Visual inspection equipment

Abstract

To provide an appearance inspection technique with excellent reproducibility and accuracy. The visual inspection device (10) comprises a camera (32) which is composed of an imaging optical system and an image sensor and acquires an image (18) to be used for visual inspection, a mechanism (31) which changes the positional relationship between the camera (32) and an object (30) to be inspected at a movement pitch equal to the division pitch when the field of view of the camera (32) is divided into M × N (2≦M × N) equal parts, and an image processing inspection unit (23) which processes the image (18) acquired from the camera (32) and performs inspection, characterized in that the camera (32) acquires at least one image (18) for each movement pitch by the mechanism unit (31), acquires M × N images of all the test area of ​​the object (30), and the acquired images (18) are inspected and processed by the image processing inspection unit (23).

Description

[Technical Field]

[0001] The present invention relates to a visual inspection technique for inspecting various products using image processing technology. [Background technology]

[0002] Visual inspection equipment that uses a camera, a device that captures images, to inspect the appearance of various products is becoming widespread.A camera is composed of an imaging optical system that forms an optical image of the object under test, and an image sensor (generally a CMOS image sensor) that photoelectrically converts the light intensity of that image into an electronic image, and the size of the image obtained in one capture is called the field of view.

[0003] The field of view can be changed by changing the magnification of the lens. However, in inspection, pixel resolution, which is the size on the test object equivalent to one pixel on the imaging device, is the primary factor that determines inspection performance. Therefore, the magnification of the imaging optical system must be determined to obtain the desired pixel resolution, and the field of view cannot necessarily be freely set. Therefore, when inspecting a test object that is larger than the field of view, the camera or the test object must be moved and multiple fields of view must be used to inspect the entire test object. For example, if the camera's field of view is 11 x 11 mm and the test object is 20 x 20 mm, the entire test object can be inspected using four fields of view. This type of inspection is referred to as multi-field inspection below.

[0004] As a specific example, bump inspection in the semiconductor packaging process (post-processing) is described below. IC (integrated circuit) chips need to be packaged in resin to protect against deterioration and heat. Packaging involves mounting the chip on a multilayer wiring board, connecting the electrodes on this board to the electrodes on the chip, and then sealing it in resin. While the wire mounting method, in which wires are used to connect electrodes, has traditionally been the norm, in recent years the flip-chip mounting method, in which ball-shaped microelectrodes (hereafter referred to as "bumps") are arranged two-dimensionally in an array and connected, has become increasingly popular.

[0005] In flip-chip mounting, electrodes are directly overlapped, so it is important that the bumps are uniform in size. This is because any variation in bump size will result in poor connection. Therefore, it is necessary to accurately inspect the shape of the bumps before connection (see, for example, Patent Document 1).

[0006] Visual inspection of bumps is performed as part of in-line inspection during the manufacturing process, by photographing the arrayed bumps from above with a camera. In recent years, full inspection has become common, so inspection speed is of great importance. Currently, bumps have diameters ranging from 10 to 80 μm, are arranged at pitches ranging from 20 to 130 μm per multilayer wiring board, and hundreds to tens of thousands of them are mounted. There is a demand for high-speed inspection of all of these bumps per multilayer wiring board, taking one to several tens of seconds.

[0007] In recent years, packaging using the chiplet concept has been promoted, and as more chips are mounted on multilayer wiring boards, the size of the multilayer wiring boards has increased. On the other hand, as circuits have become more miniaturized, the bump diameter has become smaller, and fine pixel resolution is required for appearance inspection, which has resulted in a smaller field of view. As a result, multi-field inspection using a large number of fields of view has become necessary. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4984332 Summary of the Invention [Problem to be solved by the invention]

[0009] One problem with image-based inspections is the issue of aberration in the imaging optical system. Due to aberration in the imaging optical system, the image quality is not uniform within the field of view; for example, the state of aberration differs between the center and periphery of the field of view, resulting in different image quality. If the image quality differs, the inspection results may not be the same. For example, when inspecting to check the height of a bump, there may be a difference between the height value at the center of the field of view and the height value at the periphery of the field of view, even for the same bump. (First issue)

[0010] Furthermore, as test objects become smaller and require higher-precision inspections, the relationship between the digital pixel arrangement and the position of the test object can affect the inspection results. For example, because a ball-shaped bump is relatively mirror-like, when illuminated from directly above, the reflected light returning is limited to the apex. Therefore, as the diameter of the bump becomes smaller, the area from which the reflected light returns also becomes smaller, and the size of the apex imaged becomes smaller than the pixel size of the camera. This means that the reflected light from the apex of the bump may be captured by one pixel or by multiple adjacent pixels. Therefore, depending on the case, the morphological information of the bump may differ, posing a problem of reduced accuracy and reproducibility of the inspection results (the second problem).

