JPS61243303A - Visual inspection system for mounted substrate - Google Patents

Abstract

PURPOSE:To accurately detect the mounting position of a part to be mounted to a surface by using such illuminating means as to image the profile portion of a part mounted to a substrate in high brightness as compared with the other portion and detecting the position of the highly bright portion. CONSTITUTION:A parallel light beam is projected on a substrate with an inclination and the illumination of the light beam is restricted to a specific direction to the utmost when the substrate is viewed from above. By adopting such an illumination system, only the light beam projected on the edge portion of a chip part 10 is inputted to a TV camera. In result, the output of the TV camera 21 has an image with a high level of brightness only in the portion shown by a thick full line in the accompanying drawing. By detecting the position of the highly bright portion, the mounting position or attitude of the part on the substrate is recognized.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an electronic component mounted on a printed circuit board.

In particular, the present invention relates to improvements in visual inspection equipment for inspecting the mounting position accuracy of surface-mounted components such as square chip components and flat pack ICs.

(Conventional technology and its problems) The density of component mounting on printed circuit boards has recently become higher and higher, and the mounting format has changed from the conventional lead insertion format to chip components and crack pack type. I
There is a strong tendency to shift to an imposition format using C or the like. By the way, in general, an automatic lead component insertion machine can easily detect whether or not there is a 9-sided insertion error when inserting a component, whereas an automatic 9-sided component mounting machine can detect a shift in the mounting position immediately after mounting the component.

Alternatively, it is difficult to detect that an abnormality has occurred in the mounting position. For this reason, after mounting a nine-sided component, an external appearance inspection of the mounting position is usually performed using visual inspection or the like, and the need for this is becoming stronger as boards become more densely packed.

As described above, visual inspection not only causes extreme fatigue to workers, but also tends to lead to frequent operational errors, so efforts have been made to mechanize this inspection. One example is a video comparator-type chip component mounting board appearance inspection apparatus shown in FIG. This device uses two sets of illuminators 23 and two TV cameras, one of which 21-a inputs the image of the good board 1-a, and the other 21-b inputs the image of the board 1-a to be inspected at the same position. After inputting the two images, the comparator 25 examines the difference between these two images.

As a result, if there is a component mounting error on the board to be inspected, the difference in the image level for that part will become noticeable, and by displaying this on a TV monitor (not shown), visual inspection can be easily performed, or signal Processing circuit (not shown)
Visual inspection can be automated by outputting to the outside via etc. In addition, if the field of view of the TV camera is narrow, the inspection can be continued while moving the board by a constant value using an xy table 30 or the like (・oHowever, this device had the following drawbacks.

(1) Depending on the type of chip component, it may not be possible to obtain a visual contrast between the background substrate and the chip component, making it difficult to detect positional deviation.

(2) The standard for mounting positional deviation is a good board, and it is difficult to require perfection from this, so there is a limit to the accuracy of detecting positional deviation.

(3) It is necessary to accurately match the field of view size, relative position, and posture of the two TV cameras.

Adjustment is difficult.

(Objective) The present invention eliminates these drawbacks and provides a recognition method capable of accurately detecting the mounting position of a nine-sided component regardless of the state of the board.

At the same time, another object of the present invention is to improve the accuracy of detecting deviation in one position by providing a standard for detecting deviation in mounting position of a nine-sided component from the board mounting design pattern itself.

(Example) Before explaining the basic principle of the present invention, let us first explain the third reason why it is difficult to recognize the position of surface-mounted parts in the above method depending on the conditions.
This will be explained using FIGS. 4 and 5. FIG. 3 shows a model of the imaging part, where l is a board, 10 is a surface-mounted component mounted on the board, 21 is a TV camera, and 22
Reference numeral 23 indicates a magnifying lens for a camera, and 23 indicates an illuminator, such as a ring-shaped light. On the other hand, FIG. 4 shows a model of a square chip component, which is an example of a surface-mounted component.
) shows the top surface, (b) shows the side surface, and (c) shows the back surface (
・Ru. In the figure, 11 is a ceramic base material, and 12
is the main body.

Further, 13 is a metallic electrode portion. Such chip components are mounted on a substrate with either the top surface (a) or the back surface (C) facing upward depending on the conditions. Next, FIG. 5 shows the video signal level when such a chip component or the board itself is imaged with a TV camera in the state shown in FIG. 3. The horizontal axis in FIG. 5 represents the aperture of the lens, or in other words, the brightness of the object as seen from the TV camera. In FIG. 5, C indicates a chip component. C
1 is a ceramic part and is white, so the video signal level is very high (... However, the main body of the chip part comes in various colors depending on the part, for example, light brown is C2, black is C1. There is a large difference in level.Also, as shown by the shaded area C8, the level variation in the electrode part is very wide (.This is because the electrode part has a somewhat specular reflection characteristic.

This is because the surface is not flat. Furthermore, as shown in B, the background substrate also shows various levels depending on the location. For example, B is a dark green resisted base material, B2 is a solder plated land part IB, which is a resisted copper pattern part, and B4 is a copper plated land part, although the level is low. The level becomes higher.

In this way, the chip component that is the detection target and the board part that is the background overlap at the video level (・), so it may be difficult to identify them using a black and white image.For example, the ceramic part of the chip component may be on the upper side. When mounted like this, the presence or absence and positional deviation can be easily recognized, whereas when a light brown chip component is mounted on a copper-plated land, the difference in the image level between the two is small, so the presence or absence and positional deviation can be easily recognized. In order to solve this problem, it is necessary to create some kind of difference between the image of the chip component itself and the board part, so that the position of the chip component can be clearly recognized. Must be.

