JP2018179665A - Inspection method and inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method that can acquire highly accurate height information with a small number of shooting, and to provide an inspection device using the inspection method.SOLUTION: An inspection method packaged in an inspection device has the steps of: acquiring a short-cycle measurement image of an inspected body having a short-cycle stripe pattern projected; acquiring a stationary measurement image of a subject having a stationary pattern in synchronization with a long-cycle stripe pattern projected; detecting a position of an image of the stationary pattern from the stationary measurement pattern; determining a long-cycle phase serving as a phase of the image on the basis of a preliminarily acquired long-cycle reference image; determining a short-cycle phase serving as a phase of the image on the basis of a preliminarily acquired short-cycle reference image; and calculating a height of the inspected body from the long-cycle phase and the short-cycle phase for each position of the image.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an inspection method for inspecting the appearance of an object to be inspected, and an inspection apparatus using this inspection method.

  In recent years, electronic circuit boards have come to be mounted on various devices, but in devices on which this type of electronic circuit board is mounted, downsizing and thinning have always been an issue, From this point, it is required to increase the density of mounting of the electronic circuit board. In the inspection apparatus which inspects the application | coating state of the solder of such an electronic circuit board, the mounting state of an electronic component, etc., the phase shift method is used from the precision. The phase shift method is configured to measure the height using a long-period fringe pattern and a short-period fringe pattern (see, for example, Patent Document 1).

JP 2012-053015

  However, in the method of obtaining the height from an image obtained by projecting the long-period stripe pattern and the short-period stripe pattern as described above, the number of times of image capturing (the number of images for calculating the height) increases. The problem is that the throughput of the Also, if the object to be inspected is a bright object, saturation tends to occur if a long-period stripe pattern is projected and imaged, and if saturation occurs, it is necessary to perform imaging again, in which case the number of times of imaging the image Also had the task of increasing that much. Although a method for obtaining high-precision height information with a smaller number of times of imaging has been devised, further reduction of the number of times of imaging is required in order to improve inspection throughput.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an inspection method capable of acquiring highly accurate height information with a small number of imaging times, and an inspection apparatus using this inspection method. I assume.

  In order to solve the above problem, the inspection method according to the present invention is synchronized with the step of acquiring a short period measurement image which is an image of the inspection object onto which the short period fringe pattern is projected, and the long period fringe pattern. The step of acquiring a fixed measurement image which is an image of the inspection object onto which the fixed pattern is projected, the step of detecting the position of the image of the fixed pattern from the fixed measurement image, and the fringe pattern of the long period are projected Determining a long-period phase that is a phase of the position of the image based on a long-period reference image acquired in advance, and a reference on which the fringe pattern of the short period is projected Determining a short-period phase that is a phase of the position of the image based on a short-period reference image acquired in advance, and a long-period phase for each position of the image; Serial and a short-period phase, and having the steps of: calculating a height of the object to be inspected.

  In the inspection method according to the present invention, preferably, the fixed pattern is a dot.

  Further, in the inspection method according to the present invention, the step of detecting the position of the image of the fixed pattern divides the fixed measurement image into a plurality of regions, and for each of the regions, the images of the images included in the regions are divided. It is preferred to detect the position.

  Preferably, the inspection method according to the present invention includes the step of binarizing the fixed measurement image before the step of detecting the position of the image of the fixed pattern.

  Further, in the inspection method according to the present invention, in the step of binarizing the fixed measurement image, it is preferable to determine a threshold of binarization based on luminance information of the short cycle measurement image.

  In addition, an inspection apparatus according to the present invention includes: a projection unit that projects a pattern on an inspection object; a camera unit that acquires an image of the inspection object on which the pattern is projected; and a storage unit that stores the image And a control unit that calculates the height of the inspection object by the inspection method described above.

  According to the present invention, highly accurate height information can be acquired with a small number of times of imaging.

