JP3337794B2 - Circuit board inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting a circuit board, and more particularly to an appearance inspection of a circuit board by a camera.

[0002]

2. Description of the Related Art Circuit board inspection methods are roughly classified into a method of electrically measuring and a method of inspecting from the appearance.
In the electrical measurement, the probe on the signal supply side and the probe on the measurement section side are brought into contact with the point to be measured, and the conduction state, current, voltage, etc. between them are actually measured, so high reliability is achieved. Inspection can be performed.

[0003] However, in the electrical inspection, for example, in the lead terminals of a chip component or an IC package, for example, although they are soldered and brought into a conductive state,
It is not clear whether the position is displaced or it is easily peeled off. Also, the electrical inspection cannot detect the polarity of a polarized capacitor, the presence or absence of a bypass capacitor, and the like.

[0004] Therefore, when there is a possibility of the above-mentioned omission of inspection, an appearance inspection is performed. However, since visual inspection is extremely inefficient, the appearance inspection is automatically performed by a camera and its image processing. FIG. 10 shows an example of such a case.

[0005] That is, first, a non-defective substrate P as an inspection reference is imaged by the camera 1, and features of the image are extracted by the image processing device 2 and stored in a memory as a reference model. In this case, the feature extraction of the image is performed by a standard normalized correlation method, a contour extraction method, or the like, and is stored in a memory as binary data, for example.

In the inspection, the circuit board Pa to be inspected is imaged by the camera 1, the image processing device 2 extracts the features of the image in the same manner as described above, reads the reference model from the memory, and matches the two. Compare and judge the mismatch.
This comparison is determined based on a value obtained by scoring the degree of overlap (duplication rate) of the images. For example, when the score value is larger than a preset reference score value, it is determined to be non-defective.

[0007]

According to this, the appearance inspection can be automatically performed in a short time. However, conventionally, since the entire circuit board is imaged, a physically large defect such as a missing part can be recognized.However, for example, a small part such as a misalignment of a lead part or a soldering state can be recognized. Testing is likely to be overlooked.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and its structural feature is that it is movable in an XY direction in a plane parallel to a circuit board to be inspected. in part, it fitted with a camera capable of capturing the fine portion of the circuit board to be inspected at any magnification, above prior to testing
The same good circuit board as the circuit board to be inspected with the camera
Imaging a portion corresponding to the measured point of extracting features of the image by the image processing unit, which memory is stored as a reference model, at the time of inspection, it is captured by the reference model and the camera comparison determines the circuit board test by comparing determining means and the image of the measured point of the circuit board to be inspected
In the method, the image processing means includes a standard normalized correlation method.
And the contour extraction method, the image captured by the camera
From the circuit board to be inspected.
When comparing an image with its reference model,
One of the standard normalized correlation method and the contour extraction method uses the ratio
If the comparison cannot be made, the other
To do .

In this case, the comparing and judging means includes
Score the overlap rate between the quasi-model and the image of the circuit board to be inspected
That a reference value is set as a standardized judgment level
Is preferred.

Furthermore, on the examiner査時, first, a reference mark provided on the circuit board to be inspected is imaged by the camera is compared with the reference model of a reference mark which is previously stored in memory and the image It is preferable to correct the initial position at the time of the inspection .

[0011] To implement the above-described inspection method, the invention includes a plurality of movable portions which can move an X-Y direction in the circuit board to be inspected and a plane parallel to said target probe to the movable portion The probe is mounted so as to be able to ascend and descend so as to be able to come into contact with the test circuit board, and the probe is moved to a predetermined test point on the test circuit board via the movable portion, and the probe contacts the test point In a circuit board inspection apparatus for performing electrical measurement by performing a measurement, a camera attached to any of the movable parts and capable of capturing an image of a fine portion of the circuit board to be inspected at an arbitrary magnification is the same as the circuit board to be inspected. extracts the features from the captured image in the portion of the camera corresponding to the measuring points of the good circuit board, a memory including image processing means for storing as a reference model it, at the time of inspection, in the camera The matching, and a comparison and determination means for determining a mismatch by comparing the reference model corresponding to the measured points stored in the image and the memory of the captured measured point of the circuit board to be inspected, In addition to electrical measurements
The feature is that appearance inspection by image processing is also possible.
ing.

[0012]

According to the above arrangement, the camera moves to a preset point to be measured and picks up an image of that portion. And
The image is compared with a reference model of the same part, and a pass / fail judgment is made based on a specific value based on the overlapping rate.

[0013]

FIG. 1 is a schematic plan view showing one embodiment of a circuit board inspection apparatus according to the present invention. According to this, the circuit board inspection apparatus includes, for example, three guide rails 10a to 10c oriented along the X axis, and each of the guide rails 10a to 10c has an arm 11a to 11c extending in the Y axis direction. It is held movably in the X-axis direction along the guide rail.

