JPH0221209A - Apparatus and method for inspecting soldering of printed wiring board - Google Patents

Abstract

PURPOSE:To obtain a judge image wherein only a bridge periphery is divided clearly by using a threshold value dividing a solder part, a lead wire, a wiring pattern and any other board part to perform the processing of a binary image on the basis of a preliminarily stored wiring pattern. CONSTITUTION:An inspection apparatus is constituted of an image input system for converting the surface image of a printed wiring board 2 to which a circuit element 1 is soldered to an image signal and an image processing system 7 for confirming the soldered state of the printed wiring board 2 on the basis of said signal. The image input system 5 outputs the image signal to the image processing system 7 having an industrial TV camera 26 from the window 24 of the diffusion reflecting plate 23 arranged so as to surround the board 2 and said signal is binarized in said image processing system 7 and, when said signal is binarized, a threshold value is set by a histogram forming part 38. This forming part 38 forms the histogram of the brightness of a pixel and subsequently sets the threshold value when the image signal is binarized to output the same to a binarizing part 31. Then, a judge image wherein only a bridge periphery is divided clearly is obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a printed wiring board soldering inspection device and an inspection method for inspecting the soldering condition of a printed wiring board on which circuit elements are mounted. The present invention relates to an apparatus and method for inspecting solder bridges occurring between lands of a printed wiring board.

[Prior Art] When soldering circuit elements to a printed wiring board, solder bridges may occur between lands of the printed wiring board. It is difficult to completely eliminate such defects, and conventionally, as in Japanese Patent Laid-Open No. 62-299709, a printed wiring board on which circuit elements are mounted is first imaged with an industrial television camera, and this captured image is then The images were binarized using a predetermined threshold value to create a binary image used for detecting bridges. That is,
Since the parts of the solder that form the bridge have stronger reflected light than other parts, a binary image is created by separating the high-brightness parts with strong reflected light and the low-brightness parts with weaker reflected light using a predetermined threshold. Was. Then, only the solder portion is extracted based on the binary image, and the presence or absence of a bridge is detected based on a change in the area value of the solder portion.

[Problems to be Solved by the Invention] However, if the width of the bridge formed on the printed wiring board is wider than the pixels of a television camera, the bridge is determined to be a high-brightness part and is not displayed on the binary image. An image can be obtained, but if the width of the edge is narrower than the width of one pixel, the strong light reflected by the edge and the weak light reflected by the board are received together by one pixel, resulting in low light. As a result, the bridge does not appear on the binary image, causing a problem in that it is incorrectly determined that there is no bridge.

As a countermeasure to this problem, it is possible to increase the resolution by enlarging the object to be imaged with a lens, but in this case, the amount of data to be processed increases in proportion to the square of the resolution.
Another problem has arisen in that the inspection time becomes long and it is not possible to speed up the inspection.

On the other hand, when lowering the threshold for detecting bridges,
Along with thin bridges, wiring patterns with weak reflected light are also judged as high-brightness areas and appear on the binary image, so if a wiring pattern overlaps a lead wire extending from a land, it will be mistakenly judged as a bridge. None of the measures solved the above problem.

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

[Means for Solving the Problem] The invention of claim 1 made to solve the above problem provides that when a circuit element is soldered to a land on a board on which a wiring pattern is formed, a problem occurs between the lands. This is a soldering inspection device for a printed wiring board that detects bristle of solder, which irradiates light onto the printed wiring board to which the circuit element is soldered and receives the reflected light. An imaging device that captures an image, and two images captured by the imaging device.
a threshold value setting means for setting a threshold value used for value conversion to distinguish between high brightness parts of solder parts and wiring patterns with strong reflected light and low brightness parts of other board parts with weak reflected light; and the threshold value setting means. Binary image creation means for binarizing an image captured by the imaging device and outputting a binary image based on a threshold value set by the means; A wiring pattern storage means for storing the area between lands as a limited wiring pattern, and a wiring pattern other than 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. A printed wiring comprising: a discrimination image creation means for creating a discrimination image from which a wiring pattern is removed; and a bridge detection means for detecting a bridge based on the discrimination image created by the discrimination image creation means. The invention according to claim 2, characterized by a board soldering inspection device, detects solder bridges that occur between lands when circuit elements are soldered to lands on a board on which a wiring pattern is formed. A soldering inspection method for a board, which irradiates light onto a printed wiring board to which the circuit elements are soldered, receives the reflected light, and captures an image, and detects a high brightness with strong reflected light from the solder portion and wiring pattern. The captured image is binarized to form a binary image using a threshold value that distinguishes between the part of the board and the low-luminance part of the other board parts where the reflected light is weak. Among the wiring patterns of this binary image, Summary of a printed wiring board soldering inspection method characterized by forming a bridge identification image by treating areas other than those located between predetermined lands as low-luminance areas, and detecting bridges based on this identification image. shall be.

