JP2843388B2 - Wire bonding condition inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a wire bonding state inspection apparatus having a visual function for automatically inspecting a wire bonding state of an integrated circuit or the like. Imaging means for imaging a bonding ball at the tip of a wire bonded to a pad, and a pixel for digitally processing an output video signal of the imaging means to generate pixels Generating means, a gray-scale image memory for storing pixels in a test area of a predetermined size among the pixels generated by the pixel generating means, and an automatic binarization calculating method from all pixels read from the gray-scale image memory A threshold calculating means for calculating a threshold value by using the threshold value, and binarizing the image in the inspection area with the threshold value;
Distance converting means for performing distance conversion on the binary image obtained by the threshold value calculating means, and searching for the value of each pixel of the image whose distance has been changed from the direction opposite to the wire to obtain the maximum value of the first detected value A center detecting means for detecting a center of a pixel position as a center position of the bonding ball; and a distance between a center position detected by the center detecting means and a pixel position of a predetermined value among pixels of the distance-converted image. It comprises a shape inspection means for calculating and inspecting the bonding ball shape.

[Industrial applications]

The present invention relates to a wire bonding state inspection apparatus, and more particularly to a wire bonding state inspection apparatus having a visual function for automatically inspecting a wire bonding state of an integrated circuit or the like.

In recent years, integrated circuits (ICs) and large-scale integrated circuits (LSIs) have been used widely and in large quantities, so that visual inspection of the wire bonding state of ICs and LSIs has been automated. It has become. In the appearance inspection of the wire bonding state, it is necessary to accurately detect the center position of the bonding ball.

[Conventional technology]

FIG. 10 shows a configuration diagram of an example of a conventional wire bonding state inspection apparatus. In the figure, reference numeral 1 denotes a lead frame on which an IC chip 2 is mounted. Pads 3 are formed on the IC chip 2. Reference numeral 4 denotes a wire, one end of which is fixed on the pad 3 by forming a bonding ball 5.

The lead frame 1 is transported by a frame feeder 6 which is a transport device, directly below the illumination device 7 and the imaging device 8. Thus, the bonding ball 5 is illuminated by the illumination device 7 and is imaged by the imaging device 8. The video signal extracted from the imaging device 8 is supplied to an information processing device 9 where the shading is corrected by analog processing or digital processing so that the image is made uniform and shaded, and then a binary value is automatically obtained. Then, the wire bonding state of the captured image is inspected.

Here, in the conventional wire bonding state inspection apparatus, as a process in the information processing 9, after detecting the pad 3, the bonding ball 5 is detected based on the maximum value of the line segment crossing the portion of the pad 3 excluding the wire 4. The diameter is calculated, and the center position of the bonding ball 5 is detected from the diameter (for example, JP-A-57-172746).
Alternatively, assuming that the planar shape of the bonding ball 5 is a perfect circle, a contact point that changes from a bonding ball image to a pad image in each of the x direction and the y direction is detected, and passes through the contact point.
There is known a method of drawing perpendicular lines in the x and y directions and detecting their intersection as a ball center position (for example, JP-A-53-124066).

[Problems to be solved by the invention]

However, although the former conventional device seeks a portion excluding the portion of the wire 4, the bonding ball 5 is an end point of the wire 4. In practice, it is difficult and limits the accuracy of bonding state inspection.

In the latter conventional device, the plane shape of the bonding ball 5 is assumed to be a perfect circle. However, since the actual plane shape of the bonding ball 5 is almost not a perfect circle, the ball center position can be accurately determined. If the bonding ball 5 is deformed, a position extremely deviated from the ball center position is detected as the ball center position.

The present invention has been made in view of the above points, and provides a wire bonding state inspection apparatus that can accurately detect a bonding ball center and inspect a wire bonding state without being affected by a wire image or a ball deformation. The purpose is to:

[Means for solving the problem]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, 10
Is an imaging means for imaging the bonding ball at the tip of the wire bonded to the pad. Reference numeral 11 denotes a pixel generation unit, and reference numeral 12 denotes a gray-scale image memory, which generates pixels from a video signal from the imaging unit 10 and stores pixels in an inspection area of a predetermined size.

