JP2001013079A - Method and apparatus for inspecting flaw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect a flaw highly accurately on the basis of the difference image obtained from two inspection images which are obtained by photographing works the same in pattern even if there are variations equal to or more than the brightness difference of a flaw part in the difference between the brightnesses corresponding to the surface parts of both inspection images. SOLUTION: For example, a part of a work having a predetermined pattern is photographed by using vertical illumination to input a first inspection image and the different part of the work having the same pattern is photographed under the same condition to input a second inspection image and clipping processing allowing brightness higher than a preset clipping level to coincide with the level is applied to the first and second inspection images and the difference image of the first and second inspection images after clipping processing is formed to inspect a flaw on the basis of the difference image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection method and apparatus which are particularly suitable for application to the visual inspection of a work manufactured by processing a thin metal plate such as a lead frame into substantially the same pattern. .

[0002]

2. Description of the Related Art A work, such as a lead frame, manufactured by processing a thin metal plate into a substantially identical pattern is coated with a resist film having a predetermined repetitive pattern on both sides of the thin metal plate by printing or the like. It is manufactured by depositing and etching away the exposed metal portion using the resist film as a mask.

Therefore, such a work as a lead frame or the like is arranged such that a substantially identical pattern portion is arranged in a plurality of rows and a plurality of columns as shown in FIG. Are formed repeatedly.

As a method of inspecting the appearance of such a lead frame in which substantially the same pattern is repeatedly formed, before cutting the same portion into units,
As also shown in FIG. 7, the line sensor camera 1
0, the inspection image is captured for the pattern portion of the first row while moving the work W in the direction of the arrow,
In some cases, an inspection image is similarly captured for a pattern portion in a column, a difference is obtained between adjacent images of substantially the same pattern, and a defect inspection is performed based on the difference image.

For example, if the surface of a work (lead frame) W is imaged using epi-illumination, an inspection image obtained with almost gray luminance to be imaged is shown in FIG.
As shown schematically in (A) and (B), a part of the lead frame of the same pattern is schematically shown in an enlarged manner, the normal part of the metal surface has high luminance (white area) and the defective part (hole part) D The brightness becomes low (shaded area). Using such image data,
Along with the above-described defect portion D on the surface, although not shown, a defect such as a short circuit in which a part of the lead is connected or a disconnection in which the lead is interrupted in the middle can be inspected at the same time. In this manner, a difference is taken between adjacent images of the same pattern, a difference image as shown in FIG. 8C is created, and inspection is performed based on the image. Here, since the absolute value is taken, a portion where the luminance value after the difference processing is large, that is, a high luminance portion (white) is the defective portion D. The difference image shown in FIG. 8C is binarized after post-processing such as noise removal in the same manner as usual, and the obtained binary image is labeled with a region that is considered to be a defective portion. An inspection for finally determining a defect is performed in consideration of the size and the like.

[0006]

However, in the above-mentioned work, since fine irregularities are present on the metal surface, these appear as shading (difference in luminance value) of the image in the inspection image. Occurs.

FIG. 9A shows an image of a cross section of a metal surface where a concave defect D is present, and FIG. 9B shows a luminance obtained by imaging this surface with a line sensor camera. Profile) image,
Even in the same sample, fine irregularities are present on the surface, and the variation (difference) G in the luminance value caused by the irregularities indicates that the defective portion D
And the average luminance level indicated by the broken line may be equal to or larger than Gd.

Therefore, as described above, in the method of inspecting by taking a difference between two images in which the same pattern adjacent to each other or the same pattern between different works is picked up in the same work, for example, the unevenness of the surface is reduced. Because of the randomness, the luminance difference in the normal part obtained by the difference may be larger than the luminance difference in the defective part, which causes erroneous detection.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and when detecting a defect based on a difference image obtained from two inspection images obtained by imaging a workpiece or a workpiece portion having the same pattern, the present invention has been made in consideration of the above circumstances. It is an object of the present invention to provide a defect inspection method and apparatus capable of inspecting a defect with high accuracy even when a difference in luminance corresponding to a surface portion of an inspection image has a variation equal to or greater than a luminance difference of a defect portion.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a first inspection image is input by capturing an image of a workpiece having a predetermined pattern or a portion thereof using epi-illumination, and under the same conditions, different images having the same pattern are input. A second inspection image is input by imaging a workpiece or a different part of the same workpiece, and the first inspection image and the second inspection image are input.
The inspection image is subjected to a clipping process for matching a luminance lower than a preset clipping level to the predetermined level, and a difference image between the first inspection image and the second inspection image after the clipping process is created. The above problem has been solved by inspecting for defects based on the following.