It is an explanatory view for explaining the composition of an inspection device. It is explanatory drawing explaining the relationship between the phase of a reference plane, and the measured phase. It is an explanatory view explaining a relation of a stripe pattern and a fixed pattern. It is a flowchart of the inspection method. It is explanatory drawing explaining the method to detect the position of the image of a fixed pattern.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, the configuration of the inspection apparatus 10 according to the present embodiment will be described with reference to FIG. The inspection apparatus 10 is an apparatus for inspecting the inspection object 12 using an inspection object image obtained by imaging the inspection object 12. The inspection object 12 is, for example, an electronic circuit board to which a solder is applied. The inspection apparatus 10 determines the quality of the application state of the solder based on the inspection object image.

  The inspection apparatus 10 includes an inspection table 14 for holding the inspection object 12, an imaging unit 20 for illuminating and imaging the inspection object 12, an XY stage 16 for moving the imaging unit 20 with respect to the inspection table 14, and imaging And a control unit 30 for controlling the operation of the unit 20 and the XY stage 16 and performing an inspection of the inspection object 12. For convenience of explanation, as shown in FIG. 1, the inspection object disposition surface of the inspection table 14 is an XY plane, and the direction perpendicular to the disposition surface (ie, the imaging direction by the camera unit 21 configuring the imaging unit 20 (camera unit 21) is the Z direction.

  The imaging unit 20 is attached to a moving table (not shown) of the XY stage 16 and can be moved in the X direction and the Y direction by the XY stage 16. The XY stage 16 is, for example, a so-called H-type XY stage. Therefore, the XY stage 16 supports the Y drive unit for moving the movable table in the Y direction along the Y direction guide extending in the Y direction, supports the Y direction guide at its both ends, and moves the movable table and the Y direction guide in the X direction. It comprises two X-direction guides and an X-driving unit configured to be movable. The XY stage 16 may further include a Z movement mechanism for moving the imaging unit 20 in the Z direction, and may further include a rotation mechanism for rotating the imaging unit 20. The inspection apparatus 10 may further include an XY stage that allows the inspection table 14 to move. In this case, the XY stage 16 that moves the imaging unit 20 may be omitted. Moreover, a linear motor and a ball screw can be used for X drive part and Y drive part.

  The imaging unit 20 includes a camera unit 21 for capturing an image in a direction (Z-axis direction) perpendicular to the inspection surface (substrate surface) of the inspection object 12, an illumination unit 22, and a projection unit 23. . In the inspection apparatus 10 according to the present embodiment, the camera unit 21, the illumination unit 22, and the projection unit 23 may be configured as an integral imaging unit 20. In the integrated imaging unit 20, the relative positions of the camera unit 21, the illumination unit 22, and the projection unit 23 may be fixed, or each unit may be configured to be relatively movable. Also, the camera unit 21, the illumination unit 22, and the projection unit 23 may be separated and configured to be separately movable.

  The camera unit 21 includes an imaging device that generates a two-dimensional image of an object, and an optical system (for example, a lens) for forming an image on the imaging device. The camera unit 21 is, for example, a CCD camera. The maximum visual field of the camera unit 21 may be smaller than the inspection subject mounting area of the inspection table 14. In this case, the camera unit 21 divides the image into a plurality of partial images and images the entire inspection object 12. The control unit 30 controls the XY stage 16 so that the camera unit 21 is moved to the next imaging position each time the camera unit 21 captures a partial image. The control unit 30 combines partial images to generate an entire image of the inspection object 12.

  The camera unit 21 may include an imaging element that generates a one-dimensional image, instead of the two-dimensional imaging element. In this case, the entire image of the test object 12 can be acquired by scanning the test object 12 with the camera unit 21.

  The illumination unit 22 is configured to project illumination light for imaging by the camera unit 21 on the surface of the inspection object 12. The illumination unit 22 includes one or more light sources that emit light of a wavelength or a wavelength range selected from the wavelength range that can be detected by the imaging element of the camera unit 21. The illumination light is not limited to visible light, and ultraviolet light, X-rays, etc. may be used. When a plurality of light sources are provided, each light source is configured to project light of different wavelengths (for example, red, blue, and green) onto the surface of the inspection object 12 at different projection angles.

