JPH0560535A - Wiring pattern inspection device - Google Patents

Abstract

PURPOSE:To form an accurate and stable modulated stripe pattern at the through-hole section of a printed circuit board, and enable the land section thereof to be inspected by detecting an image of light reflected from the board and an image of transmitted light with a single image pickup device. CONSTITUTION:A printed circuit board 101 is illuminated with a lighting device 102 from above, and an image of reflected light is inputted as a variable density image via an image input means 105. Concurrently, modulated illumination light is irradiated from under the board 101 at the predetermined cycle, and an image of reflected light is inputted with the means 105. Then, an image from the means 105 is compared with the predetermined threshold value by means of the first binary coding means 107, and converted to a binary coded image. Also, the threshold value is so selected that the modulated stripe pattern of the through-hole section clearly appears for a thinned image, and binary coded with the second binary coding means 108. A hole separation means 109 extracts the stripe pattern of a through-hole zone from the output of the second binary coding means 108, and the image so obtained is interpolated and magnified to an image of original magnification with an interpolation and magnification means 110. A defect detection means 111 performs theoretical operation with a binary coded image for hole filling and detects a disagreement zone. Namely, this disagreement zone is detected as a defect in the land section of the printed circuit board 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring pattern inspection device for inspecting a wiring pattern on a printed circuit board, a photomask or the like.

[0002]

2. Description of the Related Art Conventionally, visual inspection by humans has been used to inspect defective printed circuit boards and the like. However, as products become smaller and lighter, wiring patterns become finer and more complex. Under such circumstances, it is difficult for a person to keep a very fine wiring pattern for a long time while maintaining high inspection accuracy, and automation of inspection is strongly desired. Especially in the inspection of a board having a through hole, the inspection standard of the line width of the wiring pattern and the inspection standard of the residual width of the land are different, and it is necessary to separately inspect the through hole portion and the wiring pattern, The complexity of inspection is increasing. In the through-hole substrate, the wiring pattern and the through-hole portion can be separated roughly into two methods, that is, the transmitted illumination light and the reflected illumination light emitted from below the substrate have two wavelengths and the wavelengths are separated and detected by two separate sensors. One method is to detect the reflected light and the transmitted light with one sensor and separate the through hole from the image data in which the reflected image and the transmitted image are mixed. In the latter method, the transmitted illumination light is modulated in synchronization with the horizontal period of the CCD camera to form a striped pattern in the through-hole portion, and is separated from the image data in which the reflected light and the transmitted light are mixed. Since the through-hole portion can be easily separated by processing, it will be described below as a conventional example.

FIG. 10 is a block diagram of a conventional wiring pattern inspection apparatus. In the figure, 1000 is a printed circuit board, 1001 is a lighting device, 1002 is a modulated light generation device,
1003 is a CCD camera, 1004 is a binarization circuit, 10
Reference numeral 05 is a hole separation processing unit, 1006 is an edge detection unit, 1
Reference numeral 007 denotes an expansion processing unit, 1008 denotes a contraction processing unit, and 1009.
Is an expansion processing unit, and 1010 is a defect detection unit. The operation of the wiring pattern inspection apparatus configured as above will be described below. The printed circuit board 1000 is illuminated from above and below by an illuminating device 1001 and a modulated light generating device 1002, and reflected light and transmitted light passing through a through hole are simultaneously generated.
It is detected by a CCD camera 1003 using a one-dimensional CCD sensor or the like. At this time, the modulated light generation device 1002 modulates the illumination light so as to blink in a line unit in synchronization with the horizontal period of the CCD sensor. The binarization circuit 1004 is C
The grayscale image from the CD camera is binarized and converted into a binary image in which the wiring pattern is 1, the base material portion is 0, and the stripe pattern of 1 and 0 is formed in the through hole portion. Hall separation processing unit 1
005 separates and extracts a through hole image from the stripe pattern of the sulu hole part from the binary image, and detects the defect detecting part 10
Reference numeral 10 is the through-hole separated image and the binarization circuit 1004.
The defect of the land portion of the through hole is detected from the binary image from. In the hole separation processing unit 1005, first, the edge detection unit 1006 converts the binary image into a contour image,
The expansion processing unit 1007 thickens the contour image by one pixel to fill the stripe pattern in the through hole portion. Shrinkage processing unit 10
In 08, the expanded image is contracted by 3 pixels, and the image other than the through hole portion is erased to obtain a contracted image of the through hole portion.
The expansion processing unit 1009 corrects the through-hole image to the original size by thickening the contracted image of the through-hole by 2 pixels. In the defect detection unit 1010, the through-hole portion of the wiring pattern is filled up, and the separated through-hole image is subjected to an arbitrary amount expansion processing and logically operated with the filled-in binary image, so that the mismatched portion is a defect of the land portion of the through hole. Can be detected as

