JPH04250347A - Inspecting device for bonding wire - Google Patents

Abstract

PURPOSE:To precisely inspect the configuration of a bonding ball by detecting a pad by the use of a bonding-wire inspecting device which automatically inspects the appearance of a bonding wire of an IC or the like. CONSTITUTION:A bonding-wire inspecting device in which at least that portion of a pad to which a bonding ball located at the end of a bonding wire is electrically connected serves as a subject 100 for inspection and which has an image pickup means 101, a light illuminating means 102, an image input means 103 and an image storage means 104, includes a window image generating means 105, a pad detecting means 106 and a ball form inspecting means 107. The contour of the pad is detected. The ball form inspecting means 107 detects the position of the bonding ball relative to that of the pad for detection.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding wire inspection apparatus for automatically inspecting the appearance of bonding wires for integrated circuits, etc.

[0002]In recent years, integrated circuits (ICs), large-scale integrated circuits (LSIs), etc. have been widely used, and as they have become finer and have higher integration densities, the use of bonding wires in ICs and LSIs has increased. It is becoming increasingly important to automatically visually inspect whether the electrical connections to the pads are properly made. In this visual inspection of the bonding wire, it is necessary to accurately detect the ball-shaped edge of the electrically connected portion of the tip of the bonding wire with the pad.

0003

2. Description of the Related Art FIG. 5 shows a configuration diagram of an example of a conventional bonding wire inspection device. In the figure, 1 is an IC chip,
A large number of bonding wires are connected to predetermined pads and mounted on the frame feeder 2, and thereby transported to a position directly below the imaging device 3. The surface of this IC chip 1 is irradiated with epi-light from a coaxial epi-illumination device 4 in a perpendicular direction. This is because the pad is made of metal and has a flat surface, and its light reflectance is extremely high.
The connection part of the tip of the bonding wire to the pad is ball-shaped (bonding ball), and since the cross-sectional shape of the bonding ball is approximately hemispherical,
When incident light is irradiated from a direction perpendicular to the IC chip surface,
This is to ensure that a large amount of reflected light from the pad is incident on the imaging device 3, while reflected light from the bonding ball is dispersed, so that only a small amount of reflected light is incident on the imaging device 3. As a result, the imaging device 3 images the pad brightly and the bonding ball darkly.

[0004] The output imaging signal of the imaging device 3 is input to an image input circuit 5, where it is converted into a digital signal of, for example, 256 gradations, and then stored in an image memory 6.

Furthermore, the above-mentioned digital signal is read out from the image memory 6, generated by the window image generation circuit 7 into a window image of the bonding ball and its vicinity, and stored in the image processing memory 8. The ball shape inspection circuit 9 performs second-order differentiation on the digital signal of the window image read from the image processing memory 8 to extract the shape of the bonding ball, calculates the area of the bonding ball from the data, and determines that the area is a predetermined area. When the value is less than the value, it is checked that the bonding wire is connected to the pad.

[0006]

However, since the conventional bonding wire inspection apparatus detects the shape of the bonding ball without detecting the position and shape of the bonding pad, it has the following problems. That is, the window image read out from the image processing memory 8 is shown in FIG. 6(A).
As shown in FIG. 2, if the bonding ball 11a at the tip of the bonding wire 11 made of gold, for example, partially protrudes from the pad 12 made of aluminum and extends to the insulating part (made of silicon dioxide, for example) 13 on the surface of the IC chip, , the brightness of the image on the line Yi is as shown in FIG. Due to interference, the brightness becomes intermediate.

For this reason, when the ball shape inspection circuit 9 performs second-order differentiation, the second-order differentiation output has a zero crossing point X1a at a position corresponding to an edge portion with a large change in brightness, as shown in FIG. A waveform having ˜X4a is obtained. In this case, the conventional device does not detect the position and shape of the pad 12, so X1a to X2a are detected by the bonding ball 1.
It is detected as an edge of 1a.

