JPH06305110A - Apparatus and method for testing blinding of printing screen - Google Patents

Abstract

PURPOSE:To prevent in advance defects such as disconnection after a circuit being printed by installing a means which detects optically the blinding of a screen for printing a circuit pattern from a mesh surface side by illuminating the screen from over and under and input an image by photoelectric conversion. CONSTITUTION:Light 303 directly reflected at the metal part 302 of a printing screen, which is not the opening of the pattern of the printing screen, is picked up by a camera 104 by upper illumination 102. Transmitted light passed through the opening of the pattern of the printing screen is picked up by the camera 104 by illumination 103 which is grounded under the printing screen. Light reflected on the metal grid part 301 of the printing screen which forms meshes does not return to the camera 104, for a mesh surface has different angles. As a result, an image in which a mesh part is dark and the other parts are light, is obtained by the camera 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal wire (mesh) knitted in a lattice for forming a circuit on a ceramic substrate.
The present invention relates to a device for inspecting a screen for printing a circuit pattern which is lined with, and more particularly to automatic detection of clogging of a printing material or the like in a metal wire portion knitted in a grid pattern.

[0002]

2. Description of the Related Art Conventionally, the clogging of a printing screen has not been inspected, and the clogging of the printing screen can be confirmed by visually observing a circuit pattern on a ceramic substrate formed by trial printing or by wiring on the substrate. It has been detected as a pattern abnormality in a print pattern inspection in a subsequent process due to disconnection of the wiring, a conduction failure in an electric conduction test, or the like.

[0003]

After printing, the printing screen is washed and stored in the stocker for the next printing. If the cleaning is not performed properly, the printing material remains on the mesh and hardens, causing clogging. If the clogging has reached the entire section of the mesh, the pattern of the clogging part will not be printed properly on the substrate when printing is performed in that state next time, and there will be a defect such as a broken circuit or a missing conductive pad. Therefore, a large number of defective substrates are sent to the subsequent process. To prevent this, it is necessary to inspect the clogging state of the printing screen in advance before starting printing.

[0004]

The technical solution of the present invention for solving the above-mentioned problems is an image inputting means for optically detecting and photoelectrically converting a printing screen, and a bright field for the image inputting means. Illuminating means for configuring illumination and illumination means for configuring transmitted light illumination for the print screen illuminate the print screen to be inspected, and the grayscale image obtained by the image input means is a binary image. It is composed of a binarizing means for converting the image into a binary image, an expanding means for expanding the binary image from the binarizing means to a predetermined size, and a defect detecting means for detecting a clogging portion of the printing screen from the image from the expanding means. It is a thing.

[0005]

The direct reflected light from the portion other than the circuit pattern and the mesh becomes a bright portion on the printing screen by the incident illumination and is input to the image input means. Further, the circuit pattern portion becomes a bright portion by the transmitted light illumination placed below and is input to the image inputting means, and the dark portion in the image obtained by the two illuminations is only the grid mesh. Therefore, if this image is binarized and the bright portion of the binarized image that is equal to or greater than the preset threshold value is expanded by a predetermined number of pixels, the grid-like mesh portion that is the dark portion can be erased. . On the other hand, if one of the meshes is clogged and crushed, the area of the dark part at that location becomes large, and even if the bright part is expanded by a predetermined number of pixels to erase the grid-like mesh, it will be clogged. The portion causing the defect remains without being erased, and the defective portion can be detected.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a printing screen clogging inspection apparatus according to an embodiment of the present invention.
In FIG. 1, reference numeral 101 is a printing screen lined with a metal wire woven in a lattice pattern to be inspected. After that,
The metal wire knitted in a lattice will be simply called a mesh. The mesh is stretched at 45 degrees with respect to the XY directions of the printed circuit pattern. A light source 102 illuminates the printing screen from above, and a light source 103 illuminates the printing screen from below. 104 is CC
It is means for optically detecting an object such as a D camera and inputting an image by photoelectric conversion. Reference numeral 105 is a binarizing means for binarizing the grayscale image input by 104, 106 is an expanding means for expanding the binary image by a predetermined size, and 107 is 1
Defect detection means for determining the presence or absence of a defect based on the image processed in 06. 108 is the above 105, 106, 1
This is a processing device that executes the functions of 07.

The operation of the above arrangement will be described below. In FIG. 2, the printing screen 101 is installed on a movable table (not shown) which can be controlled from the outside with the mesh surface facing upward. The illumination 102 installed above the printing screen is 2
The half mirror shown by 01 is configured by a cube beam splitter or the like to form a coaxial incident illumination system (bright field illumination system).