[0011] The present invention has been made in consideration of the above circumstances, and has as its object to provide an appearance inspection technique that is highly reproducible and accurate. [Means for solving the problem]

[0012] The visual inspection device of the present invention comprises a camera composed of an imaging optical system and an image sensor for acquiring images to be used for visual inspection, a mechanism for changing the positional relationship between the camera and the object under test at a movement pitch approximately equal to the division pitch when the field of view of the camera is divided into M×N (2≦M×N) equal parts, and an image processing inspection unit for processing the images acquired from the camera and carrying out inspection, characterized in that the camera acquires at least one image each time it moves by the movement pitch, acquiring M×N images of all the test area of ​​the object under test, and the acquired images are inspected and processed by the image processing inspection unit. [Effects of the Invention]

[0013] The present invention provides a highly accurate appearance inspection technique. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram of a visual inspection apparatus according to a first embodiment of the present invention. [Figure 2] (A) A top perspective view of a multilayer wiring board with bumps arranged in an array, and (B) a side perspective view of a multilayer wiring board with chips mounted on the multilayer wiring board via bumps. [Figure 3] 3A to 3F are explanatory diagrams illustrating the operation of the visual inspection device according to the embodiment. [Figure 4] 4(G) to 4(L) are explanatory diagrams illustrating the operation of the visual inspection device according to the embodiment. [Figure 5] (A) Side view showing the reflected light from the vertices of bumps of different sizes entering the camera, and (B) top view of the same. [Figure 6] (A) A bump image showing the reflected light from the vertex detected by one pixel, (B) a bump image showing the same reflected light detected by two pixels, and (C) a bump image showing the same reflected light detected by four pixels. [Figure 7] Formula for visual inspection algorithm. DETAILED DESCRIPTION OF THE INVENTION

[0015] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. For the sake of specificity, bump inspection will be taken as an example. FIG. 1 is a block diagram of a visual inspection device 10 according to a first embodiment of the present invention. FIG. 2(A) is a top perspective view of a multilayer wiring substrate (subject to test) 30 on which bumps 14 are arranged in an array. FIG. 2(B) is a side perspective view of an IC package 37 in which a chip 36 is mounted on the multilayer wiring substrate 30 via the bumps 14.

[0016] As shown in FIG. 2, in an IC package 37, electrodes of a multilayer wiring substrate 30 (hereinafter simply referred to as "substrate 30") and electrodes of an IC chip 36 are electrically connected by bumps 14. This method of electrical connection using bumps 14 is called flip-chip mounting. In this embodiment, the bumps 14 arranged on the substrate 30 are inspected. Thereafter, the chip 36 is mounted and further packaged 35 with resin to prevent deterioration and heat, thereby completing the IC package 37. Note that, although a substrate 30 with bumps 14 arranged thereon is shown as an example of an object to be tested by the visual inspection apparatus 10 in this embodiment, this is not particularly limited.

[0017] As shown in FIG. 1, a plurality of substrates 30 (3 × 5 = 15 in the figure) on which bumps 14 (FIG. 2) are arranged are accommodated on a tray 38. Tray 38 thus accommodating a plurality of substrates 30 is placed on inspection table 39 and inspected by visual inspection device 10. After inspection, tray 38 is transferred to the next process, and a new tray 38 accommodating substrates 30 yet to be inspected is placed on inspection table 39. Note that a multilayer wiring board is shown as one example of substrate 30 on which bumps 14 are arranged, and there is no particular limitation.

[0018] 3(A) to 3(F) and 4(G) to 4(L) are diagrams illustrating the operation of the appearance inspection device 10 for bumps 14 according to the embodiment. The explanation will continue with reference to FIG. 1. The field of view 12 of the camera 32 is divided into four equal 2 x 2 sections, each of which will be called a segment 11. The device includes a mechanism 31 that sequentially moves the field of view 12 in a stepwise manner to a test area 14a where a group of bumps 14 exists at a movement pitch equal to the division pitch of the segments 11, and an image processing and inspection unit 23 that processes and inspects an image 18 of the field of view 12 acquired from the camera 32.

[0019] In the above explanation, the segments 11 are each sized to divide the field of view 12 of the camera 32 into four equal parts, but this does not need to be exact. When performing multi-field inspection, it is common to set a slight overlapping area between adjacent fields of view. For example, in the case of a bump, if the bump is divided and imaged in adjacent fields of view, the measurement process becomes complicated. Therefore, to ensure that the bump is imaged without being divided into either field of view, the images are overlapped so that an area equal to or greater than the bump pitch is imaged in both fields of view. It is sufficient to exclude such areas and divide the field of view into four equal parts; it does not need to be exactly 1 / 4 of the field of view. This is indicated by the fact that the sizes of the field of view 12 and the four segments 11 in Figures 3 and 4 do not match.

