JPH1151621A - Soldering inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and securely decide whether or not soldering is good. SOLUTION: An image pickup device 8 is used to obtain the image of a given area on a printed board 2 including an electrode to be soldered. A data processor 6 performs a luminance smoothing process for smoothing the luminance at the respective parts of the image obtained by the image pickup device 8 and also generates the luminance histogram of the smoothed image. When the luminance value at which the luminance histogram has a peak is less than the given value, it is decoded that the soldering is defective.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering inspection device, and more particularly, to a soldering inspection device for inspecting the presence or absence of a soldering defect based on a luminance distribution of light reflected from a soldering portion.

[0002]

2. Description of the Related Art Soldering defects include "excessive soldering"
There are "insufficient solder" and "holes" in which through holes are partially exposed due to insufficient solder wettability. In order to automate the inspection of these soldering failures, various proposals have been made which use reflected light from a soldered portion. For example, the number of pixels for each brightness (density) of an image of a soldered portion is determined by a brightness histogram. And calculate the sum of the frequency difference with the standard brightness histogram registered in advance, and specify the standard brightness histogram having the smallest sum to determine whether the soldering is “normal”, “perforated”, “no solder”, etc. Is known (JP-A-6-174444).

[0003]

However, since the frequency difference from the standard luminance histogram varies depending on the shape of the electrode to be soldered, etc., the reliability of the judgment by the above-mentioned conventional inspection apparatus is still not sufficient. There was no problem.
In the inspection process, it is not usually necessary to particularly distinguish “perforated”, “no solder”, and the like, and it is only necessary to collectively determine that there is a solder failure.

Accordingly, the present invention is to solve such a problem, and an object of the present invention is to provide a soldering inspection apparatus which can easily and surely inspect various soldering defects as solder defects by the same process.

[0005]

In order to achieve the above object, according to the present invention, there is provided an imaging means (8) for obtaining an image of a predetermined area on a substrate (2) including an electrode (9) to be soldered, Brightness histogram creating means (61, step 10) for creating a brightness histogram of the image obtained by the means (8)
And 4) determining means for determining that the solder is defective when the luminance value indicating the peak of the luminance histogram is equal to or less than a predetermined value.
1, step 105).

[0006] In the present invention, in the case of any of the solder failures of "insufficient solder", "holes", and "excessive solders", the image obtained by the imaging means has a lower luminance than the normal soldered portion. The area increases. Therefore, when a brightness histogram of these solder failure images is created, the brightness value indicating the peak thereof is equal to or less than a predetermined value. Therefore, by confirming that the luminance value indicating this peak is equal to or less than the predetermined value, various soldering defects can be easily and reliably inspected as solder defects by the same process.

The luminance value indicating the peak of the luminance histogram is multiplied by a coefficient smaller than 1 to obtain a binarization threshold, and the image obtained by the imaging means (8) is binarized by the binarization threshold (61). , Step 106), and it is also possible to determine a solder defect based on the binarized image (61, step 107). According to this, since the binarization threshold is dynamically changed according to the luminance value indicating the peak, an appropriate binarized image is always obtained regardless of the fluctuation of the luminance of the entire image. As a defect determination method in this case, for example, a predetermined window (M) is provided in the binarized image, and a low-luminance area of the image crosses the window (M) or a fixed amount is set in the window (M). A solder defect is determined by approaching the above. Further, it is also possible to determine a defective solder on the basis of the area ratio of the high-luminance area of the binarized image, the peripheral length of the high-luminance area, and the like.

[0008] As a step prior to creating a luminance histogram, it is preferable to perform luminance smoothing processing on the image obtained by the imaging means (8). By this luminance smoothing process, it is possible to prevent the narrow high luminance region generated in the outer peripheral boundary region of the soldered portion from affecting the luminance histogram.
Further, prior to the luminance smoothing process, the electrode (9)
It is advisable to mask other parts (61, step 102). With this masking, the pixel luminance value around the soldered portion does not affect the luminance smoothing process.

[0009] The reference numerals in the parentheses indicate the correspondence with specific means described in the embodiments described later.

[0010]

FIG. 1 shows the overall configuration of a soldering inspection apparatus. In the figure, a lead 11 of a discrete component 1 is inserted into a through hole 21 of a printed circuit board 2 and is connected and fixed to an electrode (not shown) on the printed circuit board 2 by a soldering portion 3. The printed circuit board 2 is mounted on a moving table 4, and among a large number of discrete components 1 soldered on the printed circuit board 2, an object to be inspected is placed directly below a lighting device 5, which will be described in detail later. 4 and is positioned. The moving table 4 has an X-axis stage 41 and a Y-axis stage 4
2, the printed circuit board 2 can be positioned on a two-dimensional XY plane. X axis stage 41 and Y
The axis stage 42 is servo-controlled by the output of the positioning circuit 72.