[Function] The present invention images a printed wiring board to which circuit elements are soldered by using an imaging device to receive reflected light of irradiated light. The captured image is then binarized using a threshold value. Set to a value that separates the brightness into low brightness areas. Therefore, by performing binarization using this threshold value, a binary image in which the solder portions and wiring patterns are clearly separated from the other board portions can be obtained. Then, wiring patterns other than the limited wiring patterns between predetermined lands are removed from this binary image to form a determination image.

Through this processing, if a bridge exists, an image of the bridge in which lands are connected is obtained on the discrimination image, so that the bridge can be detected based on this discrimination image.

That is, if the threshold value for binarizing an image is lowered, thin solder bridges of one pixel or less can also be detected, but wiring patterns are also detected at the same time, which becomes a hindrance to detecting bridges. However, in the present invention, since parts of the wiring pattern other than between predetermined lands are removed from the image, the threshold value is lowered to detect only the parts where bridges between lands are likely to occur. It also becomes possible to detect thin bridges.

[Examples] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 is a schematic diagram of a soldering inspection apparatus for printed wiring boards as an embodiment of the present invention. The inspection apparatus of this embodiment includes an image human power system 5 that converts an image of the surface of a printed wiring board 2 to which a circuit element 1 is soldered into an image signal, and a soldered state of the printed wiring board 2 based on this image signal. and an image processing system 7 that recognizes.

Here, in the printed wiring board 2 to be inspected, as shown in FIG. 2, the lead wires 12 of the circuit element 1 are inserted into the lands 10 of the printed wiring board 2 and fixed with solder 14. The inspection device of this embodiment detects bridges of solder 14 formed between lands 10.

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

The diffuse reflector 23 blocks external disturbance light and reflects light from the lighting device 21 to provide uniform diffused light to the printed wiring board 2.
0 surface. The reflected light from the printed wiring board 2 passes through the window 24 and enters the imaging lens 27 of the industrial television camera 26.

The industrial television camera 26 converts the image of the printed wiring board 2 into an image signal and outputs it to the image processing system 7.

Next, the image processing system 7 includes a binarization unit 31 that binarizes the image signal to form a binary image, a wiring pattern removal unit 32 that corrects this binary image, and a wiring pattern removal unit 32 that corrects the binary image.
and a processing section 34 that performs image processing based on the output from. Furthermore, a histogram creation section 35 determines a threshold value for binarizing the image signal, and a wiring pattern storage section 35 stores wiring patterns used in processing in the wiring pattern removal section 32. and a land pattern memory g that stores the land shape pattern (land pattern) of the printed wiring board 2.
Equipped with iPJ40.

The histogram creation section 3 creates a histogram of pixel brightness and then uses a threshold value T for binarizing the image signal.
is determined and output to the 2-fuffi conversion unit 31. As shown in the histogram in Figure 3, the brightness of the pixels is in descending order of brightness: the part (first bright part) indicating the solder 14 and lead wire 12 of one or more pixels, the wiring pattern, and the solder of one pixel or less. Part showing 14 (second bright part) LS2
．． Part showing only the printed wiring board 2 (first white part') LS3
Since three large peaks corresponding to appear, the valley between the second bright portion LS2 and the third bright portion LS3 is set as the threshold value T. Therefore, the first bright part L brighter than this threshold value T
The SI and the second bright part LS2 are binarized as a high brightness part, while the third bright part LS3, which is darker than the threshold value T, is binarized as a low brightness part. Note that to determine this threshold T, a method of finding a valley between these peaks (so-called mode method) or the like can be used.

The binarization unit 31 converts the image signal into a binary image based on the threshold (direction T) output from the histogram creation unit 38 to create a binary image.
In order for the bridge to be displayed as a high-brightness portion, the width of the bridge must be at least a certain value.

For example, as shown in Fig. 4, if the width of one pixel G is 1 and the middle amount of bridge B is a (0<a<1), then the brightness S of one pixel G is calculated by the following formula (1). It is expressed as

Further, when the bridge B spans two pixels G as shown in FIG. 5, the brightness of one pixel G is expressed by the following equation (2).

