KR0152885B1 - Classifying method of soldering for pcb - Google Patents

Abstract

The present invention relates to a method for classifying solder states of a printed circuit board. In the related art, a three-stage color fluorescence illumination method is a method in which an image is obtained by simultaneously irradiating an object with three stages of RGB circular fluorescence illumination in three layers. It is suitable as an economical ring-shaped light source, but as the use time elapses, the light source shows uneven illumination and concentration of light in the inspection area decreases, so it is difficult to accurately divide the RGB area because different color components are mixed in the acquired image. There is a problem that reduces the reliability of the. Therefore, in the present invention, the LED is used as an illumination source, so that the linearity of the light is excellent, so that the concentration of the soldering area can be increased, and the three-level LED lighting can be maintained to maintain uniform intensity according to the use time. First, only the location information of the inspection area is extracted from the three-stage image, and then the inspection time can be reduced by extracting the features of the first and second stages.

Description

Method of classifying solder state of printed circuit board.

1 is an overall configuration diagram of a conventional soldering inspection device.

2 is a reflection characteristic of the fluorescent lighting apparatus and the solder in FIG.

3 is an image pattern diagram obtained using the three-stage color illumination of FIG.

4 is a process chart for the solder classification method of the conventional solder inspection apparatus.

5 is a block diagram of a soldering inspection device of the present invention.

6 is a configuration diagram of the lighting apparatus in FIG.

7 shows the type and type of solder to be tested.

8 is a reflection characteristic of the solder with respect to the illumination angle.

9 is a process diagram for the soldering state classification method of the printed circuit board of the present invention.

10 is a three-stage illumination image of a lead, which is normal and insufficient.

11 is an image showing the result of soldering region extraction in FIG.

12 is an image diagram for each classification type.

* Explanation of symbols for main parts of the drawings

18: image acquisition unit 18: camera

19: lighting device 20: lighting controller

21: host 22: table

23: substrate 24: parts

24a: Lead 24b: Solder

25c: pad

The present invention is to automatically check the soldering state of the surface-mounted PCB (PCB) by using an image, in particular, input three images using a ring-shaped three-stage LED (LED) with different irradiation angles and the input image It relates to a soldering state classification method of a printed circuit board to classify the soldering state from.

With the development of surface mount technology, many printed circuit board components have been rapidly made high density and surface mount.

However, the parts inspection for these parts is becoming more difficult due to the densification of the parts themselves, and the inspections performed by humans also show a lot of defects, so that in the manufacturing field, it is possible to substitute for humans and also to perform fast processing. There is a growing demand for visual inspection devices.

The inspection target parts are QFP, SOP, square chip, PLCC, SOJ, etc. The soldering inspection items are soldering presence, soldering excess, soldering shortage and bridge.

Soldering test of the printed board is largely affected by the lighting structure and the illumination source of the inspection apparatus as the size of the solder to be inspected is small, the reflection of the surface is large, and three-dimensional image analysis is required.

Therefore, the overall configuration of the soldering time inspection apparatus that can be processed quickly on behalf of humans in the manufacturing field is as shown in FIG. 1, the table 6 on which the substrate to be inspected is placed, and the director and inspection of the entire system. A host (5) for performing a light, a fluorescent lighting device (3) for irradiating an RGB three-color ring-shaped illumination onto a substrate on the table (6) in multiple layers in multiple angles, and obtaining one image; According to the control output of (5), the lighting control unit 4 for simultaneously turning on or off the illumination of the three stages of the fluorescent lighting device 3, and the substrate according to the lighting control of the lighting control unit 4 It consists of a camera 2 for reading an image, and an image acquisition unit 1 for acquiring an image of a soldered part of the substrate through the camera 2.

Looking at the prior art configured as described above in detail.

When the inspection target substrate 7 on which the component 9 is mounted is placed on the table 6 as shown in FIG. 2, the component 9 is soldered onto the substrate 7. In order to inspect the soldering 8 part, a control signal for turning on the lighting from the host 5 to the lighting control unit 4 is output.

The lighting control unit 4 controls the fluorescent lighting device 3 to turn on three color fluorescent lights 3a, 3b, 3c at the same time.

Here, the three-stage color fluorescent light (3a) (3b) (3c) has an annular shape, the bottom light (3a) is red (Read), the middle light (3b) is green ( Green), the topmost light (3c) consists of components of blue, and the image obtained by irradiating R, G, and B lights simultaneously on the object to be examined has different colors reflected depending on the curvature of the object surface. This three-stage color fluorescence illumination method uses this principle.

Then, the camera 2 reads the image reflected when the fluorescent lighting device 3 simultaneously irradiates the soldering 8 portion of the substrate 7 under the control of the host 5 and provides the image to the image acquisition unit 1. .

That is, when simultaneously irradiating the soldered portion as shown in FIG. 3 (a), it is reflected and the image as shown in FIG. 3 (b) is acquired by the image acquisition unit 1 through the camera 2.

