JPS6248894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for optically detecting pellet and lead positions in order to perform wire bonding between pellets and leads of an IC.

In order to automate the wire bonding work in the IC manufacturing process, the pellet position and lead position must be automatically detected and this information must be input into an automatic control device.

The above-mentioned position detection methods include optical methods and mechanical methods, each of which has its advantages and disadvantages, but as a practical matter, there are technical constraints on its application as described below.

Generally, there is a step between the pellet and the lead on the IC package, so if you try to detect the position optically, it cannot be automated without the use of complicated equipment such as an automatic focusing mechanism.

When attempting to use a mechanical detection method to avoid the above-mentioned difficulties, it is easy to apply to glass-type ICs, but difficult to apply to ceramic-type ICs.

Due to the above-mentioned circumstances, the manufacturing process of ceramic type ICs cannot yet be completely automated, and the detection of lead positions relies on manual work by workers.

An object of the present invention is to automatically detect the pellet position and lead position using the same optical system without requiring automatic focus adjustment when there is a step difference between the pellet on the IC package and the lead. To provide a wire bonding method.

In order to achieve the above object, the present invention has the same
A method of wire bonding between pellets of an IC package and leads using a wire bonder equipped with an optical system for detecting the position of the bonding point on the pad, an image processing means, and an X-Y drive means. In this method, the above-mentioned optical system detects the pattern of the pellet by imaging the pellet and the lead at different focal positions while focusing on the pellet, and also detects the pattern of the pellet. The blurred image of the circular mark is binarized into the circular mark and the other parts by image processing means, and the image is divided into areas and displayed, and the circular mark provided on the lead is determined based on the outline shape. It is characterized by recognizing the center position and aligning it.

Next, the structure and function of a conventional automatic wire bonding apparatus will be explained with reference to FIG. 1A.

The TV camera 1 includes an optical system 2 to take an enlarged image of the IC package 3 located below it, and inputs its output signal to the automatic operation device 10 via the image processing device 4. 6 is a pellet, 7, 7... is a lead.

FIG. 1B is a vertical sectional view of the IC package 3, pellet 6, and lead 7. As shown in this figure, there is often a step between the pellet 6 and the lead 7.

Wire bonding head 9 with wire bonding tool 8, TV camera 1 and optical system 2
is mounted on a stand (hereinafter referred to as an XY table) 5 that can be freely driven in the illustrated I am forced to do it.

The automatic operation device 10 has a program installed in advance, and the program is inputted via the image processing device 4.
In response to the video output signal from the TV camera 1, the XY table 5 is driven and the wire bonding tool 8 is caused to perform a bonding operation via the wire bonding head 9. In the above-mentioned operation, the mechanism by which the automatic operating device 10 recognizes the position of the pellet 6 and the lead 7, determines the bonding position, and commands the wire bonding operation will be explained with reference to FIG. Figure 2 is
The vicinity of pellet 6 in an example of an IC package is shown, and in this example, 16 leads 7a, 7b...
7p is provided. A hole 11 as a lead positioning mark is formed in the lead 7b, and a hole 12 is formed in the lead 7k. The automatic operating device 10 changes the field of view of the TV camera 1 to the first field of view 1 by driving the XY table 5.
3 and then to the second field of view 14 to transmit image signals of the alignment holes 11 and 12. Once the positions of these two points are recognized, the relative arrangement of the 16 leads 7a, . to determine the wire bonding position.

The position of the pellet 6 is recognized by similarly moving the field of view of the TV camera to the first field of view 15 and then to the second field of view 16, and detecting the characteristic shape of the pad in both fields of view.

The apparatus required to carry out the method of the present invention differs from the conventionally used apparatus shown in FIG. 1 only in the following points. That is, as the image processing device 4, it is necessary to use one having a function of binarizing the video signal as described later, but the other members can be used without any special modification.

When taking an image with the TV camera 1, if there is a step between the pellet 6 and the lead 7, by focusing the optical system 2 on either the pellet 6 or the lead 7, the image of the other will be slightly blurred. However, in the present invention, the image is taken with the pellet 6 in focus. For this reason, the image of the lead 7 and the blurred video signals of the positioning holes 11 and 12 provided in the lead 7 are subjected to electrical processing in the image processing device 4, and then inputted to the automatic operation device 10 to form a circular mark. The center position of the holes (holes 11 and 12 in this example) is detected.