[0020] Also, dividing into four equal parts is just one example, and generally speaking, it is divided into M×N equal parts (2≦M×N). As a result, by sequentially moving the field of view 12 in steps at a movement pitch equal to the division pitch of the segments 11, all bumps are imaged M×N times. This allows the morphological information 24 of the bumps 14 to be determined using information from M×N images, thereby improving the determination accuracy.

[0021] The mechanism 31 sequentially moves the camera 32 in a step-like manner at a movement pitch equal to the division pitch of the segments 11. As a modified example of the mechanism 31, although not shown in the drawings, it is also possible to adopt a configuration in which an inspection table 39 on which a tray 38 is placed is sequentially moved in a step-like manner.

[0022] The operation of the bump appearance inspection device 10 is as follows: first, as shown in Figure 3(A), the field of view 12 of the camera 32 is positioned so that it includes one segment 11 located at the corner of the test area 14a where a group of bumps 14 exists, and an image 18 is acquired in the image processing inspection unit 23 (Figure 1).

[0023] Next, as shown in FIG. 3(B), the field of view 12 is advanced by one step along the row of bumps 14 at a movement pitch equal to the division pitch, and images 18 are acquired by the image processing inspection unit 23. Furthermore, the sequential advancement of the field of view 12 along the row of bumps 14 and the acquisition of images 18 are repeated up to the opposite end, as shown in FIG. 3(C). Thereafter, the field of view 12 is advanced by one step in the perpendicular direction, as shown in FIG. 3(D), and the sequential advancement of the field of view 12 in the reverse direction and the acquisition of images 18 are repeated up to the opposite end, as shown in FIG. 3(E). Similarly, from FIG. 3(F) to FIG. 4(G)-(L), the sequential advancement in steps at a movement pitch equal to the division pitch of the segments 11 and the acquisition of images 18 are repeated.

[0024] In this way, the image processing inspection unit 23 acquires M×N (four in the figure) images 18 for each of the plurality of segments 11. Each of the same segment 11 captured in the plurality of images 18 is captured in a different region of the field of view 12 divided into M×N regions.

[0025] Generally, images 18 are affected by aberrations in the imaging optical system. Generally, aberrations increase from the center to the periphery of the field of view, resulting in a tendency for image quality to deteriorate. Furthermore, the effects of this aberration are not necessarily point-symmetric due to manufacturing errors such as decentering. Meanwhile, bumps 14 captured in different regions of the field of view 12 are located in different locations with different aberration conditions in the images 18, and it is thought that each image has different accuracy. Therefore, the M × N (four in the figure) images 18 may be detected in the center or periphery of the field of view 12. Then, by statistically processing these detection values, the accuracy of the morphological information 24 used to determine the bumps 14 can be made uniform.

[0026] FIG. 5(A) is a side view showing reflected light 26 (26x, 26y) from vertices 27 of bumps 14 (14x, 14y) of different sizes, which enters camera 32. FIG. 5(B) is a top view of the same. Because ball-shaped bumps 14 are relatively close to a mirror surface, when illuminated from directly above, the reflected light 26 (26x, 26y) entering camera 32 is limited to the area of ​​vertices 27 (27x, 27y). Therefore, as the diameter of bump 14 decreases, the area of ​​vertex 27 from which reflected light 26 returns also becomes smaller.

[0027] 6(A) is an image 18 of a bump 14 showing the reflected light 26 from the vertex 27 detected by one pixel 22, (B) is an image 18 of the bump 14 showing the reflected light 26 detected by two pixels 22, and (C) is an image 18 of the bump 14 showing the reflected light 26 detected by four pixels 22. As such, when the bump 14 becomes smaller and the size of the captured vertex 27 becomes equal to or smaller than the size of the camera's pixel 22, the vertex 27 may be captured by one pixel or by multiple adjacent pixels.

[0028] The movement pitch of the field of view 12 is the size of the segment 11 (= division pitch), but by making the movement pitch an integer multiple of the pixel resolution and adding 1 / M (for vertical movement pitch) or 1 / N (for horizontal movement) of the pixel resolution, if the amount of movement is accurate, it is possible to obtain M×N images 18 in which the positional relationship of the bump to the pixel 22 is shifted by 1 / M vertically and 1 / N horizontally.

[0029] In other words, the division pitch of the segment 11 is multiplied by the magnification of the imaging optical system, and the result is divided by the size of the pixel 22 of the camera 32 (pixel size), and the result is rounded to the nearest integer, and then 1 / M times the pixel size is added vertically and 1 / N times the pixel size horizontally, and the result of dividing these values ​​by the magnification of the imaging optical system becomes the vertical and horizontal size of the movement pitch.

[0030] This pixel shifting has the effect of improving pixel resolution, making it possible to reduce the effect on measurement values ​​caused by differences in the positional relationship between pixels and the object, as shown in Figure 6, and improving the accuracy and reproducibility of inspection results.