  In the inspection apparatus 10 according to the present embodiment, the illumination unit 22 is a side illumination source that projects illumination light in an oblique direction with respect to the inspection surface of the inspection object 12, and in the present embodiment, the upper light source 22a The position light source 22b and the lower light source 22c are provided. In the inspection apparatus 10 according to the present embodiment, the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are side illumination sources, are ring illumination sources, surround the optical axis of the camera unit 21, and are inspected The illumination light is projected obliquely to the inspection surface of the body 12. Each of the upper light source 22a, the middle light source 22b, and the lower light source 22c, which are the side illumination sources, may be configured by arranging a plurality of light sources in an annular shape. Further, the upper light source 22a, the middle light source 22b and the lower light source 22c, which are side illumination sources, are configured to project illumination light at different angles with respect to the inspection surface.

  The projection unit 23 projects a pattern on the inspection surface of the inspection object 12. The inspection object 12 on which the pattern is projected is imaged by the camera unit 21. The inspection apparatus 10 creates a height map of the inspection surface of the inspection object based on the captured pattern image of the inspection object 12. The control unit 30 detects local inconsistencies in the pattern image with respect to the projection pattern, and determines the height of the portion based on the local inconsistencies. That is, the change in the imaging pattern with respect to the projection pattern corresponds to the change in height on the inspection surface.

  The projection pattern is preferably a one-dimensional stripe pattern in which bright lines and dark lines are alternately and periodically repeated. The projection unit 23 is arranged to project a stripe pattern from an oblique direction to the inspection surface of the inspection object 12. Discontinuities in height on the inspection surface of the inspection object 12 appear as pattern deviations in the fringe pattern image. Therefore, the height difference can be obtained from the amount of deviation of the pattern. For example, the control unit 30 creates a height map by PMP (Phase Measurement Profilometry) method using a fringe pattern in which the brightness changes according to a sine curve. In the PMP method, the shift amount of the fringe pattern corresponds to the phase difference of the sine curve.

  The projection unit 23 includes a pattern forming apparatus, a light source for illuminating the pattern forming apparatus, and an optical system for projecting the pattern onto the inspection surface of the inspection object 12. The patterning device may be, for example, a variable patterning device capable of dynamically generating a desired pattern such as a liquid crystal display or the like, or fixed patterning in which a pattern is fixedly formed on a substrate such as a glass plate It may be an apparatus. When the patterning device is a fixed patterning device, the projection position of the pattern can be made variable by providing a moving mechanism for moving the fixed patterning device or by providing an adjustment mechanism in an optical system for pattern projection. preferable. Moreover, the projection unit 23 may be configured to be able to switch between a plurality of fixed patterning devices having different patterns.

  A plurality of projection units 23 may be provided around the camera unit 21. The plurality of projection units 23 are arranged to project a pattern onto the inspection object 12 from different projection directions. In this way, it is possible to reduce the area where the pattern is not projected due to a shadow due to the height difference on the inspection surface.

  The control unit 30 shown in FIG. 1 totally controls the entire apparatus. The hardware is realized by the CPU, memory, and other LSIs of an arbitrary computer, and software is loaded into the memory. Although realized by a program or the like, here, functional blocks realized by their cooperation are illustrated. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  An example of the configuration of the control unit 30 is shown in FIG. The control unit 30 is configured to include an inspection control unit 31 and a memory 35 which is a storage unit. The inspection control unit 31 includes a height measurement unit 32, an inspection data processing unit 33, and an inspection unit 34. The inspection apparatus 10 further includes an input unit 36 for receiving an input from a user or another device, and an output unit 37 for outputting information related to an inspection, and the input unit 36 and the output unit 37. Are connected to the control unit 30, respectively. The input unit 36 includes, for example, input means such as a mouse and a keyboard for receiving an input from a user, and communication means for communicating with another device. The output unit 37 includes known output means such as a display and a printer.