5=a-5t/2+ (1a/2)+s3''' (2)
Here, the threshold value T and the brightness S are expressed by the following formula (3)% formula% (3
), that is, when the brightness S of the bridge B11 - the pixel G to be imaged exceeds the threshold T, the bridge B can be expressed on a binary image, so from equations (2) and (3), the following We obtain equation (4).

a>2 (T-93) / (Sl-93) −
(4) That is, even if the width a of bridge B is thinner than the width of one pixel G, if formula (4) is satisfied, bridge B is
Values can be displayed on the image.

The wiring pattern storage unit 35 stores in advance all wiring patterns formed on the printed wiring board 2, and also stores limited wiring patterns located between predetermined lands where bridges B are likely to occur among the wiring patterns. There is. The wiring pattern storage unit 35 then outputs a modified wiring pattern based on the wiring pattern and the limited wiring pattern, but in this modified wiring pattern, the image of bridge B displayed in the binary image described above is not cut. Similarly, limited wiring patterns are removed from all wiring patterns.

The wiring pattern removal unit 32 removes an 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.

Land pattern storage section 40 stores land patterns formed on 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 detects a bridge if the area exceeds a certain ratio.

Next, the processing executed in the inspection apparatus will be explained based on the flowchart shown in FIG. 6 and the explanatory diagrams of images shown in FIGS. 7 to 11.

First, in step 100, the land pattern of the printed wiring board 2 shown in FIG. 7 is manually entered into the land pattern storage section 40. Specifically, a process of manually inputting the design data of the land pattern of the printed wiring board 2, or a process of mounting the printed wiring board 2 without the circuit element 1 inserted into this inspection apparatus and capturing an image of the land pattern, etc. .

Next, in step 110, the wiring pattern H of the printed wiring board 2 shown in FIG. 8 is manually input into the wiring pattern storage section 35. Specifically, similar to the above-mentioned land pattern, the process of manually inputting the design data of the wiring pattern H of the printed wiring board 2;
Alternatively, processing to image the wiring pattern "l" is performed.

Then, in step 120, the design data of the limited wiring pattern DH of the wiring patterns H is input into the wiring pattern recorder 1 section 35.

In the subsequent step 130, the limited wiring pattern DH manually created in step 120 is removed from the wiring pattern H manually created in the step 110 to obtain a modified wiring pattern SH shown in FIG. Note that this process does not need to be performed every time, and may be performed when the type of printed wiring board 2 to be inspected is changed.

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

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

Subsequently, in step 150, the image is created using the threshold T output from the histogram creation section 3, that is, the threshold T that separates the first bright area LSI, the second bright area LS2, and the third bright area LS3 described above. Binarize the signal. As a result, the image signal is binarized with the solder portion, the lead wire 12, and the wiring pattern H as high-brightness portions, and the other board portions as low-brightness portions. That is, since the threshold level is lowered, even if the width of the bridge B is smaller than the width of one pixel G, the bridge B as well as the wiring pattern H is determined as a high brightness portion as shown in FIG.

Next, in step 160, the above binary image (FIG. 10)
Corrected wiring pattern 5F obtained in step 130 above from
-1 (Figure 9) is removed. By this process, the 11th
A discrimination image as shown in the figure is created.

Next, a process performed using the discrimination image obtained by the above-described process, that is, a process for detecting bridge B that is performed subsequent to the step 160 will be described.

At step 170, based on the discrimination image of FIG.
Measure the area of each land. Here, land L in Figure 7
Assuming that there is a bridge B between land L1 and land L2 among lands 1 to L8, in FIG. be done.

Next, in step 180, the area of the lands LL2 to LL8 measured in this way is calculated from the areas of the lands l''Ll to Ll in FIG.
8, it is determined whether the area of the corresponding land has increased by a certain ratio (for example, 1.5) or more.

This determination utilizes the property that when a plurality of lands are integrated by the bridge B, the area increases. Therefore, land L1, land L2, and land LL22
If the area has increased by a certain ratio or more, as in the relationship with , the process proceeds to step 190 and it is determined that bridge B exists. On the other hand, lands L3 to L8 and lands LL3 to LL
8, if the increase in area is less than a certain ratio, the process proceeds to step 200 and it is determined that bridge B is absent. Thereby, the presence or absence of a bridge can be determined based on the discrimination image obtained in step 160 above.