Numeral 13 denotes a threshold value calculating means for calculating a threshold value from all the pixels read from the gradation image memory 12 by an automatic binarization calculation method, and binarizing the image in the inspection area with the threshold value to obtain a gradation image.

Numeral 14 denotes a distance conversion means for converting the density of the gray image into a distance.
Reference numeral 15 denotes a center detecting means for searching the value of each pixel of the distance-converted image from the direction opposite to the wire, and detecting the first detected maximum value as the center position of the pixel position as the center position of the bonding ball. Further, 16 is a shape inspection means,
The shape of the bonding ball is inspected by calculating the distance between the detected center position and the pixel position of a predetermined value among the pixels of the grayscale image whose distance has been converted.

[Action]

In the present invention, the grayscale image obtained by the threshold value calculating means 13 is distance-converted by the distance converting means 14, and the value of each pixel of the distance image is set to "1" at the outermost periphery (contour portion). And Thereafter, among the pixel values of the distance-converted gray image, the maximum value is detected from the opposite direction of the wire by the center detecting means 15, and the center of the pixel position of the maximum value detected first is determined as the center of the bonding ball. By setting the center position, the center position of the bonding ball can be detected without being affected by the wire image or the ball deformation.

Further, since the maximum value itself is the maximum radius of the bonding ball, the present invention detects the minimum radius of the distance conversion image by the shape inspection means 16 with reference to the detected center position, thereby obtaining the wire image and the ball deformation. The ball shape can be inspected without being affected by the above.

〔Example〕

FIG. 2 shows a block diagram of one embodiment of the present invention. In the figure,
The same components as those in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 2, the lighting device 7 and the imaging device 8
Constitutes the imaging means 10 shown in FIG. In FIG. 2, reference numeral 21 denotes an image input circuit which constitutes the pixel generation means 11 and digitally processes an input video signal. Reference numeral 22 denotes an image memory, 23 denotes an image processing memory, and these constitute the gradation image memory 12.

Reference numeral 24 denotes an image processing processor,
13, distance conversion means 14, center detection means 15, and shape inspection means 16
The threshold value is calculated according to a flowchart shown in FIG. An image display circuit 25 causes the display 26 to display an image. The above image input circuit
21, image memory 22, image processing memory 23, image processing processor 24 and the pixel data transfer between the image display circuit 25,
This is performed via the image bus 27.

A program memory 28 stores a program for controlling the entire wire bonding state inspection apparatus. Reference numeral 29 denotes a system processor, which comprehensively controls the entire circuit of the wire bonding state inspection apparatus according to a program from a program memory 28.

A camera controller 30 controls the operation of the imaging device 8. An illumination controller 31 adjusts the amount of illumination of the illumination device 7 with respect to the IC chip 2 to optimize the S / N of the video signal. Reference numeral 32 denotes a frame feeder controller which controls the transfer of the frame feeder 6 which is a transfer device. 33 is I / O
Controller and keyboard and joystick 34,
The interface between the printer 35 and the system processor 29 is provided. The keyboard and the joystick 34 are used for setting inspection conditions and the like, and the printer 35 is used for printing out inspection results and the like.

A floppy disk controller (FDC) and a hard disk controller (HDC) are connected to the floppy disk 37 and the hard disk. The floppy disk 37 and the hard disk 38 store inspection results, inspection standards, and the like. 39 is a system bus,
This is a data transfer bus between the above circuits.

Next, the operation of this embodiment will be described. The imaging device 8
IC chip 2 of wire 4 bonded to IC chip 2
An image of the bonding ball 5 formed at the end on the side is taken, and a video signal obtained thereby is supplied to the image input circuit 21. The image input circuit 21 digitally processes the input video signal to generate image data in which the pixel groups are synthesized in time series,
The image data is transferred to the image memory 22 via the image bus 27.
To be stored. The system processor 29 cuts out pixels (image data) in a region D of a predetermined position and size from the image memory 22 and stores them in the image processing memory 23.