Further, as shown in the window image in FIG. In the case where the bonding balls 11b are formed on two pads 12, the brightness at the line Yi of the image sharply increases at the edge portion of the bonding ball 11b of the adjacent pad, as shown in FIG. Since the bonding ball 11b exists at the edge portion of the pad that should originally be connected, the brightness is dark.

For this reason, in the conventional device, when this image data is subjected to second-order differentiation in the ball shape inspection circuit 9, the second-order differentiation output becomes as shown in FIG. 7(C). Detected as the edge of the ball.

Therefore, in the case of FIG. 6, the conventional bonding wire inspection apparatus incorrectly detects the edge position X1a of the adjacent pad as the edge of the bonding ball 11a, and in the case of FIG.
Even if the edge of the pad can be detected, a problem arises in that it is not possible to detect that a part of the edge extends over the adjacent pad.

The present invention has been made in view of the above points, and
An object of the present invention is to provide a bonding wire inspection device that can accurately inspect the shape of a bonding ball by detecting pads.

0012

[Means for Solving the Problems] FIG. 1 shows a basic configuration diagram of a bonding wire inspection apparatus according to the present invention. In the same figure,
Reference numeral 100 is an object to be inspected, which has a pad electrically connected to a bonding ball at the tip of a bonding wire. 10
Reference numeral 1 denotes an imaging means that images the inspection object illuminated by the light irradiation means 102. Reference numeral 103 denotes an image input means, and 104 denotes an image storage means, which stores an image signal from the image input means 103, which is input based on the image signal from the image pickup means 101, in the image storage means 104.

The present invention provides an apparatus for inspecting bonding wires based on the image signal stored in the image storage means 104, in which the window image generation means 105 generates a window image signal from the image signal read out from the image storage means 104. and pad detection means 10 for detecting the outline of the pad based on the generated window image signal.
6, and a ball shape inspection means 107 for inspecting the shape of the bonding ball by detecting the relative positional relationship of the bonding ball with respect to the detection pad.

[0014]

[Operation] In the present invention, the position and shape of the pad are detected by detecting the outline of the pad by the pad detection means 106.
In step 07, it is possible to prevent the pad from being detected as the edge of the bonding ball, or to detect that the bonding ball is protruding into an adjacent pad.

[0015]

Embodiment FIG. 2 shows a configuration diagram of an embodiment of the present invention. In the figure, the same components as in FIGS. 1 and 5 are designated by the same reference numerals. In FIG. 2, a pad detection circuit 21 corresponds to the pad detection means 106, and a ball shape inspection circuit 22 corresponds to the ball shape inspection means 107.

The pad detection circuit 21 is configured to detect the shape and position of the pad by respectively detecting the vertical and horizontal contours of the pad based on the window image data read from the image processing memory 8. ing.

First, the operation of the pad detection circuit 21 during normal operation when the bonding ball is located only within the pad will be explained with reference to FIG. The window image based on the window image data stored in the image processing memory 8 is shown in FIG.
Assuming that the bonding ball 11c at the tip of the bonding wire 11 is located only within one pad 12 as shown in A), the brightness of the image on the line Yi at that time is as shown in FIG. 11c and bonding wire 11, and pad 12
It is the same as the conventional method in that the brightness is bright in the part shown in FIG.

Therefore, the brightness of the image is determined by the boundary between the pad 12 and the insulating portion 13, and between the pad 12 and the bonding ball 1.
1c and the boundary between the pad 12 and the bonding wire 11, respectively. Therefore, the window image data regarding this brightness is sent to the pad detection circuit 2.
1, by passing it through a known Laplacian filter, etc., the line Yi is shown in Fig. 3(C).
As shown in the figure, a second-order differential output having a zero crossing point is obtained at X1 to X6.

In other words, the above zero intersection is the right edge X1 of the adjacent pad on the left in FIG.
2 left edge X2, left edge X3 of bonding ball 11c, right edge X4 of bonding ball 11c
, corresponds to the right edge X5 of the pad 12 of interest and the left edge X6 of the adjacent pad on the right. Although a ball edge happens to be detected on line Yi, many edges are not detected in the ball portion from line Y1 to Yn.