[0004]

As described above, the transmitted illumination light is reduced to 1
A method has been described in which a stripe pattern is generated in a through hole portion of a binarized image by modulating in line units, and an edge image is contracted or expanded to separate a through hole image. This method can be said to be a promising method in which through holes can be separated from an image detected by one sensor by a simple masking process and a land defect can be reliably detected.

However, according to this method, it is difficult to obtain an accurate through-hole image unless a stable stripe pattern is formed in the through-hole portion, and when the S / N of the grayscale image signal from the CCD sensor is deteriorated, the through-hole image is transmitted. The striped pattern in the hole portion is crushed or missing, which makes it difficult to stably separate the through-hole image. The dark current characteristic and the afterimage characteristic are raised as the factors of the S / N deterioration of the CCD sensor. Generally, in a one-dimensional CCD sensor, photodiodes are arranged in a straight line, CCD shift registers are arranged in parallel with the CCD shift registers, and charges accumulated in the photodiodes in one horizontal cycle are read into the CCD shift register by a shift gate pulse to form pixels. The charge of the CCD shift register is shifted in synchronism with the clock to extract an image signal for one scan. For example, “Goto: Trends in high-density line sensors” (Television Society Journal, Vol.44, No.2, pp.122-126 (199)
(0)) describes the recent technological trends of CCD line sensors, and with the increase in sensor density and speed,
Improvement of sensitivity and S / N is a technical issue. In particular, in order to obtain a high quality image, reduction of dark output and reduction of afterimage have been raised as problems. The dark output is an output when light is not incident on the sensor, and is a characteristic that determines the lower limit of the dynamic range of the sensor. The residual image is a phenomenon in which the charge accumulated in the photodiode in a certain scanning cycle is not completely transferred to the CCD shift register and the remaining charge is output in the next scanning period. Are mixed and output, the gradation in the sub-scanning direction deteriorates. This afterimage characteristic has a great influence on the detection characteristic of the modulated light in the through hole portion. Figure 1
1 shows the characteristic of the modulated light in the through hole portion. FIG. 11A shows a method of detecting modulated light when the image forming magnification (projected image: subject) of the CCD camera is 1: k (k> 1).
The light from the modulated light source 1104 is diffused by the diffusion plate 1103 and illuminates the through hole 1102 of the printed board 1101. Transmitted light that passes through the through-hole in the illumination light 1
106 and reflected light 1107 on the inner wall of the through hole are detected by the CCD camera 1105. FIG. 11B shows the gradation characteristic of the image signal affected by the afterimage characteristic detected at this time. When θ1 is selected as the threshold for binarization by the binarization circuit 1004, the transmitted light of the land 1110 and the through hole becomes 1, but the reflected light of the inner wall 1111 of the through hole becomes 0, and the stripe pattern is not formed. The threshold θ
If 2 is selected, the stripe pattern in the through-hole portion will be painted over, and there will be a problem that an accurate binary image cannot be obtained.

In view of the above-mentioned problems of the prior art, the present invention is a wiring pattern inspection which has a simple structure and forms an accurate and stable modulation fringe pattern in a through hole portion, and enables inspection such as land breakage. The purpose is to provide a device.