  The examination control unit 31 is configured to execute various control processes for examination based on the input from the input unit 36 and the examination related information stored in the memory 35. The inspection related information includes a two-dimensional image of the inspection object 12, a height map of the inspection object 12, and substrate inspection data. Prior to the inspection, the inspection data processing unit 33 creates substrate inspection data using the two-dimensional image of the inspection object 12 and the height map which are guaranteed to pass all the inspection items. The inspection unit 34 executes an inspection based on the created substrate inspection data, and the two-dimensional image and height map of the inspection object 12 to be inspected.

  The substrate inspection data is inspection data created for each type of substrate. The board inspection data is, so to speak, a collection of inspection data for each solder applied to the board. The inspection data of each solder includes an inspection item necessary for the solder, an inspection window which is an inspection area on the image for each inspection item, and an inspection standard which is a criterion for determining the quality of each inspection item. One or more examination windows are set for each examination item. For example, in an inspection item for determining the quality of the solder application state, the inspection windows of the same number as the number of solder application areas of the component are usually set in an arrangement corresponding to the arrangement of the solder application areas. Further, with regard to an inspection item using an image obtained by subjecting the image of the inspection object to a predetermined image processing, the content of the image processing is also included in the inspection data.

  The inspection data processing unit 33 sets each item of inspection data in accordance with the substrate as substrate inspection data creation processing. For example, the inspection data processing unit 33 automatically sets the position and size of each inspection window for each inspection item so as to conform to the solder layout of the substrate. The examination data processing unit 33 may receive an input from the user for a part of the examination data. For example, the inspection data processing unit 33 may accept the tuning of the inspection standard by the user. The inspection standard may be set using height information.

  The inspection control unit 31 executes an imaging process of the inspection object 12 as a pre-process of substrate inspection data creation. The inspection object 12 used is one that has passed all inspection items. As described above, the imaging process is performed by illuminating the test object 12 with the illumination unit 22 while controlling the relative movement between the imaging unit 20 and the inspection table 14 and sequentially capturing partial images of the test object 12 . Several partial images are imaged so that the whole to-be-inspected object 12 may be covered. The inspection control unit 31 combines the plurality of partial images to generate an entire substrate surface image including the entire inspection surface of the inspection object 12. The inspection control unit 31 stores the entire substrate surface image in the memory 35.

  Further, the inspection control unit 31 controls the relative movement between the imaging unit 20 and the inspection table 14 while projecting a pattern onto the inspection object 12 by the projection unit 23 as pre-processing for height map creation, The pattern image of the body 12 is divided and sequentially imaged. The pattern to be projected is preferably a fringe pattern whose brightness changes according to a sine curve based on the PMP method. The inspection control unit 31 combines the captured divided images to generate a pattern image of the entire inspection surface of the inspection object 12. The inspection control unit 31 stores the pattern image in the memory 35. The pattern image may be generated not for the whole but for a part of the inspection surface.

  The height measurement unit 32 creates a height map of the entire inspection surface of the inspection object 12 based on the pattern on the imaging pattern image. First, the height measurement unit 32 obtains a phase difference map of the inspection surface of the inspection object 12 by obtaining the local phase difference between the imaging pattern image and the reference pattern image for the entire image. The reference pattern image is a pattern image projected by the projection unit 23 (that is, an image generated by the pattern forming device incorporated in the projection unit 23). The height measurement unit 32 creates a height map of the inspection object 12 based on the reference surface which is the reference of height measurement and the phase difference map. The reference surface is, for example, the substrate surface of the electronic circuit substrate to be inspected. The reference surface may not necessarily be a flat surface, and may be a curved surface on which a deformation such as a warp of a substrate is reflected.

  Specifically, the height measurement unit 32 obtains the phase difference of the fringe pattern between each pixel of the imaging pattern image and the pixel of the reference pattern image corresponding to the pixel. The height measurement unit 32 converts the phase difference into a height. The conversion to height is performed using the local fringe width in the vicinity of the pixel. This is to compensate for the difference in stripe width on the captured pattern image depending on the location. Since the distance from the projection unit 23 differs depending on the position on the inspection surface, the stripe width changes linearly from one end of the pattern projection area of the inspection surface to the other end even if the stripe width of the reference pattern is constant. It is because it The height measurement unit 32 obtains the height from the reference surface based on the converted height and the reference surface, and creates a height map of the inspection object 12.