Next, FIG. 3 shows how light is transmitted and reflected on the printing screen by both upper and lower illumination. FIG. 3 is a sectional view of the printing screen, the upper surface of which is a meshed surface. Reference numeral 301 denotes a mesh, 302 denotes a metal including an opening portion of a print pattern, a shaded portion in the drawing is a metal portion, and an opening corresponding to a portion having a broken middle shade corresponds to a pattern to be printed. It is a part. The illumination 102 causes the imaging device 104 to capture an image of the directly reflected light at a portion of the printing screen that is not the opening portion of the pattern. Lighting 10 installed below the printing screen
3 is a transmitted light illumination, which passes through an opening of the pattern of the printing screen, and the transmitted light is imaged by the image pickup device 104. Reference numeral 303 represents a light beam emitted from the light source 102, which is reflected by the metal part. Reference numeral 304 denotes a light source emitted from the light source 103, and shows how the light directly reaches the image pickup device 104 through the pattern opening. The light reflected on the mesh does not return to the imaging device 104 because the mesh surface has various angles as shown in FIG. As a result, the mesh portion is dark and the other portions are bright, and an image is obtained by the imaging device 104. 4 to 6 are schematic diagrams of images obtained by each illumination.
Shown in.

FIG. 4 illustrates an image pickup device 1 illuminated by the illumination 102.
The schematic diagram of the image obtained in 04 is shown. The reflected light from the illumination 102 does not return from the mesh portion and the opening of the pattern to be printed, and only the metal portion is brightly imaged. FIG. 5 shows a schematic diagram of an image illuminated by the illumination 103 and obtained by the imaging device 104. Since the illumination light from the illumination 103 passes through the opening of the pattern to be printed and is imaged by the imaging device 104, the printed pattern portion becomes bright. The image obtained using both illuminations is shown in FIG. As shown in FIG. 6, it is possible to obtain an image in which the dark portion, which is the mesh portion, is dominant, regardless of the arrangement of the patterns opened in the metal portion. In FIG. 3, the metal opening is illustrated as being cut vertically, but in reality, the edge of the pattern opening is slightly inclined due to etching or the like, so that the reflected light from the illumination 102 is reflected by the imaging device 104. not returning. Therefore, as shown in FIG. 6, the edges of the print pattern remain as fine lines. However, since the shadows of these pattern edges are usually thinner than the mesh pattern, they are erased at the same time by the mesh image removal process described below.

The image shown in FIG. 6 is binarized by the binarizing means 105 using an appropriate threshold value set in advance.
As a result of the binarization, the wire portion of the mesh which is a dark portion is set to 0, and the other bright portion is set to 1. The binarized portion or the binarized area is hereinafter referred to as a bright portion in FIG. Since the thickness of the mesh is constant,
The mesh can be deleted by expanding the binarized area by a predetermined number of pixels. As a method of expanding the binarized region,
Expansion processing according to the shape of the binarized figure is desirable. As shown in FIG. 7, the mesh diameter is a / √2 at the intersection of the meshes, where a is the diagonal distance of the intersection. Here, when a certain pixel is 1 at the binarization level, as shown in FIG. Give. The * in FIG. 8 indicates that the value may be 0 or 1. Each time this process is executed once, the binarized area, which is a square mesh hole, is enlarged by one pixel width on each side, as shown in FIG. In FIG. 9, 0
The pixels of are represented by black and the pixels of 1 are represented by white. In the actual screen, the black portion corresponds to the mesh and the white portion corresponds to the other portion. Strictly speaking, one pixel is enlarged in the vertical and horizontal directions, and 1 / √2 pixels are enlarged in the 45 ° direction. Therefore, when the resolution of one pixel is d,
From the difference between the vertical and horizontal expansion widths and the expansion width in the diagonal 45 degree direction, and the width relationship of the intersecting portions of the mesh described in FIG. 8, geometrically, a mesh is obtained by performing a / (2d) times The area can be erased. Actually, the mesh can be deleted by performing expansion processing once more than this due to the quantization error of the image.

The defect detecting section 107 detects whether or not there is a 0 region in the binary image generated by the expansion process. Printing paste etc. that cause clogging is
The reflectance of incident light is lower than that of metal, and the light is diffused and reflected, so that when it is attached to the mesh, it remains as a region of 0 when binarized, that is, a dark portion. Therefore, when one of the meshes is clogged, that part remains without being erased even after the expansion process is performed a predetermined number of times. Therefore, by detecting the part of the value 0 left after the expansion process, It becomes possible to detect. However, since it is considered that such a process is vulnerable to noise and more false alarms occur, it is desirable to add a labeling function to the defect detection unit 107. In this case, the labeling process is to identify a concatenated block of 0 regions and perform numbering (labeling) for each region. Therefore, if the area of the value 0 remaining after the expansion process is divided into areas, the area of each area is calculated, and only the area having a certain area or more is detected and the area is clogged, erroneous detection can be reduced.

