JPH02247510A - Appearance inspection device - Google Patents

Abstract

PURPOSE:To detect the height defect of an object to be inspected regardless of the shape of the reference surface thereof by providing a photographing device, an extraction means, a characteristic quantity comparison means and a defect decision means. CONSTITUTION:The photographing device 1 photographs the object to be inspected 2 from plural distances (a1) - (a3). Besides, it is no matter whether the photographing device 1 obtains either a one-dimensional image or a two-dimensional image. The characteristic quantity extraction means 3 extracts the characteristic quantity of the brightness distribution of a photographed image, for example, peak height, peak width, peak area in the brightness distribution in a direction of crossing the object to be inspected, or the one that the peak height is divided by the peak width or the like. The characteristic quantity comparison means 4 compares the characteristic quantities on the different distances. The height defect decision means 5 decides whether a defect exists on the height of the object to be inspected or not on the basis of the compared result of the characteristic quantities. Then, by utilizing the condition of focusing, the height defect of the object to be inspected is detected. Therefore, the reference surface is fixed in accordance with the distance of the photographing device and the height defect is detected regardless of the shape of the reference surface of the object to be inspected.

Description

[Detailed Description of the Invention] [Summary] This invention relates to an appearance inspection device that detects height defects of an object to be inspected by using the degree of focus, and particularly for linear objects such as bonding wires installed between two points. Regarding visual inspection equipment suitable for visual inspection of objects, the purpose is to be able to detect height defects of objects to be inspected regardless of the shape of the reference surface for the objects to be inspected. A photographing device for photographing an object, a feature m extraction means for extracting a feature of the luminance distribution of a photographed image, a feature comparison means for comparing the feature for different distances to the object, and a comparison result of the feature. and height defect determination means for determining whether or not there is a defect in the height of the inspection object.

[Industrial Field of Application] The present invention relates to an appearance inspection device that detects height defects in an object to be inspected by using the degree of focus, and particularly relates to a visual inspection device that detects height defects in an object to be inspected by using the degree of focus, and particularly for detecting a linear object such as a bonding wire installed between two points. The present invention relates to a visual inspection device suitable for visual inspection.

[Prior art] Fig. 7 shows a pad 12 and a lead 14 on an IC chip IO.
A state in which the bonding wire 16 is connected between the two is shown. The shape of the bonding wire 16 is normally as shown in FIG. 9A. However, due to an abnormality in the clamper of the wire bonder, the bonding wire 16 may become loose and become too high as shown in FIG. 9A, or the center portion of the bonding wire 16 may droop as shown in FIG.
As shown in Figure D, the bonding wire 16 may become too tensioned. Bonding wire +6 has a diameter of 25
Since the bonding wire 16 is extremely thin at ~30 μ-, if a thermosetting resin is supplied and molded to such a bonded wire, there is a possibility that the bonding wire 16 that is too loose may come into contact with other bonding wires 16 or hang down. Bonding wire! 6 may come into contact with the frame, or the bonding wire 16 that is too stretched may break. Although these defects can be detected by electrical testing of the circuit, geometric defects in the bonding wire cannot be identified. Moreover, since this shape defect may occur repeatedly due to the same cause, it is necessary to detect it by visual inspection immediately after bonding.

Here, the optical cutting method is used for visual inspection of printed wiring. As shown in FIG. 8, this method irradiates a slit-shaped light beam from an oblique direction at an angle θ to the substrate 20 on which the printed wiring 18 is formed.
0. An optical cutting line is formed on the printed wiring 18, and when this optical cutting line is viewed from directly above, the optical cutting line on the printed wiring I8 is separated from the optical cutting line on the board 20 according to the height h of the printed wiring 18. This method takes advantage of the fact that there is a shift by a distance d,
The height h is determined as h-d4anθ. This optical cutting method can be used when the reference surface is substantially flat like the substrate 20.

[Problems to be Solved by the Invention] However, as shown in FIG. 9A, the bonding wire I6
In this case, the height between the chip 10 and the leads 14, which is the reference plane, changes irregularly, and the adhesive 21, etc., which is irregularly shaped for fixing the chip 10 to the lead frame, also changes to the reference plane. Therefore, the appearance of the bonding wire 16 cannot be inspected using the optical cutting method.

SUMMARY OF THE INVENTION In view of these problems, an object of the present invention is to provide an appearance inspection apparatus that can detect height defects of an object to be inspected regardless of the shape of a reference surface for the object.