  The inspection control unit 31 creates an inspection object image having a height distribution by correlating the height information of the height map of the inspection object 12 with each pixel of the two-dimensional image of the inspection object 12 It is also good. The inspection control unit 31 may perform three-dimensional modeling display of the inspection object 12 based on the inspection object image with height distribution. Further, the inspection control unit 31 may superimpose the height distribution on the two-dimensional inspection object image and display it on the output unit 37. For example, the inspection object image may be color-displayed by height distribution.

  Hereinafter, a method of projecting a pattern by the projection unit 23 and measuring the height in such an inspection apparatus 10 will be described.

  First, a conventional height measurement method by the PMP method using a stripe pattern will be described. Focusing on one measurement point in the fringe pattern projection area, when the fringe pattern is projected while the phase is spatially shifted (in other words, when the fringe pattern is scanned in the repeating direction of the fringes), Brightness fluctuates periodically. Although the average brightness is different for each measurement point according to the surface characteristics of the measurement point such as color and reflectance, a periodic brightness fluctuation corresponding to the stripe pattern occurs at any measurement point. Therefore, the phase of the fringe pattern when making the measurement point brightest, for example, represents the height information of the measurement point. If it is generalized, it can be said that the initial phase of the periodic brightness fluctuation gives the height information of each measurement point.

  Using such fringe pattern characteristics, conventional height measurement methods determine height using at least two patterns with different periods. The rough height is determined by the first pattern of long period (that is, thick stripes), and the accurate height is determined by the second pattern of short periods (thin stripes). As described above, since the PMP method obtains the height based on the phase, if the height difference is large and the stripes are shifted by one or more cycles, the height can not be uniquely identified. By obtaining the height in combination with the first stripe pattern, it becomes possible to uniquely identify the height even when the stripes are shifted by one or more cycles when the second stripe pattern is projected.

  However, when heights are measured with a plurality of different patterns and the results are integrated to obtain a height map, it is generally considered that projection and imaging are performed individually for each pattern. In principle, in the PMP method, at least three times and typically four times of imaging with one phase being shifted with respect to one kind of fringe pattern is required. Corresponding to the fringe pattern being a sine wave, the brightness fluctuation of each measurement point is also a sine wave. Since the pitch of the stripes is known, if the mean value of the brightness, the amplitude and the initial phase are known, a sine wave representing the brightness variation is identified.

  By obtaining the brightness measurement value of the measurement point from at least three captured images, three variables of the brightness average value, the amplitude, and the initial phase can be determined. Further, assuming that the luminance of a certain pixel when imaging one stripe pattern 90 ° out of phase at four times each is l0 to l3, the initial phase φ of the measurement point corresponding to that pixel is tan (φ) = (l3−3) It is known that it is represented by l1) / (l2-l0). Assuming that the pitch of the fringe pattern is P, the deviation amount of the fringe pattern is obtained by P × (φ / 2π). The height of the position can be obtained from the pattern deviation amount using the projection angle of the pattern.

  Using two patterns results in at least six or eight imagings. In order to inspect one subject 12, a plurality of partial areas are imaged to obtain an entire image. Further, one partial area is imaged by each of the plurality of projection units 23. For example, if 10 partial areas are imaged by 3 projection units, 10 × 3 × 6 (or 8) = 180 (or 240) imagings will be required. Thus, the number of times of imaging required for one examination tends to be large, and the number of times of imaging has a large influence on the examination required time.