[0007]

In order to achieve this object, the present invention provides an image input means for picking up an image of a wiring pattern formed on a printed circuit board, and the printed circuit board modulated by transmitted light at a predetermined cycle. A modulated light generating means for illuminating the input image, a first binarizing means for converting the grayscale image from the image input means into a binary image, a thinning / reducing means for thinning out the input image at a predetermined interval, and a thinning image for 2 Second binarizing means for converting into a value image, hole separating means for separating the wiring pattern and the through hole portion in the thinned image, interpolation enlarging means for enlarging the separated through hole image to the original magnification, and wiring It has a structure of a defect detecting means for filling a through hole portion of a pattern and expanding a separated through hole image by an arbitrary amount to perform a logical operation.

[0008]

According to the present invention, the wiring pattern and the through hole portion are separated by the above structure, the through hole portion of the wiring pattern is filled, and the separated through hole image is subjected to an arbitrary expansion processing to fill the filled binary image and the logical operation. By doing so, the mismatched portion can be detected as a defect in the land portion of the through hole.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a pattern inspection apparatus according to an embodiment of the present invention. In FIG. 1, 10
Reference numeral 1 is a printed circuit board, 105 is an image inputting means provided with a diffused illumination device such as a ring-shaped light guide in 102 and an image pickup device such as a CCD camera in 104, and 103 is a modulated light for illuminating by modulating light passing through a through hole. Generating means,
Reference numeral 105 is a first binarizing means for converting the grayscale image into a binary image, 106 is a thinning reducing means for thinning out the input image every other line to reduce the image, and 107 is converting the thinned reduced image into a binary image. Second binarizing means 108, hole separating means 108 for separating the wiring pattern from the through hole portion, 109 is interpolation enlargement for interpolating the separated through hole image line by line and enlarging it to the same magnification as the input image. means,
Reference numeral 110 superimposes the interpolated through-hole images to fill the through-hole portion, and detects a mismatched portion by a logical operation between the expanded image of the through-hole image and the filled-in binary image to detect a defect in the through-hole. The defect detection means to detect is shown.

The operation of the pattern inspection apparatus configured as described above will be described. First, printed circuit board 1
Image input means 105 which is illuminated by a diffused illumination device 102 such as a ring-shaped light guide from above the wiring pattern formed on 01, and is equipped with an imaging device 104 such as a CCD camera.
Input as a grayscale image with. At this time, at the same time, illumination light modulated at a predetermined cycle is emitted from below the printed circuit board 101 and input to the image input means 105. In this embodiment, an example in which a one-dimensional CCD camera is used as an image pickup device will be described.

The printed circuit board 101 is installed on a moving table (not shown) and drives the CCD camera in synchronization with the moving table. At this time, the modulated light generation means 103 synchronizes with the horizontal synchronization SYNC of the one-dimensional CCD sensor and outputs 2
When the transmitted light is flickered on a line-by-line basis, the grayscale image obtained from the image pickup device 104 becomes an image in which the image signal level is modulated on a line-by-line basis in the sub-scanning direction in the through-hole area. FIG. 2 is a diagram showing the relationship between the horizontal period SYNC of the one-dimensional CCD sensor, the input light and the output signal of the sensor. The figure (a) shows the case where the input light is modulated every one cycle in synchronization with the SYNC, and the figure (b) shows the case where the input light is modulated every two cycles. In the case of FIG. 3A, signals of two adjacent cycles interfere with each other due to the afterimage characteristic of the CCD sensor, so that a modulation signal in a narrow range with respect to the dynamic range (0 to Vsat) of the sensor is detected. In this case, it becomes difficult to form a stable stripe pattern in the through hole portion by the binarization processing described later. On the other hand, in the case of (b), the signals of two cycles which are the same for the same reason also interfere and a transient response signal output is obtained, but the signals S2 and S4 received in the horizontal cycles T2 and T4 are relatively above. The output is well reflected by the contrast of the input light without being affected by the decrease in the dynamic range due to signal interference. In this embodiment, in order to prevent the deterioration of the detection accuracy of the modulated light due to the influence of the afterimage of the CCD in this way, the modulated light generation means 103
Illuminates the printed circuit board 101 with light modulated in units of two lines in synchronization with the horizontal period of the CCD camera, and the thinning / reducing means 106 selects the latter (S) of the detected light in units of two lines.
2, S4) Select an image signal. First binarizing means 106
Then, the grayscale image from the image input means 105 is compared with a predetermined threshold value and converted into a binary image in which the wiring pattern portion is 1 and the base material portion is 0. Further, the second binarizing means 108 selects a threshold value so as to clearly show the modulation fringes of the through-hole portion in the thinned image and binarizes it, and as shown in FIG. An image of a striped pattern in which 1s and 0s alternate in the scanning direction is obtained. The second binarizing means 108
A more stable binarized image can be obtained by providing a spatial filter in the preceding stage to emphasize the modulation fringes and increase the contrast. The hole separating means 109 extracts the stripe pattern of the through hole area from the output of the second binarizing means 108, and the obtained through hole image is interpolated and enlarged by the interpolation enlarging means 110 to the image of the original magnification. The defect detecting means 111 obtains a filled-in binary image in which the through-hole portion of the original binary image is filled with the interpolated through-hole image, and at the same time expands the through-hole image by an arbitrary amount to obtain the filled-in binary image. The logical operation is performed to detect the non-matching area. In other words, this mismatch area is
It will be extracted as a defect of the remaining seat width violation in the land of the through hole.