[Means to solve the problem] FIG. 1 is a block diagram showing the basic configuration of the present invention.

In the figure, 1 is a photographing device, and a plurality of object distances, e.g.
The inspection object 2 is photographed at lx at and as. This photographing device may be one that obtains either a one-dimensional image or a two-dimensional image, or may be one that scans the object to be inspected with a light beam to obtain the brightness of each point. Also,
Shooting at multiple object distances may be performed simultaneously using multiple image sensors, etc., or may be performed sequentially by using a single image sensor, etc. and moving the photographic lens or image sensor, etc. Good too.

Reference numeral 3 is a characteristic oil volcanic mountain means, which measures the characteristic amount of the brightness distribution of the photographed image, for example, the peak height, peak width, peak area, or peak height divided by the peak width in the brightness distribution in the direction across the inspection object. Extract the things that have been done.

Reference numeral 4 denotes a feature comparison means, which compares the feature quantities for different object distances.

Reference numeral 5 denotes a height defect determining means, which determines whether or not there is a defect in the height of the object to be inspected based on the comparison result of the feature amounts.

[Effect] This feature amount differs depending on the degree of in-focus. Therefore, by comparing feature quantities for different object distances, it is possible to detect height defects in the object to be inspected.

Furthermore, in the present invention, since the reference plane is determined by the object distance of the photographing device, height defects can be detected regardless of the shape of the reference plane on the side of the object to be inspected.

[Example code] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 2 shows the overall configuration of the visual inspection device. Bonded ICs as shown in FIG. 7 are arranged and placed at regular intervals on a transport device 22 that moves in the horizontal direction. The conveying device 22 is intermittently driven in steps at this constant interval. A photographing device 26 is disposed on the transport device 22 and has a ring-shaped illumination light 24 attached to the outer periphery of the lower surface.

An example of the configuration of this photographing device 26 is shown in FIG.

This optical system includes a photographing lens 261 facing the object to be inspected.
is arranged, an image sensor 262 is arranged directly above it, half mirrors 263 and 264 are arranged between the photographing lens 261 and the image sensor 262, and the half mirror 2
A mirror 265 is placed on the side of the mirror 63, and an image sensor 266 is placed directly above the mirror 265.
A mirror 267 is arranged on the side of 264, and the mirror 267
An image sensor 268 is arranged directly above the image sensor 268.

This half mirror 263 has a reflectance of 1/3 and a transmittance of 2/3.
3, and the half mirror 264 has a reflectance of 1/2 and a transmittance of 172.

In addition, images existing on the object planes Fl, F2, and F3 below the photographing lens 261 are most clearly formed in the captured images of the two-dimensional image sensors 262, 266, and 268, respectively. That is, the distances between the object planes F1, F2, and F3 and the principal point of the photographing lens 261 are respectively a1, a2, and
a3, the principal point of the photographing lens 261 and the image sensor 2
62,266,268 respectively.
s bl,b, and the focal length of the photographic lens 261 is f.
Then, the following formula holds true.

17a+ + l /b, = 1 / fl /a*
+l/bt=l/fl 7as+l/b,
= l /f Therefore, the images formed on the image sensors 262, 266, and 268 are such that the objects to be inspected are on the object planes Fl and F, respectively.
2. The closer to F3, the sharper the image.

The height of the bonding wire 16 with respect to the depth IO is I
Although it varies depending on the type of C, it is usually about 400 μ-, so the object plane P1. The distance between F2 and between the object planes F2 and F3 is also set to about 400 μm.

Image sensor 262.266.268 is driver 2
The luminance signals of each pixel are electrically scanned by a drive pulse supplied from 69, and are sequentially extracted from each pixel. , 272, and the A/
The luminance data is supplied to the D converters 28A, 128B, and 28C for digital conversion, and then written to addresses specified by the driver 269 of the image memories 30A, 30B, and 30C.

Here, a height defect determination method applied to the apparatus of this embodiment will be explained.

FIG. 4 shows an image taken by the image sensor. in fact,
For high-speed processing, all the bonding wires of the l chip are photographed, but to simplify the explanation, the explanation will focus on one bonding wire 16.

The brightness along line A-B in Fig. 4 is in focus (
In the case of (in-focus), as shown in Figure 5A, the peak width
becomes smaller, and the peak height B becomes larger. On the other hand, in the case of defocus (out of focus), as shown in FIG.
becomes smaller. Therefore, as a feature of this brightness distribution,
For example, in-focus ff1E defined by the following equation is used.