  Therefore, in the present embodiment, a rough height is obtained by triangulation using a fixed pattern synchronized with a long period pattern (first pattern which is a thick stripe) in the PMP method, and a short period in the PMP method The number of times of imaging is reduced by obtaining the precise height with the stripe pattern (the second pattern which is a thin stripe). Here, in the triangulation method, a fixed pattern is projected from the projection unit 23 onto the inspection object 12, and the height of the image captured by the camera unit 21 is based on the amount of deviation from the image of the fixed pattern in the reference plane. Is a way to In addition, although a fixed pattern can use a checker, a square wave, a dot etc., it demonstrates as a dot by subsequent description.

  In FIG. 2, as shown in (a), a phase obtained from an image captured by the camera unit 21 by projecting a stripe pattern by the projection unit 23 onto the reference plane S is shown in (c), and (b) As shown in (d), when the phase obtained from the image captured by projecting the same fringe pattern and imaging it with the object O placed on this reference plane S is shown in (d), the height of the object O is It can be calculated from the amount of deviation (phase difference = measured phase−phase of reference plane). The phase difference can be calculated for each pixel of the image captured by the camera unit 21. By multiplying the phase difference obtained for each pixel by a coefficient, the height of the position corresponding to that pixel can be calculated. . This coefficient is determined, for example, by tan (projection angle) × stripe pitch / 2π.

  Here, as shown in FIG. 3, instead of using the stripe pattern Pt, consider the case of using the dot pattern Pd, which is a fixed pattern synchronized with the stripe pattern Pt. "Synchronization" means that dots (fixed pattern) of the dot pattern Pd are arranged at positions of predetermined phases in the stripe pattern Pt. As described with reference to FIG. 2, when the reference plane S and the object O placed on the reference plane S are imaged using the stripe pattern Pt, the phase difference Δφ is the measured phase φ and the phase of the reference plane It is obtained by the following equation (1) from φ0.

Δφ = φ−φ0 (1)

  On the other hand, when dots of the dot pattern Pd are formed at the position of the phase 0 of the stripe pattern Pt, the phase (measured phase) φ of the image of the dot projected onto the surface of the reference plane S or the object O is 0 The phase difference Δφ ′ at the position of the dot image captured by the camera unit 21 is expressed by the following equation (2).

Δφ '= 0-φ0 = -φ0 (2)

  When the stripe pattern Pt is used, the phase difference is obtained for each pixel of the image captured by the camera unit 21 and the height can be calculated, whereas when the dot pattern Pd is used, dots are formed. Although it is possible to obtain only the phase difference and height at different positions, it is not necessary to calculate the amount of movement of the dots (difference between the positions of the dots in the image of the reference plane S and the positions of the dots in the measured image). Using the image of the stripe pattern Pt with respect to the plane S, the phase difference can be determined directly from the position of the dot image in the captured image, using equation (2). That is, the stripe pattern Pt is a stripe pattern of the long period described above, and the dot pattern Pd is synchronized with the stripe pattern of this long period (for example, dots are formed at the position of phase = 0 of the stripe pattern). An image captured by projecting the pattern Pd onto the inspection object 12 can be treated the same as an image acquired by projecting a long-period pattern in the PMP method. Moreover, as described above, in the PMP method, at least three times of imaging are required to shift the phase of the long-period pattern in order to obtain the phase difference, but using this dot pattern Pd, one imaging Then, the phase difference at the position where the dot image is present can be obtained. Therefore, even if three imagings are required for measurement with a short-period pattern for one visual field area, height measurement with the same accuracy as the PMP method can be performed with a total of four imagings. .

  Here, the phase difference determined from the dot pattern at the predetermined position (the position where the dot image is detected) and the image of the reference plane on which the long-period stripe pattern is projected is Δφw, and the short-period stripe pattern is Assuming that the phase difference obtained from the image (the image of the reference plane and the phase difference obtained from the measured image) is φf, and the ratio of the fringe pattern of the long period fringe pattern to the short period fringe pattern is N, The height h of the position at which the image of H is detected is determined by the following equation (3). However, Round () is a function that rounds off the decimal point.

h = Round ((N × Δφw−Δφf) / 2π) × 2π + Δφf (3)

  As in the PMP method, if the measurement result by the dot pattern (long-period fringe pattern) deviates by half or more of the pitch of the short-period fringe pattern (when it is phase shifted by π), the correct result can be obtained. It disappears. However, in the inspection of the solder application state of the electronic circuit board, etc., there is no large difference in height between the surface of the board and the solder part (ie, an object of a shape having a small object in a flat surface having a gentle curvature). On the other hand, with this method, it is possible to measure the height of sufficient accuracy.