In this way, the pad detection circuit 21 detects lines Y1 to Yn of the window image shown in FIG. 3(A).
The number of zero crossing points (
frequency). As a result, as shown in FIG. 3(D),
The number of horizontal zero intersections projected in the vertical direction is pad 1
Positions Xa, Xb, Xe corresponding to the edge parts of 2
and Xf, the most common bonding ball 11
A frequency distribution is obtained in which the frequency distribution is quite small at positions XC and Xd corresponding to the edges of c, and is zero or extremely small at positions corresponding to other parts.

This is because, as can be seen from FIG. 3(A), the pad 12 is a rectangle with relatively long sides in the vertical and horizontal directions, so the edge portions are long in both the vertical and horizontal directions, whereas the bonding ball This is because 11c has a substantially circular plane and its edge portions are quite small in the vertical and horizontal directions.

Therefore, the pad detection circuit 21 is configured as shown in FIG.
Compare the histogram in (D) with a preset reference value S1 and find the position
a, Xb, Xe and Xf are detected as the vertical contour of the pad 12.

Similarly, the pad detection circuit 21 is configured as shown in FIG.
The above quadratic differentiation is also performed on the data located on each vertical line at regular intervals among the window image data in A), and the zero crossing point obtained thereby is expressed as each line Y1 ~
The number of zero crossing points and the frequency distribution of lines Y1 to Yn are obtained by projecting horizontally for each Yn and accumulating them. Subsequently, in the frequency distribution, a vertical position where the number of zero crossings is equal to or greater than a predetermined reference value is detected as a horizontal contour of the pad 12. As a result, the contours of the upper and lower sides of the pad of interest 12 are detected.

Next, the operation of the pad detection circuit 21 when the bonding ball protrudes from the pad of interest will be explained with reference to FIG. Assuming that the bonding ball 11d at the tip of the bonding wire 11 is also located in the insulating part (band) between one pad 12 of interest and the adjacent pad as shown in FIG. 4(A), the line at that time is The brightness of the image at Yi is shown in the same figure (
The result will be as shown in B).

Therefore, when this window image data regarding brightness is subjected to second-order differentiation in the pad detection circuit 21, a second-order differentiation output as shown in FIG. 4(C) is obtained. This quadratic differential output corresponds to the zero intersection X1 corresponding to the right edge of the pad adjacent to the left of the pad 12 of interest, the zero intersection X4 corresponding to the right edge of the bonding ball 11d, and the right edge of the pad 12 of interest in FIG. 4(A). Zero intersection X5 corresponding to the left edge of the right adjacent pad
However, since the left edge of the pad 12 of interest is hidden by the bonding ball 11d, the zero crossing points X2 and X3 that occur in the normal state do not occur on the line Yi.

However, the left edge of the pad 12 of interest is not entirely covered by the bonding ball 11d, and some edge portions are not covered by the bonding ball 11d. On the other hand, bonding ball 1
There are almost no right edges of 1d other than line Yi.

Therefore, in the pad detection circuit 21, the zero crossing points obtained by second-order differentiation in the horizontal direction of the screen are projected in the vertical direction for each position X to obtain the frequency distribution of each position X and the number of zero crossing points. As shown in FIG. 4(D), this frequency distribution is maximum at the positions Xa, Xe, and Xf corresponding to the zero crossing points X1, X5, and X6, and is small at the position Xd corresponding to the zero crossing point X4,
Further, the number of zero crossing points at the position Xb corresponding to the left edge of the pad 12 of interest exhibits a relatively large value.

Therefore, the pad detection circuit 21 compares the frequency with the reference value S1 and selects positions Xa, Xe, and Xf where the number of zero crossings is greater than or equal to S1 of the pads not covered with the bonding ball 11d. Detected as a vertical contour. Further, the pad detection circuit 21 compares the second reference value S2, which is slightly smaller than the reference value S1, with the above-mentioned histogram, and determines that the position Xb where the number of zero crossings greater than or equal to S2 is obtained is covered by the bonding ball 11d. Detected as the edge of the pad.