According to the present invention, a work having a predetermined pattern or a part thereof is imaged by using oblique illumination, and a first inspection image is inputted. Under the same conditions, a different work or the same work having the same pattern is obtained. Imaging different parts of
An inspection image is input, and a clipping process is performed on the first inspection image and the second inspection image so that luminance lower than a preset clipping level matches the level.
The above problem is also solved by creating a difference image between the first inspection image and the second inspection image after the clipping process and inspecting the defect based on the difference image.

The present invention is also directed to an illuminating means for epi-illuminating a workpiece having a predetermined pattern, an imaging means for imaging the workpiece illuminated by the illuminating means, and an imaging means for imaging the workpiece or a part thereof by the imaging means. A first image memory that stores a first inspection image that is input by inputting a second inspection image that is input by imaging a different workpiece having the same pattern or a different portion of the same workpiece under the same conditions. A two-image memory, and a clipping processing unit that performs processing for matching a luminance higher than a preset clipping level with the first inspection image and the second inspection image read from each of the image memories to the level. A difference processing unit that creates a difference image between the first inspection image and the second inspection image after the clipping process; and a determination unit that determines a defect based on the difference image. By and is obtained by solving the above problems as well.

The present invention also provides illumination means for obliquely illuminating a work having a predetermined pattern, imaging means for imaging the work obliquely illuminated by the illumination means, and imaging the work or a part thereof by the imaging means. A first image memory that stores a first inspection image that is input by inputting a second inspection image that is input by imaging a different workpiece having the same pattern or a different portion of the same workpiece under the same conditions. A two-image memory, and a clipping processing unit that performs processing for matching a luminance lower than a preset clipping level with the first inspection image and the second inspection image read from each of the image memories to the level. A difference processing unit that creates a difference image between the first inspection image and the second inspection image after the clipping process; and a determination unit that determines a defect based on the difference image. By and is obtained by solving the above problems as well.

That is, in the present invention, when the luminance value of each of the first and second inspection images for creating a difference image exceeds the clipping level that causes erroneous detection (epi-illumination), or falls below it. In this case (oblique illumination), in each case, the processing for matching the luminance value to the same level is performed, so that the defect can be accurately inspected based on the difference image created from both the processed images. It becomes possible.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic front view showing a main part of an entire defect inspection apparatus according to a first embodiment of the present invention, and FIG. 2 is a block diagram schematically showing a control system thereof.

A defect inspection apparatus according to the present invention includes a line sensor camera (image pickup means) 10 for picking up an image of a work W illuminated by an illumination device 12 in an inspection section, and an inspection image picked up by the line sensor camera 10 and inputted. A processing unit 14 for performing a process for an inspection described later using the image.

The inspection section is composed of a belt conveyor 16 and lifts a work W to be inspected loaded on the upstream side thereof by a loader 18 having a suction pad.
By moving it in the direction of the arrow and placing it on the conveyor 16, it is conveyed to the illustrated inspection position. The work W is imaged by the line sensor camera 10 while being conveyed by the belt conveyor 16, and when the inspection is completed, the work W is conveyed downstream by the conveyer 16. Next, it is lifted by the unloader 20, is sorted into a non-defective product (OK product) and a defective product (NG product) based on the inspection result, and is loaded.

The illumination device 12 installed in the inspection apparatus is a so-called co-axial illumination, and as shown in FIG.
Illumination light guided from the optical fiber 12A connected to the light source 21 is reflected in the optical axis direction of the camera 10 by the half mirror 12B, and a work (metal) W at a position where an image is taken by the camera 10 Is applied to the surface.