The lighting device 5 includes a plurality of annular lighting rings 51.
These illumination rings 51 to 54 are arranged concentrically at intervals in the vertical direction, and have a smaller diameter as they go upward. The illumination ring 51 is divided into four sections in the circumferential direction, and a large number of light emitting diodes are provided for each section. Other illumination rings 52 to 54 have the same structure. The illumination rings 51 to 54 are respectively provided with illumination control circuits 7
1 and the lighting control circuit 71
The light emitting diode group can be energized to emit light for each of the 54 sections. The uppermost illumination ring 54 is used when the printed circuit board 2 is aligned, and the remaining lower illumination rings 51 to 53 are used in the soldering inspection.

The discrete component 1 to be inspected has its leads 11 (ie, through holes 21) positioned on the central axis of the lighting device 5, and each lighting ring 51
Illumination light emitted from the soldering portion 3 of the lead 11
With different angles. The incident angle of each illuminating light becomes larger as it is emitted from the upper illuminating ring 53, and is set in the range of 3 ° to 70 ° in the present embodiment. As shown in FIG. 2, the "normal" soldering section 3 has a mountain-shaped cross section rising from a gentle skirt to a steep top, and light L1 incident on the printed circuit board 2 at a large angle is soldered. The light L2 that is reflected at the bottom of the attachment portion 3 and goes upward, and is incident at a small angle, is reflected at the top and goes upward. Therefore, in the “normal” soldered portion 3, high-luminance reflected light is generated almost upward on the entire surface of the electrode 9.

Here, FIG. 3 shows a cross section of the soldering portion 3 in the case of "insufficient soldering". In this case, the cross section of the soldered portion 3 is reduced in a similar manner as compared with the case where the cross section of the soldered portion 3 is normal. FIG. 4 is a cross-sectional view of the “perforated” soldering portion 3 in which the through-hole 21 is partially exposed. In this case, in the region where the solder is attached, reflected light of high luminance is generated upward, The portion without solder has very low brightness.
FIG. 5 is a cross section of the soldering portion 3 of “excessive soldering”. In this case, the inner peripheral portion of the soldering portion 3 has a flat surface and the outer peripheral portion has a steep surface. The area of the moderately inclined surface which causes the above is also reduced.

In FIG. 1, an image pickup device 8 such as a CCD camera is provided above a lighting device 5 on its central axis.
The imaging device 8 receives reflected light upward from the soldering section 3 to obtain an image thereof. The image obtained by the imaging device 8 is sent to the image processing unit 61 in response to a command from the information processing unit 62 of the data processing device 6, and is subjected to processing described later. The data processing device 6 is composed of a personal computer or the like, has a CPU, various memories including a video RAM, an I / O interface, and the like, and is connected to a monitor, a printer, and the like. The image processing unit 61 and the information processing unit 62 are realized by software, and the information processing unit 62 includes the illumination control circuit 71 described above.
In addition to controlling the operation of the positioning circuit 72, the inspection result of each soldering unit 3 in the image processing unit 61 is displayed on a monitor or printed out.

The processing procedure in the image processing section 61 will be described below with reference to the flowchart of FIG. In step 101 of FIG. 6, an image obtained by the imaging device 8 is captured. In the following step 102, as shown in FIG. 7, a rectangular inspection window L is set around the soldering portion 3, and the soldering portion 3 (the electrode 9 on the printed circuit board 2) in the inspection window L is set. A masking process is performed to replace the area excluding the area with low-luminance pixels (hatched lines in FIG. 7). This is to prevent the pixel brightness value around the soldering section 3 from affecting the process in the brightness smoothing process described later. That is, the result of the brightness smoothing process differs between the case where the periphery of the soldering portion 3 is a dark base material and the case where the wiring pattern is a relatively bright one. In the above image, lead 1
The central region N of the soldering portion 3 where the tip of the soldering portion 1 is exposed (see FIG. 2) has a low luminance region because there is almost no reflected light upward.

In step 103, a brightness smoothing process for smoothing the brightness of each part of the masked soldered portion image is performed. This luminance smoothing process is performed by, for example, a moving average method. The moving average method will be described with reference to FIG.
This is sequentially performed for all the pixels in the soldered portion image while replacing the luminance value of No. 4 with the average value of the luminance values of the eight pixels P0 to P3 and P5 to P8 around it. Note that the average of the luminance values is 8 in a 3 × 3 pixel area as described above.
24 pixels in 5 × 5 pixel area
It can also be taken from the number of neighboring pixels. Such luminance smoothing processing is repeated about three times. The entire image is blurred by the smoothing process, and a narrow high-luminance portion in the outer peripheral boundary region of the soldering portion 3 is blurred, so that the influence on the luminance histogram is reduced.