The pad detection circuit 21 also detects the contour in the horizontal direction in the same manner as described above by detecting the number of zero crossing points for each line, obtaining the projected frequency, and comparing the frequency with the reference value.

The pad contour data obtained by the pad detection circuit 21 in this way is used by the ball shape inspection circuit 2 shown in FIG.
2 is input. As a result, the ball shape inspection circuit 22
detects the relative positional relationship of the bonding balls 11c and 11d with respect to the detection pad 12, and inspects the shape of the bonding balls.

As described above, according to this embodiment, since the shape and position of the pad are detected, the edge of the bonding ball can be detected accurately.

It should be noted that the present invention is not limited to the above embodiment; for example, the pad detection circuit 21 may be
Rather than performing second-order differentiation in each vertical direction, a two-dimensional second-order differentiation may be performed using a known Laplacian filter, and if a clear window image can be obtained, the pad is calculated based on the first-order differential output. Detection may also be performed.

[0033]

As described above, according to the present invention, by detecting the position and shape of the pad, it is possible to prevent the pad from being detected as the edge of the bonding ball. The shape can be detected accurately, and therefore, it is suitable for automatic inspection of the appearance of bonding wires of IC chips, where the distance between adjacent pads tends to become shorter due to smaller size and higher integration density. It has the following features.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

[Figure 3] Figure 2 when the bonding ball is inside the pad
FIG. 3 is an explanatory diagram of the operation of the pad detection circuit of FIG.

FIG. 4 is an explanatory diagram of the operation of the pad detection circuit of FIG. 2 when the bonding ball protrudes from the pad.

FIG. 5 is a configuration diagram of an example of a conventional device.

FIG. 6 is an explanatory diagram of the conventional device when the boarding ball is protruding from the pad.

FIG. 7 is an explanatory diagram of a conventional device when a bonding ball extends to an adjacent pad.

[Explanation of symbols]

11 Bonding wire 11a ~ 11d Bonding ball 12 Pad 13 Insulation part 21 Pad detection circuit 22 Ball shape inspection circuit 100 Inspection target 101 Imaging means 102 Light irradiation means 103 Image input means 104 Image storage means 105 Window image generation means 106 Pad detection means 107 Ball shape inspection means

Claims (3)

[Claims] 1. At least a portion where the bonding ball at the tip of the bonding wire is electrically connected to the pad is to be inspected (100), and an imaging means (101)
irradiates the inspection object (100) with light using a light irradiation means (102) so that the pad can be imaged brightly and the bonding can be imaged darkly, and an image is generated based on the imaging signal from the imaging means (101). Image input means to input (1
03) and an image storage means (104) for storing the output of the image input means (103).
In a bonding wire inspection apparatus that inspects a bonding wire from an image signal read out from the image storage means (104), the inspection object (
window image generation means (105) for generating a window image of 100); and pad detection means (106) for detecting the outline of the pad based on the window image signal.
), and ball shape inspection means (107) for inspecting the shape of the bonding ball by detecting the relative positional relationship of the bonding ball to the detection pad based on the detection output of the pad detection means (106). A bonding wire inspection device comprising: 2. The pad detection means (106) calculates a first number of zero crossing points projected in the vertical direction from a value obtained by performing second-order differentiation in the horizontal direction of the screen on the window image signal. At the same time, the second number of zero crossing points projected in the horizontal direction is calculated from the value obtained by performing second-order differentiation in the screen vertical direction on the window image signal, and
, the bonding wire inspection apparatus according to claim 1, wherein when the second number of zero crossing points is a predetermined value or more, the outline of the pad is detected. 3. The pad detection means (106) has a function of detecting whether the first number of zero crossing points and the second number of zero crossing points are values within first and second setting ranges, respectively. When the first number of zero crossing points is detected to be within the first setting range, or the second number of zero crossing points is detected to be within the second setting range, the ball shape inspection means (107) 3. The bonding wire inspection apparatus according to claim 2, wherein when it is detected that the bonding ball is within the range, it is determined that a part of the bonding ball is located on the contour of the pad.