  Now, a specific measurement method will be described with reference to FIG. The pattern projected by the projection unit 23 is a stripe pattern with a long period, a dot pattern (fixed pattern) synchronized with the stripe pattern with the long period, and a stripe pattern with a short period. Further, in the following description, measurement processing for one visual field area will be described. However, when the inspection object 12 straddles a plurality of visual field areas, the following processing is performed for each visual field area.

  First, prepare for measurement. For example, when an execution command of the preparation process is input from the input unit 36, the control unit 30 causes the projection unit 23 to project a short-period stripe pattern on a reference plane, and the camera (short-period reference image) The image is taken by the unit 21 and stored in the memory 35 (step S100). Next, the control unit 30 causes the projection unit 23 to project a long-period stripe pattern on the reference plane, captures the image (long-period reference image) with the camera unit 21, and stores it in the memory 35 (step S110). , End the preparation process. A substrate on which no component is mounted may be set on the inspection table 14 as a reference plane, or a dedicated member to be the reference plane may be set on the inspection table 14.

  Next, the inspection object 12 is placed on the inspection table 14 and inspection (measurement) is performed. For example, when an execution command of inspection processing is input from the input unit 36, the control unit 30 causes the projection unit 23 to project a short-period stripe pattern on the inspection object 12 and causes the camera unit 21 to display the image (short-period The measurement image is acquired and stored in the memory 35 (step S200). In this step S200, as described above, at least three images in which the stripe pattern is shifted with respect to one visual field area are acquired. Next, the control unit 30 causes the projection unit 23 to project a dot pattern onto the inspection object 12, the camera unit 21 acquires the image (fixed measurement image), and stores it in the memory 35 (step S210). As described above, the dot pattern image may be captured once for one field of view.

  The control unit 30 reads the short cycle measurement image from the memory 35, and performs phase calculation from the short cycle measurement image (step S220). As described above, the imaging when the short-period fringe pattern is projected onto the inspection object 12 is shifted in phase and imaging is performed at least three times. The relationship between the phase shift in these imagings and the luminance when the low-period fringe pattern projected onto the inspection object 12 is a sine wave is expressed by the following equation (4). In the equation (4), v represents luminance, A represents an amplitude dependent on the brightness of the inspection object 12, C represents an offset of the brightness dependent on the camera unit 21 or the environmental luminance, and B Represents the phase to be determined, λ represents the amount of phase shift, and x represents the number of shifts.

v = A × sin (λ × x + B) + C (4)

  The control unit 30 reads out the fixed measurement image from the memory 35, and based on the luminance information of the short period fringe pattern, that is, the fixed measurement image based on the threshold determined by the amplitude A and the offset C of the equation (4) described above. Are binarized (step S230). Here, the threshold may be, for example, C or C-A / 2. By binarizing the fixed image based on the luminance information of the low-period measurement image (the luminance information of the low-frequency fringe pattern projected for capturing the low-frequency measurement image), the luminance and color of the inspection object 12 Regardless, the stable dot image can be detected. Further, the control unit 30 executes a noise reduction filter on the binarized fixed measurement image to remove noise (step S240).

  Further, the control unit 30 detects the position of the dot image in the fixed measurement image which has been binarized and from which noise has been removed (step S250). As a method of detecting a dot image from this fixed measurement image, an algorithm of template matching or labeling can be used, but since it is a sequential process, it is difficult to implement with a GPU (Graphics Processing Unit) or the like, and it is realistic The time of detection may be longer than the time of imaging or movement of the camera unit 21 (change of the visual field area).

