JPH0654223B2 - Printed circuit board soldering inspection apparatus and inspection method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a printed wiring board soldering inspection apparatus and inspection method for inspecting a soldered state of a printed wiring board on which circuit elements are mounted. The present invention relates to an apparatus and method for inspecting a solder bridge generated between lands of a printed wiring board.

[Prior Art] When soldering a circuit element to a printed wiring board, a solder bridge may occur between lands of the printed wiring board. It is difficult to eliminate such defects, and conventionally, for example, as in JP-A-62-299709, a printed wiring board on which a circuit element is mounted is first imaged by an industrial television camera or the like, and this image is taken. Binarize with a predetermined threshold,
A binary image used to detect the bridge was created. That is, since the solder portion forming the bridge has a stronger reflected light than the other portions, a high-luminance portion having a strong reflected light and a low-luminance portion having a weaker reflected light are divided by a predetermined threshold value.
I was creating a value image. Then, only the solder portion is extracted based on the binary image, and the presence or absence of the bridge is detected by the change in the value of the area of the solder portion.

[Problems to be Solved by the Invention] However, when the width of the bridge formed on the printed wiring board is thicker than the pixel of the television camera, the bridge is determined to be a high-intensity portion and the image is displayed on the binary image. Although it can be obtained, when the width of the bridge is narrower than the width of one pixel, the strong light reflected by the bridge and the weak light reflected by the substrate are received together by one pixel and are judged to be the low brightness portion. As a result, since the bridge does not appear on the binary image, there is a problem that it is erroneously determined that there is no bridge.

As a countermeasure against this, it is conceivable to increase the resolution by enlarging with a target lens to be imaged, but in this case, the data to be processed increases in proportion to the square of the resolution, so that the inspection time becomes long. Another problem was that the inspection could not be speeded up. On the other hand, when the threshold value for detecting a bridge is lowered, a wiring pattern with weak reflected light is also judged to be a high-luminance portion along with a thin bridge and appears on the binary image, so that the wiring pattern overlaps the lead wire extending from the land. Has a problem of being erroneously determined to be a bridge, and none of the measures has solved the above problem.

An object of the present invention is to speed up inspection without increasing the amount of data and to detect a bridge more easily and accurately.

[Means for Solving the Problems] The invention according to claim 1 made to solve the above problems is generated between lands when a circuit element is soldered to lands on a substrate on which a wiring pattern is formed. A soldering inspection device for a printed wiring board, which detects a solder bridge, wherein the printed wiring board on which the circuit element is soldered is irradiated with light and the reflected light is received to image the printed wiring board. And a threshold value used for binarizing an image captured by the imaging device, a high brightness portion where the reflected light of the solder portion and the wiring pattern is strong and a low brightness portion where the reflected light of the other substrate portion is weak. A threshold value setting means for setting a threshold value for discriminating between the two, and a binary image creator for binarizing the image picked up by the image pickup device based on the threshold value set by the threshold value setting means and outputting a binary image. And a wiring pattern storage means for storing the wiring pattern and for storing a predetermined land among the wiring patterns as a limited wiring pattern, and based on the wiring pattern and the limited wiring pattern stored by the wiring pattern storage means, A bridge image is detected based on a discrimination image creating unit that creates a discrimination image in which a wiring pattern other than the limited wiring pattern is removed from the image created by the binary image creating unit, and a discrimination image created by the discrimination image creating unit. A gist is a soldering inspection device for a printed wiring board, which comprises:

According to a second aspect of the present invention, there is provided a soldering inspection method for a printed wiring board, which detects a bridge of solder generated between the lands when the circuit element is soldered to the lands on the board on which the wiring pattern is formed, The printed wiring board to which the circuit element is soldered is irradiated with light, the reflected light is received and imaged, and the high-brightness portion where the reflected light of the solder portion and the wiring pattern is strong and the reflected light of the other substrate portion The captured image is binarized to form a binary image by using a threshold value for distinguishing from a low-luminance portion having weak intensity, and a portion other than a portion located between predetermined lands in the wiring pattern of the binary image is formed. A soldering inspection method for a printed wiring board is characterized in that a bridge discrimination image is formed by processing as a low-luminance portion and the bridge is detected based on the discrimination image.

