JP2003130811A - Inspection for inspection object using wavelength- selecting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of determining easily a wavelength range suitable for obtaining an image of an inspection object when the optional inspection object is inspected. SOLUTION: A plurality of images as to lights in the plural wavelength ranges is acquired in an inspection-objective area on the inspection object. Image characteristic quantities are calculated as to the plural images, and the wavelength range R7 suitable for the inspection is selected based on the image characteristic quantities. The images of the respective inspection objects are obtained in order as to the light of the selected wavelength range R7, and the inspection objects are inspected based on the images, in the inspection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for inspecting a plurality of inspection objects of the same type by utilizing image processing.

[0002]

2. Description of the Related Art A printed circuit board for an electronic circuit is a printed circuit board on which a conductive pattern such as circuit wiring and a conductive pad and silk characters are printed on an insulating substrate. In the inspection of the printed circuit board, the quality of the printed state of the conductor pattern and silk characters is inspected.

As a method of inspecting a printed circuit board, for example, a method described in Japanese Patent Laid-Open No. 9-21760 is known. In this method, images of the printed circuit board are respectively acquired using an infrared cut filter and a blue filter, and defects in the solder portion are detected based on these images.

[0004]

However, even though the use of the infrared cut filter and the blue filter is suitable for the inspection of the solder portion of the printed circuit board, it is not necessary to use other wavelengths for the inspection of other parts of the printed circuit board. There may be cases where it is preferable to use light in the range. When the inspection object is not a printed circuit board, which wavelength range of light is suitable for the inspection largely depends on the material of the inspection object. Therefore, conventionally, there has been a demand for a technique capable of easily determining a wavelength range suitable for acquiring an image of an inspection target when inspecting an arbitrary inspection target.

The present invention has been made to solve the above-mentioned conventional problems, and when inspecting an arbitrary inspection object, a wavelength range suitable for acquiring an image of the inspection object is easily set. The purpose is to provide a technology that can be determined.

[0006]

In order to achieve the above object, the present invention provides a method and apparatus for sequentially inspecting a plurality of inspection objects of the same type. The inspection apparatus, for an inspection target area on each inspection target, an imaging unit capable of acquiring a plurality of images of light in a plurality of wavelength ranges, and at least one inspection target of the plurality of inspection objects, Based on a plurality of images acquired with respect to light of a plurality of wavelength bands, a wavelength band selection unit that selects a wavelength band suitable for inspection from the plurality of wavelength bands, and with respect to the light of the selected wavelength band An inspection execution unit that executes inspection of each inspection target based on the image of each inspection target acquired by the imaging unit.

According to this inspection apparatus, the wavelength range suitable for the inspection is selected based on the plurality of images acquired for the light of the plurality of wavelength ranges, and the inspection is executed using the light of this wavelength range. When inspecting an arbitrary inspection object, it is possible to easily determine a wavelength range suitable for acquiring an image of the inspection object.

It is preferable that the wavelength band selecting unit calculates a predetermined image feature amount for each of the plurality of images and selects the wavelength band based on the image feature amount.

According to this structure, it is possible to automatically select an appropriate wavelength range according to the image feature amount.

It is preferable that the image feature amount is a relative value between a predetermined inspection target point and a non-inspection target point in the inspection target area. For example, the contrast between the inspection target point and the non-inspection target point can be used as the image feature amount.

The present invention can be realized in various forms, for example, a method and a device for inspecting an object to be inspected, a method and a device for selecting a wavelength range, and a function of those methods or devices. It can be realized in the form of a computer program for carrying out, a recording medium recording the computer program, a data signal including the computer program and embodied in a carrier wave, and the like.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in the following order based on examples. A. Device Configuration: B. Procedure of Example: C.I. Other image feature amount: D. Modification:

A. Device Configuration: FIG. 1 is an explanatory diagram showing the configuration of an inspection device 100 as an embodiment of the present invention.
The inspection apparatus 100 includes an inspection stage 20 for mounting a printed circuit board PCB, a white light source 30 for illuminating the printed circuit board PCB, a color filter plate 40 having a plurality of color filters, a camera 50, and an apparatus. And a computer 60 for controlling the whole. An external storage device 70 for storing image data and a computer program is connected to the computer 60.