Next, the modulated light generating means 103, the hole separating means 109, and the defect detecting means 111 will be described in more detail.

FIG. 4 is a block diagram of an optical system centering on the modulated light generating means 109. In the figure, 401 is a printed circuit board, 402 is an optical lens, 403 is a CCD camera, 404 is a ring-shaped light guide, 405 is a light source such as a halogen lamp, 406 is a diffusion plate, 407 is a line light source such as an LED array, and 408 is 408. Line light source driver, 40
9 is a frequency dividing circuit, 410 is a CCD camera driving circuit, 41
Reference numeral 1 denotes a pixel clock of the CCD camera (hereinafter abbreviated as CLK), and 412 denotes a horizontal synchronization clock of the CCD camera (hereinafter abbreviated as SYNC). The operation will be described below. Illumination light from the light source 405 illuminates the printed board 401 by the ring-shaped light guide 404. At the same time, the illumination light from the line light source 407 is transmitted through the through hole of the printed circuit board 401 via the diffuser plate 406 and C
It is incident on a CD camera. The CCD camera has a drive circuit 4
10 supplies CLK411 and SYNC412,
The grayscale image signal is output from the output terminal 413. At this time,
The line light source 407 divides the SYNC 412 by the frequency dividing circuit 209.
Then, the frequency is divided into four and supplied to the line light source driver 408.
As a result, the line light source 407 blinks every two cycles in synchronization with the SYNC 412, and the image signal of the through hole portion is ON / OFF for the input light at T1 to T4 as shown in FIG. 2B. The signal has a strong contrast in S2 and S4.

Next, FIG. 5 shows a block diagram of the hole separating means 107, which will be described below. In the figure, 501
Is a binary image including a stripe pattern, 502 is a filling circuit, 503 is an expansion processing circuit, and 504 is a contraction processing circuit. Binary image 5 including the stripe pattern as shown in FIG.
Input 01 and the filling circuit 502 generates an image in which only the stripe pattern of the through hole portion is filled. The area where the stripes are completely formed is the filling circuit 502.
However, if even a single pixel forming a stripe is missing, there may be a hole in the filled area.
The filled area is inflated by a predetermined amount in 3, and the figure is reduced in a predetermined amount by the subsequent contraction processing circuit 504 to match the area size of the stripe pattern. A filling circuit 502, an expansion processing circuit 503, and a contraction processing circuit 504 will be described below with reference to FIGS. 6 and 7.
The image signal processing of will be described in more detail. Figure 6
(A) shows the configuration of the window scanning process in the filling circuit 502. In the figure, 601 is a binary image signal including a striped pattern, and 603 is 3 × 3 for detecting an alternating pattern.
Scanning windows, 604 to 607 are alternation detection circuits that output 1 when an alternating pattern is detected, and 0 when it is not detected, 60
8 to 609 scan the output image of the alternation detection circuit 3
A × 3 scanning window, 612 to 615 are contraction circuits for contracting the output image of the alternating detection circuit by one pixel, and 616 is an AND circuit. The binary image 601 is scanned by the 3 × 3 scanning window 603,
Alternation detection circuits 604 to 607 detect the change point (1 to 0 or 0 to 1) of the image signal. Although the window scanning circuit using the line memory is a known technique and a detailed description thereof will be omitted, the series of processing shown in FIG. 6A is performed by shifting pixel by pixel in synchronization with a pixel clock CLK (not shown). And The processing in the alternating detection circuits 604 to 607 is performed by the pixel d0 of the 3 × 3 scanning window shown in FIG.
~ D8, and (1) to (Equation 1) to
It can be calculated by the logical expression (4).