[Operation] According to the present invention, the reflected light of the emitted light is received by the image pickup device to image the printed wiring board to which the circuit element is soldered. Then, the captured image is binarized by using a threshold value. The threshold value used for the binarization is set to a high brightness portion where the reflected light of the solder portion and the wiring pattern is strong, and a reflected light of the other substrate portion where the reflected light is weak. Set it to a value that is divided into the low-intensity part. Therefore, by binarizing using this threshold value, a binary image in which the solder portion and the wiring pattern and the other substrate portion are clearly separated can be obtained. Then, a wiring pattern other than the limited wiring pattern between the predetermined lands is removed from this binary image to form a determination image. By this process, if a bridge exists,
Since the image of the bridge in which the lands are connected is obtained on the discrimination image, the bridge can be detected based on the discrimination image.

That is, if the threshold for binarizing an image is lowered, a thin solder bridge of 1 pixel or less is detected, but at the same time, a wiring pattern is also detected, which hinders the detection of the bridge. However, in the present invention, since portions other than the predetermined lands in the wiring pattern are removed from the image, it means that the threshold value of only the portion where the bridge between the lands is likely to occur is lowered and detected. It also enables the detection of thin bridges.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a printed wiring board soldering inspection apparatus as an embodiment of the present invention. The inspection apparatus of this embodiment includes an image input system 5 for converting an image of the surface of the printed wiring board 2 to which the circuit element 1 is soldered into an image signal, and a soldering state of the printed wiring board 2 based on the image signal. And an image processing system 7 for recognizing.

Here, on the printed wiring board 2 to be inspected, as shown in FIG. 2, the lead wire 12 of the circuit element 1 is inserted into the land 10 of the printed wiring board 2 and fixed by the solder 14. The inspection apparatus of the present embodiment detects the bridge of the solder 14 formed between the lands 10.

In FIG. 1, first, the image input system 5 is the printed wiring board 2
A diffused lighting device 21 arranged obliquely below and surrounding the printed wiring board 2, and the printed wiring board 2 and the lighting device 21.
A dome-shaped diffuse reflection plate 23 provided so as to cover the
An industrial television camera 26 provided above the window 24 at the top of the diffuse reflection plate 23.

The diffuse reflection plate 23 shields ambient light and reflects the light from the lighting device 21 to generate uniform diffused light.
Irradiate the surface of. Then, the reflected light from the printed wiring board 2 enters the imaging lens 27 of the industrial television camera 26 through the window 24. The industrial television camera 26 converts the image on the printed wiring board 2 into an image signal and outputs it to the image processing system 7.

Next, the image processing system 7 binarizes the image signal to form a binary image, a binarizing unit 31, a wiring pattern removing unit 32 that corrects the binary image, and the wiring pattern removing unit 32.
And a processing unit 34 that performs image processing based on the output from the. Furthermore, a histogram creation unit 38 that determines a threshold value when binarizing an image signal, a wiring pattern storage unit 35 that stores a wiring pattern used for processing in the wiring pattern removal unit 32, and a land shape of the printed wiring board 2 A land pattern storage unit 40 that stores a pattern (land pattern) is provided.