The computer 60 has the functions of a wavelength range selection unit 62 and an inspection execution unit 64. Wavelength range selection unit 62
Includes an image feature amount calculation unit 66. Functions of these units 62, 64, 66 (described later) are realized by the computer 60 executing a computer program stored in the external storage device 70.

The color filter plate 40 has a plurality of color filters having different transmission wavelength bands. FIG. 2 is a graph showing the transmittance of a plurality of color filters. Here, the characteristics of seven color filters having seven wavelength regions R1 to R7 as transmission regions are shown. Here, the "transmission region" means a wavelength region having a transmittance of 10% or more. The transmission areas of the plurality of color filters are different from each other. However,
The transmission areas of the respective color filters may slightly overlap each other.

The white light emitted from the white light source 30 is reflected on the surface of the printed circuit board PCB, and the reflected light is 7
Camera 5 after passing through any one of the two color filters
Reach 0. Therefore, using the white light source 30, the color filter plate 40, and the camera 50, seven wavelength ranges R1 to R
Images related to 7 can be sequentially acquired. The camera 50 may be a monochrome camera in order to acquire images regarding these seven wavelength ranges R1 to R7. However, in this embodiment, a camera capable of capturing a color image is used as the camera 50.

B. Processing procedure of the embodiment: FIG. 3 is a flowchart showing the processing procedure of the inspection in the embodiment. In step T1, a master substrate (also called “reference substrate”)
1 is prepared, and a color image of the inspection target area on the master substrate is captured using the inspection apparatus of FIG. Here, the "master board" means a standard printed board used for determining a wavelength range used for inspection. As the master board, at least one arbitrary printed board selected from a plurality of printed boards of the same type can be used. When capturing a color image in step T1, white light is used as it is without using a color filter.

FIG. 4 is an explanatory view showing a color area on the surface of the printed circuit board PCB. The surface of the printed circuit board PCB is
The first green area G where the resist is applied on the substrate base
1, a second green area G2 coated with a resist on the copper wiring, a gold area GL plated with gold, a brown area BR of the substrate base, and white silk characters printed on the substrate base. The white area WH is included. Since the substrate base which is the base of the first green area G1 is brown and the copper wiring which is the base of the second green area G2 is copper colored, the colors of these two areas G1 and G2 are slightly different. , Both are still green. Therefore, in the present embodiment, these two green regions G1 and G2 are collectively referred to as "green region GR".

In the present embodiment, these various color regions G
Among 1, G2, GL, BR, and WH, the gold area GL is an inspection target. That is, it is inspected whether or not the shape of the gold area GL is normal.

In step T2, the color image as shown in FIG. 4 is displayed on the display section of the computer 60, and the operator designates the sample points to be inspected and the sample points to be inspected on the color image. here,
The "inspection target sample point" is a point in the color region that is the inspection target, and the "non-inspection target sample point" is a point in the color region that is not the inspection target. In step T4 described later, pixel values are acquired from these sample points. For example, when the gold-plated portion is to be inspected, the inspected sample point is designated in the gold area GL, and the other color areas (brown area BR, green areas G1, G)
2, and the non-inspection target sample points are designated in the white area WH). It should be noted that the sample point may be a region including at least one pixel, but in the present embodiment, a region including a plurality of pixels is used as each sample point. Therefore, in this embodiment, the sample points are also referred to as “sample areas”. The inspection target sample points and the non-inspection target sample points are also simply referred to as “inspection target points” and “non-inspection target points”.

At step T3, seven images for the seven wavelength bands R1 to R7 (FIG. 2) are respectively acquired using the seven color filters. In step T4, the wavelength band selection unit 62 calculates a predetermined image feature amount for each of the seven images, and selects a wavelength region suitable for inspection based on the image feature amount. In this embodiment, the contrast between the inspection target sample point and the non-inspection target sample point is used as the image feature amount.