At this time, the acquired image is divided into three areas of R, G, and B. In order to separate the three areas, each area is extracted according to the hue value. Extracts only the red component from, selects only the value above the predetermined value, and calculates the center of the red area if it is above a certain size.

In the calculation method for the center of the region, if you draw an outer rectangle contacting the outside of the extracted region, the radius between the contact portion and the vertex becomes a radius and the center of the region can be known using the contact portion.

In this way, if the soldering area is divided into three areas of R, G, and B, as shown in (c) to (d) in FIG. 3, soldering is normal, insufficient lead, excessive lead, etc. according to the area and shape of the area. Can be classified as.

Referring to the above process again based on FIG. 4, first, when the three-stage color lights 3a0 (3b) and 3c are turned on at the same time, the camera 2 is reflected by the soldering 8 portion of the substrate 7. When an image is input to the image acquisition unit 1 through the input image, the R, G, and B regions are separated from the input image, and the size and shape of each separated region are extracted to classify the soldering state.

However, in the conventional technology as described above, the three-stage color fluorescence illumination method is a method of obtaining an image by irradiating an object with three layers of fluorescence illumination of R, G and B annular layers at the same time. Although it is suitable as a light source of the light source, the light source shows uneven illumination as the use time elapses and the concentration of light in the inspection area decreases, so it is difficult to accurately divide the R, G, and B areas because different color components are mixed in the acquired image. There is a problem that reduces the reliability of the.

Accordingly, an object of the present invention is to use a LED light source for the illumination source is excellent in the straightness of the light to increase the concentration in the soldering area and the soldering state of the printed circuit board to maintain a uniform intensity according to the use time To provide a classification method.

Another object of the present invention is to provide a soldering state classification method of a printed circuit board to reduce inspection time by extracting only the location information of the inspection area from the three-stage image and extracting the features of the first and second stages. Is in.

The present invention for achieving the above object is a soldering region extraction step of extracting the soldering region with respect to the image input when the three-stage lighting on (ON) when the board input subject to inspection; A feature value extraction step of extracting feature values by using the average brightness of the first stage and the third stage and the number of highlights of the first stage and the second stage when the extraction of the soldering region is completed; A solder classification step is used to classify the solder state using the feature values obtained in the above step.

The apparatus for performing the method consisting of the above steps includes a table 22 on which a board to be inspected is placed as shown in FIG. 5, a host 21 for administering and inspecting the entire system, and the table. (22) The lighting device 19 to obtain a single image by irradiating a three-stage annular LED (LED) light on multiple boards in multiple angles on the board, and the three-stage lighting on the lighting device (19) Lighting controller 20 alternately turning on or off, a camera 18 reading an image of a substrate according to the lighting control of the lighting controller 20, and the camera 18 It consists of an image acquisition part 17 which acquires the solder part image of a board | substrate through.

The operation and effect of the present invention configured as described above will be described in detail with reference to FIGS. 5 to 12 as follows.

When the user puts the board to be examined on the table 22, the lighting controller 20 outputs a signal for turning on the lighting to the lighting controller 20. ) Outputs a driving signal for turning on the three-level LED lighting 19a.

The reason for using the LED lighting is because it is excellent in the straightness of the light can increase the concentration in the soldering area, it is possible to maintain the intensity according to the use time.

Since the surface of the solder has almost no diffuse reflection property and most of the total reflection property, the reflection intensity varies depending on the shape of the surface when irradiated with varying the incident angle of illumination.

In this case, in FIG. 8, the solid line is the angle of incidence 41 of the illumination, the direction indicated by the dotted line is the visual direction 42 of the camera, and the thick line represents the tangential direction 40 of the surface. In the reflection characteristic, the normal vector is divided into the incident angle and the reflected angle of light.

Therefore, the portion a close to the lead 24a has a normal vector of about 45 degrees, so it is brightly reflected only when the light is irradiated at an angle close to the horizontal, and the portion c close to the pad 24b has a normal vector close to the vertical. The light is reflected most brightly when irradiated at an angle close to the vertical.

As a result, the angles of the LED lighting of the third, second, and first stages of FIG. 8 are 25 degrees, 45 degrees, and 75 degrees.

As the three-stage LED lighting 19a of the lighting device 19 is turned on, the image acquisition unit 17 receives an image through the camera 18.

When the image is input through the camera 18, the host 21 accurately finds the soldering part through binarization and projection, which is the lead 24a and the pad 24b as shown in FIG. To find the part in between.

When using the three-stage LED lighting (19a) as described above, as shown in Fig. 7 (a) is normal and without solder as shown in (b), that is, both the lead (24a) and the pad (24b) is total reflection Since the dark part does not appear due to the characteristics close to, it is impossible to divide the area, such as the rightmost lead in FIG. 12 (b), and the lack of soldering as in (c), that is, in FIG. Likewise, the soldered portions 24c between the leads 24a and the pads 24b are darkened due to their reflection characteristics and separated from each other.