FIG. 6 shows the principle of the present invention to make this possible.

This will be explained with reference to FIGS. 7 and 8. FIG. 6 shows that the illumination direction when taking pictures and viewing the board from above is limited to a specific direction as much as possible. By adopting such an illumination method, only the light beam that illuminates the edge portion of the chip component 10 is input to the TV camera, as shown in the state diagram in FIG. As a result, the TV camera outputs an image with a high luminance level only in the portion indicated by the thick black line in FIG. In FIG. 8, when the illumination direction is only in the X direction, the brightness level of the thick solid black line is high, and if the illuminator is further set in the X direction, the brightness level of the thick black broken line is also high. This brightness level corresponds to the vicinity of the upper limit of the variation range of C0 in FIG. 5, so it can be clearly distinguished from the background portion of the substrate. In addition, as shown in FIG. 8(b), when the chip component 10 is inclined with respect to the xy axis.

This is usually a mounting error and can be easily recognized because the high brightness level portion does not occur. Needless to say, if such a chip mounting state is included in the board layout design, an additional illuminator may be installed in the direction to detect this state.

If you use the above principle, as shown in Figure 1.

It is possible to realize an external appearance inspection device using just one W camera 21 without using a standard non-defective board. 29 is a signal processing device that can store the mounting position and type of components.Of course, in the actual device, it also controls the movement of the xy table 30 and loads/unloads the board.

Alternatively, the pre-inspection work, such as linking with a component mounting machine, may be systemically complex, but this is outside the scope of the present invention and will not be described here.

In the inspection apparatus having such a configuration, the mounting state of the chip components can be recognized using nine different techniques. For example, FIG. 9 shows a method using an exploratory algorithm. In (a) P.

is the mounting center position of the component, and in this case, the outline position of the component should be in the state shown by the broken line 41.

Further, a broken line 42 indicates a limit position beyond which the external position of the component must not be exceeded. These pieces of information are stored in advance in the signal processing device 29 in FIG. 1, and are sequentially transmitted to the image processing device 28 in accordance with the inspection process. In this case, if the edge of the chip component is actually at the position indicated by the thick black line 15, then the position can be recognized from FIG. 9(b) (
This can be done by following the procedure shown in d). First, as shown in (b), a slit-shaped window 40 is set at a location corresponding to the left end of the limit position 42. Unless a high brightness portion is detected within this window 40, the window is sequentially moved to the right in the figure.

If this movement reaches the right end of the limit position without detecting a high-brightness portion, it is determined that the chip component is in an abnormal mounting state. However, in the case of Figure 9, detection is performed in state (c),
It is recognized that the mounting position of the chip component in the X direction is within the permissible range. At this stage, the window is moved in the X direction or enlarged in the vertical direction as shown in Figure 1. This movement or enlargement is performed until no increase in the high brightness portion within the window is recognized, and ends in the state of (d). As a result, the position of the chip component in the X+Y direction is recognized, and it is determined whether this is within the allowable range. Depending on the case, there may be only one window (・.

FIG. 10 is an example of another recognition method, in which window portions 40a to 40 have a plurality of meshes corresponding to each vertex of the limit position.
40d, and the positional deviation of the chip component is recognized by measuring the position of the high brightness portion 15 within each window or from the degree of correlation of the high brightness portion patterns within each window. However, there may be cases where two or one windows are sufficient. Figure 11 is an example of yet another recognition method, and is intended for the case where the outer edge of the tip part can be obtained with a high brightness of 15 in all four directions. . That is, the position of the high-brightness portion within the four slits 0 set corresponding to the limit position in the x+y direction is checked, and the position of the chip component in the X or X direction is recognized. In this case, there may be two slit windows, for example 40-a and 40-c.

Although the present invention has been described above in detail with respect to square chip components, the concept itself can be applied to other types of surface-mounted components. Furthermore, the present invention can be implemented regardless of the type of illuminator, and it is within the scope of the present invention to use optical filters to easily distinguish high-brightness areas from other areas. Include it in the song. Furthermore, this method always includes only one target part within the field of view of the TV image.

Yes (・ means any method in which the field of view is expanded to include multiple target parts within one field of view.

It is possible to apply the present invention. Of course, the principles of the present invention may also be applied to the video comparator type inspection device shown in Fig. 2.

(Effects) As described above, according to the present invention, the position of the target component within the board can be identified very clearly, which is extremely effective in improving the performance of the visual inspection apparatus for mounted boards.

[Brief explanation of drawings]

FIG. 1 is a hardware configuration diagram of an embodiment of the present invention. FIG. 2 is a configuration diagram of a conventional appearance inspection device, and FIG. 3 is a diagram. 4 and 5 are diagrams explaining the limits of the performance of the conventional device; FIGS. 6, 7, and 8 are diagrams explaining the details of the present invention; FIGS. 9, 10, and 11. The figure is an explanatory diagram of a recognition method using the principle of the present invention. l: Board, 2]: TV camera, 23: Illuminator, 2
8: Image processing device, 29: Signal processing device. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] By employing illumination means that images the contour part of a component mounted on a board with higher brightness than other parts, and by detecting the position of this high-brightness part, An external appearance inspection method for a mounted board, which is characterized by recognizing the mounting position or orientation of the board.