[0031] The image processing inspection unit 23 (FIG. 1) determines the morphological information 24 of the target bump 14 based on the four (M×N) vertex pixels 22a sequentially acquired. The morphological information 24 specifically includes the position, height, and outer diameter of the bump 14, as well as other shape abnormalities of the bump 14, and further includes the height of the substrate 30 and surface foreign matter.

[0032] The measurement values ​​of these morphological information 24 are calculated one by one from each of the four (M×N) images 18 showing the shape of each bump 14 based on the brightness values ​​of the vertex pixels 22a and / or their surrounding pixels 22, for a total of four (M×N) values, and these multiple measurement values ​​are then statistically processed to output one representative value for each bump 14. Note that the measurement values ​​and their representative values ​​representing the morphological information 24 of the bump 14 are not limited to one item, but are determined for multiple items.

[0033] FIG. 7 shows the formula for the algorithm of the visual inspection. The representative value V of the shape information 24 is calculated from the multiple measured values ​​v according to the following multiple (three types) algorithms. i However, the method for calculating the representative value V is not limited to these algorithms.

[0034] The first algorithm is "simple averaging." This "simple averaging" is a function of M × N measurements v i (i=1 to M×N) are averaged according to equation (1) in Figure 7 to calculate the representative value V. Due to the effect of averaging (law of number of units, central limit theorem), one measurement value v i This is more reliable than selecting V as the representative value.

[0035] The second algorithm is the "weighted average by reliability." This "weighted average by reliability" is calculated by taking M × N measured values ​​v according to equation (2) in Figure 7. i The reliability value t of the pixel 22 that derived each of (i=1 to M×N) i is used as a weighting factor to calculate the corresponding measurement value v iThen, a weighted average is performed to calculate the representative value V. This "weighted average based on reliability" can suppress the effects of pixel cracking shown in Figures 6(B) and 6(C), improving the reliability of the representative value V.

[0036] Here, the reliability value is a quantity that indicates the degree of reliability of the inspection value and measurement value of each pixel, and differs depending on the method of visual inspection. For example, the brightness value of a pixel indicates the amount of light, which is the signal, so it can be said to indicate reliability in the sense of whether the signal is being obtained reliably, and is an example of a reliability value.

[0037] The third algorithm is "weighted averaging by distance from the center." This "weighted averaging by distance from the center" is performed by taking M × N measured values ​​v according to equation (3) in Figure 7. i The distance L from the center position of the visual field 12 of the pixel 22 that guided each of (i=1 to M×N) i (i=1~M×N) is used as a weighting factor to calculate the corresponding measurement value v i This is then weighted averaged to calculate the representative value V. This "weighted average based on distance from the center" places emphasis on values ​​measured near the center of the field of view, suppressing the effects of aberration and improving the reliability of the representative value V.

[0038] This invention can reduce the effects of aberrations in the imaging optical system (problem number 1) and pixel cracks (problem number 2) in visual inspections using images, thereby improving the reliability of the inspection. However, there is a clear negative factor of increased inspection time. The larger M × N, the more reliable the inspection, but the longer the inspection time. However, by incorporating the functions of this invention into a visual inspection device, the user can select the optimum reliability and speed, which is considered to be a significant advantage. [Explanation of symbols]

[0039] 10...visual inspection device, 11...segment, 12...field of view, 14...bump, 14a...group of bumps (test area), 15...adjustment unit, 18...image, 22...pixel, 22a...vertex pixel, 23...image processing inspection unit, 24...morphological information, 26...reflected light, 27...vertex, 30...multilayer wiring board (board, test object), 31...mechanism, 32...camera, 35...packaging, 36...IC chip, 37...IC package, 38...tray, 39...inspection table.

Claims

1. a camera configured with an imaging optical system and an image sensor for acquiring an image used for appearance inspection; a mechanism for changing the positional relationship between the camera and the object to be inspected at a moving pitch equal to the division pitch when the field of view of the camera is divided into M×N equal parts (2≦M×N); an image processing and inspection unit that processes the image obtained from the camera and performs an inspection; An appearance inspection device characterized in that at least one image is acquired by the camera each time the mechanism unit moves by the movement pitch, M x N images are acquired of the entire test area of ​​the test object, and the acquired images are inspected and processed by the image processing inspection unit.

2. 2. The visual inspection apparatus according to claim 1, The visual inspection device is configured so that the division pitch multiplied by the magnification of the imaging optical system is divided by the pixel size of the camera, the result is rounded to the nearest integer, and then 1 / M times the pixel size in the vertical direction and 1 / N times the pixel size in the horizontal direction are added, and the values ​​divided by the magnification of the imaging optical system become the vertical and horizontal sizes of the movement pitch.

Images