By applying the above processing to the entire area of the printing screen, it becomes possible to perform the clogging inspection of the entire printing screen. In order to detect another area of the printing screen, the printing screen may be installed on a table whose movement can be controlled from the outside, and the defect detection may be performed while moving the table. FIG. 10 shows the above processing flow.
First, the printing screen is set on the above-mentioned table, and the table is moved to the first place according to a predetermined inspection order. After the movement, wait for the table to stand still, and turn on the illuminations above and below the printing screen to input an image. As described above, the input image is binarized, and the binarized image obtained as a result is subjected to a predetermined number of pixel expansion processing, and labeling is performed on the dark area (“0” portion) remaining in the image. The area of each labeled area is examined by processing, and it is checked whether or not there is an area having a preset area threshold value TH or more. When there is a region equal to or larger than the area threshold value TH, defect position information and the like are output to a CRT, a printer, or a device capable of displaying and recording the information connected to the outside. After the above processing is completed, if there is a next inspection area according to a predetermined inspection order, the table is moved to that location and the same processing is repeated again. When there are no more inspection areas, the inspection is ended. The table may be moved immediately after the image is input, and the process after binarization of the image may be performed at the same time while the table is being moved.

The processing device for carrying out the binarization, expansion processing, and defect detection described in this embodiment is a device incorporating the function shown by 108 in FIG. 1, and binarizes the image signal. , Sampled at fixed time intervals, stored in memory,
Any known processing device having a function of freely processing the memory contents by a program may be used. Further, the above-described binarization, expansion processing, and labeling processing if necessary, may be performed by any known hardware processing form instead of being processed by a program.

[0014]

As described above, according to the present invention, it is possible to detect clogging of the grid of the printing screen, so that it is possible to prevent occurrence of defects such as disconnection after the circuit is printed, and to prevent the printed circuit board from being damaged. It has the effect of improving reliability.

[Brief description of drawings]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a coaxial incident illumination system.

FIG. 3 is a diagram showing a cross section of a print screen to be inspected and a reflection state of illumination light at a corresponding portion.

FIG. 4 is a schematic diagram of an image obtained by coaxial epi-illumination of a print screen as an inspection target.

FIG. 5 is a schematic diagram of an image obtained by transmitted illumination of a printing screen which is an inspection target.

FIG. 6 is a schematic diagram of an image obtained when coaxial epi-illumination and transmitted illumination of a print screen to be inspected are used simultaneously.

FIG. 7 is a diagram showing dimensions at intersections of meshes.

FIG. 8 is an explanatory diagram of an operator for expanding a binarized image.

FIG. 9 is a diagram showing an example of expansion of a binarized image.

FIG. 10 is a flowchart of the entire operation.

[Explanation of symbols]

101 ... Printing screen, 102 ... Bright field illumination light source, 103 ... Transmitted light illumination light source, 104 ... Image input device, 105 ... Image binarization processing unit, 106 ... Binary image expansion processing unit, 107 ... Defect detection unit, 10
8 ... Image processing device, 201 ... Half mirror, 301 ... Printing screen metal grid part, 302 ... Printing screen metal part, 303 ... Reflected light on the metal 302 by the illumination 102, 304 ...
Illumination light from the illumination 103.

Claims (8)

[Claims] 1. A clogging of a screen for printing a circuit pattern, which is lined with a metal wire (mesh) knitted in a grid pattern for forming a circuit on a substrate, is printed by illuminating from above and below the printing screen. An apparatus for inspecting clogging of a printing screen, comprising means for optically detecting the printing screen from the mesh surface side of the screen and inputting an image by photoelectric conversion. 2. An apparatus for inspecting clogging of a printing screen according to claim 1, wherein the illumination from above is a coaxial epi-illumination in the same direction as the imaging direction of the printing screen. 3. The device for inspecting clogging of a printing screen according to claim 1, wherein the means for inputting an image is a two-dimensional solid-state camera. 4. The image obtained according to claim 1,
Characterized by performing a binarization process and performing a dilation process of the binarized image on the binarized image to erase the mesh image of the screen from the image and detect the remaining portion as clogging. An inspection device for printing screen clogging. 5. A clogging of a screen for printing a circuit pattern, which is lined with a metal wire (mesh) knitted in a grid pattern for forming a circuit on a substrate, is printed by illuminating from above and below the printing screen. A method for inspecting clogging of a printing screen, comprising means for optically detecting the printing screen from the mesh surface side of the screen and inputting an image by photoelectric conversion. 6. The method for inspecting clogging of a printing screen according to claim 5, wherein the illumination from above is coaxial epi-illumination in the same direction as the imaging direction of the printing screen. 7. The method for inspecting clogging of a printing screen according to claim 5, wherein the means for inputting an image is a two-dimensional solid-state camera. 8. The image obtained according to claim 5, wherein
Characterized by performing a binarization process and performing a dilation process of the binarized image on the binarized image to erase the mesh image of the screen from the image and detect the remaining portion as clogging. A method for inspecting the clogging of printing screens.