As shown in FIG. 2, the inspection apparatus according to the present embodiment has an input unit 22 including the line sensor camera 10 and the illumination device 12, the processing unit 14, and a display unit 24 for monitoring and displaying inspection results and the like. And a transport unit 26 including the belt conveyor 16 are controlled by a control unit 28 such as a computer.

The processing section 14 will be described in detail. A first inspection image inputted by imaging a part of the work W having a predetermined pattern (for example, the first row in FIG. 7) by the line sensor camera 10 is inputted. Image memory A to store
Under the same conditions, an image memory B that stores a second inspection image input by imaging a different work portion having the same pattern (for example, the second column in FIG. 7), and both memories A,
A clipping processing unit 30 that performs processing for matching the luminance exceeding a preset clipping level to the same level for each of the first inspection image and the second inspection image read from B, and both inspection images after the processing. about,
A position correction unit 32 that compares known coordinate values of the feature pattern unit and performs position correction on both images based on the amount of deviation;
A difference processing unit 34 that creates a difference image (data) by calculating a difference between the brightness values of the corresponding pixels between the two inspection images after the position correction, and a brightness (difference value) of the difference image, for example, an absolute value And use it to determine 2
A binarization processing unit 36 for binarizing, a labeling unit 38 for labeling an area considered to be defective with respect to the obtained binary image (data), a size of the labeled image area, etc. And a judging unit 40 for judging whether or not there is a defect.

The clipping processing unit 30 which is a feature of the present embodiment will be described in detail. In this embodiment, as shown in FIG. If there is a defect such as a concave portion, an image at a position corresponding to the defect always becomes a dark portion.

Therefore, as shown in FIG. 4 (A) in which the profile image of the luminance on the image caused by the unevenness of the metal surface is enlarged, the upper limit value of the luminance which cannot be considered in the target defect portion is indicated by a broken line. The clipping level is set as shown, and as shown in FIG. 3B, the processing of replacing (matching) all the luminances of the image area exceeding the level with this level value is performed. The clipping level is experimentally determined to be an appropriate value in advance.

The clipping processing section 30 performs such clipping processing on the entire first and second inspection images. In one image before processing, FIG.
As shown in (A), even if there is a large difference in luminance indicated by G even if it is not a defective portion, by performing this processing, it can be reduced to g as shown in FIG.
This relationship has substantially the same effect even when the difference is obtained between the two inspection images, so that it is possible to reduce the variation in the difference value of the region other than the defect in the difference image, and as a result, the accuracy of the defect inspection is improved. Can be raised.

FIG. 5 is an enlarged view, corresponding to FIG. 3, showing the line sensor camera 10 and the illuminating device 12 constituting the input unit provided in the inspection apparatus according to the second embodiment of the present invention. It is a front view.

The inspection apparatus of the present embodiment is substantially the same as that of the first embodiment except that the illumination device 12 illuminates the metal surface imaged by the line sensor camera 10 by so-called oblique illumination. Are identical.

When oblique illumination is used as in the present embodiment, the reflected light from a normal metal surface does not go in the optical axis direction of the camera 10 to form a dark field, whereas the reflected light is irregularly reflected at a defective portion. Therefore, the defective portion is always imaged as a bright portion.
Therefore, in the present embodiment, as shown in FIG. 6 corresponding to FIG. 4, the lower limit value of the luminance that cannot be considered in the target defect portion is set as a clipping level indicated by a broken line in FIG. The clipping processing unit 30 performs a process of experimentally setting in advance the pixel values having a luminance value smaller than the level and replacing them with the clipping level.

By performing such clipping processing on the first and second inspection images, respectively, the defect inspection can be performed with high accuracy also in the present embodiment.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, in the above-described embodiment, the first and second inspection images are picked up by a lead frame (work) before separation in which a plurality of rows of the same pattern as shown in FIG. 7 are formed. However, it is needless to say that the present invention is not limited to this, and the present invention is not limited thereto.