FIG. 5 is a flow chart showing the detailed procedure of step T4 when the contrast is adopted as the image feature amount. In step T11, the average pixel value of the sample points to be inspected is calculated in the image of each wavelength range.
In the present embodiment, the inspection target sample point is designated within the gold region GL, and the inspection target sample point includes a plurality of pixels. The wavelength range is divided into seven.
Therefore, in step T11, 7
In each of the images, the average pixel value regarding the inspection target sample point in the gold region GL is calculated.

In step T12, the average pixel value of the non-inspection sample points in the image of each wavelength range is calculated.
In the seven images for the seven wavelength regions, the gold region G
Average pixel values for the non-inspection target sample points designated in the regions G1, G2, BR, and WH other than L are calculated.

At step T13, for each wavelength band,
A ratio (contrast) between the average pixel value of the inspection target sample points and the average pixel value of the non-inspection target sample points is calculated.
Then, in step T14, the wavelength range that maximizes the contrast is selected.

FIG. 6 is a graph showing the spectral reflectance characteristics of the gold area and the brown area. In general, the contrast of two areas is proportional to their reflectance. Therefore, the contrast between the gold region GL and the brown region BR is the largest in the wavelength range R7, and smaller than this in the other wavelength ranges. The gold area GL may appear as a brown area in a normal color image, and thus it may not be possible to clearly distinguish the two. On the other hand, in the image captured in the wavelength range R7, the contrast between the gold area GL and the brown area BR is large,
It is possible to clearly distinguish the gold area GL and the brown area BR.

Although not shown, the contrast between the other color areas G1, G2, WH and the gold color area GL also becomes maximum in this wavelength range R7. Therefore, step T
In 14, the wavelength range R7 is selected as the wavelength range suitable for the inspection. As can be understood from this description, it is preferable that the contrast is calculated individually for the inspection target sample point and each non-inspection target sample point. By doing so, in a certain wavelength range, when the contrast between the non-inspection target sample point in the specific color region and the inspection target sample point is low, it can be determined that the wavelength range is not selected, and the preferable wavelength It is possible to determine the range more accurately. Two or more preferable wavelength ranges can be selected.

When the wavelength range is selected in this way, in step T5 of FIG. 3, the inspection execution unit 64 sequentially executes inspections on a plurality of printed circuit boards PCBs. In particular,
An image of each printed circuit board PCB is acquired using a color filter corresponding to the selected wavelength region R7, and the quality of the shape of the gold region GL (gold plated portion) is inspected using this image.
Since the image captured in the wavelength range R7 has a high contrast between the gold color region GL and the other color regions, the gold color region GL can be clearly distinguished from the other color regions. Therefore, it is possible to accurately inspect the shape of the gold region GL.

As a concrete method of the inspection, binary comparison, multi-value comparison, visual comparison between the image of the master substrate and the image of each inspection target substrate, or CAD data and each inspection target substrate is performed. It is possible to use the comparison with the image of.

As described above, in the present embodiment, at least one wavelength range suitable for the inspection is selected from the plurality of wavelength ranges based on the predetermined image feature amount regarding the inspection target sample point and the non-inspection target sample point. One of them is selected, and at the time of inspection, an image of the printed circuit board PCB is acquired using this wavelength range. Therefore, even when the materials used on the surface of the printed circuit board PCB are different, it is possible to select an appropriate wavelength range according to this and perform the inspection. As a result, it is possible to accurately execute the inspection using the image processing.

C. Other image feature amount: A value other than contrast can be used as the image feature amount, and a relative value of an arbitrary value calculated based on the image at the inspection target point and the non-inspection target point is used. It is possible to Also, the sharpness of the image, the distribution of pixel values in the image,
Standard deviations of pixel values, entropy of pixel values, etc. can also be used as image feature amounts. The entropy of the pixel value can be calculated using the following equation (1), for example.

[0031]

[Equation 1]

Here, i is a pixel value (0 to 255) of each pixel forming an image, and h (i) is a histogram showing the frequency of the number of pixels having a pixel value of i. Also, the operator
ln [] means an operation that takes a natural logarithm. The histogram h (i) is a value (that is, the probability of appearance of the pixel value i) standardized so that the integrated value becomes 1. The entropy H1 is an index value indicating the amount of information when the image is considered as the information source. Therefore, entropy H1
Tends to have a larger value as the change in the pixel value in the image increases. In equation (1) above, the natural logarithm
Instead of ln [], logarithm log ₂ [] with base ₂ may be used.