In the following step 104, a luminance histogram is created for the image subjected to the luminance smoothing process.
This luminance histogram is obtained by taking the luminance on the horizontal axis and the number of pixels on the vertical axis. If the luminance histogram has severe irregularities, it is advisable to average the neighbors at three points before and after. Step 10
In 5, the defective soldering is determined based on whether or not the luminance value indicating the highest peak in the luminance histogram (that is, having the largest number of pixels) is equal to or less than a predetermined value. Here, "Solder too low",
FIGS. 9 to 11 show examples of the luminance histogram for each of the images “perforated” and “excessive solder”. In FIG. 9, a solid line x is a luminance histogram of a normal soldering portion, a broken line y is a normal limit, and a dashed line z is "low soldering". Looking at the luminance value indicating the highest peak in the luminance histogram, the luminance value exceeds 200 in the normal and normal limits. On the other hand, when “solder is too low”, the luminance value indicating the highest peak in the luminance histogram falls to 150 or less. Note that “no solder” is also included in “insufficient solder”.

FIG. 1 shows a luminance histogram of “perforated”
At 0, the solid line x is a luminance histogram of a normal soldered portion, the broken line y is a medium “perforated”, and the chain line z is a large “perforated”. In this case as well, the luminance value indicating the highest peak in the luminance histogram exceeds 200 for a normal one as shown by a solid line x, whereas when a large "hole" appears, the luminance value indicating the peak becomes It has dropped to nearly 100. However, in the case of a medium “perforation”, the luminance value indicating the peak is 200 or more. Therefore, in order to determine this, it is necessary to binarize an image, which will be described later.

In FIG. 11 showing "excessive soldering", the luminance value indicating the highest peak in the luminance histogram is represented by a solid line x
As shown in the above, while the number of normal ones exceeds 200,
At the normal limit indicated by the dashed line y, the luminance value indicating the peak is between 150 and 200. When “excessive soldering” occurs, the luminance value indicating the peak becomes 1 as indicated by a chain line z.
It drops to about 50. Therefore, the judgment luminance value is set to 1
If it is set to 60, "low solder", large "hole",
"Excessive soldering" can be reliably eliminated as poor soldering.

In step 106, the above-mentioned step 105
In order to determine a medium “perforation” that could not be determined in step, the image subjected to the luminance smoothing process in step 103 is binarized. In the binarization, the binarization threshold is set to a value P (<1) times the luminance value indicating the highest peak in the luminance histogram. P is, for example, 0.8. In step 107, a smaller window M similar in shape to the electrode 9 (that is, the soldered portion 3) is set in the inspection window L (FIG. 7), and the lowering of the image binarized by the binarization threshold is performed. When the luminance area enters the window M or approaches the window M by a certain amount or more, it is determined that the soldering is defective due to “perforation”. According to this, it is also possible to determine “insufficient solder”. The diameter of the window M is, for example, about 60% of the electrode diameter.

In the above-described embodiment, the determination of "insufficient solder" and "perforation" may not be performed on the luminance histogram, but may be performed only on the binarized image.

[0022]

As described above, according to the soldering inspection apparatus of the present invention, various soldering defects can be easily and reliably inspected as solder defects by the same processing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a soldering inspection device.

FIG. 2 is a vertical sectional view of a normal soldering portion.

FIG. 3 is a vertical cross-sectional view of a soldering portion of “insufficient solder”.

FIG. 4 is a vertical sectional view of a “perforated” soldered portion.

FIG. 5 is a vertical sectional view of a soldering portion of “excessive soldering”.

FIG. 6 is a flowchart illustrating an image processing procedure in the data processing apparatus.

FIG. 7 is a photographed image of a soldering portion.

FIG. 8 is an explanatory diagram of a luminance smoothing process.

FIG. 9 is a luminance histogram of “insufficient solder”.

FIG. 10 is a luminance histogram of “perforated”.

FIG. 11 is a luminance histogram of “excessive soldering”.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Discrete parts, 2 ... Printed circuit board, 3 ... Soldering part, 6 ... Data processing device, 61 ... Image processing part, 8 ...
Imaging device, 9 ... electrodes.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H05K 3/34 512 G06F 15/62 405A (72) Inventor Keiichi Watanabe 41-1, Chuku-ji, Yokomichi, Nagakute-cho, Aichi-gun, Aichi-pref. Inside Toyota Central R & D Laboratories Co., Ltd. (72) Inventor Tomohiro Arakawa 100 Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture Inside Toyota Auto Body Co., Ltd. (72) Inventor Yutaka 100 Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture Toyota Auto Body Stock In company

Claims (1)

[Claims] An imaging unit for obtaining an image of a predetermined area on a substrate including an electrode to be soldered; a luminance histogram creating unit for creating a luminance histogram of the image obtained by the imaging unit; A soldering inspection device comprising: a determination unit configured to determine a solder failure when the indicated brightness value is equal to or less than a predetermined value.