[0016]

[Equation 1]

The outputs of the alternation detection circuits 604 to 607 are individually subjected to the contraction processing of one pixel by the contraction circuits 612 to 615. The processing in the contraction circuits 612 to 615 can be calculated by the logical expression of (Equation 2).

[0018]

[Equation 2]

The output images of the contraction circuits 612 to 615 are input to the logical product circuit 616, and their common areas are detected.
Image 60 with only the stripe pattern of the through hole filled
2 can be obtained.

FIG. 7 shows n × n scanning windows used in the expansion processing circuit 503 and the contraction processing circuit 504. Expansion processing circuit 50
3 is a process of expanding the input image by N pixels in all directions. For example, even if there is a hole of size N pixels in the painted area, the hole can be expanded by expanding N pixels. Specifically, in FIG. 7, it is realized by performing the logical sum operation of all the pixels with the number N or less. The contraction processing circuit 504, on the contrary, is a process of contracting the input image by M pixels in all directions, and is realized by performing a logical product operation of all pixels having a number M or less in FIG.

Next, the specific processing of the defect detecting means 111 will be described with reference to FIG. In the figure, reference numeral 801 is an image obtained by separating and extracting sulu holes, 802 is an image in which wiring patterns and stripe patterns are mixed, 806 is an expansion processing circuit 1, 803 is an image in which through holes are filled, 807 is expansion processing circuits 2 and 804. Is an expanded through-hole image, 8
Reference numeral 05 is a land rest width violation signal. The expansion processing circuit 806 expands the through-hole image from the interpolation enlarging means 110 by a predetermined size, and the pattern / hole mixed image 80.
It is adapted to the through hole size of 2, and the hole filling image 802 is obtained by the following logic circuit 809. Next, the expansion processing circuit 807 expands the land width of the through hole portion by the number of allowable range pixels. For example, resolution 10 μm
5 to detect land width less than 50 microns
It suffices to expand the pixels. The logic circuit 809 performs a logical operation on the expanded image 804 of the through hole and the filled-in image 803 to detect a non-coincidence portion, and the rest width violation signal 805.
Is output. FIG. 9 shows a processing example of the defect detecting means 111. The shaded portion is the defective portion of the land detected as the non-matching area 903.

As described above, according to the present embodiment, the downward illumination is modulated in a unit of a plurality of lines and a line having a large contrast is selected to form a stable stripe pattern in the through hole portion, and a stripe pattern is formed from the binary image. By separating the through hole area that has become a pattern, performing interpolation expansion processing, expanding processing by the allowable number of pixels of the land width, and performing exclusive OR with the hole filling signal of the through hole portion, the mismatch area is detected. Land defects can be easily detected.

[0023]

As described above, according to the present invention, one image pickup device detects a reflected light image and a transmitted light image of a printed circuit board and modulates the transmitted light in a unit of a plurality of lines to select a scanning line. Even if there is an afterimage in the device, a stable striped pattern can be formed in the through hole part, the alternating pattern of the striped through hole part is detected and separated, and the through hole image is filled and the separated through hole image is landed. An excellent wiring pattern inspection device that can easily set defects in through-hole lands by expanding the number of pixels in the allowable width range and performing exclusive OR with the fill-in signal in the through-holes Can be realized.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a wiring pattern inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing input light and an afterimage characteristic of an imaging device which is a main part of the wiring pattern inspection device in the example.