By using all the pixels in the area D stored in the image processing memory 23 in this manner, the image processor 24
According to the flowchart shown in FIG.
Each process from to the shape inspection means 16 is performed.

First, as shown in FIG. 3, the image processor 24 reads out (cuts out) all the pixels in the area D (step 4).
1). Next, the image processor 24 performs gradation interpolation (sub-pixel generation) between the read pixels (step 42 in FIG. 3). The inter-pixel gray scale interpolation as shown in FIG. 4, among the pixels in the region D read out from the image processing memory 23, shows four pixels Tonariru any phase by a black circle P ₁ to P _4, also P ₁ = f ′ (i, j), P ₂ =
f ′ (i + 1, j), P ₃ = f ′ (i, j + 1), P ₄ = f ′ (i +
1, when j + 1) to, white circle following equation to the position indicated by the SP f (x, y) = P 1 · (1-α) · (1-β) + P 2 · α · (1-β) + P 3 · ( 1-α) · β + P 4 · α · β represented by f (x, a method for generating a sub-pixel having the tone value of y). However, the horizontal distance from the above formula alpha P _1, beta denotes the vertical distance from P _1.

By this inter-pixel gradation interpolation, sub-pixels are generated between the four pixels P _{1 to} P _{4 at the} positions indicated by white circles in FIG. 4 in the same manner as described above. As a result, the image of the bonding ball 5 before the above-described inter-pixel tone interpolation has a large jagged portion in the oblique image portion as shown in FIG. 5 (A). As a result, the jagged portion of the image of the bonding ball 5 in the oblique image portion is greatly reduced as shown in FIG. 7B, and an image in which the quantization error associated with digitization is greatly reduced can be obtained.

Next, from the image processor 24, the binarization threshold T is automatically calculated from all the pixels (including sub-pixels) of the inspection area D.
The automatic binarization is calculated by a binarization process (step 43 in FIG. 3).
arization). By this adaptive binarization, the total number of pixels in the inspection area D is N,
Assuming that the pixel gradation value is f (x, y) · γ at a predetermined ratio, the binarization threshold T is given by the following equation. It is calculated based on the following equation.

After the above-described calculation of the binarization threshold value T, the image in the inspection area D when the pixel having the gradation value larger than T is set to “0” and the pixel having the gradation value equal to or smaller than T is set to “1” 6 is a binarized image as schematically shown in FIG. However, in FIG. 6, illustration of each pixel having a value “0” is omitted. This binarized image is the sixth image
As shown in the figure, the shapes of the wires 4 and the bonding balls 5 having a smaller video signal intensity than the IC chip 2 and the pad 3 in the inspection area D are shown. The data of the binarized image is stored in the image processing memory 23 in an area different from the pixel storage area.

Next, the image processor 24 converts the distance of the binary image (step 44 in FIG. 3). In this distance conversion, the value of the outermost pixel forming the outline of the binarized image is set to “1”, and the value of the pixel is set to 1 each time one pixel advances from there toward the center of the binarized image. This is the process of increasing the number. In other words, the distance conversion is a process of assigning a value indicating the number of each pixel constituting the binary image from the contour to the pixel. Therefore, by this distance conversion, the value of each pixel constituting the above-mentioned binary image is set as shown in FIG.

Next, the image processor 24 searches for a pixel value from the position facing the wire 4 toward the wire 4 with respect to the image in the inspection area D after the distance conversion, and determines the center position of the bonding ball 5. It is detected (step 45 in FIG. 3). That is, as shown in FIG. 8, the value of each pixel constituting the image after the above-mentioned distance conversion is detected from the direction opposite to the position where the wire 4 is located, and the maximum value (here, “6”) detected first is detected. The center of the pixel (shown by hatching in FIG. 8) is the center position C of the bonding ball 5.

Here, since there are two pixels having the maximum detection value "6" indicated by oblique lines in FIG. 8 in the same row, the boundary between the two pixels is defined as the center position C of the bonding ball 5, and the maximum detection value R _MAX is
It is 6.5. The wire 4 of the bonding ball 5
The detection direction from the position facing to the wire 4 to the wire 4 can be identified because the positions and directions of the IC chip 2, the pad 3, the wire 4, and the bonding ball 5 with respect to the imaging device 8 are known in advance.