It is also possible to use fuzzy entropy H2 given by the following equations (2a) and (2b) instead of the entropy H1.

[0034]

[Equation 2]

M × N is the size of the image (the number of pixels). Te (i) is a fuzzy member function that defines a fuzzy set, and its shape is given by equation (2b). In the present embodiment, the coefficients a, b, and c defining the form of the fuzzy member function Te (i) are a = 0, b = 12.
7.5, c = 255 is used. This fuzzy entropy H2 also has a meaning as an index value indicating the information amount of the image.

When the image feature amount such as the sharpness of the image, the variance of the pixel value in the image, the standard deviation of the pixel value, and the entropy of the pixel value is used, the feature amount of the entire captured image is Since it is an evaluation target, it is not necessary to specify sample points.

The inspection using the feature amount of the entire image can be used, for example, in determining the end point of the surface polishing of the semiconductor wafer. At this time, an image of the wafer surface is picked up during the polishing, and the feature amount (sharpness or entropy) is used to determine the end point of the polishing. At this time, if the wavelength range in which the correlation between the change in the image feature amount and the polishing end point is maximized is selected, it is possible to accurately determine the polishing end point.

D. Modifications: The present invention is not limited to the above-described embodiments and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are also possible. is there.

D1. Modification 1: In the above embodiment, the inspection target sample points are specified in one color area, but the inspection target sample points may be specified in a plurality of color areas. In this case, the wavelength range suitable for the inspection is selected for the sample points to be inspected in each color region.

D2. Modification 2: In the above embodiment, the wavelength range suitable for the inspection is automatically selected based on the image feature amount, but instead of this, the images captured in a plurality of wavelength ranges are output, and the operator Alternatively, the wavelength range suitable for the inspection may be selected by performing visual comparison. Here, “outputting an image” includes both the case of displaying an image on the display unit and the case of forming an image by a printer.
As can be understood from this description, in the present invention, the wavelength range suitable for the inspection may be selected from the plurality of wavelength ranges based on the plurality of images acquired regarding the light in the plurality of wavelength ranges. .

D3. Modified Example 3: In the above embodiment, the images regarding the seven wavelength bands R1 to R7 were acquired, but any number of two or more can be applied as the number of wavelength bands. However, depending on the reflectance or transmittance of the surface of the inspection object,
In order to be able to select the wavelength range suitable for inspection,
It is preferable to set the number of wavelength ranges to 3 or more.

D4. Modification 4: In the above embodiment, an image of visible light having a wavelength range of 400 to 700 nm was acquired, but a wavelength range including an ultraviolet light range and an infrared light range (for example, 30
An image regarding light of 0 to 900 nm) may be acquired.

D5. Modification 5: In the above-described embodiment, the white light source 30, the color filter plate 40, and the camera 50 are used to acquire a plurality of images regarding a plurality of wavelength bands, but an imaging unit having a different configuration is used. Thus, a plurality of images regarding a plurality of wavelength bands may be acquired. For example, a scanner may be used instead of the camera 50.
Alternatively, a multi-band camera or scanner with a built-in color filter may be used.

D6. Modification 6: In the various embodiments described above, the inspection is performed using the printed circuit board PCB as the inspection target, but the present invention can be applied to the inspection of any inspection target other than the printed circuit board.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inspection apparatus as a first embodiment of the present invention.

FIG. 2 is a graph showing the transmittance of a plurality of color filters of a color filter plate 40.

FIG. 3 is a flowchart showing a processing procedure of inspection in the embodiment.

FIG. 4 is an explanatory view showing a color area on the surface of a printed circuit board PCB.

FIG. 5 is a flowchart showing a detailed procedure of step T4.

FIG. 6 is a graph showing spectral reflectance characteristics of a gold region and a brown region.