The operations and effects when the optical system 2 is focused on the pellet 6 will be described below.

Since the focus is on the pellet 6, there is no particular problem with respect to the function of recognizing the position of the pellet 6, as in the prior art.

FIG. 3 is an image obtained when the lead 7b is focused in the field of view 13 of the TV camera, and the hole 11 as a positioning mark is clearly shown. However, if you focus on the pellet, the fourth
The image will be slightly blurred as shown in the figure. The shaded area in the figure is the transition area from the white image of the lead 7b to the dark part of the background, that is, the range of blur. A completely dark background is projected inside the inner peripheral circle 17 of the blur, and a completely white image of the lead 7b is projected outside the outer peripheral circle 18 of the blur. The portion sandwiched between the two circles 17 and 18 becomes lighter gray as it approaches the outer circumferential circle 18, and becomes darker gray as it approaches the inner circumferential circle 17, and no clear division is recognized.

In order to locate the center position of the image shown in FIG. 4, the image signal is binarized at an appropriate binarization threshold level by an image processing device (screen reference number 4 in FIG. 1). That is, among the gray parts of the area indicated by diagonal lines, gray parts lighter than a certain level are converted to white, and gray parts darker than the certain level are electrically processed to be converted to black. Then,
The image in FIG. 4 becomes a circular image 19, which is smaller than the outer circumferential circle 18 and larger than the inner circumferential circle 17, as shown in FIG. The size of this circular image 19 changes slightly compared to the clear image of the hole 11 in FIG. 3, and its shape is slightly distorted. However, the center position can be considered unchanged in practice. The reason is as follows.

Each lead has a considerable width, for example lead 7a has a width W. The diameter of the hole 11 serving as a positioning mark is a fraction of W. Therefore, even if there is an error of about a fraction of the hole diameter in detecting the position of the hole 11, the error is much smaller than the width dimension W of the lead, and the bonding to the lead There is no risk that the positional aim will deviate from the lead surface due to the above-mentioned error.

As can be easily understood from the above-mentioned functions and effects, the holes 11 as the alignment marks are
Even if it is not a circle but a polygon (for example, a regular hexagon), the blurred image is indistinguishable from a circle, and the same effect as in the embodiment (circular mark) is achieved.

Therefore, the term "circular mark" in the present invention is not limited to a geometrically strict circle, but includes a shape that looks similar to a circle in a blurred image.

As described above, the automatic operating device is inputted with the information of the binarized image as shown in Fig. 5, so it recognizes the position of the lead from the above image information based on the program installed in advance. can issue a command for wire bonding operation.

As explained above, the present invention images a pellet and a lead with a step on an IC package using the same optical system, focusing on the pellet, and obtains a blurred image of the lead by this imaging. By detecting the center position from the image of the alignment circular mark, there is no need to install an automatic focus adjustment device, and the pellet position and lead position can be automatically recognized using the same optical system. The bonding position can be determined.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the structure of a conventional wire bonding device, Figure 2 is a plan view of the IC chip pellet and leads, and Figures 3 to 5 are the vicinity of alignment holes provided in the leads. Figure 3 shows the image when focused, and Figure 4 shows the image when the focus is adjusted.
The figure shows an out-of-focus image, and FIG. 5 is an image obtained by binarizing the image in FIG. 4 in an embodiment of the present invention. 1...TV camera, 2...Optical system, 3...IC package, 4...Image processing device, 6...Pellet, 7, 7a, ~7p...Lead, 10...Automatic operation device, 11, 12 ...Positioning hole, 1
7... Inner circumference circle of image blur, 18... Outer circumference circle of image blur, 19... Circular image.

Claims (1)

[Claims] 1. An optical system for detecting the position of the bonding point of the IC package in order to wire bond the pellet and the lead of the IC package with a thin wire;
In a method of bonding using a wire bonder equipped with an image processing means and an X-Y driving means, the above-mentioned optical system images a pellet and a lead having different focal positions while focusing on the pellet. At the same time, the blurred image of the circular mark provided on the out-of-focus lead is binarized into the circular mark and other parts by image processing means, and the pattern is divided into regions. An IC wire bonding method characterized by displaying an image of the circular mark provided on the lead and recognizing and aligning the center position of a circular mark provided on the lead based on the outline shape.