A movable portion 12a to 12c is held on each of the arms 11a to 11c so as to be movable along the Y-axis direction. Although not shown in detail, each of the movable portions 12a to 12c is Have probes 13a to 13
c is attached to the circuit board P so as to be able to move up and down freely.

Although any of the arms 11a to 11c may be used, in this embodiment, another movable portion 12d is held by the intermediate arm 11b so as to be movable along the Y-axis direction. As shown in FIG. 2, a camera 14 capable of capturing the details of the circuit board P at an arbitrary magnification is attached.

Although not shown, the guide rail 10a
1 to 10c are provided with first driving means including a servomotor for reciprocating the arms 11a to 11c in the X-axis direction.
A second drive unit including a servomotor for reciprocating 2a to 12d along the Y-axis direction is provided.

Accordingly, the camera 14 can be arbitrarily moved in a plane parallel to the circuit board P in the same manner as the probes 13a to 13c by the first and second driving means. The image data is sent to a central processing unit (CPU) 20.

Each of the probes 13a to 13c is also connected to the CPU 20 via a suitable I / O port (not shown). In this case, the CPU 20 stores an image processing section and its image processing program. ROM (R
and a RAM (Random Access) for storing image-processed data.
Memory).

In this embodiment, two standard image processing methods, a standard normalized correlation method and a contour extraction method, are used to extract image features. Generally, reference marks M are provided at two opposite corners of the circuit board P. FIG. 3A shows a reference model M1 in which the features of the reference marks M are extracted by the standard normalized correlation method. FIG. 2B shows a reference model M2 in the case of using the contour extraction method.

For example, the reference mark M is composed of a square and a circle inscribed in the circle. When the color is different between the inside and outside of the circle, for example, when the inside of the circle is white and the outside is black, In the standard normalized correlation method, the white area and the black area are converted into binary data.

On the other hand, in the contour extraction method, only the portion where the color is changed, that is, only the contour portion is converted into binary data.

Next, the inspection method will be described. First,
Import the reference data. To do this, a non-defective circuit board P is set at a predetermined position, and the camera 14 is moved over the reference mark M by the operation unit 21 to image the reference mark at a predetermined magnification.

Then, the features of the image are converted into binary data by the standard normalized correlation method and the contour extraction method, and the converted data are used as reference models M1 and M2 (see FIGS. 3A and 3B). Write to RAM. The image is displayed on the display 22.

Next, the operation unit 21 is operated to move the camera 14 over the measurement point, and the reference model is fetched in the same manner as described above. FIG. 4 shows a state in which a reference model is obtained from a chip-type resistor R mounted on a circuit board P, for example.

That is, assuming that, for example, a bar code or a number indicating a product number or a rating is attached to the exterior body of the chip-type resistor element R, an image is taken as an optimal target of the reference model.

In this case, the display 22 shown in FIG.
A vertically long frame as shown in FIG. 1 appears, and the image in the frame is subjected to image processing by the standard normalized correlation method and the contour extraction method, respectively, and the feature thereof is extracted.

FIG. 4B shows a reference model M3 obtained by the standard normalized correlation method, and FIG. 4C shows a reference model M4 obtained by the contour extraction method. When the reference model is fetched, its address is also stored in the RAM at the same time.

Further, the operation unit 21 sets a judgment level for each measurement point. Although this determination level is arbitrarily determined, in this embodiment, it is assumed that an image obtained from the circuit board to be inspected completely overlaps the reference model.
The points are scored as 0 points. Therefore, the determination level is set by a numerical value such as 700 points or 800 points.

As described above, after the reference model and the address of the measurement point are fetched and the determination level is set, an actual inspection is performed.

FIG. 9 shows a flowchart at the time of this inspection. In this embodiment, first, for each measurement point,
An image correlation search is performed by the standard normalized correlation method (mark detection routine A). If an image to be compared cannot be detected by this, the image is automatically detected by the contour extraction method. (Mark detection routine B). Contrary to this, the contour extraction method may be performed first, and if this is not successful, the standard normalized correlation method may be performed.

When the circuit board Pa to be inspected is set at a predetermined position and the inspection is started, first, the camera 14 is moved to a reference mark position to image the reference mark. The image is converted to binary data by the standard normalized correlation method, and R
This is compared with the reference model M1 read from the AM.

This state is displayed on the display 22, as shown in FIG. If RM1 is of the circuit board Pa to be inspected and there is a deviation from the reference model M1 as shown in FIG.
This is fed back to U20, and the initial position of the camera 14 is corrected so that they match.

FIG. 6 shows a case where the contour extraction method is used. According to the contour extraction method, an image RM2 of the reference mark obtained from the circuit board Pa to be inspected is partially missing as shown in FIG. In this sense, it can be said that the detection ability is higher than the standard normalized correlation method.

