holding unit that holds an object to be inspected;
a detector;
a driving unit that changes the relative positions of the radiation source and the object and the detector held by the holding unit;
a control unit;
The control unit
When the radiation source and the object to be inspected and the detector held by the holding unit are in predetermined relative positions by the drive unit, the radiation emitted from the radiation source and transmitted through the object to be inspected is An inspection apparatus for detecting a deviation amount of a surface to be inspected of the object to be inspected from a predetermined reference plane based on at least one transmission image of the object detected by a detector. The control unit
detecting the amount of deviation at a plurality of positions on the object to be inspected;
2. The inspection apparatus according to claim 1, wherein the displacement amount of a position for which the displacement amount is not detected is calculated by linear interpolation using the detected displacement amount. The control unit
3. The inspection apparatus according to claim 2, wherein, in calculating the displacement amount of the position where the displacement amount is not detected, linear interpolation is performed using the value of the position where the displacement amount is known in addition to the detected displacement amount. The control unit
one transmission image when the radiation source, the object to be inspected held by the holding unit, and the detector are at predetermined relative positions; and the inspection of the object to be inspected at the predetermined relative positions. The inspection apparatus according to any one of claims 1 to 3, wherein the deviation amount is detected using a reference image that is a transmission image when the target surface is on the predetermined reference surface. The control unit
5. The inspection apparatus according to claim 4, wherein the same feature shape in the transmission image and the reference image is detected by a phase-only correlation method, and the shift amount is detected based on a difference in magnification of the feature shape. The control unit
5. The inspection apparatus according to claim 4, wherein the same feature shape in the transmission image and the reference image is detected by a feature amount matching method, and the deviation amount is detected based on a difference in magnification of the feature shape. The control unit
generating cross-sectional images of the subject by reconstructing two or more transmission images when the radiation source, the subject and the detector held by the holding unit are at different positions; 4. The inspection apparatus according to any one of claims 1 to 3, wherein the deviation amount is detected using the cross-sectional image. The control unit
8. The inspection apparatus according to claim 7, wherein a cross-sectional image that best matches a reference image of the cross-sectional images is specified from among the cross-sectional images, and the deviation amount is detected from the position of the cross-sectional image. The control unit
The inspection apparatus according to claim 8, wherein a cross-sectional image that best matches a reference image of the cross-sectional images is specified from the cross-sectional images by a phase-only correlation method, and the deviation amount is detected from the position of the cross-sectional image. The control unit
A correction value for the position of the predetermined reference plane is calculated from the shift amount for each position where the transmission image on the subject is acquired, and based on the correction value, the radiation source and the holding unit hold the correcting the relative position between the object to be inspected and the detector;
Based on the corrected relative positions, the transmission image is generated at a predetermined relative position while changing the relative positions of the radiation source and the object and the detector held by the holding unit by the driving unit. The inspection device according to any one of claims 1 to 9.

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