[0031]

As described above, according to the present invention,
When detecting a defect based on a difference image obtained from two inspection images obtained by imaging a workpiece having the same pattern, even if the difference in luminance corresponding to the surface portion of both inspection images has a variation equal to or greater than the luminance difference between the defect portions. In addition, defects can be inspected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a main part of an overall configuration of a defect inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a control system of the inspection apparatus.

FIG. 3 is an enlarged schematic front view showing an input unit applied to the first embodiment;

FIG. 4 is a diagram illustrating a clipping process performed in the first embodiment;

FIG. 5 is an enlarged schematic front view showing an input unit applied to the second embodiment;

FIG. 6 is a diagram illustrating a clipping process performed in a second embodiment.

FIG. 7 is a perspective view showing how a line sensor camera captures an image of the same pattern portion of a workpiece.

FIG. 8 is an explanatory diagram showing the principle of defect inspection using a difference image.

FIG. 9 is an explanatory diagram showing the reason why erroneous detection of a defect occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Line sensor camera 12 ... Illumination device 14 ... Processing part 16 ... Belt conveyor 18 ... Loader 20 ... Unloader

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masahiko Soeda 1-1-1, Ichigaya-Kagacho, Shinjuku-ku, Tokyo Inside Dai Nippon Printing Co., Ltd. (72) Inventor Takayuki Totsuka 1-1-1, Ichigaga-cho, Shinjuku-ku, Tokyo No. 1 Dai Nippon Printing Co., Ltd. F term (reference) 2G051 AA61 AA65 AA90 AB02 BB17 CA03 DA01 EA08 EA11 EA23 EB01 5B057 AA01 BA02 CA02 CA08 CA12 CA16 CE20 DA03 DB02 DB05 DB08 DC32

Claims (4)

[Claims] An image of a workpiece having a predetermined pattern or a part thereof is captured using an epi-illumination, and a first inspection image is input. Under the same conditions, different workpieces having the same pattern or different parts of the same workpiece are detected. A second inspection image is captured and input, and a clipping process is performed on the first inspection image and the second inspection image so that a luminance higher than a preset clipping level matches the level. A defect inspection method comprising: creating a difference image between an inspection image and a second inspection image; and inspecting a defect based on the difference image. 2. A work having a predetermined pattern or a part thereof is imaged by using oblique illumination, and a first inspection image is input. Under the same condition, a different work having the same pattern or a different part of the same work is detected. The second inspection image is captured and input, and the first inspection image and the second inspection image are subjected to a clipping process for matching a luminance lower than a preset clipping level to the predetermined level. A defect inspection method comprising: creating a difference image between an inspection image and a second inspection image; and inspecting a defect based on the difference image. 3. An illuminating means for epi-illuminating a workpiece having a predetermined pattern, an imaging means for imaging the workpiece illuminated by the illuminating means, and an image of the workpiece or a part thereof being input by the imaging means. A first image memory for storing a first inspection image, and a second image memory for storing a second inspection image inputted by imaging different workpieces having the same pattern or different parts of the same workpiece under the same conditions. A clipping processing unit that performs processing for matching the luminance higher than a preset clipping level with the first inspection image and the second inspection image read from each of the image memories to the level, and after the clipping processing. A difference processing unit that creates a difference image between the first inspection image and the second inspection image; and a determination unit that determines a defect based on the difference image. Defect inspection apparatus according to claim. 4. An illuminating means for obliquely illuminating a work having a predetermined pattern, an imaging means for imaging the work obliquely illuminated by the illuminating means, and an image of the work or a part thereof is input by the imaging means. A first image memory for storing a first inspection image, and a second image memory for storing a second inspection image inputted by imaging different workpieces having the same pattern or different parts of the same workpiece under the same conditions. A clipping processing unit that performs a process of matching a luminance lower than a preset clipping level to a preset clipping level with respect to the first inspection image and the second inspection image read from each of the image memories; A difference processing unit that creates a difference image between the first inspection image and the second inspection image; and a determination unit that determines a defect based on the difference image. Defect inspection apparatus according to claim.