After the initial position has been corrected in this way, the camera 14 moves to each measurement point to perform an appearance inspection. FIG. 7 shows the chip type resistance element R described above.
5 schematically shows a state where the reference model M3 is compared with an image RM3 obtained from the circuit board Pa to be inspected by the standard normalized correlation method.

The CPU 20 counts the area overlap rate of the image RM3 on the inspection side with respect to the reference model M3 to obtain a score, and compares the score with the judgment level value to judge the appearance.

FIG. 8 is a schematic diagram showing a case where comparison is determined by the contour extraction method. Also in this case, the reference model M
The quality of the appearance is determined based on the overlap ratio between the image RM4 and the image RM4 on the inspected side. The comparison target is only the outline, and even if there is partial chipping on the image RM4, the accuracy is high. The quality of appearance can be determined.

Although the above embodiment is mainly concerned with the appearance inspection, it is also possible to conduct an electrical inspection by means of probe pins before and after the appearance inspection or at the same time.

[0038]

As described above, according to the present invention, the reference model of the appearance is stored in the memory for each measurement point from the non-defective substrate, and at the time of inspection, the reference model and the image obtained from the substrate to be inspected are stored. Are compared, and the quality of the appearance is determined based on the degree of overlap (graphical overlap rate), so that the appearance can be inspected with high reliability even to a fine portion of the circuit board.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing one embodiment of a circuit board inspection apparatus according to the present invention.

FIG. 2 is a perspective view showing a mounted state of the camera in the embodiment.

FIG. 3 is an explanatory diagram showing a reference model obtained by performing image processing on a reference mark on a circuit board.

FIG. 4 is an explanatory diagram showing a reference model obtained by performing image processing on a chip-type resistive element.

FIG. 5 is an explanatory diagram for explaining a mark detection state by a standard normalized correlation method.

FIG. 6 is an explanatory diagram for explaining a mark detection state by a contour extraction method.

FIG. 7 is an explanatory diagram for explaining a comparison state with a reference model by a standard normalized correlation method.

FIG. 8 is an explanatory diagram for explaining a comparison state with a reference model by a contour extraction method.

FIG. 9 is a flowchart for explaining an operation at the time of inspection.

FIG. 10 is a schematic diagram for explaining a conventional example.

[Explanation of symbols]

 10a-10c Guide rail 11a-11c Arm 12a-12d Movable part 13a-13c Probe 14 Camera 20 CPU 21 Operation part 22 Display

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Takahashi 81, Sakuracho, Koizumi, Ueda-shi, Nagano Prefecture Inside of Hioki Electric Co., Ltd. (56) References JP-A-4-138344 (JP, A) JP-A-1 -295139 (JP, A) JP-A-62-180252 (JP, A) JP-A-5-73149 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/88- 21/956 G06T 7/00 H05K 3/00

Claims (3)

(57) [Claims] 1. An XY plane in a plane parallel to a circuit board to be inspected.
Attach a camera capable of imaging a fine portion of the circuit board to be inspected at an arbitrary magnification to a movable portion that can move in a direction,
Prior to the inspection and imaging the portion corresponding to the measured point of the same good circuit board and the circuit board to be inspected at the camera,
Extracting features of the image by the image processing unit, which memory is stored as a reference model, at the time of inspection, the image of the reference model and the measured points of the circuit board to be inspected picked up by the camera In the circuit board inspection method for comparing and determining by the comparison determining means , the image processing means includes a standard normalized correlation method and a contour extraction method.
From the images captured by the camera
Of the circuit board to be inspected and its reference
When comparing and judging the model,
Comparison judgment is not possible with either the correlation method or the contour extraction method.
A circuit board inspection method , in which, in some cases, a comparison judgment is made by the other method. 2. The method according to claim 1, wherein the comparing and judging means includes the reference model.
And the overlap rate between the image of the circuit board to be inspected and
2. The circuit board inspection method according to claim 1, wherein a reference value as a constant level is set . 3. An XY plane in a plane parallel to a circuit board to be inspected.
It has a plurality of movable parts that can move in the
So that the lobe can contact the circuit board under test.
The probe is mounted so that it can be moved up and down.
Moved to a predetermined measurement point on the circuit board to be inspected through
Circuit for making electrical measurements by contacting the measured point
In the substrate inspection apparatus, the circuit under inspection attached to any of the movable parts
A camera capable of imaging a fine portion of the plate at an arbitrary magnification;
The above-mentioned measurement of the same good circuit board as the above-mentioned circuit board to be inspected
From the image of the part corresponding to the point captured by the above camera
An image that extracts its features and stores it as a reference model
A memory including an image processing means;
Image of the measured point on the circuit board to be inspected imaged by the camera
And the measured point stored in the above memory
A ratio that compares with the reference model to determine the match or mismatch
Means for comparing and judging by image processing in addition to electrical measurement.
Circuit board inspection characterized in that
Inspection equipment.