The histogram creation unit 38 creates a histogram of the brightness of the pixels, and then the threshold value T when binarizing the image signal.
Is output to the binarization unit 31. That is, as shown in the histogram of FIG. 3, in order of the brightness of the pixels, the solder 14 of 1 pixel or more and the portion (first bright part) LS1 showing the lead wire 12 and the wiring pattern and the solder 14 of 1 pixel or less are arranged. Three large peaks corresponding to the indicated portion (second bright portion) LS2 and the portion (third bright portion) LS3 indicating only the printed wiring board 2 appear, and thus the second bright portion LS2 among them.
The valley between the third bright part LS3 and the third bright part LS3 is set as the threshold value T. Therefore, the first bright portion LS1 and the second bright portion LS2 which are brighter than the threshold value T are binarized as the high luminance portion, while the third bright portion LS3 which is darker than the threshold value T is binarized as the low luminance portion. In order to determine the threshold value T, a method of finding a valley between these peaks (a so-called mode method) or the like can be used.

The binarization unit 31 binarizes the image signal based on the threshold value T output from the histogram creation unit 38 and creates a binary image. When the threshold value T is binarized, the width of the bridge needs to be a certain value or more in order to be displayed as a high brightness portion. For example, as shown in FIG.
The width of the pixel G is 1, and the width of the bridge B is a (0 <a <1)
Then, the brightness S of one pixel G is expressed by the following equation (1).

_{S = a + S 1 + (} 1-a) + S 3 ... (1) S 1: the first light portion Mode S _3: Mode The bridge B of the third light portion is two pixels G as shown in Figure 5 In the case of straddling, the brightness of one pixel G is expressed by the following equation (2).

_{S = a + S 1/2} + (1-a / 2) + S 3 ... (2) where is the threshold value T and brightness S, if the following expression is satisfied (3) T <S ... ( 3), i.e. the bridge When the brightness S of the pixel G that images B is higher than the threshold value T, the bridge B can be expressed on the binary image, and therefore the following expression (4) is obtained from the expressions (2) and (3).

a> 2 (T-S3) / (S1-S3) (4) That is, even if the width a of the bridge B is smaller than the width of one pixel G,
When the expression (4) is satisfied, the bridge B can be displayed on the binary image.

The wiring pattern storage unit 35 stores in advance all the wiring patterns formed on the printed wiring board 2, and also stores the limited wiring pattern located between the predetermined lands in which the bridge B is easily formed among the wiring patterns. There is. Then, the wiring pattern storage unit 35 outputs the corrected wiring pattern based on the wiring pattern and the limited wiring pattern, but the image of the bridge B displayed in the above-described binary image is not cut off in the corrected wiring pattern. Similarly, the limited wiring pattern is removed from all the wiring patterns.

The wiring pattern removal unit 32 removes the image corresponding to the corrected wiring pattern output from the wiring pattern storage unit 35 from the binary image created by the binarization unit 31 to create a discrimination image.

The land pattern storage unit 40 stores the land pattern formed on the printed wiring board 2.

The processing unit 34 compares the area of each land obtained from the discrimination image with the area output from the land pattern storage unit 40, and if a certain ratio or more, detects it as a bridge.

Next, the processing executed in the inspection apparatus will be described based on the flowchart shown in FIG. 6 and the image explanatory views shown in FIGS. 7 to 11.

First, in step 100, the land pattern of the printed wiring board 2 shown in FIG. 7 is input to the land pattern storage unit 40. Specifically, the process of inputting the design data of the land pattern of the printed wiring board 2 or the process of mounting the printed wiring board 2 in which the circuit element 1 is not inserted into the inspection device and imaging the land pattern is performed. .

Next, at step 110, the wiring pattern H of the printed wiring board 2 shown in FIG. 8 is input to the wiring pattern storage unit 35. Specifically, similar to the land pattern, a process of inputting design data of the wiring pattern H of the printed wiring board 2,
Alternatively, a process of capturing an image of the wiring pattern H is performed.

Then, in step 120, the design data of the limited wiring pattern DH of the wiring patterns H is input to the wiring pattern storage unit 35.

In a succeeding step 130, the limited wiring pattern DH input in the step 120 is removed from the wiring pattern H input in the step 110, and a process for obtaining the corrected wiring pattern SH shown in FIG. 9 is performed. This process does not have to be performed every time and may be performed when the type of the printed wiring board 2 to be inspected is changed.