As explained above, the soldering inspection apparatus for the printed wiring board 2 of this embodiment uses two images obtained by imaging the printed wiring board 2.
By setting the threshold value T low when converting into a value, the solder parts other than the board part, the lead wire 12 and the wiring pattern H
In addition, the bridge B, which is narrower than the convergence of one pixel G and has less reflected light, is also determined to be a high-brightness portion, and these images can be displayed on a binary image. However, since the wiring pattern H is also displayed in the same way as bridge B in this binary image, by removing the corrected 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 a bridge is formed between the land L4 and the land L7. In addition, this modified wiring pattern SH is obtained by removing the limited wiring pattern DH from the wiring pattern H, so (1
When the positive wiring pattern S H is removed, Burundi B
It is possible to create a discrimination image in which the bridge B connecting the land L1 and the land L2 is clearly displayed without cutting the land L1 and the land L2. Therefore, by using this discrimination image, high-speed inspection can be performed without increasing the resolution, and bridge B can be detected more easily and reliably.

Note that in the above embodiment, the brightness histogram is used to calculate 2
I found the threshold for value conversion, but even without using a histogram,
For example, if the image does not have much variation in brightness, humans do not have to change the threshold value in advance.2 (Observe the old image and set the threshold value to create the optimal binary image, and use that threshold value from now on.) In addition, the processing section of the above embodiment performs area comparison as a method of detecting bridges from the discrimination image, but this method is similar to that described in the previous patent application by the present inventor (Japanese Patent Application No. 62-230808). ), bridges may be detected by checking the connectivity between lands.Incidentally, without using the dome-shaped diffuse reflection plate 23,
Light may be emitted from above the printed wiring board 2 using a lighting device.

[Effects of the Invention] As explained above, according to the present invention, the solder parts, lead wires, and wiring patterns can be separated by using a threshold value that distinguishes the solder parts, lead wires, and wiring patterns from other board parts. In addition, it is possible to form a binary image that displays bridges that are thinner than the width of one pixel and have less reflected light, and by processing the 21-direction image using pre-stored wiring patterns, it is possible to create a binary image without increasing the resolution. , it is possible to obtain a discrimination image in which only the area around the bridge is clearly separated. Therefore, based on this discrimination image, it is possible to quickly and accurately determine the presence or absence of brilliance.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a soldering inspection device 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 histogram of reflected light, and FIGS. 5
FIG. 6 is an explanatory diagram showing the bridge, FIG. 6 is a flowchart 1 showing the inspection process, and FIGS. 7 to 11 are explanatory diagrams showing the image processing process. 1... Circuit element 2... Printed wiring board 10, Ll
~L8. LL2 to LL8 pot◆◆Land 12... Lead wire 14... Bow read 31... Binarization section 32.
...Wiring pattern removal section 34...Processing section 35.
...Wiring pattern storage section 3 days...Histogram creation section 40...φ land pattern storage section B...Bridge G...Pixel H...φ wiring pattern DH-φ・Limited wiring pattern S
H... Modified wiring pattern patent attorney Tsutomu Setate (and 2 others) Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. A printed wiring board soldering inspection device that detects solder bridges that occur between lands when circuit elements are soldered to lands on a board on which a wiring pattern is formed, , an imaging device that captures an image of the printed wiring board by irradiating light onto the printed wiring board to which the circuit element is soldered and receiving the reflected light; and use for binarizing the image captured by the imaging device. a threshold value setting means for setting a threshold value to distinguish between a high brightness part of the solder portion and the wiring pattern where the reflected light is strong and a low brightness part of the other board part where the reflected light is weak; a binary image creation means for binarizing an image captured by the imaging device and outputting a binary image based on a threshold value, and storing the wiring pattern and limiting between predetermined lands in the wiring pattern; A wiring pattern storage means for storing wiring patterns, and a wiring pattern other than the limited wiring pattern from the image created by the binary image creation means based on the wiring pattern and limited wiring pattern stored by the wiring pattern storage means. Soldering of a printed wiring board characterized by comprising: a discrimination image creating means for creating a removed discrimination image; and a bridge detecting means for detecting a bridge based on the discrimination image created by the discrimination image creating means. Inspection equipment. 2. A printed wiring board soldering inspection method for detecting solder bridges that occur between lands when circuit elements are soldered to lands on a board on which a wiring pattern is formed, the circuit elements being soldered The attached printed wiring board is irradiated with light, and the reflected light is received and imaged, and the high-brightness parts of the solder parts and wiring patterns with strong reflected light and the low-brightness parts of other board parts with weak reflected light are detected. The captured image is binarized to form a binary image using a threshold value that distinguishes between A soldering inspection method for a printed wiring board, comprising: forming a discrimination image of a bridge, and detecting a bridge based on the discrimination image.