[Explanation of symbols]

20 ... Inspection stage 30 ... White light source 40 ... Color filter plate 50 ... Camera 60 ... Computer 62 ... Wavelength range selector 64 ... Inspection execution unit 66 ... Image feature amount calculation unit 70 ... External storage device 100 ... Inspection device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G01B 11/24 F (72) Inventor Atsushi Imamura 4-chome Tenjin Kitamachi, Horikawa-dori Temple, Kamigyo-ku, Kyoto No. 1 Dainippon Screen Mfg. Co., Ltd. (72) Inventor Hiroshi Sano No. 1 Tenjin Kitamachi 4-chome Tenjin Kitacho, Horikawa-dori Teranouchi, Kamigyo-ku, Kyoto City No. 1 Dai Nippon Screen Mfg. Co., Ltd. (72) Inventor Fujimoto Hiromi 1-chome, Tenjin Kitamachi, 4-chome, Horikawa-dōji, Kamigyo-ku, Kyoto, Japan In-house company of Dai Nippon Screen Manufacturing Co., Ltd. No. 1 Dainippon Screen Mfg. Co., Ltd. In-company F-term (reference) 2F065 AA56 BB02 CC01 GG24 JJ03 JJ19 JJ26 LL22 PP12 QQ24 QQ25 QQ42 QQ43 RR09 SS02 SS13 2G051 AA65 AB11 AB14 BA08 BA20 BB07 CA03 CA04 CB01 DA07 EA11 EA14 EB01 EB02 EC02 EC03 ED07 FA10 2G059 AA05 BB10 BB15 DD13 EE02 EE11 FF08 CG10 CA05 CA08 BA05 MM02 HI 04 H01 DB02 DB06 DB09 DC22 DC23 DC30 DC32 5L096 AA02 AA06 BA03 CA04 FA32 FA37 JA11 JA18

Claims (9)

[Claims] 1. A method of sequentially inspecting a plurality of inspection objects of the same type, comprising: (a) a plurality of wavelengths for an inspection object region on at least one inspection object among the plurality of inspection objects. Respectively acquiring a plurality of images relating to the light in the region, and (b) selecting at least one wavelength region suitable for inspection from the plurality of wavelength regions based on the plurality of images, (c) ) Sequentially acquiring images of each inspection object with respect to light in the selected wavelength range,
(D) a step of inspecting each inspection object based on an image of each inspection object relating to the light in the selected wavelength range, the inspection method of the inspection object. 2. The inspection method according to claim 1, wherein the step (b) includes a step of calculating a predetermined image feature amount based on the plurality of images, and a step of calculating the predetermined image feature amount based on the image feature amount. And a step of selecting a wavelength range. 3. The inspection method according to claim 2, wherein the step (b) further includes the step of designating an inspection target point and a non-inspection target point in the inspection target area, The inspection method, wherein the amount is calculated as a relative value between the inspection target point and the non-inspection target point. 4. The inspection method according to claim 3, wherein the image feature amount is a contrast between the inspection target point and the non-inspection target point. 5. The inspection method according to claim 1, wherein in the step (b), the step of outputting the plurality of images and the selection of the wavelength range based on the plurality of displayed images are performed. And a step of performing. 6. An apparatus for sequentially inspecting a plurality of inspection objects of the same type, comprising: an imaging unit capable of acquiring a plurality of images of light in a plurality of wavelength bands for each inspection object area on each inspection object. A wavelength range suitable for inspection from among the plurality of wavelength bands based on a plurality of images acquired for light of the plurality of wavelength bands for at least one inspection target among the plurality of inspection targets. A wavelength range selection unit that selects at least one, and an inspection execution unit that executes an inspection of each inspection target object based on an image of each inspection target object acquired by the imaging unit regarding the light of the selected wavelength range. An inspection apparatus comprising: 7. The inspection apparatus according to claim 6, wherein the wavelength band selection unit calculates a predetermined image feature amount for each of the plurality of images, and determines the wavelength band based on the image feature amount. An inspection device that performs selection. 8. The inspection apparatus according to claim 7, wherein the image feature amount is a relative value between an inspection target point and a non-inspection target point which are designated in advance in the inspection target area. 9. The inspection apparatus according to claim 8, wherein the image feature amount is a contrast between the inspection target point and the non-inspection target point.