If it is possible to separate from the image obtained through the binarization and projection process, it is a normal or poor soldering state and extract the soldering region as shown in FIG. 11, and if it is impossible to separate, the host 21 again the lighting controller 20 ) To turn on the two-stage LED lighting (19b) of the lighting device (19).

Accordingly, the soldered region as shown in FIG. 12 (d) is extracted through binarization and projection by receiving the image by the two-level LED lighting 19b.

As described above, in the case of normal and poor soldering state after the extraction of the soldering region, the second stage LED lighting 19 is turned on by the control of the host 21 to extract a specific value, and the image of the stage is input and the first stage LED is again. After the illumination 19c is turned on and the image is input, the average brightness value of the first and third stage LED lights 19c and 19a and the number of highlights of the first and second stage LED lights 19c and 19b are used. Extract feature values.

If there is no soldering, the first stage LED lighting 19c is immediately turned on and the image input at that time is accepted, and the average brightness values of the first and third stage LED lights 19c and 19a and 1, The feature values are extracted using four types of highlights of the two-stage LED lights 19c and 19b, which can be expressed by the following equation.

Where T is the threshold of the highlight brightness value.

As described above, the feature value is a quantitative representation of the type of solder. The condition of the feature value should be quick to calculate, and the feature values of the objects belonging to the same class should have similar values. There should be a lot of difference.

In addition, using multiple feature values enables more reliable classification.

Average brightness value in the first stage k1 appears very bright only in normal and dark in case of no soldering and poor soldering.

3 levels of average brightness k2 appears dark in normal, while lack of soldering and no soldering are relatively high.

In case of electric phase, the part near the lead 24a is the brightest in the first stage, the part in the third stage is the darkest, and the highlight in the first stage. k3 appears only in the normal case, two-stage highlight k4 appears only when it is normal and when there is a lack of soldering.

Eventually, the solder state is classified according to these characteristics.

Referring to the operation as described above based on the flow chart of FIG. 9, when the board is first placed on the table 22, the third stage LED lighting 19a of the lighting device 19 is turned on and totally reflected through the board. The camera 18 transmits the image to the image acquisition unit 17.

Then, the host 21 performs binarization and projection on the transmitted image to check whether the lead 24a and the pad 24b can be separated. However, after turning on the LED light (19b) and inputting the video at that time, and turning on the 1st LED lighting (19c) again and receiving the video at that time, the average brightness value of the 1st and 3rd stages and the number of highlights of the 1st and 2nd stages are displayed. Calculate the extracted feature value and classify the soldering state by the extracted feature value.

If it is impossible to separate the lead 24a and the pad 24b from the above, this is a case where there is no soldering. Then, the second stage LED illumination 19b is turned on again to extract the soldering region, and then binarization and projection are performed on the input image. Extract the area.

After the 1st stage LED lighting (19c) is turned on and the image is received, the average brightness value of 1st and 3rd stage and the number of highlights of 1st and 3rd stage are calculated, and the feature value is extracted. Classify

As described above, when the soldering region extraction and the feature value extraction are completed, the solder state is classified by the extracted feature values.

As described in detail above, the present invention is excellent in the straightness of the light can increase the concentration in the soldering area and using one LED light source of three stages (LED) light source that can maintain a uniform intensity according to the use time It is effective to extract the location information of the inspection area from the image when it is turned on, and to perform feature extraction with 3 levels of LED lighting, and to accurately classify the lead state according to the feature extraction.

Claims (5)

A soldering region extraction step of extracting a soldering region with respect to the image input when the 3-stage lighting is turned on when the board to be inspected is input; A feature value extraction step of extracting feature values by using the average brightness of the first stage lighting and the third stage lighting and the number of highlights of the first stage lighting and the second stage lighting when the extraction of the soldering region is completed; Soldering classification method of the printed circuit board, characterized in that consisting of a soldering classification step for classifying the soldering state by using the feature value obtained in the step. The method of claim 1, wherein the step of extracting the soldering region comprises: a first step of checking whether the lead and the pad can be separated after performing binarization and projection on the image input when the three-stage lighting is on; and if the separation is possible in the first step, A second process of extracting a soldering region at that time by determining that it is normal and poor in soldering; and a third process of receiving an image after turning on two-stage lighting by determining that there is no soldering if separation in the first process is impossible And a fourth step of extracting a soldering area by performing binarization and projection on the image received in the third step. The method of claim 1, wherein the extracting of the feature value comprises inputting the image of the second stage light immediately after turning on the second stage light and receiving the image of the same stage after the first stage lighting is turned on if the lead and the pad can be separated in the soldering region extraction step. A first process, a second process of calculating an average brightness value of the first and third stage lights, a third process of calculating the number of highlights of the first and second stage lights, and the second and third processes And a fourth process of calculating a feature value using the average brightness value and the number of highlights calculated in the above. The method of claim 1, wherein the illumination uses three stages of annular LED lighting. The method of claim 1, wherein the three-stage, two-stage, and one-stage illuminations are composed of 25 degrees, 45 degrees, and 75 degrees, respectively.