FIG. 3 is a conceptual diagram of a binary image showing a stripe pattern of through holes of the wiring pattern inspection apparatus in the same example.

FIG. 4 is a block connection diagram of a modulated light generating means which is a main part of the wiring pattern inspection apparatus in the embodiment.

FIG. 5 is a block connection diagram showing a configuration of hole separating means, which is a main part of the wiring pattern inspection apparatus in the embodiment.

FIG. 6A is a detailed block connection diagram of window scanning processing of a filling circuit of the wiring pattern inspection apparatus according to the same embodiment. FIG. 6B is a 3 × 3 wiring pattern inspection apparatus according to the same embodiment.
Conceptual diagram showing the scanning window

FIG. 7 shows n × of the wiring pattern inspection device in the same embodiment.
Conceptual diagram showing n-scan window

FIG. 8 is a block connection diagram of a defect detection unit which is a main part of the wiring pattern inspection apparatus in the embodiment.

FIG. 9 is a conceptual diagram of an image showing processing of the defect detecting means.

FIG. 10 is a block connection diagram of a conventional wiring pattern inspection device.

FIG. 11 is a gradation characteristic diagram of an image signal in a through hole portion of the same wiring pattern inspection device.

[Explanation of symbols]

 101 Printed Circuit Board 102 Illuminating Device 103 Modulated Light Generating Means 104 Imaging Device 105 Image Input Means 106 Decimation and Reduction Means 107 First Binarization Means 108 Second Binarization Means 109 Hole Separation Means 110 Interpolation Enlargement Means 111 Defect Detection Means 401 Printed circuit board 402 Optical lens 403 CCD camera 404 Ring-shaped light guide 405 Light source 406 Diffuser plate 407 Line light source 408 Line light source driver 409 Dividing circuit 410 CCD driving circuit 411 Pixel clock 412 Horizontal synchronization clock 413 Output terminal 501 Binary image 502 Filling Circuit 503 Expansion processing circuit 504 Contraction processing circuit 601 Binary image signal 602 Filled image 603 3 × 3 scanning window 604 Alternate detection circuit 1 605 Alternate detection circuit 2 606 Alternate detection circuit 3 607 Alternate Detection circuit 4 608 3 × 3 scanning window 609 3 × 3 scanning window 610 3 × 3 scanning window 611 3 × 3 scanning window 612 contraction circuit 613 contraction circuit 614 contraction circuit 615 contraction circuit 620 3 × 3 scanning window 801 hole separation image 802 Mixed pattern / hole image 803 Filled binary image 804 Expanded through-hole image 805 Seat residual width violation signal 806 Expansion processing circuit 1 807 Expansion processing circuit 2 808 Logical sum circuit 901 Filled binary image 902 Expanded through-hole image 903 Mismatch area 1000 Printed circuit board 1001 Illumination device 1002 Modulated light generation device 1003 CCD camera 1004 Binarization circuit 1005 Hole separation processing part 1006 Edge detection part 1007 Expansion processing part 1008 Shrinkage processing part 1009 Expansion processing part 1010 Defect detection part 1101 Print Substrate 1102 reflected light 1110 lands 1111 through hole inner wall of the through hole 1103 diffuser 1104 modulated light source 1105 CCD camera 1106 transmitted light 1107 through hole's inner wall

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidehiko Kawakami 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Prefecture Matsushita Giken Co., Ltd.

Claims (1)

[Claims] 1. An image input means for picking up an image of a wiring pattern formed on a printed circuit board, a modulated light generating means for illuminating the printed circuit board by modulating the transmitted light at a predetermined cycle, and an image input means from the image input means. First binarization means for converting the grayscale image into a binary image, thinning reduction means for thinning out the grayscale image at a predetermined interval to reduce, and second thinning means for converting the reduced grayscale image into a binary image. Binarizing means, hole separating means for separating the wiring pattern and the through hole, interpolation enlarging means for enlarging the separated through-hole image to the original magnification, and through for separating the through-hole portion of the wiring pattern and separating it. A wiring pattern inspection device equipped with defect detection means for expanding a hole image by an arbitrary amount and performing a logical operation.