E=B/W Bonding wire using this in-focus amount E!
The normality/defect determination for the shape No. 6 is performed as follows. That is, for example, the in-focus jlE is determined for the luminance distribution along a line segment perpendicular to the ribboning wire 16 passing through each of the points P%Q in the fourth drawing. Bonding wire 16
When the shape is normal, Et>Et holds true at point P, and Et>Es holds true at point Q, as shown in FIG. 6A. However, if the bonding wire 16 is hanging down, Effi<El at point Q, as shown in FIG. 6B, and if the bonding wire 16 is too tensioned, at point P, as shown in FIG. 6C. E, <El. Therefore, Et>Et holds true at point P, and Et>Et holds true at point Q.
If s holds true, it is determined that the shape of the bonding wire 16 is normal, and if either of these conditions does not hold, it is determined that the shape of the bonding wire 16 is defective.

In FIG. 2, image memories 30A and 30B.

Among the luminance data written in 30C, the address of the pixel along the above-mentioned line segment passing through points P and Q shown in FIG. , 34C.

This line segment is set in advance in the control circuit 32 by operating the keyboard 36. Focus evaluation circuit 34A, 3
4B and 34C are in focus ff1E, respectively.
E, ,E, are determined and supplied to the defect determination circuit 38. The defect determination circuit 38 also has an in-focus t value corresponding to the position of the line segment when the shape of the bonding wire 16 is normal.
The magnitude relationship of aE is supplied from the control circuit 32.

This magnitude relationship is also set in advance in the control circuit 32 by operating the keyboard 36. The defect determination circuit 38 determines whether the bonding wire I6
Determine whether the shape is normal or defective, and determine whether the shape is defective or defective.
Outputs no signal. This signal is recorded together with the IC identification number, and is also used as a control signal for a defective product sorting device (not shown).

Note that the present invention includes various other modifications.

For example, the reflectance of the half mirrors 263 and 264 is not particularly limited, and the configuration may be such that the gains of the amplifiers 270 to 272 are adjusted according to the reflectance using a suitable one.

Further, the number of image sensors 262 is not particularly limited,
The configuration may be such that the object plane F is changed by moving the photographic lens 261 up and down using one image sensor.

Furthermore, it goes without saying that the object to be inspected is not limited to a linear object such as a bonding wire.

[Effects of the Invention] As explained above, according to the visual inspection device according to the present invention, height defects of the inspection target are detected using the degree of focus, so that the reference plane is set at the object distance of the photographing device. This has the excellent effect of being able to detect height defects regardless of the shape of the reference surface on the side of the object to be inspected, and greatly contributes to the automation of visual inspection of bonding wire shapes, etc.

Figure 5A is the A- shown in Figure 4 in the case of in-focus.
The brightness distribution diagram along line B, Figure 5B is the case of defocus, and the brightness distribution diagram shown in Figure 4 is A-[
The brightness distribution diagrams along the three lines, Figures 6A to 60, show the normal/normal shape of the bonding wire 16.
It is a defect determination explanatory diagram.

Fig. 7 is a perspective view of the main parts showing the IC wire bonding state, Fig. 8 is an explanatory diagram of height measurement using the conventional optical cutting method, and Fig. 9A
Figures 9-9D are diagrams showing various shapes of bonding wires.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention. 2 to 6C relate to one embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the external appearance inspection device, and FIG.
4 is a block diagram of the photographing device 26 shown in FIG. The focus evaluation circuit 36 is the keyboard 38, the defect determination circuit 261 is the photographic lens 262, 266, 268 is the image sensor 263, 26
4 is a half mirror; 265 and 267 are mirrors; FIG. 1; Structure diagram of the imaging device 26 shown in FIG. 2; FIG. 3; FIG. 4; Normal/defect determination explanatory diagram 6A
Figure 6B Figure 6C Shape of bonding wire

Claims (1)

[Scope of Claims] A photographing device (1) that photographs an inspection object (2) at a plurality of object distances (a_1, a_2, a_3), and a feature extracting means (1) that extracts a feature of a luminance distribution of a photographed image. 3), a feature amount comparison means (4) for comparing the feature amounts for different object distances, and a height for determining whether there is a defect in the height of the inspection object based on the comparison result of the feature amounts. A visual inspection device comprising: a defect determining means (5);