Next, the above-mentioned land pattern and repair wiring pattern S
Processing of a captured image using various data such as H will be described. In the following description, the land L shown in FIG.
It is assumed that a bridge B is formed between 1 and the land L2.

In step 140, the printed wiring board 2 to be inspected is mounted on the inspection apparatus of this embodiment, the surface thereof is imaged by the industrial television camera 26, and the image signal corresponding to the captured image is sent to the image processing system 7. input.

Then, in step 150, the histogram creation unit 38
The image signal is binarized by using the threshold value T output from the above, that is, the threshold value T that divides the first bright portion LS1 and the second bright portion LS2 and the third bright portion LS3. As a result, the image signal is binarized with the solder portion, the lead wire 12 and the wiring pattern H as the high-luminance portion, and the other substrate portion as the low-luminance portion. That is, since the threshold level is lowered, even if the width of the bridge B is narrower than the width of one pixel G, the bridge B is discriminated as a high-luminance portion together with the wiring pattern H as shown in FIG.

Next, at step 160, the above binary image (FIG. 10).
From the corrected wiring pattern SH obtained in step 130 from
Remove (Fig. 9). By this processing, a discrimination image as shown in FIG. 11 is created.

Next, a process performed using the discriminant image obtained by the above-described process, that is, a process of detecting the bridge B performed after step 160 will be described.

At step 170, based on the discrimination image of FIG.
Measure the area of each land. Here, the land L in FIG. 7
If there is a bridge B between the lands L1 and L2 among the lands 1 to L8, the lands L1 and L2 are integrated lands LL2 in FIG. 11, and the other parts are recognized as isolated lands LL3 to LL8, respectively. To be done.

Next, in step 180, the areas of the lands LL2 to LL8 measured in this manner are set to the lands L1 to L8 of FIG.
It is determined whether or not the area of the corresponding land has increased by a certain ratio (for example, 1.5) or more compared with the area of No. This determination utilizes the property that the area increases when a plurality of lands are integrated by the bridge B. Therefore, the land L1 and the land L2 and the land LL
If the area increases by a certain ratio or more as in the case of the relationship with 22, the process proceeds to step 190 and it is determined that the bridge B exists. On the other hand, lands L3 to L8 and lands LL3 to
If the increase in area is equal to or less than a certain ratio as in the relationship with LL8, the process proceeds to step 200 and it is determined that the bridge B does not exist. As a result, the presence or absence of the bridge can be determined based on the determination image obtained in step 160.

As described above, the soldering inspection apparatus for the printed wiring board 2 according to the present embodiment provides the image obtained by picking up the image of the printed wiring board 2.
By setting the threshold value T when the value is set low, the solder portion other than the substrate portion, the lead wire 12 and the wiring pattern H
In addition, the bridge B, which is narrower than the width of one pixel G and has a small amount of reflected light, is also determined to be a high-luminance portion, and these pixels can be displayed on the binary image. However, since the wiring pattern H is displayed in the same manner as the bridge B in this binary image,
By removing the modified wiring pattern SH from the binary image, it is possible to prevent the lead wire 12 and the wiring pattern H from being connected. Therefore, it is not erroneously determined that the bridge is formed between the land L4 and the land L7. Further, since the modified wiring pattern SH is obtained by removing the limited wiring pattern DH from the wiring pattern H, the bridge B is not cut when the modified wiring pattern SH is removed, and the land between the land L1 and the land L2 is not cut. It is possible to create a discrimination image in which the connected bridge B is clearly displayed. Therefore, by using this discrimination image,
High-speed inspection can be performed without increasing the resolution, and the bridge B can be detected more easily and reliably.