  Therefore, in the present embodiment, as shown in FIG. 5A, the fixed measurement image is divided into a plurality of grids (regions), a dot image is detected in each grid, and the position is determined. ing. With such a configuration, scanning can be performed independently for each grid, so that the number of grids can be parallelized, and processing can be performed at high speed using a GPU or the like. The grid can be accurately detected by overlapping with the adjacent grid by the size of the dot image. Further, as shown in FIG. 5B, the position of the dot image is the maximum value (xmax) and the minimum value (xmin) in the x direction of the luminance position, and the maximum value (ymax) and the minimum value in the y direction. From these values, the central coordinates (x ', y') of the dot image can be determined from these values by the following equations (5) and (6).

x '= (xmin + xmax) / 2 (5)
y '= (ymin + ymax) / 2 (6)

  Then, when the position (center coordinates) of the dot image in the fixed measurement image is determined as described above, the control unit 30 reads the long period reference image from the memory 35, and from this position and the long period reference image, The phase is acquired (step S260). The acquisition method is as described above. A rough height (rough height) for each grid can be calculated from the phase obtained from the long-period reference image.

  Here, as shown in FIG. 5A, a dot image can be detected, and a grid whose rough height can be detected, and a grid whose dot image can not be detected and whose rough height can not be known, Exists. Therefore, for a grid whose height is unknown, the rough height is propagated by determining the height of the grid from the rough height of the surrounding grids (step S270). Finally, the control unit 30 calculates the detailed height of the position of the dot image by combining the rough height and the phase obtained from the short cycle image based on the above-mentioned equation (3) (step S280). ). As is apparent from the above equation (3), when calculating the rough height, the phase difference obtained from the long-period pattern is rounded by rounding off the decimal point by the Round function, so the dot image is somewhat Even if it is deformed, it does not affect the accuracy of the height finally obtained.

  As described above, when the inspection method according to the present embodiment is used, imaging is performed while shifting the phase in a state in which the fixed pattern is projected and the short-period pattern is projected to one visual field region. High-accuracy height information can be obtained by imaging four times in total three times, so inspection throughput can be improved while maintaining accuracy. In addition, by setting the fixed pattern as a dot pattern, the fixed measurement image can be divided into grids and parallel processing using a GPU or the like can be performed, so that the throughput can be further improved. The number of times of imaging (the number of shifts) in which the short-period stripe pattern is projected may be four or more.

10 Inspection Device 21 Camera Unit 23 Projection Unit 30 Control Unit

Claims (6)

Acquiring a short-period measurement image, which is an image of an inspection object onto which a short-period fringe pattern is projected;
Acquiring a fixed measurement image, which is an image of the inspection object onto which the fixed pattern synchronized with the long-period fringe pattern is projected;
Detecting the position of the image of the fixed pattern from the fixed measurement image;
Determining a long-period phase that is a phase of the position of the image based on a long-period reference image on which the long-period fringe pattern is projected and which is acquired in advance;
Determining a short-period phase that is a phase of the position of the image based on the short-period reference image on which the short-period fringe pattern is projected and which is acquired in advance;
Calculating the height of the inspection object from the long period phase and the short period phase for each position of the image.   The inspection method according to claim 1, wherein the fixed pattern is a dot.   The step of detecting the position of the image of the fixed pattern comprises dividing the fixed measurement image into a plurality of areas, and detecting the position of the image included in the area for each of the areas. Test method described.   The inspection method according to any one of claims 1 to 3, further comprising the step of binarizing the fixed measurement image prior to the step of detecting the position of the image of the fixed pattern.   The inspection method according to claim 4, wherein in the step of binarizing the fixed measurement image, a threshold of binarization is determined based on luminance information of the short cycle measurement image. A projection unit for projecting a pattern onto a subject to be inspected;
A camera unit for acquiring an image of the inspection object on which the pattern is projected;
A storage unit that stores the image;
The control apparatus which calculates the height of the said to-be-tested object by the inspection method as described in any one of Claims 1-5, The inspection apparatus characterized by the above-mentioned.