Next, the image processor 24 calculates the distance from the center position C to each pixel constituting the contour whose value is “1” in the image after the distance conversion, thereby changing the shape of the bonding ball 5. Inspect (Step in Fig. 3
46). That is, in this step 46, the distance between the center position C indicated by the arrow in FIG. 9 and the contour pixel is calculated, and the minimum value R _MIN is calculated. This minimum value R _MIN represents the minimum radius of the bonding ball 5.

Thereafter, the image processor 24 determines the quality of the bonding ball 5. This pass / fail judgment is performed in steps
The positional deviation of the bonding ball 5 is inspected from the deviation between the central position C of the bonding ball 5 and the central position of the pad 3 detected in 45, and it is determined whether or not the positional deviation is within an allowable range. The minimum value (minimum ball radius) R _MIN , the maximum value (maximum ball radius) R _MAX detected in step 45, and the reference ball diameter R _STD (for example, 35 μm to 65 μm)
μm) to determine whether or not the ball deformation determined from the ratio is within an allowable range. The determination regarding the latter ball deformation is, for example, that the minimum ball radius R _MIN is 70 _% of the reference ball diameter R _STD .
% And the maximum ball radius R _MAX is 13 of the standard ball diameter R _STD
This is a determination as to whether or not it is within an allowable range of 0% or less.

Therefore, according to the present embodiment, the bonding ball 5 can be precisely formed without being affected by the wire 4 and the ball deformation.
Can be detected.

The present invention is not limited to the above-described embodiment. For example, the sub-pixel generation process in step 42 in FIG. 3 is a desirable process for obtaining a more accurate inspection result. Can be omitted.

〔The invention's effect〕

As described above, according to the present invention, since the ball shape can be inspected without being affected by the wire image and the ball deformation, it is possible to perform a state inspection of the bonding ball with higher accuracy than in the past. It has.

[Brief description of the drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of one embodiment of the present invention, FIG. 3 is a flowchart for explaining the operation of one embodiment of the present invention, and FIG. FIG. 5 is a diagram showing an example of an image before and after gray-scale interpolation between pixels, FIG. 6 is a diagram showing a binarized image of a bonding ball, FIG. 7 is a diagram showing a converted image of a bonding ball distance, FIG. FIG. 9 is an explanatory diagram of detection of a bonding ball center position, FIG. 9 is an explanatory diagram of bonding ball shape inspection, and FIG. 10 is a configuration diagram of an example of a conventional device. In the figure, 2 is an IC chip, 3 is a pad, 4 is a wire, 5 is a bonding ball, 10 is an imaging means, 11 is a pixel generation means, 12 is a gradation image memory, 13 is a threshold value calculation means, and 14 is a distance conversion. Means, 15 is a center detection means, 16 is a shape inspection means, and 24 is an image processor.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/60 321 H01L 21/66 G01N 21/88 H01L 21/60 301

Claims (1)

(57) [Claims] An image pickup means (10) for picking up an image of a bonding ball at the tip of a wire bonded to a pad, and a pixel generation means (11) for digitally processing an output video signal of the image pickup means (10) to generate a pixel. ), A gray-scale image memory (12) for storing the pixels in the inspection area of a predetermined size among the pixels generated by the pixel generating means (11), and all of the pixels read from the gray-scale image memory (12). Threshold calculating means for calculating a threshold value from the pixels by an automatic binarization calculation method and binarizing the image in the inspection area with the threshold value (13)
Distance conversion means (14) for distance-converting the binary image obtained by the threshold value calculation means (13); and searching for the value of each pixel of the distance-converted image from the direction opposite to the wire. A center detecting means (15) for detecting the center of the pixel position of the maximum value detected first as the center position of the bonding ball; and a center position detected by the center detecting means (15) and an image of the distance-converted image. And a shape inspection means (16) for calculating a distance from a pixel position of a predetermined value in each pixel to inspect a bonding ball shape.