In the above embodiment, the brightness histogram is used to calculate 2
I calculated the threshold value, but without using the histogram,
For example, in the case of an image in which there is not much variation in brightness, a method is used in which a human observes a binary image while changing the threshold value in advance and sets a threshold value that provides an optimal binary image, and then uses that threshold value. May be. In the processing unit of the above embodiment, area comparison is performed as a method of detecting a bridge from a discriminated image. However, as described in the previous patent application (Japanese Patent Application No. 62-230808) by the present inventor, Bridges may be detected by checking connectivity between lands. In addition, without using the dome-shaped diffuse reflection plate 23,
Light may be emitted from above the printed wiring board 2 by an irradiation device.

[Effects of the Invention] As described above, according to the present invention, by using the threshold value for distinguishing the solder portion, the lead wire and the wiring pattern from the board portion other than the solder portion, the lead wire and the wiring pattern, In addition, it is possible to form a binary image in which a bridge narrower than the width of one pixel and less in reflected light is displayed, and by processing the binary image using a wiring pattern stored in advance, it is possible to increase the resolution. It is possible to obtain a discrimination image in which substantially only the periphery of the bridge is clearly divided. Therefore, the presence or absence of the bridge can be accurately determined at high speed based on the determination image.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a soldering inspection apparatus for a printed wiring board as an embodiment of the present invention, FIG. 2 is a sectional view of the printed wiring board, FIG. 3 is a reflected light histocrum, FIG. 4 and FIG. 5
FIG. 7 is an explanatory diagram showing a bridge, FIG. 6 is a flowchart showing an inspection process, and FIGS. 7 to 11 are explanatory diagrams showing an image processing process. DESCRIPTION OF SYMBOLS 1 ... Circuit element, 2 ... Printed wiring board 10, L1-L8, LL2-LL8 ... Land 12 ... Lead wire, 14 ... Solder 31 ... Binarization part, 32 ... Wiring pattern removal part 34 ...... Processing unit 35 ...... Wiring pattern storage unit 38 …… Histogram creation unit 40 …… Land pattern storage unit B …… Bridge, G …… Pixel H …… Wiring pattern, DH …… Limited wiring pattern SH …… Modification Wiring pattern

Claims (2)

[Claims] 1. A soldering inspection device for a printed wiring board, which detects a bridge of solder generated between lands when a circuit element is soldered to a land on a board on which a wiring pattern is formed, An image pickup device for picking up an image of the printed wiring board by irradiating the printed wiring board to which the circuit element is soldered with light and receiving the reflected light, and a threshold used for binarizing the image picked up by the image pickup device. Is a threshold value setting means for setting a threshold value for distinguishing between a high-brightness portion of the solder portion and the wiring pattern where the reflected light is strong and a low-brightness portion of the other substrate portion where the reflected light is weak, and the threshold value setting means. A binary image creating unit that binarizes an image captured by the image capturing device based on a threshold value and outputs a binary image; and stores the wiring pattern, and a predetermined one of the wiring patterns. Wiring pattern storage means for storing between the lands as a limited wiring pattern, and the limited wiring pattern from the image created by the binary image creation means based on the wiring pattern and the limited wiring pattern stored by the wiring pattern storage means. And a bridge detection unit for detecting a bridge based on the discrimination image created by the discrimination image generation unit. Wiring board soldering inspection device. 2. A soldering inspection method for a printed wiring board, which detects a bridge of solder generated between lands when soldering a circuit element to a land on a board having a wiring pattern formed thereon. The printed circuit board to which the circuit element is soldered is irradiated with light, and the reflected light is received and imaged, and the high-brightness portion where the reflected light of the solder portion and the wiring pattern is strong and the reflected light of the other substrate portion The captured image is binarized to form a binary image by using a threshold value for distinguishing it from a weak low-luminance portion, and the wiring pattern of the binary image except the portion located between predetermined lands is reduced. A soldering inspection method for a printed wiring board, characterized in that a bridge discrimination image is formed by processing as a luminance portion and the bridge is detected based on this discrimination image.